Estimates of Volumes and Exposed Surface Areas of Stored Animal ...
J. agric. Engng Res. (1997) 66, 239 – 250
Estimates of Volumes and Exposed Surface Areas of Stored Animal Manures and Slurries in England & Wales R. J. Nicholson*; A. J. Brewer† *ADAS, Boxworth, Cambridge CB3 8NN †ADAS, Nobel House, 17 Smith Square, London SW1P 3JR (Receiy ed 1 February 1996; accepted in rey ised form 12 December 1996)
Estimates of animal manure (solid material) and slurry (liquid material) stored on farms are needed by the Ministry of Agriculture, Fisheries & Food (MAFF) for compiling national inventories of gaseous emissions. Data needed for this purpose include the total volume and surface area of stored manures and slurries from different livestock species. Existing sources of data were reviewed but have limitations in the context of an emissions inventory. Suppliers of prefabricated stores were approached for numbers and sizes of stores sold since 1970. ADAS pollution control consultants made informed estimates of the geographic distribution of methods of storage in use in England & Wales for manure and slurry from dairy cows, other cattle and pigs. This information was combined with June 1992 census figures to provide estimates of volumes (raw and diluted) and exposed surface areas of stored manures and slurries. ADAS livestock consultants were used to interpret census data and provide estimates of the distribution of poultry manure handling methods. A computer spreadsheet was used to store and process this data and is available to allow future adjustments or sensitivity analyses. In this paper, these estimates are reported on a national basis but they were originally gathered separately for each of 15 areas and appended to a report produced for MAFF. These detailed figures are available on request. The majority of diluted livestock slurry is stored in earth-banked lagoons, with an estimated total volume of 15?5 Mm3 and an estimated surface area of 7?0 Mm2. The total volume of stored solid manure is 14?9 Mm3 with an estimated surface area of 11?9 Mm2. The estimates were compared with data from other sources and show an acceptable level of agreement. ÷ 1997 Silsoe Research Institute 0021-8634 / 97 / 040239 1 12 $25.00 / 0 / ag960139
1. Introduction Housed livestock and stored manures (solid) and slurries (liquid) are thought to contribute significantly to emissions of ammonia and methane from agriculture.1 Because of their environmental effects, an inventory of these gaseous emissions is needed to guide policy makers. MAFF has recently commissioned such an inventory. MAFF is funding research on gaseous emission rates from stored animal excreta which is largely being undertaken by Silsoe Research Institute and the Institute for Grassland and Environmental Research. To complement this research, data on types and numbers of slurry and manure stores in the UK were needed in order to complete the proposed inventory. Limited data on this subject were included in a study by Manchester University2 and a survey by the former Milk Marketing Board (MMB),3 but the figures were not comprehensive, nor were they presented in a form which was suitable for compiling the proposed inventory. Therefore ADAS produced estimates of the types and numbers of manure and slurry stores in use in England and Wales, with data presented in a form that would allow them to be used to produce the proposed inventory. The results of the ADAS work4 form the subject of this paper. The exposed surface area of stored material is likely to be a major factor influencing the amounts of ammonia emitted.5 Method of storage, physical form of the material, and species from which it originates are likely to be important in determining emission rates. Existing information6 indicates that the y olume of stored material, its dry matter content, and the species from which it originates are the major factors influencing methane emissions. For both ammonia and
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methane, the period of storage will influence the amounts of gas emitted. It was agreed that it would be desirable to have an indication of the geographical distribution of amounts and types of stored manures and slurries: this was undertaken for England and Wales. It was concluded that estimates of actual numbers and sizes of stores were not as relevant in this context as total surface area and volume.
2. Existing data The following sources of data were reviewed, and their limitations identified before formulating a strategy for compiling the required estimates.
Table 1 Storage facilities for manure and slurry on farms in Great Britain with dairy herds (estimated numbers and percentages of farms)2 All sizes , population estimate Type of store Midden with impermeable base Midden with permeable base Underfloor slurry tank Slurry: steel tank concrete tank weeping wall store lagoon, impervious lining lagoon, without impervious lining Other
Number
%
12370 2300 4560 4940 3620 1830 2830 3910 2360
34 6 12 14 10 5 8 11 6
* Stores per 100 farms
2.1. MAFF Farm and Consery ation Grant Scheme Data have been collected by MAFF Countryside Division on the uptake of the Farm and Conservation Grant Scheme and its precursors, but records are only easily accessible from 1986 at the earliest. The existing database could be interrogated to provide information on numbers of holdings claiming grant, amount of expenditure, and species, in relation to improvements to waste handling facilities. However no central records were kept of the detail of improvements, such as store type or size. This source of information therefore, while essential in detailing which industry sectors have taken up grant aid, is of no use in providing information for an emission inventory. 2.2. Manchester Uniy ersity study A study by Manchester University,2 provides data on the uptake and effectiveness of the MAFF Farm and Conservation Grant Scheme, and contains useful estimates of types and numbers of manure and slurry stores in use in 1991 based on a sample of around 900 farms. However, the data do have a number of limitations as they make no estimate of size of stores, do not include poultry, and are therefore difficult to interpret in the context of a gaseous emission inventory. The study included an assessment of types of storage facility on farms with dairy herds, on nondairy farms with cattle, and on farms with pigs. Information was presented for small, medium and large farm businesses in a survey of 900 farms in England, Wales and Scotland. However, an estimate for all farm sizes, based on the sample studied,
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* Some farms have more than one type of store, e.g. provision for both slurry and solid manure.
indicated the number of different types of store on farms with dairy herds, non-dairy farms with cattle and farms with pigs (Tables 1, 2 and 3). The study also provides information on the destination of dilute effluent (commonly called dirty water) arising from contaminated run-off following rainfall and washing water from dairy, cattle and pig farms. This indicates that 32% of dirty water on dairy farms
Table 2 Storage facilities for manure and slurry on non-dairy farms in Great Britain with cattle (estimated numbers and percentages of farms)2 All sizes , population estimate Type of store Midden with impermeable base Midden with permeable base Underfloor slurry tank Slurry: steel tank lagoon, impervious lining lagoon, unlined Other No specific store*
Number
%
8900 4000 2800 2000 800 1700 3600 27400
17 7 5 4 1 3 7 51
* For farms with housed cattle: many leave manure in bedded yards. Note: data presented as given in original source.
VOLUMES AND EXPOSED SURFACE AREAS OF STORED ANIMAL MANURES AND SLURRIES
Table 3 Storage facilities for manure and slurry on farms in Great Britain with pigs (estimated numbers and percentages of farms)2 All sizes , population estimate Type of store * Midden with impermeable base Midden with permeable base Underfloor slurry tank Slurry: steel tank concrete tank lagoon, impervious lining lagoon, pervious lining Other (including field heaps) *Stores per 100 farms
%
2.5 . MAFF census data
4100 540 2930 520 1460 870 540 940
41 5 30 5 15 9 6 9 120
June census data collected annually by MAFF Census Branch at Guildford provide very accurate information on numbers and types of livestock on a county basis. This information was used in conjunction with advisers’ estimates as described in Section 3.3.
is stored with slurry and 13% is stored separately; on pig farms 16% of dirty water is stored with slurry and 10% is stored separately. Hence dirty water must be taken into account when calculating slurry store capacity. 2.3. MMB sury ey The survey carried out by MMB3 in 1993 included questions on slurry storage methods. All milk producers in England and Wales were sent a questionnaire which drew replies from 8212 producers (a 28% response rate). The majority of farms in the sample housed cows in cubicles (83%). For farms with some form of slurry and manure storage, the different types of store were assessed (Table 4). 2.4. Liy estock housing Estimates produced by ADAS, for MAFF Environmental Protection Division, on types and numbers of Table 4 Slurry and manure storage methods on dairy farms in England & Wales3 (An unspecified number of farms had no storage facilities)
Towers* Earth-walled lagoons Weeping wall stores Concrete pads Other
poultry houses and types and numbers of pig housing in England and Wales provided useful background data on the forms in which excreta are likely to be handled. The data on poultry housing are reasonably straightforward, while the data on pig housing are complex and difficult to interpret.
Number
* Some farms have more than one type of store.
Store type
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Percentage of farms % 20 30 15 19 23
* ‘‘Towers’’ are above-ground cylindrical stores. Note: some farms have more than one type of store. Data presented as given in original source.
3. Methodology 3.1 . Oy erall approach While attempts were made to collect data on numbers and types of prefabricated stores, it was apparent that this would not take account of large numbers of structures built in -situ . ADAS consultants in the field were not able to give a direct estimate of store numbers, or volumes and surface areas of stored material. However, using their experience they could reliably assign values to the percentages of different types of system installed in their particular geographic area, and relate these values to class of livestock. Therefore, it was decided that an indirect approach would be adopted. MAFF census figures for numbers of livestock are known to be accurate. ‘‘Text-book’’ values7,8 of excreta output for a particular livestock species give realistic estimates and are extensively used for calculating storage capacity needed on a particular site. It was concluded that the best accuracy, within the limitations of an indirect approach, could be achieved by calculating total volumes of undiluted excreta from livestock numbers and excreta output, and then subsequently estimating the proportion stored by different methods. Therefore, effort was targeted on collecting information in the broad sub-divisions of species, for the form in which excreta are handled (solid or liquid), and type of store and storage period (Table 5, the categories in this table apply to more than one species and the table is not to be read across line by line). Manure and slurry stored within buildings was not included in this study. In respect of storage capacity (Table 5) it was arbitrarily decided to ignore any storage capacity of less than two weeks, because it was unlikely to be significant in contributing to overall emissions. An attempt was made, in the case of dairy cows, to make
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Table 5 Categories used for data collection and presentation Species / Numbers Dairy cows Other cattle Pigs
Slurry storage Above-ground circular Weeping wall Lagoons and compounds (below-ground)
Manure storage Concrete pad Field heap
Storage capacity Months
Quantitatiy e data Volume stored Exposed surface area
Poultry
a separate estimate of quantities of dilute effluent (dirty water) stored for more than two weeks. As estimates drew heavily on the knowledge of local ADAS pollution control consultants, any data on geographical distribution were based on the fifteen ADAS Consultancy Centres which existed in 1993 / 4. 3.2. Manufacturers ’ data Manufacturers and suppliers of prefabricated slurry stores, in particular circular above-ground structures and weeping-wall structures, were presumed to have records of numbers of stores sold. A decision was made to approach them for this information but it was accepted that any data collected by this route could have limitations if replies were not received from all companies. A large number of stores currently in use (e.g. earth-banked structures and manure stores) are constructed locally and would not be covered by this approach. A total of 21 manufacturers or suppliers of prefabricated slurry stores were sent questionnaires to obtain information on the likely population of above-ground circular stores and weeping-wall stores in England and Wales. They were asked to estimate store numbers and typical store size, by livestock species (pigs and cattle) and by area (ADAS Business Centre) installed since 1970. For those who could not provide this level of detail, an opportunity was given to record information for ‘‘Southern Counties’’, ‘‘Northern Counties’’ and Wales or on a total (England and Wales) basis. 3.3. ADAS estimates ADAS pollution control consultants have good local knowledge of types of store in use, largely through pollution control advisory visits. Questionnaires were developed to obtain informed estimates of manure and slurry storage methods on dairy, beef and pig farms. Each questionnaire broadly followed the same format but allowed for differences in slurry management between livestock species. In addition, to improve the quality of these estimates, the ‘‘dairy cow’’ questionnaire contained questions for herds of less than 100 cows and for herds of 100 cows and over. Consultants from each Business Centre
were asked to reach a consensus opinion on the proportion of manure and slurry stored for each livestock species. Methods of storing manure and slurry were estimated as percentages of their respective total volumes. For each storage method an estimate was made of typical capacity (months) and typical storage depth (m). The destination of dirty water was assessed and allocated to ‘‘stored with slurry’’ or ‘‘stored separately’’ or ‘‘stored for less than two weeks’’. Methods of storing dirty water separately (i.e. not with slurry) were assessed and a proportion was allocated to above-ground circular stores and lagoons. Data from the questionnaires were processed using a computer spreadsheet (Microsoft Excel). Data for livestock numbers were taken from the June 1992 MAFF Census Frequency Distribution Tables. Information on volumes of excreta produced was based on standard data,7,8 but modified to accord with the appropriate feeding method (pigs), weight, age, and class of livestock where necessary. Spreadsheets were developed for each livestock species, that is, for dairy cows, other cattle and pigs. Specialist ADAS consultants for cattle and pigs assisted with interpretation of census data. Estimates of manure output from two classes of poultry (laying hens and broilers) were made separately with assistance from a specialist ADAS consultant. Spreadsheets were developed for each class.
3.3 .1 . Data inputs For each livestock species, an appropriate set of data was used in the calculation of manure, slurry and dirty water volumes and exposed surface areas. Examples are given in Tables 6 and 7. Common data used in these calculations, such as dilution factors and storage depths, are given in Table 8. The effect of changing any of these data could be demonstrated by allowing the appropriate spreadsheet to re-calculate volumes and surface areas. A dilution factor for above-ground circular slurry stores has been used to take account of incident rainfall. Similarly, a dilution factor for lagoons serves the same purpose and allows for the typical surface
VOLUMES AND EXPOSED SURFACE AREAS OF STORED ANIMAL MANURES AND SLURRIES
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Table 6 Example input data for cattle and pigs Dairy
Beef
Pigs
Age
Excreta output *
Age (months )
Excreta output * m 3 d 21 animal 21
Adult
0?057 m3 d21 cow21
,6 6 – 12 12 – 24 .24
0?007 0?012 0?022 0?027
Parlour wash water Fouled, unroofed yard area
*18 l d21 cow21 10 m2 cow21
Wash water Fouled, unroofed yard area
Not applicable 1 m2 animal21
Weight / type
Excreta output * m 3 d 1 pig 21
Breeding (dry fed) Breeding (wet fed) ,20 kg 20 to 40 kg Finishing (dry fed) Finishing (wet fed, 3?5 to1)
0?0065 0?0075 0?002 0?003 0?0045 0?007
Finishing (wet fed, 5 to 1) Finishing (swill) Clean down water Fouled, unroofed yard area
0?011 0?014 *0?0005 Not applicable
* Volumes based on sources.7,8
area of a lagoon to be greater than for an aboveground circular store of similar volume. Where manure is collected as a ‘‘solid’’ it is most often mixed with straw bedding. The addition of straw provides greater bulk and the volume assessment uses the ‘‘straw addition factor’’ to take account of this. It is impossible to estimate surface areas of stored manure without making assumptions about typical stack size, since exposed surface areas will consist of stack top plan area and the area of its sloping sides. For the purpose of this study it is assumed each stack is rectangular with a flat top and vertical sides. A consensus of opinion from ADAS pollution control consultants indicated that the plan area of a typical stack is 200 m2 with 20 m by 10 m sides (perimeter is 60 m). The combined surface area of a series of stacks of this size, forming an estimated total volume arising from a particular species and / or geographical area can then be calculated as follows (all dimensions in m): Estimated number of stacks (n ) 5 Total estimated volume of manure / 200D Total exposed surface area 5 n 3 [200 1 60D ] where D is the depth (or height) of stack.
Similarly, following consultation with ADAS pollution control consultants, typical values have been assumed for solid manure depth in buildings and for slurry depth under slats. These values allow for checking calculations and provide consistency in spreadsheet operation although manure and slurry storage within buildings is not included in this study. Considerable amounts of dirty water are produced, particularly on dairy farms, and where this is added to slurry it will increase the size of slurry store required. No specific surveys have been carried out on quantities arising. The ADAS Agro-meteorological Unit therefore provided an average October to March rainfall for each of the 15 areas to enable appropriate calculations to be made. Values ranged from 309 mm (Bury St Edmunds) to 748 mm (Cardiff). 3.3 .2 . Census data June census data for all dairy cows and according to herd size were used in the calculations.9 Non-dairy cattle numbers were derived from the total numbers of cattle and calves10 less the numbers of dairy cows.9 The percentage distribution of all non-dairy cattle by age was combined with individual county estimates to
Table 7 Example input data for poultry
Excreta output* kg d21 bird21 Specific volume of manure l kg21 Housing occupancy % * Source.8
Laying hens
Broilers
0?115 1?0 96
0?073 1?0 88
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Table 8 Standard dilution factors and store dimensions Dimension
Measurement
Dilution factor, circular slurry stores Dilution factor, slurry lagoons Straw addition factor (for farmyard manure) Solid manure depth in buildings Solid manure store perimeter Solid manure store area Under-slat slurry depth Depth of typical above-ground circular stores Depth of typical lagoons
1?15 1?35 1?5 0?75 m 60 m 200 m2 1m 3?5 m 2?5 m
provide the distribution of such animals for each of the 15 areas. This has been aggregated (Table 9) into estimates for England and for Wales. For simplicity, census data on pigs relating to herd size groups 1 – 9, and 10 – 19 pigs were omitted both for the breeding herd11 and for total pigs12 as these represented very small numbers. Data for the remaining pig breeding herd were multiplied by a factor of 1?22 to take account of boars, maiden gilts and barren sows. Data for all other pigs 20 kg and over13 were subtracted from data for total pigs to arrive at numbers of pigs 20 kg and under. For pigs 20 kg and over, 30% were calculated to be in the 20 kg to 40 kg weight range and 70%, 40 kg and over. Census data for all laying hens14 and all broilers15 according to flock size were used in the calculations. 3.3.3. Dairy cows , calculation The volume of excreta produced per month was calculated and data from the questionnaires were used to allocate this output into slurry and solid manure. Slurry store volumes were calculated using the consultants’ estimates of the proportion allocated to different store types, multiplied by the storage capaTable 9 Percentage distribution of non-dairy cattle by age Age Fully grown animals: 2 yrs old and over Growing cattle: 1 yr to 2 yr old Six months to 1 yr old Calves under six months old Total
England
Wales
33%
38%
30% 20% 17% 100%
28% 17% 17% 100%
city (months). A value was given for undiluted excreta and for a dilute product (rainfall and dirty water added). The dilute slurry volume was calculated by applying the appropriate dilution factor to the excreta volume and then adding any dirty water (subsequently calculated) which was destined to be stored with slurry. Any dirty water added in this way was assumed to be stored for the same period and was allocated on a pro-rata basis only to above-ground circular stores and to lagoons. Surface areas were calculated by dividing volume by depth. Excreta volume was converted into an ‘‘excreta and straw’’ manure volume by using the straw addition factor. Exposed surface areas of manure heaps or stacks were calculated using the formula given in Section 3.3.1. Dirty water production per month was calculated from the standard figure for parlour wash water with the addition of rainfall from unroofed fouled yard area (10 m2 cow21). An assessment of the destination of dirty water was made because some is stored with slurry and some is stored separately. Volumes of dirty water stores were calculated using a proportion allocated to different store types multiplied by the storage capacity (months). Surface areas were calculated by dividing volume by depth.
3.3 .4 . Non dairy cattle , calculation Calculations were made in a similar way to those for dairy cows once the assessment of excreta output (m3 month21) had been made. However, there was no parlour wash water and a nominal 1 m2 animal21 fouled yard area was used to calculate an allowance for dirty water production.
3.3 .5 . Pigs , calculation There is large variation in slurry output from finishing pigs depending on weight of pig and feeding regime. It is estimated that approximately 35% of finishing pigs (40 kg and over) are wet fed and 65% dry fed but with variations across the country (Table 10). Pig numbers were split into 8 categories (Table 6) and a value of excreta output (m3 month21) assigned to each, taking into account these regional estimates of feeding methods. Again, calculations were made in a similar way to those for dairy cows. However, there were some differences. It was assumed there were no weepingwall stores. An allowance for pen cleaning water and disinfection, and drinker leakage was based on 0?5 l pig21 day21. Dirty water run-off was calculated from
VOLUMES AND EXPOSED SURFACE AREAS OF STORED ANIMAL MANURES AND SLURRIES
4. Results
Table 10 ADAS estimates of feeding method for finishing pigs (40 kg and over) ADAS Business Centre Bury St Edmunds Wales Guildford Huntingdon Oxford Preston Starcross Taunton Leeds Lincoln Maidstone Newcastle Wolverhampton Worcester
% Dry fed
% Wet fed
85 40 70 80 80 50 30 30 80 85 70 80 60 60
15 60 30 20 20 50 70 70 20 15 30 20 40 40
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4.1 . Manufacturers ’ data
the exposed surface areas of solid manure heaps stored on concrete pads. No other fouled yard areas were assumed. It was assumed there was no separate dirty water storage on pig farms; and slurry and foul water were stored together. 3.3.6. Poultry , calculation The calculation of laying hen excreta output (m3 month21) assumed that its specific volume is 1 m3 t21. The amount of excreta was calculated according to the percentage of the bird population in each type of housing (deep pit, cages, perchery and free range). An estimate was made of the percentage split of manure spread directly to land and of that destined for storage from each housing type. It was assumed that all excreta which is subsequently stored is in the solid manure category and the stack volumes (field heaps) were calculated using an assumed average period of storage (6 months). Calculations were made in a similar way for broilers except that all birds were assumed to be housed on a deep litter system.
There were twelve replies, including all known major suppliers, but only three of these were able to provide detailed information on a regional basis. The remainder gave information on a national basis. The number of stores and their size allowed typical slurry volumes and exposed surface areas to be estimated. This information was aggregated (Table 11). Seven of the replies contained estimates of store numbers and five were ‘‘actual figures’’. One supplier of weeping-wall stores indicated that a number of their stores were sold as ‘‘lagoon’’ types with no gaps to allow seepage. It is likely that other suppliers of weeping-wall stores have also included such stores. At least two suppliers indicated their records did not go back to 1970 and therefore their estimates are likely to be low. Many companies were not in business in 1970 and one company contacted had gone into liquidation. There are many other types of slurry store on farms which are not pre-fabricated. These include reinforced concrete structures, farm constructed weeping-wall stores using railway sleepers / steel supports and earthbanked lagoons (lined and unlined).
4.2 . ADAS estimates The output data from the calculations were presented as follows (1) Estimated slurry volumes stored given as undiluted excreta (slurry) and diluted slurry. (2) Estimated exposed surface areas of stored diluted slurry. (3) Estimated manure volumes stored given as excreta and excreta plus straw / litter. (4) Estimated exposed surface areas of stored manure (including straw / litter). (5) Estimated volumes and exposed surface areas of stored dirty water where appropriate.
Table 11 Manufacturers’ data on store types for cattle and pig slurry in England and Wales, installed since 1970 Store type
Store numbers
Slurry y olume (m 3 )
Exposed surface area (m 2)
Weeping-wall stores Above-ground circular stores Total
1669 6735 8404
951,990 6,800 6,908,790
446,511 1,530,716 1,977,277
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16
14
Volume stored Mm3
12
10
8
6
4
2
0 Aboveground circular stores
Earthbanked lagoons
Weeping- Concrete Field heaps walls (manure) pads (manure)
Above- Earth-banked lagoons* ground circular stores*
Storage method
Fig. 1. Slurry (dilute) , manure and dirty water storage in England & Wales: ADAS estimates of total y olumes stored. ......... uuu layer hens; h pigs ; h non-dairy cattle; h broilers; h h dairy cows. * Used for dirty water storage only
of field manure heaps (including straw bedding) was attributed to non-dairy cattle at 6?6 Mm3, with 3?2 Mm3 from dairy herds, 1?2 Mm3 from pig herds, 0?5 Mm3 from broilers (including litter) and 0?2 Mm3 from laying hens (excreta only). Manure stored on concrete pads accounted for 1?6 Mm3 (non-dairy cattle), 1?0 Mm3 (dairy cattle) and 0?5 Mm3 (pigs). Exposed surface areas were based on the estimated volumes. Above-ground circular stores containing diluted cow slurry had surface areas of about 1?2 Mm2, earth-banked lagoons 4?7 Mm2, and weeping-wall stores 0?8 Mm2. For non-dairy cattle the exposed surface area estimates were 0?07 Mm2, 1?6 Mm2 and 0?2 Mm2 respectively. For pig slurry the estimates were 0?1 Mm2 (above-ground circular stores) and 0?7 Mm2 (earth-banked lagoons). Exposed surface area of dirty water stores is only significant on dairy units, accounting for 0?7 Mm2. Surface areas of field manure heaps (including straw bedding) were 5?3 Mm2 (non-dairy cattle) , 2?5 Mm2 (dairy cattle), 1?0 Mm2 (pigs), 0?3 Mm2 (broiler, including litter) and 0?1 Mm2 (laying hens, excreta only). Manure stored on concrete pads accounted for 1?3 Mm2 (non-dairy cattle), 0?7 Mm2 (dairy cattle) and 0?5 Mm2 (pigs).
5. Discussion 5.1. Compatibility of estimates from different sources
The estimated volumes related to the maximum amount of slurry, manure or dirty water that were likely to be stored at any one time. They did not include slurry and manure stored within or beneath livestock buildings. Estimates for each of the 15 areas were calculated separately; all data were brought together for England and Wales and are shown in Figs 1 , 2 and 3 . Figure 3 is for undiluted excreta volumes which are included in Figs 1 and 2 . These estimates indicated that 4?5 Mm3 of diluted cow slurry was stored in above-ground circular stores, 10?7 Mm3 in earth-banked lagoons and 1?7 Mm3 in weeping-wall stores. For non-dairy cattle the storage estimates for diluted slurry were 0?3 Mm3, 3?3 Mm3 and 0?4 Mm3 respectively. Diluted pig slurry was not normally collected in weeping-wall stores, but an estimated 0?4 Mm3 was stored in above-ground circular stores and 1?5 Mm3 in earth-banked lagoons. Some dirty water arising from dairy and non-dairy cattle enterprises was stored separately in earth-banked lagoons or above-ground circular stores; this accounted for an estimated (dairy cattle) 1?6 Mm3 and 0?3 Mm3; and (non-dairy cattle) 0?1 Mm3 and 0?02 Mm3 respectively. The largest estimated volume
Data from different sources were obtained in different ways, including postal survey, interview, estimates based on a representative sample of farms and, in this study, consultants’ informed opinion. Some sources had different objectives compared with this study where the intention was to provide input to a gaseous emissions inventory. Comparisons of estimates from various sources were made in respect of above-ground circular stores, weeping-wall stores and earth-banked lagoons (Tables 12, 13 and 14). These tables contain information on store numbers and volumes which includes slurry and all dirty water. Information from the Manchester University study includes Scotland and contains some double counting. The MMB Survey also includes some double counting and, since it was a postal survey, the results may not be from a representative sample. An unspecified number of farms had no storage facilities which indicates that the MMB estimate of store numbers is likely to be too high. The estimated volumes arising from slurry store manufacturers’ data are based on an estimate of typical store size by each manufacturer. Since this has been done, in the main on a national basis, there will
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247
10 9 8
Surface area Mm2
7 6 5 4 3 2 1 0 Aboveground circular stores
Earthbanked lagoons
Weepingwalls
Concrete pads (manure)
Field heaps (manure)
Aboveground circular stores*
Earth-banked lagoons*
Storage method
Fig. 2. Slurry (dilute) , manure and dirty water storage in England & Wales: ADAS estimates of exposed surface areas. ......... uuu layer hens; h pigs ; h non-dairy cattle; h dairy cows . * Used for dirty water storage only h broilers; h
9 8
Volume stored Mm3
7 6 5 4 3 2 1 0 Above-ground circular stores
Earth-banked Weeping-walls lagoons
Concrete pads (manure)
Field heaps (manure)
Storage method
Fig. 3. Slurry and manure storage in England & Wales: ADAS estimates of y olumes of undiluted excreta stored. h pigs; j non-dairy cattle; h dairy cows
be further error in deriving store volume from store numbers. The number of above-ground circular stores (Table 12) associated with dairy cows (MMB and Manchester University) and total store numbers (Manchester University and manufacturers) are in reasonable agreement; the total volumes estimated (manufacturers and ADAS) are also similar. If it is assumed that the majority of weeping-wall stores (Table 13) will be found on dairy farms, there is some agreement between two sets of data (Manchester University and manufacturers). ADAS estimates of volume are double those of the manufacturers’ estimates. This is not surprising since ADAS consultants were asked to consider not just prefabricated stores, that is, those provided by manufacturers, but also their estimates will include farm constructed stores such as those made from ex railway sleepers / steel supports. The ADAS estimate of volume stored is therefore likely to be the more reliable. There is reasonable agreement on earth-banked lagoon numbers (Table 14) associated with dairy cows and the authors conclude that if a typical earth-
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Table 12 Number and volume of above-ground circular stores, comparison of estimates Liy estock species Dairy cows Non-dairy cattle Pigs Total store numbers Total volume Mm3
MMB 3†
Manchester Uniy ersity 2*
Store manufacturers
ADAS
5865 NA NA NA NA
4940 2000 1460 8400 NA
NA NA NA 6735 5?95
NA NA NA NA 5?42
NA Not available. * Manchester University data include Scotland. † Based on 29,328 registered milk producers.
banked lagoon holds 1500 m3 slurry, the ADAS total estimate of 17 M m3 equates to 11,333 stores.
5.2. Limitations of ADAS estimates The census data used in the calculations are accurate but for non-dairy cattle and pigs estimates have been made of age distribution, liveweight distribution and (for pigs) feeding regime by geographical area. Consultants estimates of types of storage were based on a consensus of opinion from more than one person at each ADAS Business Centre. Some Centres have a wide variability in rainfall and topography. Stores of less than 2 weeks capacity were not considered relevant to this study. In three Centres, consultants believe there are substantial numbers of below-ground tanks which contain dirty water with greater than 2 weeks capacity. These were excluded from the results, since dirty water was assumed to be stored in above-ground circular tanks or earth-banked lagoons. Factors and assumptions used in the calculations were based on the best available information and
published data. At best the ADAS estimates are likely to represent the true figure to within Ú10% for surface area and volume and at worst within Ú20%. However, when ADAS output data are compared with existing figures (see Section 5.1), there is good agreement for specific store types.
5.3 . Storage period It should be noted that storage capacity relates to the physical size of the facility and that storage period is the time for which the facility is in use. Storage period is likely to be an important factor in compiling a gaseous emissions inventory. No specific data were collected on the likely storage period for each store type or livestock species. An individual slurry store may be emptied and refilled continuously during the year. Typically an above-ground circular store on a dairy farm may have three months storage capacity, but could contain slurry from October until May, and possibly all year round. A similar store used for pig slurry would be likely to contain some slurry throughout the year.
Table 13 Number and volume of weeping-wall stores, comparison of estimates Liy estock species Dairy cows Non-dairy cattle Total store numbers Total volume Mm3
MMB 3†
Manchester Uniy ersity 2*
Store manufacturers
ADAS
4899 NA NA NA
1830 NR NA NA
NA NA 1669 0?95
NA NA NA 2?13
NA Not available. NR Not recorded. * Manchester University data include Scotland. † Based on 29,328 registered milk producers.
VOLUMES AND EXPOSED SURFACE AREAS OF STORED ANIMAL MANURES AND SLURRIES
249
Table 14 Number and volume of earth-banked lagoons, comparison of estimates Liy estock species Dairy cows Non-dairy cattle Pigs Total store numbers Total volume Mm3
MMB 3†
Manchester Uniy ersity 2*
ADAS
8798 NA NA NA NA
6740 2500 1410 10,650 NA
NA NA NA NA 17?0
NA Not available. * Manchester University data include Scotland. † Based on 29,328 Registered milk producers.
Weeping-wall stores for cattle slurry usually require a period for drying out and are often emptied in mid-July and August, therefore the storage period is likely to total at least nine months, although typical storage capacity is only six months. Earth-banked lagoons containing cattle slurry will be continuously filled during the winter housing period, and apart from dewatering (removing liquid) on some farms, the contents are likely to be removed from April / May onwards. Pig slurry in earth-banked lagoons is likely to be stored over winter and pumped out during the Spring and Summer, but there will be a continuous input of ‘‘new’’ slurry. Storage periods for solid manure are extremely variable ranging from a few weeks to months and sometimes years. However, in the majority of situations three to nine months would be typical. 6. Conclusions The majority of diluted livestock slurry from farms in England and Wales is stored in earth-banked lagoons accounting for an estimated 15?5 Mm3, with another 1?7 Mm3 stored separately as dirty water. Slurry and dirty water from dairy herds account for about 70% of these products. Earth-banked slurry lagoons have a total exposed surface area of about 7?0 Mm2. About 5?1 Mm3 of diluted slurry is stored in aboveground circular stores, with another 0?4 Mm3 stored separately as dirty water; slurry and dirty water from dairy herds account for about 88% of these products. Above-ground circular slurry stores have a total exposed area of about 1?4 Mm2. Weeping-wall stores are used for storing slurry from both dairy and non-dairy cattle accounting for about 2?1 Mm3; slurry from dairy cows contributes about 80% of the total. Total exposed surface area is about 1?0 Mm2. The total volume of solid manure from farms in
England and Wales is 14?9 Mm3 with a total exposed surface area estimated at 11?9 Mm2. The majority is stored in field heaps accounting for an estimated 11?6 Mm3; manure from non-dairy cattle accounts for about 57%, manure from dairy cows about 27% and manure from pigs about 10% of this total. It is believed that, despite limitations, these ADAS estimates of slurry and manure storage volumes and exposed surface areas provide the best currently available data for use in a gaseous emissions inventory for England and Wales. The computer spreadsheet developed in the course of this work will allow information to be updated and sensitivity analyses to be carried out. 7. Acknowledgements Assistance has been given by many ADAS consultants whose efforts were co-ordinated at ADAS Business Centres. Interpretation of census data was carried out by John Baines, ADAS Leeds (non-dairy cattle), David Moorhouse, ADAS Crewe (pigs) and David Mercer, ADAS Nottingham (poultry). Special thanks are given to Ian Muir, ADAS Maidstone for developing the computer spreadsheet, processing data and assisting with data output. Funding from MAFF Environmental Protection Division which enabled this research to be carried out is gratefully acknowledged. References 1
2
3
4
Jarvis S C; Pain B F Ammonia volatilisation from agricultural land. Paper presented to The Fertiliser Society, London, 13th January 1990 Furness G W; Coleman D R; Webb S F; Hendry K The status of waste handling facilities on livestock farms in Great Britain. Manchester University Report to MAFF 1990 / 91 MMB Production R&D Slurry Report, January 1993. MMB publications Estimates of Types of Slurry and Manure Storage in Use
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5
6
7
8
9
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in England & Wales, Related to Livestock Species, MAFF Project No WA0611, March 1994 Sommer S G Ammonia volatilisation during storage of cattle and pig slurry: effect of surface cover. Journal of Agricultural Science 1993, 121, 63 – 71 Safley L M Global Methane Emission from Livestock and Poultry Manure: US EPA, 1992 The Code of Good Agricultural Practice for the Protection of Water, MAFF Booklet PB0587, July 1991. MAFF Publications Fertiliser Recommendations for Agricultural and Horticultural Crops, MAFF Booklet RB209. HMSO MAFF (June 1992) Agricultural Census Frequency Distribution Table 434, Dairy-type cows. MAFF Surveys and Census Branch, Guildford MAFF (June 1992) Agricultural Census Frequency Distribution Table 443, Total cattle and calves. MAFF
11
12
13
14
15
Surveys and Census Branch, Guildford MAFF (June 1992) Agricultural Census Frequency Distribution Table 444, Pig breeding herd. MAFF Surveys and Census Branch, Guildford MAFF (June 1992) Agricultural Census Frequency Distribution Table 446, Total pigs. MAFF Surveys and Census Branch, Guildford MAFF (June 1992) Agricultural Census Frequency Distribution Table 445, Pigs 20 kg and over (excluding breeding pigs and barren sows). MAFF Surveys and Census Branch, Guildford MAFF (June 1992) Agricultural Census Frequency Distribution Table 449, Hens producing eggs for eating. MAFF Surveys and Census Branch, Guildford MAFF (June 1992) Agricultural Census Frequency Distribution Table 452, Table chicken under 9 weeks. MAFF Surveys and Census Branch, Guildford
Estimates of Volumes and Exposed Surface Areas of Stored Animal Manures and Slurries in England & Wales R. J. Nicholson*; A. J. Brewer† *ADAS, Boxworth, Cambridge CB3 8NN †ADAS, Nobel House, 17 Smith Square, London SW1P 3JR (Receiy ed 1 February 1996; accepted in rey ised form 12 December 1996)
Estimates of animal manure (solid material) and slurry (liquid material) stored on farms are needed by the Ministry of Agriculture, Fisheries & Food (MAFF) for compiling national inventories of gaseous emissions. Data needed for this purpose include the total volume and surface area of stored manures and slurries from different livestock species. Existing sources of data were reviewed but have limitations in the context of an emissions inventory. Suppliers of prefabricated stores were approached for numbers and sizes of stores sold since 1970. ADAS pollution control consultants made informed estimates of the geographic distribution of methods of storage in use in England & Wales for manure and slurry from dairy cows, other cattle and pigs. This information was combined with June 1992 census figures to provide estimates of volumes (raw and diluted) and exposed surface areas of stored manures and slurries. ADAS livestock consultants were used to interpret census data and provide estimates of the distribution of poultry manure handling methods. A computer spreadsheet was used to store and process this data and is available to allow future adjustments or sensitivity analyses. In this paper, these estimates are reported on a national basis but they were originally gathered separately for each of 15 areas and appended to a report produced for MAFF. These detailed figures are available on request. The majority of diluted livestock slurry is stored in earth-banked lagoons, with an estimated total volume of 15?5 Mm3 and an estimated surface area of 7?0 Mm2. The total volume of stored solid manure is 14?9 Mm3 with an estimated surface area of 11?9 Mm2. The estimates were compared with data from other sources and show an acceptable level of agreement. ÷ 1997 Silsoe Research Institute 0021-8634 / 97 / 040239 1 12 $25.00 / 0 / ag960139
1. Introduction Housed livestock and stored manures (solid) and slurries (liquid) are thought to contribute significantly to emissions of ammonia and methane from agriculture.1 Because of their environmental effects, an inventory of these gaseous emissions is needed to guide policy makers. MAFF has recently commissioned such an inventory. MAFF is funding research on gaseous emission rates from stored animal excreta which is largely being undertaken by Silsoe Research Institute and the Institute for Grassland and Environmental Research. To complement this research, data on types and numbers of slurry and manure stores in the UK were needed in order to complete the proposed inventory. Limited data on this subject were included in a study by Manchester University2 and a survey by the former Milk Marketing Board (MMB),3 but the figures were not comprehensive, nor were they presented in a form which was suitable for compiling the proposed inventory. Therefore ADAS produced estimates of the types and numbers of manure and slurry stores in use in England and Wales, with data presented in a form that would allow them to be used to produce the proposed inventory. The results of the ADAS work4 form the subject of this paper. The exposed surface area of stored material is likely to be a major factor influencing the amounts of ammonia emitted.5 Method of storage, physical form of the material, and species from which it originates are likely to be important in determining emission rates. Existing information6 indicates that the y olume of stored material, its dry matter content, and the species from which it originates are the major factors influencing methane emissions. For both ammonia and
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methane, the period of storage will influence the amounts of gas emitted. It was agreed that it would be desirable to have an indication of the geographical distribution of amounts and types of stored manures and slurries: this was undertaken for England and Wales. It was concluded that estimates of actual numbers and sizes of stores were not as relevant in this context as total surface area and volume.
2. Existing data The following sources of data were reviewed, and their limitations identified before formulating a strategy for compiling the required estimates.
Table 1 Storage facilities for manure and slurry on farms in Great Britain with dairy herds (estimated numbers and percentages of farms)2 All sizes , population estimate Type of store Midden with impermeable base Midden with permeable base Underfloor slurry tank Slurry: steel tank concrete tank weeping wall store lagoon, impervious lining lagoon, without impervious lining Other
Number
%
12370 2300 4560 4940 3620 1830 2830 3910 2360
34 6 12 14 10 5 8 11 6
* Stores per 100 farms
2.1. MAFF Farm and Consery ation Grant Scheme Data have been collected by MAFF Countryside Division on the uptake of the Farm and Conservation Grant Scheme and its precursors, but records are only easily accessible from 1986 at the earliest. The existing database could be interrogated to provide information on numbers of holdings claiming grant, amount of expenditure, and species, in relation to improvements to waste handling facilities. However no central records were kept of the detail of improvements, such as store type or size. This source of information therefore, while essential in detailing which industry sectors have taken up grant aid, is of no use in providing information for an emission inventory. 2.2. Manchester Uniy ersity study A study by Manchester University,2 provides data on the uptake and effectiveness of the MAFF Farm and Conservation Grant Scheme, and contains useful estimates of types and numbers of manure and slurry stores in use in 1991 based on a sample of around 900 farms. However, the data do have a number of limitations as they make no estimate of size of stores, do not include poultry, and are therefore difficult to interpret in the context of a gaseous emission inventory. The study included an assessment of types of storage facility on farms with dairy herds, on nondairy farms with cattle, and on farms with pigs. Information was presented for small, medium and large farm businesses in a survey of 900 farms in England, Wales and Scotland. However, an estimate for all farm sizes, based on the sample studied,
106
* Some farms have more than one type of store, e.g. provision for both slurry and solid manure.
indicated the number of different types of store on farms with dairy herds, non-dairy farms with cattle and farms with pigs (Tables 1, 2 and 3). The study also provides information on the destination of dilute effluent (commonly called dirty water) arising from contaminated run-off following rainfall and washing water from dairy, cattle and pig farms. This indicates that 32% of dirty water on dairy farms
Table 2 Storage facilities for manure and slurry on non-dairy farms in Great Britain with cattle (estimated numbers and percentages of farms)2 All sizes , population estimate Type of store Midden with impermeable base Midden with permeable base Underfloor slurry tank Slurry: steel tank lagoon, impervious lining lagoon, unlined Other No specific store*
Number
%
8900 4000 2800 2000 800 1700 3600 27400
17 7 5 4 1 3 7 51
* For farms with housed cattle: many leave manure in bedded yards. Note: data presented as given in original source.
VOLUMES AND EXPOSED SURFACE AREAS OF STORED ANIMAL MANURES AND SLURRIES
Table 3 Storage facilities for manure and slurry on farms in Great Britain with pigs (estimated numbers and percentages of farms)2 All sizes , population estimate Type of store * Midden with impermeable base Midden with permeable base Underfloor slurry tank Slurry: steel tank concrete tank lagoon, impervious lining lagoon, pervious lining Other (including field heaps) *Stores per 100 farms
%
2.5 . MAFF census data
4100 540 2930 520 1460 870 540 940
41 5 30 5 15 9 6 9 120
June census data collected annually by MAFF Census Branch at Guildford provide very accurate information on numbers and types of livestock on a county basis. This information was used in conjunction with advisers’ estimates as described in Section 3.3.
is stored with slurry and 13% is stored separately; on pig farms 16% of dirty water is stored with slurry and 10% is stored separately. Hence dirty water must be taken into account when calculating slurry store capacity. 2.3. MMB sury ey The survey carried out by MMB3 in 1993 included questions on slurry storage methods. All milk producers in England and Wales were sent a questionnaire which drew replies from 8212 producers (a 28% response rate). The majority of farms in the sample housed cows in cubicles (83%). For farms with some form of slurry and manure storage, the different types of store were assessed (Table 4). 2.4. Liy estock housing Estimates produced by ADAS, for MAFF Environmental Protection Division, on types and numbers of Table 4 Slurry and manure storage methods on dairy farms in England & Wales3 (An unspecified number of farms had no storage facilities)
Towers* Earth-walled lagoons Weeping wall stores Concrete pads Other
poultry houses and types and numbers of pig housing in England and Wales provided useful background data on the forms in which excreta are likely to be handled. The data on poultry housing are reasonably straightforward, while the data on pig housing are complex and difficult to interpret.
Number
* Some farms have more than one type of store.
Store type
241
Percentage of farms % 20 30 15 19 23
* ‘‘Towers’’ are above-ground cylindrical stores. Note: some farms have more than one type of store. Data presented as given in original source.
3. Methodology 3.1 . Oy erall approach While attempts were made to collect data on numbers and types of prefabricated stores, it was apparent that this would not take account of large numbers of structures built in -situ . ADAS consultants in the field were not able to give a direct estimate of store numbers, or volumes and surface areas of stored material. However, using their experience they could reliably assign values to the percentages of different types of system installed in their particular geographic area, and relate these values to class of livestock. Therefore, it was decided that an indirect approach would be adopted. MAFF census figures for numbers of livestock are known to be accurate. ‘‘Text-book’’ values7,8 of excreta output for a particular livestock species give realistic estimates and are extensively used for calculating storage capacity needed on a particular site. It was concluded that the best accuracy, within the limitations of an indirect approach, could be achieved by calculating total volumes of undiluted excreta from livestock numbers and excreta output, and then subsequently estimating the proportion stored by different methods. Therefore, effort was targeted on collecting information in the broad sub-divisions of species, for the form in which excreta are handled (solid or liquid), and type of store and storage period (Table 5, the categories in this table apply to more than one species and the table is not to be read across line by line). Manure and slurry stored within buildings was not included in this study. In respect of storage capacity (Table 5) it was arbitrarily decided to ignore any storage capacity of less than two weeks, because it was unlikely to be significant in contributing to overall emissions. An attempt was made, in the case of dairy cows, to make
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Table 5 Categories used for data collection and presentation Species / Numbers Dairy cows Other cattle Pigs
Slurry storage Above-ground circular Weeping wall Lagoons and compounds (below-ground)
Manure storage Concrete pad Field heap
Storage capacity Months
Quantitatiy e data Volume stored Exposed surface area
Poultry
a separate estimate of quantities of dilute effluent (dirty water) stored for more than two weeks. As estimates drew heavily on the knowledge of local ADAS pollution control consultants, any data on geographical distribution were based on the fifteen ADAS Consultancy Centres which existed in 1993 / 4. 3.2. Manufacturers ’ data Manufacturers and suppliers of prefabricated slurry stores, in particular circular above-ground structures and weeping-wall structures, were presumed to have records of numbers of stores sold. A decision was made to approach them for this information but it was accepted that any data collected by this route could have limitations if replies were not received from all companies. A large number of stores currently in use (e.g. earth-banked structures and manure stores) are constructed locally and would not be covered by this approach. A total of 21 manufacturers or suppliers of prefabricated slurry stores were sent questionnaires to obtain information on the likely population of above-ground circular stores and weeping-wall stores in England and Wales. They were asked to estimate store numbers and typical store size, by livestock species (pigs and cattle) and by area (ADAS Business Centre) installed since 1970. For those who could not provide this level of detail, an opportunity was given to record information for ‘‘Southern Counties’’, ‘‘Northern Counties’’ and Wales or on a total (England and Wales) basis. 3.3. ADAS estimates ADAS pollution control consultants have good local knowledge of types of store in use, largely through pollution control advisory visits. Questionnaires were developed to obtain informed estimates of manure and slurry storage methods on dairy, beef and pig farms. Each questionnaire broadly followed the same format but allowed for differences in slurry management between livestock species. In addition, to improve the quality of these estimates, the ‘‘dairy cow’’ questionnaire contained questions for herds of less than 100 cows and for herds of 100 cows and over. Consultants from each Business Centre
were asked to reach a consensus opinion on the proportion of manure and slurry stored for each livestock species. Methods of storing manure and slurry were estimated as percentages of their respective total volumes. For each storage method an estimate was made of typical capacity (months) and typical storage depth (m). The destination of dirty water was assessed and allocated to ‘‘stored with slurry’’ or ‘‘stored separately’’ or ‘‘stored for less than two weeks’’. Methods of storing dirty water separately (i.e. not with slurry) were assessed and a proportion was allocated to above-ground circular stores and lagoons. Data from the questionnaires were processed using a computer spreadsheet (Microsoft Excel). Data for livestock numbers were taken from the June 1992 MAFF Census Frequency Distribution Tables. Information on volumes of excreta produced was based on standard data,7,8 but modified to accord with the appropriate feeding method (pigs), weight, age, and class of livestock where necessary. Spreadsheets were developed for each livestock species, that is, for dairy cows, other cattle and pigs. Specialist ADAS consultants for cattle and pigs assisted with interpretation of census data. Estimates of manure output from two classes of poultry (laying hens and broilers) were made separately with assistance from a specialist ADAS consultant. Spreadsheets were developed for each class.
3.3 .1 . Data inputs For each livestock species, an appropriate set of data was used in the calculation of manure, slurry and dirty water volumes and exposed surface areas. Examples are given in Tables 6 and 7. Common data used in these calculations, such as dilution factors and storage depths, are given in Table 8. The effect of changing any of these data could be demonstrated by allowing the appropriate spreadsheet to re-calculate volumes and surface areas. A dilution factor for above-ground circular slurry stores has been used to take account of incident rainfall. Similarly, a dilution factor for lagoons serves the same purpose and allows for the typical surface
VOLUMES AND EXPOSED SURFACE AREAS OF STORED ANIMAL MANURES AND SLURRIES
243
Table 6 Example input data for cattle and pigs Dairy
Beef
Pigs
Age
Excreta output *
Age (months )
Excreta output * m 3 d 21 animal 21
Adult
0?057 m3 d21 cow21
,6 6 – 12 12 – 24 .24
0?007 0?012 0?022 0?027
Parlour wash water Fouled, unroofed yard area
*18 l d21 cow21 10 m2 cow21
Wash water Fouled, unroofed yard area
Not applicable 1 m2 animal21
Weight / type
Excreta output * m 3 d 1 pig 21
Breeding (dry fed) Breeding (wet fed) ,20 kg 20 to 40 kg Finishing (dry fed) Finishing (wet fed, 3?5 to1)
0?0065 0?0075 0?002 0?003 0?0045 0?007
Finishing (wet fed, 5 to 1) Finishing (swill) Clean down water Fouled, unroofed yard area
0?011 0?014 *0?0005 Not applicable
* Volumes based on sources.7,8
area of a lagoon to be greater than for an aboveground circular store of similar volume. Where manure is collected as a ‘‘solid’’ it is most often mixed with straw bedding. The addition of straw provides greater bulk and the volume assessment uses the ‘‘straw addition factor’’ to take account of this. It is impossible to estimate surface areas of stored manure without making assumptions about typical stack size, since exposed surface areas will consist of stack top plan area and the area of its sloping sides. For the purpose of this study it is assumed each stack is rectangular with a flat top and vertical sides. A consensus of opinion from ADAS pollution control consultants indicated that the plan area of a typical stack is 200 m2 with 20 m by 10 m sides (perimeter is 60 m). The combined surface area of a series of stacks of this size, forming an estimated total volume arising from a particular species and / or geographical area can then be calculated as follows (all dimensions in m): Estimated number of stacks (n ) 5 Total estimated volume of manure / 200D Total exposed surface area 5 n 3 [200 1 60D ] where D is the depth (or height) of stack.
Similarly, following consultation with ADAS pollution control consultants, typical values have been assumed for solid manure depth in buildings and for slurry depth under slats. These values allow for checking calculations and provide consistency in spreadsheet operation although manure and slurry storage within buildings is not included in this study. Considerable amounts of dirty water are produced, particularly on dairy farms, and where this is added to slurry it will increase the size of slurry store required. No specific surveys have been carried out on quantities arising. The ADAS Agro-meteorological Unit therefore provided an average October to March rainfall for each of the 15 areas to enable appropriate calculations to be made. Values ranged from 309 mm (Bury St Edmunds) to 748 mm (Cardiff). 3.3 .2 . Census data June census data for all dairy cows and according to herd size were used in the calculations.9 Non-dairy cattle numbers were derived from the total numbers of cattle and calves10 less the numbers of dairy cows.9 The percentage distribution of all non-dairy cattle by age was combined with individual county estimates to
Table 7 Example input data for poultry
Excreta output* kg d21 bird21 Specific volume of manure l kg21 Housing occupancy % * Source.8
Laying hens
Broilers
0?115 1?0 96
0?073 1?0 88
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Table 8 Standard dilution factors and store dimensions Dimension
Measurement
Dilution factor, circular slurry stores Dilution factor, slurry lagoons Straw addition factor (for farmyard manure) Solid manure depth in buildings Solid manure store perimeter Solid manure store area Under-slat slurry depth Depth of typical above-ground circular stores Depth of typical lagoons
1?15 1?35 1?5 0?75 m 60 m 200 m2 1m 3?5 m 2?5 m
provide the distribution of such animals for each of the 15 areas. This has been aggregated (Table 9) into estimates for England and for Wales. For simplicity, census data on pigs relating to herd size groups 1 – 9, and 10 – 19 pigs were omitted both for the breeding herd11 and for total pigs12 as these represented very small numbers. Data for the remaining pig breeding herd were multiplied by a factor of 1?22 to take account of boars, maiden gilts and barren sows. Data for all other pigs 20 kg and over13 were subtracted from data for total pigs to arrive at numbers of pigs 20 kg and under. For pigs 20 kg and over, 30% were calculated to be in the 20 kg to 40 kg weight range and 70%, 40 kg and over. Census data for all laying hens14 and all broilers15 according to flock size were used in the calculations. 3.3.3. Dairy cows , calculation The volume of excreta produced per month was calculated and data from the questionnaires were used to allocate this output into slurry and solid manure. Slurry store volumes were calculated using the consultants’ estimates of the proportion allocated to different store types, multiplied by the storage capaTable 9 Percentage distribution of non-dairy cattle by age Age Fully grown animals: 2 yrs old and over Growing cattle: 1 yr to 2 yr old Six months to 1 yr old Calves under six months old Total
England
Wales
33%
38%
30% 20% 17% 100%
28% 17% 17% 100%
city (months). A value was given for undiluted excreta and for a dilute product (rainfall and dirty water added). The dilute slurry volume was calculated by applying the appropriate dilution factor to the excreta volume and then adding any dirty water (subsequently calculated) which was destined to be stored with slurry. Any dirty water added in this way was assumed to be stored for the same period and was allocated on a pro-rata basis only to above-ground circular stores and to lagoons. Surface areas were calculated by dividing volume by depth. Excreta volume was converted into an ‘‘excreta and straw’’ manure volume by using the straw addition factor. Exposed surface areas of manure heaps or stacks were calculated using the formula given in Section 3.3.1. Dirty water production per month was calculated from the standard figure for parlour wash water with the addition of rainfall from unroofed fouled yard area (10 m2 cow21). An assessment of the destination of dirty water was made because some is stored with slurry and some is stored separately. Volumes of dirty water stores were calculated using a proportion allocated to different store types multiplied by the storage capacity (months). Surface areas were calculated by dividing volume by depth.
3.3 .4 . Non dairy cattle , calculation Calculations were made in a similar way to those for dairy cows once the assessment of excreta output (m3 month21) had been made. However, there was no parlour wash water and a nominal 1 m2 animal21 fouled yard area was used to calculate an allowance for dirty water production.
3.3 .5 . Pigs , calculation There is large variation in slurry output from finishing pigs depending on weight of pig and feeding regime. It is estimated that approximately 35% of finishing pigs (40 kg and over) are wet fed and 65% dry fed but with variations across the country (Table 10). Pig numbers were split into 8 categories (Table 6) and a value of excreta output (m3 month21) assigned to each, taking into account these regional estimates of feeding methods. Again, calculations were made in a similar way to those for dairy cows. However, there were some differences. It was assumed there were no weepingwall stores. An allowance for pen cleaning water and disinfection, and drinker leakage was based on 0?5 l pig21 day21. Dirty water run-off was calculated from
VOLUMES AND EXPOSED SURFACE AREAS OF STORED ANIMAL MANURES AND SLURRIES
4. Results
Table 10 ADAS estimates of feeding method for finishing pigs (40 kg and over) ADAS Business Centre Bury St Edmunds Wales Guildford Huntingdon Oxford Preston Starcross Taunton Leeds Lincoln Maidstone Newcastle Wolverhampton Worcester
% Dry fed
% Wet fed
85 40 70 80 80 50 30 30 80 85 70 80 60 60
15 60 30 20 20 50 70 70 20 15 30 20 40 40
245
4.1 . Manufacturers ’ data
the exposed surface areas of solid manure heaps stored on concrete pads. No other fouled yard areas were assumed. It was assumed there was no separate dirty water storage on pig farms; and slurry and foul water were stored together. 3.3.6. Poultry , calculation The calculation of laying hen excreta output (m3 month21) assumed that its specific volume is 1 m3 t21. The amount of excreta was calculated according to the percentage of the bird population in each type of housing (deep pit, cages, perchery and free range). An estimate was made of the percentage split of manure spread directly to land and of that destined for storage from each housing type. It was assumed that all excreta which is subsequently stored is in the solid manure category and the stack volumes (field heaps) were calculated using an assumed average period of storage (6 months). Calculations were made in a similar way for broilers except that all birds were assumed to be housed on a deep litter system.
There were twelve replies, including all known major suppliers, but only three of these were able to provide detailed information on a regional basis. The remainder gave information on a national basis. The number of stores and their size allowed typical slurry volumes and exposed surface areas to be estimated. This information was aggregated (Table 11). Seven of the replies contained estimates of store numbers and five were ‘‘actual figures’’. One supplier of weeping-wall stores indicated that a number of their stores were sold as ‘‘lagoon’’ types with no gaps to allow seepage. It is likely that other suppliers of weeping-wall stores have also included such stores. At least two suppliers indicated their records did not go back to 1970 and therefore their estimates are likely to be low. Many companies were not in business in 1970 and one company contacted had gone into liquidation. There are many other types of slurry store on farms which are not pre-fabricated. These include reinforced concrete structures, farm constructed weeping-wall stores using railway sleepers / steel supports and earthbanked lagoons (lined and unlined).
4.2 . ADAS estimates The output data from the calculations were presented as follows (1) Estimated slurry volumes stored given as undiluted excreta (slurry) and diluted slurry. (2) Estimated exposed surface areas of stored diluted slurry. (3) Estimated manure volumes stored given as excreta and excreta plus straw / litter. (4) Estimated exposed surface areas of stored manure (including straw / litter). (5) Estimated volumes and exposed surface areas of stored dirty water where appropriate.
Table 11 Manufacturers’ data on store types for cattle and pig slurry in England and Wales, installed since 1970 Store type
Store numbers
Slurry y olume (m 3 )
Exposed surface area (m 2)
Weeping-wall stores Above-ground circular stores Total
1669 6735 8404
951,990 6,800 6,908,790
446,511 1,530,716 1,977,277
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16
14
Volume stored Mm3
12
10
8
6
4
2
0 Aboveground circular stores
Earthbanked lagoons
Weeping- Concrete Field heaps walls (manure) pads (manure)
Above- Earth-banked lagoons* ground circular stores*
Storage method
Fig. 1. Slurry (dilute) , manure and dirty water storage in England & Wales: ADAS estimates of total y olumes stored. ......... uuu layer hens; h pigs ; h non-dairy cattle; h broilers; h h dairy cows. * Used for dirty water storage only
of field manure heaps (including straw bedding) was attributed to non-dairy cattle at 6?6 Mm3, with 3?2 Mm3 from dairy herds, 1?2 Mm3 from pig herds, 0?5 Mm3 from broilers (including litter) and 0?2 Mm3 from laying hens (excreta only). Manure stored on concrete pads accounted for 1?6 Mm3 (non-dairy cattle), 1?0 Mm3 (dairy cattle) and 0?5 Mm3 (pigs). Exposed surface areas were based on the estimated volumes. Above-ground circular stores containing diluted cow slurry had surface areas of about 1?2 Mm2, earth-banked lagoons 4?7 Mm2, and weeping-wall stores 0?8 Mm2. For non-dairy cattle the exposed surface area estimates were 0?07 Mm2, 1?6 Mm2 and 0?2 Mm2 respectively. For pig slurry the estimates were 0?1 Mm2 (above-ground circular stores) and 0?7 Mm2 (earth-banked lagoons). Exposed surface area of dirty water stores is only significant on dairy units, accounting for 0?7 Mm2. Surface areas of field manure heaps (including straw bedding) were 5?3 Mm2 (non-dairy cattle) , 2?5 Mm2 (dairy cattle), 1?0 Mm2 (pigs), 0?3 Mm2 (broiler, including litter) and 0?1 Mm2 (laying hens, excreta only). Manure stored on concrete pads accounted for 1?3 Mm2 (non-dairy cattle), 0?7 Mm2 (dairy cattle) and 0?5 Mm2 (pigs).
5. Discussion 5.1. Compatibility of estimates from different sources
The estimated volumes related to the maximum amount of slurry, manure or dirty water that were likely to be stored at any one time. They did not include slurry and manure stored within or beneath livestock buildings. Estimates for each of the 15 areas were calculated separately; all data were brought together for England and Wales and are shown in Figs 1 , 2 and 3 . Figure 3 is for undiluted excreta volumes which are included in Figs 1 and 2 . These estimates indicated that 4?5 Mm3 of diluted cow slurry was stored in above-ground circular stores, 10?7 Mm3 in earth-banked lagoons and 1?7 Mm3 in weeping-wall stores. For non-dairy cattle the storage estimates for diluted slurry were 0?3 Mm3, 3?3 Mm3 and 0?4 Mm3 respectively. Diluted pig slurry was not normally collected in weeping-wall stores, but an estimated 0?4 Mm3 was stored in above-ground circular stores and 1?5 Mm3 in earth-banked lagoons. Some dirty water arising from dairy and non-dairy cattle enterprises was stored separately in earth-banked lagoons or above-ground circular stores; this accounted for an estimated (dairy cattle) 1?6 Mm3 and 0?3 Mm3; and (non-dairy cattle) 0?1 Mm3 and 0?02 Mm3 respectively. The largest estimated volume
Data from different sources were obtained in different ways, including postal survey, interview, estimates based on a representative sample of farms and, in this study, consultants’ informed opinion. Some sources had different objectives compared with this study where the intention was to provide input to a gaseous emissions inventory. Comparisons of estimates from various sources were made in respect of above-ground circular stores, weeping-wall stores and earth-banked lagoons (Tables 12, 13 and 14). These tables contain information on store numbers and volumes which includes slurry and all dirty water. Information from the Manchester University study includes Scotland and contains some double counting. The MMB Survey also includes some double counting and, since it was a postal survey, the results may not be from a representative sample. An unspecified number of farms had no storage facilities which indicates that the MMB estimate of store numbers is likely to be too high. The estimated volumes arising from slurry store manufacturers’ data are based on an estimate of typical store size by each manufacturer. Since this has been done, in the main on a national basis, there will
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247
10 9 8
Surface area Mm2
7 6 5 4 3 2 1 0 Aboveground circular stores
Earthbanked lagoons
Weepingwalls
Concrete pads (manure)
Field heaps (manure)
Aboveground circular stores*
Earth-banked lagoons*
Storage method
Fig. 2. Slurry (dilute) , manure and dirty water storage in England & Wales: ADAS estimates of exposed surface areas. ......... uuu layer hens; h pigs ; h non-dairy cattle; h dairy cows . * Used for dirty water storage only h broilers; h
9 8
Volume stored Mm3
7 6 5 4 3 2 1 0 Above-ground circular stores
Earth-banked Weeping-walls lagoons
Concrete pads (manure)
Field heaps (manure)
Storage method
Fig. 3. Slurry and manure storage in England & Wales: ADAS estimates of y olumes of undiluted excreta stored. h pigs; j non-dairy cattle; h dairy cows
be further error in deriving store volume from store numbers. The number of above-ground circular stores (Table 12) associated with dairy cows (MMB and Manchester University) and total store numbers (Manchester University and manufacturers) are in reasonable agreement; the total volumes estimated (manufacturers and ADAS) are also similar. If it is assumed that the majority of weeping-wall stores (Table 13) will be found on dairy farms, there is some agreement between two sets of data (Manchester University and manufacturers). ADAS estimates of volume are double those of the manufacturers’ estimates. This is not surprising since ADAS consultants were asked to consider not just prefabricated stores, that is, those provided by manufacturers, but also their estimates will include farm constructed stores such as those made from ex railway sleepers / steel supports. The ADAS estimate of volume stored is therefore likely to be the more reliable. There is reasonable agreement on earth-banked lagoon numbers (Table 14) associated with dairy cows and the authors conclude that if a typical earth-
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Table 12 Number and volume of above-ground circular stores, comparison of estimates Liy estock species Dairy cows Non-dairy cattle Pigs Total store numbers Total volume Mm3
MMB 3†
Manchester Uniy ersity 2*
Store manufacturers
ADAS
5865 NA NA NA NA
4940 2000 1460 8400 NA
NA NA NA 6735 5?95
NA NA NA NA 5?42
NA Not available. * Manchester University data include Scotland. † Based on 29,328 registered milk producers.
banked lagoon holds 1500 m3 slurry, the ADAS total estimate of 17 M m3 equates to 11,333 stores.
5.2. Limitations of ADAS estimates The census data used in the calculations are accurate but for non-dairy cattle and pigs estimates have been made of age distribution, liveweight distribution and (for pigs) feeding regime by geographical area. Consultants estimates of types of storage were based on a consensus of opinion from more than one person at each ADAS Business Centre. Some Centres have a wide variability in rainfall and topography. Stores of less than 2 weeks capacity were not considered relevant to this study. In three Centres, consultants believe there are substantial numbers of below-ground tanks which contain dirty water with greater than 2 weeks capacity. These were excluded from the results, since dirty water was assumed to be stored in above-ground circular tanks or earth-banked lagoons. Factors and assumptions used in the calculations were based on the best available information and
published data. At best the ADAS estimates are likely to represent the true figure to within Ú10% for surface area and volume and at worst within Ú20%. However, when ADAS output data are compared with existing figures (see Section 5.1), there is good agreement for specific store types.
5.3 . Storage period It should be noted that storage capacity relates to the physical size of the facility and that storage period is the time for which the facility is in use. Storage period is likely to be an important factor in compiling a gaseous emissions inventory. No specific data were collected on the likely storage period for each store type or livestock species. An individual slurry store may be emptied and refilled continuously during the year. Typically an above-ground circular store on a dairy farm may have three months storage capacity, but could contain slurry from October until May, and possibly all year round. A similar store used for pig slurry would be likely to contain some slurry throughout the year.
Table 13 Number and volume of weeping-wall stores, comparison of estimates Liy estock species Dairy cows Non-dairy cattle Total store numbers Total volume Mm3
MMB 3†
Manchester Uniy ersity 2*
Store manufacturers
ADAS
4899 NA NA NA
1830 NR NA NA
NA NA 1669 0?95
NA NA NA 2?13
NA Not available. NR Not recorded. * Manchester University data include Scotland. † Based on 29,328 registered milk producers.
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Table 14 Number and volume of earth-banked lagoons, comparison of estimates Liy estock species Dairy cows Non-dairy cattle Pigs Total store numbers Total volume Mm3
MMB 3†
Manchester Uniy ersity 2*
ADAS
8798 NA NA NA NA
6740 2500 1410 10,650 NA
NA NA NA NA 17?0
NA Not available. * Manchester University data include Scotland. † Based on 29,328 Registered milk producers.
Weeping-wall stores for cattle slurry usually require a period for drying out and are often emptied in mid-July and August, therefore the storage period is likely to total at least nine months, although typical storage capacity is only six months. Earth-banked lagoons containing cattle slurry will be continuously filled during the winter housing period, and apart from dewatering (removing liquid) on some farms, the contents are likely to be removed from April / May onwards. Pig slurry in earth-banked lagoons is likely to be stored over winter and pumped out during the Spring and Summer, but there will be a continuous input of ‘‘new’’ slurry. Storage periods for solid manure are extremely variable ranging from a few weeks to months and sometimes years. However, in the majority of situations three to nine months would be typical. 6. Conclusions The majority of diluted livestock slurry from farms in England and Wales is stored in earth-banked lagoons accounting for an estimated 15?5 Mm3, with another 1?7 Mm3 stored separately as dirty water. Slurry and dirty water from dairy herds account for about 70% of these products. Earth-banked slurry lagoons have a total exposed surface area of about 7?0 Mm2. About 5?1 Mm3 of diluted slurry is stored in aboveground circular stores, with another 0?4 Mm3 stored separately as dirty water; slurry and dirty water from dairy herds account for about 88% of these products. Above-ground circular slurry stores have a total exposed area of about 1?4 Mm2. Weeping-wall stores are used for storing slurry from both dairy and non-dairy cattle accounting for about 2?1 Mm3; slurry from dairy cows contributes about 80% of the total. Total exposed surface area is about 1?0 Mm2. The total volume of solid manure from farms in
England and Wales is 14?9 Mm3 with a total exposed surface area estimated at 11?9 Mm2. The majority is stored in field heaps accounting for an estimated 11?6 Mm3; manure from non-dairy cattle accounts for about 57%, manure from dairy cows about 27% and manure from pigs about 10% of this total. It is believed that, despite limitations, these ADAS estimates of slurry and manure storage volumes and exposed surface areas provide the best currently available data for use in a gaseous emissions inventory for England and Wales. The computer spreadsheet developed in the course of this work will allow information to be updated and sensitivity analyses to be carried out. 7. Acknowledgements Assistance has been given by many ADAS consultants whose efforts were co-ordinated at ADAS Business Centres. Interpretation of census data was carried out by John Baines, ADAS Leeds (non-dairy cattle), David Moorhouse, ADAS Crewe (pigs) and David Mercer, ADAS Nottingham (poultry). Special thanks are given to Ian Muir, ADAS Maidstone for developing the computer spreadsheet, processing data and assisting with data output. Funding from MAFF Environmental Protection Division which enabled this research to be carried out is gratefully acknowledged. References 1
2
3
4
Jarvis S C; Pain B F Ammonia volatilisation from agricultural land. Paper presented to The Fertiliser Society, London, 13th January 1990 Furness G W; Coleman D R; Webb S F; Hendry K The status of waste handling facilities on livestock farms in Great Britain. Manchester University Report to MAFF 1990 / 91 MMB Production R&D Slurry Report, January 1993. MMB publications Estimates of Types of Slurry and Manure Storage in Use
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6
7
8
9
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in England & Wales, Related to Livestock Species, MAFF Project No WA0611, March 1994 Sommer S G Ammonia volatilisation during storage of cattle and pig slurry: effect of surface cover. Journal of Agricultural Science 1993, 121, 63 – 71 Safley L M Global Methane Emission from Livestock and Poultry Manure: US EPA, 1992 The Code of Good Agricultural Practice for the Protection of Water, MAFF Booklet PB0587, July 1991. MAFF Publications Fertiliser Recommendations for Agricultural and Horticultural Crops, MAFF Booklet RB209. HMSO MAFF (June 1992) Agricultural Census Frequency Distribution Table 434, Dairy-type cows. MAFF Surveys and Census Branch, Guildford MAFF (June 1992) Agricultural Census Frequency Distribution Table 443, Total cattle and calves. MAFF
11
12
13
14
15
Surveys and Census Branch, Guildford MAFF (June 1992) Agricultural Census Frequency Distribution Table 444, Pig breeding herd. MAFF Surveys and Census Branch, Guildford MAFF (June 1992) Agricultural Census Frequency Distribution Table 446, Total pigs. MAFF Surveys and Census Branch, Guildford MAFF (June 1992) Agricultural Census Frequency Distribution Table 445, Pigs 20 kg and over (excluding breeding pigs and barren sows). MAFF Surveys and Census Branch, Guildford MAFF (June 1992) Agricultural Census Frequency Distribution Table 449, Hens producing eggs for eating. MAFF Surveys and Census Branch, Guildford MAFF (June 1992) Agricultural Census Frequency Distribution Table 452, Table chicken under 9 weeks. MAFF Surveys and Census Branch, Guildford
