Balanced fertilization in relation to organic fertilizers

Fertilizers and balanced fertilizer use...

1. Documentation of research results is an important precondition of successful extension.

2. P-fertilizer from national resources.

3. Local “bio-fertilizer” production site.

4. Vietnamese NPK mix based on standardized imported mineral fertilizers.

5. Comparing balanced fertilizer use (at right) with farmers’ practice (at left).

...and the results in the field.

6. Long -term fertilizer experiments at representative sites are essential for regional recommendations.

9. Balanced nutrition of crops (background) results in optimum productivity.

7. The use of FYM in addition to mineral fertilizer (left side) improves soil conditions and plant growth.

8. Balanced fertilizer use (background) improves crop growth.

10. The result of balanced fertilizer use: A healthy productive crop (left).

33

Balanced fertilization for improved fertilizer efficiency In spite of Vietnam’s impressive fertilizer consumption record, fertilizer use efficiency is estimated to be only at 35– 45% for N fertilizers, and 50–60% for P and K fertilizers. This is attributed mainly to farmers’ lack the knowledge in their proper use. Balanced fertilization (BF) or balanced crop nutrition is a relatively new concept that has been used more widely only since its introduction through the IFA-sponsored project Balanced Fertilization for Better Crops in Vietnam (BALCROP) that was initiated in 1994 (Box 2-1).

Nutrient demand Crop performance is optimized when all essential nutrients are provided in sufficient amounts and held readily available during crop growth (i.e. maximum exploitation of yield potential). Balanced fertilization is the deliberate application of essential plant nutrients to soils that are unable to supply these nutrients in order to meet crop demand at a specific location. Since agroecosystems are open and dynamic systems, BF aims at nutrient supplementation in order to assist crop performance while minimizing nutrient losses.

Box 2-1 The concept of balanced fertilization.

Balanced fertilization (BF) is one of the keys to improving fertilizer use efficiency. In principle, the concept of BF aims at a dynamic balance between nutrient requirement and nutrient uptake by crops. This is achieved by maintaining the equilibrium between nutrients available at different growth stages; between the supply of nutrients from fertilizers and from natural nutrient pools in accordance with conditions relevant to the effectiveness of fertilizer nutrient uptake (e.g. soil properties, water regimes, weather conditions, etc.). Balanced fertilization also improves nutrient use by crops in crop rotations and farming systems.

34

Sources of nutrients Nutrients sources can be of mineral or organic origin. It is desirable (and is one of the principles of BF) to make full use of both these sources in an integrated way that is economically and environmentally sound. Recently, organic farming has been promoted as an alternative to common agriculture in Vietnam. Using organic fertilizers (obtained from organic wastes) as sole nutrient sources, organic farmers claim to provide an optimum nutrient balance in support of both large sustainable crop yields and a safe environment. Under increasing cropping intensity and rising food demand in Vietnam, however, organic fertilizers can only be an additional source of nutrients as well as a factor for improving soil physical and chemical conditions. In fact, Vietnam’s agriculture depends increasingly on manufactured (and mostly imported) fertilizers as major nutrient sources. Organic fertilizers, especially farmyard manure (FYM) applied regularly at rates of 8–10 t crop-1 ha-1, continue to play an important role beyond the supply of nutrients by the enhancement of soil structure, water storage, cation exchange capacity (CEC) and biological activity.

Balanced fertilization in relation to soil nutrient contents One main characteristic of the majority of soils in Vietnam is the small amount of

(naturally available) nutrients, which is insufficient for sustaining high yields. In addition, many soils are affected by yieldlimiting factors such as severe soil acidity, aluminum toxicity, saline water intrusion and a high level of soil alkalinity. The alluvial soils of the RRD and MRD, and soils originating from basalt and limestone, usually have larger contents of soil N (0.1–0.2%), P (>0.03%) and K (1.5– 2%). Most other soils have small reserves of total N (< 0.15%), total P (0.03–0.06%) and total K (0.3–0.5%), and small contents of plant-available N, P, and K (see Table 2-1). Crops require N, P, and K nutrients in the largest quantities, and the availability of these nutrients in soils is the most significant factor in fertilizer supply. On acid soils, Ca and Mg deficiencies are particularly relevant in the choice of fertilizer materials used. Where S and Zn deficiencies occur, fertilizer sources must provide an adequate supply of these nutrients. For example, S will not be supplied where urea, diammonium phosphate (DAP), and muriate of potash (MOP) are used as the sole fertilizer nutrient sources.

Soil fertility status in Vietnam The widespread soil fertility decline in Vietnam is attributed to many factors: soil erosion, soil nutrient leaching, nutrient export in crop produce and crop residues not returned to the soil. In addition, there has been an increase in crop nutrient uptake due to cropland intensification as well as the use of modern high-yielding

35 varieties. The rapid intensification of agricultural cropland resulted in an imbalance in fertilizer use, especially excessive use of fertilizer N in comparison with other fertilizer nutrients. This increasing mobilization and uptake of P, K, and other nutrients from the soil reserves is termed ‘soil mining’.

paddy soils had a large content of total K (1.2–2.1%), and traditional rice varieties with smaller yield potentials had small requirements for nutrients. In addition, K uptake by rice was sufficient due to the generally lower levels of N application and application of large amounts of FYM as a source of K.

In general >50% of cultivated soils in Vietnam have low nutrient contents. Results of routine soil testing conducted recently reveal that 48% of soil samples are deficient in Mg, 72% in Ca, 80% in K, and 87% in P.

Between 1975 and 2000, however, the area planted annually to rice increased from 4.9 M ha to 7.8 M ha, i.e. cropping intensity has increased from 1.2 to 1.9 rice crops per year over the last 25 years. Where traditional rice systems were cropped only once or twice per year, now three or even four crops per year are produced on many of Vietnam’s irrigated lowland soils. During the same period, traditional local varieties were increasingly replaced by modern high-yielding varieties. Average paddy yields in Vietnam increased from 2.1 to 4.3 t ha-1.

Nutrient imbalance At the start of Vietnam’s latest phase of rapid intensification of croplands (around 1990), it was determined that all soils were deficient in N. Thus fertilizer N application caused remarkable yield response. Almost everywhere in Vietnam, urea as the main fertilizer N source became an economically attractive yield enhancer. However, the rapid increase in fertilizer N use and the resulting imbalance in fertilizer nutrient supply have increasingly exploited soil nutrient reserves of P, K, and other nutrients, leading to a decline in fertilizer N response. To reverse this trend, P, K, and other nutrients must be applied in fertilizers. On acid soils, for example, crop uptake of N increased from 40–50 kg N ha-1 to 120– 130 kg N ha -1 where fertilizer P was applied. Similarly, application of fertilizer K substantially enhanced N uptake on the degraded soils. Before the 1990s, K fertilizers were hardly used by farmers in Vietnam, as most

One consequence of this development is that nutrient requirements for rice per year and per crop increased substantially. Where a traditional variety (yielding 2 t paddy ha-1 yr-1) required annually 30 kg N, 5 kg P, and 30 kg K ha-1 for grain production, a 3-crop system (producing 15 t paddy ha-1 yr-1) needs 225 kg N, 38 kg P (90 kg P2O5), and 225 kg K (270 kg K2O) per ha. Vietnamese rice farmers learned during the 1970s and 1980s to meet increasing N and P demand through judicious application of fertilizer N and P. With regard to K, however, it was commonly believed (and supported by research findings at the time) that soil K reserves in Vietnam’s major rice soils – namely those derived from recent alluvial sediments in river estuaries – are sufficient to meet even enlarged requirements, especially where

36 FYM is applied regularly (as in the RRD) or straw is recycled. More recently there are clear indications that even on soils with comparatively large

contents of total K (>1.5%), plant-available K contents were reduced to levels where response to fertilizer K is commonly expected (US$ 200 ha-1 yr-1. K-supplying power is related to the soils’ weathering stage and the effect of K supplied in sediments and irrigation water in the interwoven branches of the Mekong and Vam Co river systems in the MRD. The K-supplying power of ten representative soils of the MRD was evaluated in a pot experiment (Nguyen My Hoa, 1997). Results indicate that the concentration of exchangeable K in the five alluvial soils representing the major area cultivated to rice was ‘marginal to adequate,’ and thus insufficient to support more than one rice crop without fertilizer K supply. Total K contents on these soils are >1.5%. Despite this, K fertilization is required to replace the K nutrients removed in crops and residues in order to avoid a decline in soil K fertility in the future. Without proper management, the removal of large amounts of K with each of the 2–3 crops per year may cause a reduction in nonexchangeable K, decomposition of Kbearing clay minerals and, finally, K-fixation (which can only be overcome by very large fertilizer K applications).

39

Balanced fertilization in relation to organic fertilizers With the dramatic increase in the use of mineral fertilizers in recent years in Vietnam, the importance of organic fertilizers as a nutrient source for crops has declined. The relationship between mineral and organic fertilizers as nutrient sources with regard to the nutrient supply balance, however, is particularly relevant. In principle it is expected that organic fertilizers support soil fertility maintenance

#

Crop

Soil

Treatment

by supplying nutrients and enhancing soil physical conditions, thus creating the basis for intensive farming by improving mineral fertilizer effectiveness. Crop yield is thus generally increased where organic nutrient sources (e.g. FYM) are applied in addition to mineral fertilizers (Table 3-2). From 1996 to 2001, there was a consistent increase in the yields of spring rice and summer rice on alluvial and degraded soils of the RRD when 10 t FYM crop-1 ha-1 were added to the FN treatment (fertilizer N, P, K, Ca, Mg, and S nutrient combination) (Figure 3-3). On average, yield increases due to FYM was ~13% in spring rice and

Yield t ha-1

∆%

01 Rice

Alluvial soil

NPK NPK+FYM

4.75 5.31

12

02 Maize

Alluvial soil

NPK NPK+FYM

3.45 4.33

26

03 Sugarcane

Alluvial soil

NPK NPK+FYM

67.60 69.60

3

04 Rice

Degraded soil Old alluvium

NPK NPK+FYM

3.32 4.02

21

05 Groundnuts

Degraded soil Old alluvium

NPK NPK+FYM

1.68 1.91

14

Spring soybean

Degraded soil Old alluvium

NPK NPK+FYM

2.24 2.32

4

07 Maize

Degraded soil Old alluvium

NPK NPK+FYM

6.72 7.28

8

08 Winter maize

Degraded soil Old alluvium

NPK NPK+FYM

4.21 4.79

14

09 Winter maize

Degraded soil Old alluvium

NPK NPK+FYM

6.45 6.40

(1)

10 Tobacco

Degraded soil Old alluvium

NPK NPK+FYM

1.41 1.58

12

11 Orange

Ferralsol Clay shale

NPK NPK+FYM

9.48 10.06

6

12 Tea

Ferralsol Old alluvium

NPK NPK+FYM

0.68 0.83

22

06

Table 3-2 Response to fertilizer plus farmyard manure (FYM) as compared to fertilizer NPK nutrient application in selected cropping systems of Vietnam. (Data collected from on farm trials conducted between 1991 and 2000)

40 Yield (t paddy ha-1) Alluvial soils

10 8 6

Summer rice

Spring rice J B

J B

J B

J B

J B

J B

J B

4

J B

J B

J B

J B

J B

B

FN

J

FN+FYM

B

FN

J

FN+FYM

2 0 10

Degraded soils

Spring rice

Summer rice

8 J B

6 4

J B

J B

J B

J B J B

J B

J B

J B

J B

96

97

J B

J B

2 0 96

97

98

99

'00 '01

98

99

'00 '01

Spring rice = 150 N +120 P2O5 +60 K2O +200 CaO +40 MgO +33 S (kg ha-1); Summer rice = 120 N +90 P2O5 +60 K2O +200 CaO +40 MgO +33 S (kg ha-1). FN+FYM: FN + 10 t FYM crop-1 ha-1

FN:

Figure 3-3 Effect of fertilizer N, P, K, Ca, Mg, and S nutrient application with and without farmyard manure (FYM) on paddy yield of spring and summer rice of alluvial and degraded soils of the Red River Delta in Vietnam, 1996–2000.

Yield (t green bean ha-1) 6 5 4

FN treatments E B

E B

E B

E B

-N treatments E B

E B B

FN

E

FN+FYM

3 7 7 B

2

7 B 7 B

1

7

7

B

B

B

0 6

-K treatments

-P treatments

5 4 3 7

2 1

7 B

7 B 7 B

B

7

7

B

B

7 7 B

7 B 7 B

7

7

B

B

B

0 96 97 98 99 '00 '01 96 97 98 99 '00 '01 Figure 3-4 Effect of fertilizer N, P, K, Ca, Mg, and S nutrient application with and without farmyard manure (FYM) and after omission of fertilizers N (-N treatments), P (-P treatments) and K (-K treatments) on green bean yield of coffea robusta on lateritic soils derived from basalt in Dak Lak Province,1996–2001.

41 ~18% in summer rice on alluvial soils; on degraded soils, yield increases of ~16% in spring rice and ~9% in summer rice were observed. The application of 10 t FYM crop-1 ha-1 increased grain yield of winter maize grown after spring and summer rice on alluvial and degraded soils by ~14% and ~12% respectively. Comparatively, the effect of FYM on yield of coffea robusta on a ferralitic soil in Dak Lak Province, Southern Vietnam was not as significant (Figure 3-4). The average green bean yield increased by only ~6.5% in the same period (1996–2001). In treatments where fertilizer N, P or K was omitted from the FN applications, green bean yields were reduced to 1.6, 2.7 and 1.7 t ha-1 respectively (compared with 4.5t ha-1 on average). The application of 10 t FYM crop -1 ha -1 in these treatments increased yields to 2.2, 3.1 and 3.3 t ha-1 respectively. The supply of N, P, and K in FYM, however, was obviously insufficient to raise coffee yields beyond these levels (Figure 3-4). The comparison above underlines the general finding that FYM sources in the uplands of Vietnam contain less plantavailable nutrients than FYM from the nutrient-richer lowland environments. Over time, Vietnamese farmers have collected organic matter from the upland areas for fuel, animal feed, and other purposes, transferring the resulting organic wastes (e.g. ashes, FYM) to their lowland rice fields. The considerable amount of nutrients contained in these materials was thus accumulated in the arable lowlands while their transfer contributed to the exploitation of soil nutrient resources and decline of soil fertility in the surrounding uplands.

A combination of fertilizers N, P, K, Ca, Mg, and S with 25 t FYM ha-1 was applied to coffea arabica on a ferralitic soil derived from gneiss in Phu Tho Province, Northern Vietnam. These FN+FYM treatments resulted in green bean yields of 1.7 and 2.1 t ha-1 in the 2nd and 3rd years after planting. Comparatively, the yields in FYM only treatments were 0.7 and 1.1 t ha-1 respectively. The same treatments applied to coffea arabica on a similar soil in Son La Province in 1999 resulted in yields of 2.0 and 1.4 ha-1 respectively. These results indicate that even large application rates of FYM may not provide nutrients in the quantities required to exploit the yield potential of a crop, and that a good balance between organic and inorganic nutrient sources will enhance the effectiveness of mineral fertilizers. In most of the soil types where experiments were carried out, FYM applications increased fertilizer N effectiveness significantly. Rice yields for example, are largest when the N rate supplied in manure is ~30% of total N application. Organic fertilizers also have a large effect on the efficiency of K fertilizers. On soils where total K content is 1.5–2.0%, an application of 10 t FYM crop-1 ha-1 (1 ton of FYM provides 2.5–3.0 kg K2O) can support paddy yields of 5–5.5 t ha-1 without additional K fertilizer applications. Thus on many soils derived from alluvial sediments, only a small quantity of additional fertilizer K is required to sustain larger rice yields. On the alluvial soils of the RRD (total K content 1.5–2.0%), spring and summer rice yields of ~6.0 and ~5.7 t ha -1

42 respectively were maintained over five years in FN treatments that received 10 t FYM crop-1 ha-1 but no fertilizer K nutrients (FN+FYM-K). When 60 kg K 2 O ha -1 fertilizer K was included, average yields increased to ~6.8 and ~6.7 t ha -1 respectively. This indicates a response of 13–16 kg paddy per kg K2O applied in fertilizer. In the FN+FYM-K treatments, the succeeding 3rd season crop (winter maize) in the rice-rice-maize system failed to produce grain yield during the 2000/2001 season. These results clearly show that in spite of the large soil K reserve in these alluvial soils, the amount of K supplied in 10 t FYM crop-1 ha-1 and K released from the soil is insufficient for supporting three cereal crops per year. When fertilizer K was included (FN+FYM), the maize crop grain yields averaged ~3.8 t ha-1 (Figure 3-5).

ment of soil physical characteristics is very significant. Without the application of mineral fertilizers (especially fertilizer N), however, the effectiveness of FYM is quite low. In the case of sole FYM application, for example, the response is only 30 kg of maize grain t -1 FYM. When the FYM application is combined with fertilizer N, this response is increased to 126 kg of grain t-1 FYM. Organic fertilizers can be used to reduce P-fixation on soils with a large P-sorption capacity (which are common in Vietnam). The use of FYM, crop residues, or green manure improves the effectiveness of both organic and mineral fertilizers significantly in this respect. Soil characteristics also determine the time of fertilizer application. On lighttextured soils with a low CEC, it is necessary to split fertilizer applications, in particular fertilizer N and K as these are easily leached on such soils. Phosphorus fertilizers are commonly applied in one basal rate, but on acid soils (especially acid sulfate soils) this rate should be split into two.

The role that organic fertilizers have in the rain-fed upland cropping systems is quite different from its role in the irrigated lowland rice-based systems. Most upland soils are deficient in organic carbon, thus the effects of organic inputs go beyond the nutritional aspects. As a source of organic matter, their contribution to the improveCrop yield (t kg -1) 10 8 6

Spring rice J E B G

J B E G

J B E G

J E B G

Winter maize

Summer rice J B E G

4

J B E G

J E B G

J E B G

J B E G

J B E G

2

J B G

J B G E

J B

J B

B

FN

G

FN-K

J

FN+FYM

E

FN+FYM-K

G E

0

E

96 97 98 99 '00

96 97 98 99 '00

G E

98 99 '00 '01

Spring rice = 150 N +120 P2O5 +60 K2O +200 CaO +40 MgO +33 S (kg ha-1); Summer rice = 120 N +90 P2O5 +60 K2O +200 CaO +40 MgO +33 S (kg ha-1); Winter maize = 180 N +120 P2O5 +90 K2O +200 CaO +40 MgO +33 S (kg ha-1); FN+FYM: FN + 10 t FYM crop-1 ha-1

FN:

Figure 3-5 Effect of fertilizer N, P, K, Ca, Mg, and S application with and without K and farmyard manure (FYM) on paddy yield of spring and summer rice and grain yield of winter maize grown in a rice–rice–maize system on the alluvial soils of the Red River, 1996–2001.

43

Balanced fertilization in relation to crops and varieties Crops differ substantially with regard to their nutrient requirements. Groundnut, a calcophil crop, for example, requires Ca in relatively larger amounts than many other crops. In degraded soils with low contents of Ca and Mg, the application of lime and/or fertilizer Ca can increase groundnut yields by 9–10% and 11% respectively. Besides supplying Ca as a nutrient, lime also reduces soil acidity and improves the soil environment for legumes with regard to biological N2-fixation. The excessive use of lime, however, decreases groundnut yield due to an over-representation (imbalance) of Ca2+ as compared to Mg 2+ and K + on the surface of cation exchangers in the soil. Modern high-yielding varieties require more nutrients from soils and fertilizers

than traditional low-yielding varieties. Research results indicate that traditional rice varieties in Vietnam such as Chiem chanh, Chiem bau, and Ba trang take up only 18–20 kg N ha-1 and 3–4 kg P2O5 ha-1; this is only 10–15% of the amounts of N and P taken up by improved varieties. Similarly, hybrid rice takes up much larger quantities of K per crop compared with improved varieties of rice (Table 3-3). As a consequence of the countrywide introduction of modern crop varieties in Vietnam, the total uptake of nutrients per hectare of cultivated area has increased rapidly over the last 20 years. Nutrient uptake ability by crops is also affected by soils and fertilizer materials. Thus when applying the principles of balanced fertilization to different cropping patterns, it is important to balance nutrient requirements and supply for the whole cropping system, and as well to take into account residual effects of previous crops in this respect.

Uptake (kg ha-1)

Variety

Yield (t ha-1)

N

P2O5

K2O

Chiem chanh

1.40

25.2

4.2

-

Chiem bau

1.13

19.3

3.0

-

Ba trang

0.86

14.6

2.5

-

1.07

16.8

3.3

-

Improved rice

Mè

5.0 - 5.5

100 - 120

40 - 50

100 - 120

Hybrid rice

6.5 - 7.0

150 - 180

70 - 80

Table 3-3 Rice varieties and their nutrient uptake. (Project 02A-06-01. 180 - 200 1990)

44

Balanced fertilization in relation to other nutrients Before the 1960s, the use of manufactured fertilizers was not common in Vietnam: most farmers planted only one crop per year, using traditional varieties with low productivity that required relatively small amounts of nutrients (Table 3-3). Since then, however, farmers have started using manufactured fertilizers, especially imported N fertilizers in (at the time) the form of sulfate of ammonia (SA). During this period when fertilizer was introduced to Vietnam, fertilizer N was the over-riding yield-limiting factor in all crops. Although only small amounts of fertilizers were applied, their use induced a rapid agricultural production increase in Vietnam, particularly in the case of rice. Phosphorus fertilizers were seldom used for yield improvement. However, research studies during the 1970s indicated that, due to increasing land intensification, fertilizer P had by then become the most prominent yield-limiting nutrient factor in Vietnam, after fertilizer N. Fertilizer K became an important yieldlimiting nutrient factor only after modern rice varieties were introduced widely in the 1980s. Response to fertilizer K was particularly prominent on light-textured soils with small K reserves. In the 1990s, the increasing use of hybrid varieties by rice growers in Northern Vietnam and maize farmers throughout the country, together with the introduction of improved planting materials to crop sectors other than rice, also had a significant role in making K the limiting factor.

When taking a balanced fertilization (BF) approach, it is important to take nutrient interactions into consideration. The significant impact that BF has on yield response and profitability is discussed below.

N-P balance As mentioned previously, N was the most limiting nutrient factor in crop yield in the 1960s, but during 1970–80 P replaced N in this respect. Increased P fertilizer use efficiency is attributed to the use of modern varieties, increased number of crops per year, and excessive use of N. The studies on alluvial soils, slightly acidic soils, and acid sulfate soils have shown that fertilizer N efficiency increases when applied in balance with fertilizer P. When fertilizer N is used alone, a much larger application of fertilizer N is required per kg paddy yield, compared to the amount required when fertilizers N and P are applied together (Tables 3-4 and 3-5). Soil P availability may decline rapidly with increasing cropping intensity, thus causing a decrease in the uptake efficiency of N and other nutrients. When fertilizer P was omitted from FN treatments (fertilizer N, P, K, Ca, Mg, and S nutrient combination) in a rice-rice-maize crop rotation grown on the alluvial soils of the RRD, yields declined increasingly over the five years of experimentation. Table 3-4 Balanced fertilization and rice yield on acid sulfate soils. (Project 02A-06-01. 1990)

Treatment

Yield t ha-1

Fertilizer N required kg t-1 paddy

Without fertilizers

0.38

-

60 N

1.85

40.8

60 N + 60 P2O5

3.37

20

45 Fertilizer N required kg t-1 paddy

Type of soils

Red River alluvial soils

Without P application

With P application

23 - 27

19 - 23

Mekong River alluvial soils

18 - 20

16 - 18

Acid sulfate soils of the North

34 - 36

26 - 28

Acid sulfate soils of the South

30 - 34

17 - 20

The omission of P in treatments that also did not receive FYM (FN-P) resulted in repeated crop failure in the 3rd season crop (winter maize). By the winter season of 2000/2001 (after five years of experimentation), even the addition of 10 t FYM crop-1 ha-1 (FN+FYM) could not provide sufficient P for grain production in maize (Figure 3-6).

Table 3-5 Relationship between fertilizers P and N. (Project 02A-0601. 1990)

For spring rice, treatments that did not receive fertilizer P (FN-P), the average fertilizer N requirement was 28 kg t -1 paddy. This was reduced to 22 kg t-1 paddy in treatments that received the FN+FYM treatments. For summer rice, the average fertilizer N requirement was reduced from 27 to 18 kg t-1 paddy in summer rice. We can thus conclude that fertilizer P is essential for efficient rice production in Vietnam’s most fertile lowland soils.

Paddy yields of spring and summer rice were reduced by 1.8–2.2 t paddy ha-1 in treatments that did not receive fertilizer P during the 5th year of experimentation, in spite of a judicious supply of other nutrients in fertilizer and FYM. Results from the full crop cycle in 2000/2001 indicate that fertilizer N use efficiency was reduced to ~30% due to omission of fertilizer P (FN-P), compared with ~60% in FN treatments.

Similarly, results for winter maize also indicated a smaller efficiency when only N was applied. In this case, fertilizer profitability, at a value:cost ratio (VCR) of 1.98, was also small. When fertilizer N was applied together with fertilizer P, however, the VCR increased to 2.47. When fertilizer N was applied in addition to P and K, the VCR was further increased

Crop yield (t ha-1) 10 8 6

J E B G

4

J E B G

J B E G

J B E G

Winter maize

Summer rice

Spring rice J B E G

J B E G

J E B G

J B E G

J B E G

J B E G

2

J B E

J B

G

G

J B

J B

96 97 98 99 '00

96 97 98 99 '00

FN

G

FN-P

J

FN+FYM

E

FN+FYM-P

E E

0

B

G

G E

98 99 '00 '01

Spring rice = 150 N +120 P2O5 +60 K2O +200 CaO +40 MgO +33 S (kg ha-1); Summer rice = 120 N +90 P2O5 +60 K2O +200 CaO +40 MgO +33 S (kg ha-1); Winter maize = 180 N +120 P2O5 +90 K2O +200 CaO +40 MgO +33 S (kg ha-1); FN+FYM: FN + 10 t FYM crop-1 ha-1 FN:

Figure 3-6 Effect of fertilizer N, P, K, Ca, Mg, and S nutrient application with and without P and farmyard manure (FYM) on paddy yields of spring and summer rice, and grain yield of winter maize grown in a rice-rice-maize system on the alluvial soils of the Red River, 1996–2001.

46 Yield Treatment

Yield increase*

Efficiency VCR

kg maize kg-1 nutrient

t ha-1

No fertilizer

0.45

-

N

1.48

1.03

8.6

11.2

1.98

NP

2.80

2.35

K

0.45

0

0

0

2.47

NK

2.13

1.68

8.0

2.25

NPK

3.75

3.30

11.0

2.80

Table 3-6 Balanced fertilization for maize on the alluvial soils of the Red River. (* Yield increase compared with treatments with no fertilizer applied).

to 2.8. Table 3-6 provides data to verify BF’s impact on yield response and profitability.

of plant-available P (often due to P-fixation) limit modern agricultural production to the extent of crop failure.

On the alluvial soils of the Thai Binh River and acid sulfate soils of Northern Vietnam, similar results were obtained for white potato in the 2000/2001 winter season. With a balanced fertilizer NPK and FYM application, uptake of all three nutrients was enhanced by up to 50%, with tuber yields increasing by up to 40% (Table 37). This response was induced mainly by the substantial increase in fertilizer K rates in the BF treatments. In contrast, insufficient K release from soil reserves and FYM in the standard farmers’ practice (FP) limited uptake of N and P.

In hybrid maize grown on a ferralitic soil in Binh Phuoc Province, Southern Vietnam, a combination of fertilizer N, P, K, B, Cu, and Zn nutrients with FYM and dolomitic limestone provided yields of >5 t grain ha-1 in 1998. No grain yield was received in treatments without fertilizer P.

Much of Vietnam’s upland soils are derived from Fe/Al-rich parent materials and have undergone extreme weathering. On the majority of these soils, the small contents

In 1999 a large initial rate of 300 kg P2O5 ha-1, together with fertilizer N (120 kg N ha-1), K (120 kg K2O ha-1), and dolomitic limestone (2 t ha-1) was applied to maize grown in four farms on the lateritic upland soils of Binh Phuoc Province, Southern Vietnam. Grain yields of nearly 2.9 t ha-1 on average were obtained, compared with 0.45 t ha-1 achieved under common FP using fertilizer N only.

Table 3-7 Effect of balanced fertilization (BF) compared with farmers’ practice (FP) on N, P and K nutrient uptake of winter potato grown on the alluvial and acid sulfate soils of Northern Vietnam. Treatment Soil type Alluvial soils, Thai Binh River Acid sulfate soils

Nutrient uptake

N:P2O5:K2O

FYM

kg ha-1

t ha-1

(FP) 127:46:66

14.0

N

P

K

kg ha-1

Tuber yield t ha-1

72.2

12.2

117.2

17.25

(BF) 150:90:120

14.0

94.1

15.5

145.0

21.38

(FP) 140:45:15

7.5

69.7

6.2

99.5

14.59

(BF) 150:90:120

12.5

103.0

9.0

136.7

20.23

47 These examples show clearly that soil fertility recapitalization in the highly weathered acid upland soils of Vietnam has to begin with an ameliorative fertilizer P and dolomite applications. The larger P, Ca and Mg availability will require an adequate supply of fertilizer N, K, S, and micronutrients, in order to increase crop yield and biomass production (which help to reduce soil erosion and, if residues are properly recycled, will assist in building soil fertility).

N-K balance The relation between N and K in crops is known to be of special importance and their interaction in crop productivity can be either antagonistic or synergistic. Because of this relationship, scientists view K as a major factor in adjusting N supply for crops. As discussed earlier, fertilizer K use among Vietnamese rice farmers has been minimal (or not at all) for many decades. Therefore the role of K in rice productivity has not been proven except on light-

RRD alluvial soils Treatment

Yield

Yield increase*

Yield

NP

4.52

NPK

4.75

Treatment

Recent studies have revealed an increasing number of cases in which the application of fertilizer N and P to rice on some soil types results in similar yields to zero fertilization. For example, N and P fertilization increased paddy yields by 1.17 t ha-1 on the alluvial soils of the RRD. On the degraded soils of the RRD, however, yields increased by only 0.12 t ha-1. Similar results were obtained on alluvial soils in comparison with the grey soils of the Southern MRD (Tables 3-8 and 3-9). Yield responses after fertilizer K was added to the fertilizer N and P combination indicate that fertilizer K use efficiency is

Yield increase* t ha-1

t ha 3.35

Soil type factor

MRD alluvial soils#

-1

No fertilizer

textured soils with small contents of soil K (e.g. degraded and sandy soils). As intensification and the use of modern varieties are becoming more commonly practiced, K requirements in lowland cropping systems have started to rise and response to fertilizer K have increased significantly.

-

-

-

1.17

4.09

-

0.23

4.54

0.45

RRD degraded soils

MRD degraded soils#

Yield

Yield

Yield increase* -1

t ha-1

t ha No fertilizer

2.15

NP

2.27

NPK

3.32

Yield increase*

-

-

-

0.12

2.89

-

1.05

4.09

1.20

Table 3-8 Effect of fertilizer N/K balance on rice yield (t ha-1) on soils rich in potassium. (* Yield increase compared with treatments with the least fertilizer applied). (# Source: Do Trung Binh, 1995)

Table 3-9 Effect of fertilizer N/K balance on rice yield (t ha-1) on soils poor in potassium. (* Yield increase compared with treatments with the least fertilizer applied). (# Source: Do Trung Binh. 1995)

48 2000, fertilizer K response amounted to 24–27 kg maize grain per kg K2O.

strongly related to the indigenous Ksupplying capacity (soil K content). On soils that are rich in K (e.g. alluvial soils), fertilizer K use efficiency is only 2–4 kg of paddy kg-1 K2O; however, it can reach 8– 13 kg or more paddy kg-1 K2O on degraded and sandy soils.

These results indicate that an application of fertilizer K is an absolute necessity on these soils in order to grow more than one crop successfully. Since soil K reserves on these light-textured soils are likely exhausted by a single rice crop, K supply from 10t FYM crop -1 ha -1 would be insufficient to meet nutrient demands from subsequent crops.

Response to fertilizer K was observed in a rice-rice-maize cropping system on degraded soil (derived from old alluvial sediments of the Red River, Northern Vietnam). In K omission treatments (fertilizer N, P, Ca, Mg, and S nutrient combination), spring rice yields increased from 5 to >22 kg paddy kg-1 K2O applied between 1996 and 2000. Summer rice yields increased from 8 to >32 kg paddy kg-1 K2O applied in the same period. Yield response to fertilizer K was only slightly smaller in treatments that also received additional FYM of 10t FYM crop-1 ha-1 (Figure 3-7).

Quantity factor The role of N-K balance becomes more important where larger rates of fertilizer N are applied. Studies on alluvial soils indicate that fertilizer K use efficiency is small if N supply is 150 kg N ha-1. The effect is even more pronounced on degraded soils.

Response to fertilizer K in the 2nd crop (summer rice) was generally larger than in the 1st crop (spring rice). When a 3rd crop (winter maize) was grown in 1999 and

Under these conditions, it is clear that fertilizer K increases N use efficiency in rice. Nitrogen use efficiency is usually 15–

Yield response (kg paddy kg-1 K2O) 40

Summer rice

Spring rice

E G

30 G E

20

G E E G

10

E G E G

E G

96

97

G E

G E

G

FN-K

E

FN+FYM-K

E G

G E

E G

0 FN:

98

99

'00 '01

96

97

98

99

'00 '01

Spring rice: 120 N + 90 P2O5 + 120 K2O + 200 CaO + 40 MgO + 33 S (kg ha-1); Summer rice: 90 N + 60 P2O5 + 90 K2O + 200 CaO + 40 MgO + 33 S (kg ha-1);

FN+FYM: FN + 10 t FYM crop-1 ha-1

Figure 3-7 Yield response to fertilizer K (omitted from a fertilizer N,P, K, Ca, Mg, and S nutrient combination) with and without farmyard manure (FYM) in spring and summer rice grown on degraded soils derived from old alluvial sediments of the Red River in Bac Giang Province, 1996–2001. (NISF, BALCROP Annual Reports 1997–2002)

49 Table 3-10 N/K balance for rice (hybrid rice). (* Yield increase due to K application)

Alluvial soil Rate of N

Yield Without K

With K

Degraded soils Yield increase*

kg ha-1

Yield Without K

With K

Yield increase*

t ha-1

0

4.72

4.63

-0.09

3.14

3.41

0.27

60

5.10

5.05

-0.05

3.65

4.60

0.95

90

5.41

5.55

0.14

3.88

5.24

1.36

120

5.87

6.09

0.22

4.21

6.03

1.82

150

6.43

6.82

0.39

3.92

6.15

2.23

180

6.37

6.87

0.50

3.51

5.59

2.08

210

5.42

6.37

0.95

3.01

4.63

1.62

30% without K application, but it can be as high as 39–49% when applied together with fertilizer K. Potassium also plays an important role in regulating N supply, and can assist in improving uptake of N and other nutrients in rice as well as other crops (Table 3-10). In 1996 a fertilizer nutrient omission trial was initiated on degraded soils in Bac Giang Province to monitor average fertilizer N requirement. In treatments that received the full fertilizer nutrient combination inclusive of fertilizer K and FYM, fertilizer N requirement was 24 kg N t-1 paddy for spring rice, and 20 kg t-1 paddy for summer rice. By comparison, in treatments that did not receive fertilizer K, fertilizer N requirements for spring rice were 39 kg N t-1 paddy and 35 kg N t-1 and summer rice.

Seasonal factor Recent studies have shown that the N/K balance is also affected by seasonal

factors. The comparatively higher temperatures during the summer season in Northern Vietnam are likely to cause an increase in soil K diffusion. Hence crops will take up more K from the soils compared with other seasons. Lower temperatures and lack of sunlight, on the other hand, were found to decrease fertilizer K-use efficiency. Hence, during the winter season fertilizer K-use efficiency is smaller. In general, therefore, winter crops in Northern Vietnam would require larger applications of fertilizer K.

Crop factor Studies on maize indicate that balanced N-K fertilization is comparatively more efficient in maize than in rice. Yield increase in terms of maize grain due to BF amounted to 3.3 t ha-1 on alluvial soils; 3.77 t ha-1 on degraded soils; 1.17 t ha-1 on grey soils; and 0.39 t ha-1 on ferralitic soils. It is concluded that BF practices for maize crops are more profitable on degraded and grey soils compared to alluvial and ferralitic soils (Tables 3-11 and 3-12).

50

Treatment

Alluvial soils

Degraded soils

Grey soils

Ferralitic soils

t ha-1 No fertilizer

0.45

0.44

NP

2.80

0.45

2.47

5.13

NPK

3.75

4.21

3.64

5.52

kg maize produced per kg nutrient Treatment

Alluvial soil

Degraded soil

Table 3-11 Maize yield in relationship of N/K balance. (Cong Thi Yen, 1995; Do Trung Binh. 1995)

VCR* Alluvial Degraded soil soil

t ha-1 NP

11.2

NPK

11.0

0.05 12.6

2.47

0

2.80

3.20

Nutrient balance between macro- and secondary nutrients The rapidly increasing use of fertilizer N, P, and K nutrients in cultivated areas of Vietnam has also increased the requirement for other nutrients (secondary and micronutrients). One major reason for this development is the predominant use of single fertilizer nutrient sources in Vietnam. For example, continuous addition of fertilizers with large NPK contents (e.g. urea, DAP, and MOP) induces S deficiency. In other cases, the preferred use of DAP and single superphosphate (SSP) over fused magnesium phosphate (FMP) has induced Mg deficiency. Thus NPK nutrient supply from the addition of fertilizers with large contents of these nutrients has not always increased N, P, and/or K efficiency to the extent that is expected, as it may cause detrimental conditions for the supply and uptake of other nutrients.

Table 3-12 Effectiveness of balanced fertilization for maize. (* value:cost ratio)

Studies comparing the efficiencies of urea with SA or DAP, SSP, and FMP have shown that the use of fertilizers containing secondary nutrient elements (Ca, Mg, and S) and micronutrients is more beneficial to crop performance compared with single nutrient fertilizers. For example, fertilizer N applied at a rate of 30% as SA and 70% as urea increased coffee yield by 8–16%. Similar results were obtained for maize and groundnut. The yield increase in these cases is explained by the response to fertilizer S supplied together with N in SA (Table 3-13). A comparison of DAP, FMP and SSP as P sources for coffea robusta was conducted on a ferralitic soil in Dak Lak Province, and soil samples were collected before the Table 3-13 Effectiveness of balanced fertilization for maize. (Nguyen Thi Hien, 1995)

Yield (t ha-1)

%

NP

1.34

100

Treatments NPCa

1.46

109

NPK

1.50

112

NPKCa

1.65

123

51 Yield (t green bean ha-1) 5 4

No P

3

DAP

2

FMP

1

SSP

Figure 3-8 Effect of fertilizer P nutrient sources on green bean yield of coffea robusta on a ferralitic soil derived from basalt in Dak Lak Province, 1997–2001. (NISF, BALCROP Annual Report 2002)

0 97

98

99

'00

'01

Fertilizer nutrient application: 300 N + 300 K2O + 100 P2O5 (50% in May + 50% in July) as DAP (diammonium phosphate), FMP (fused magnesium phosphate), and SSP (single superphosphate) (kg ha-1 yr-1).

experiment and again five years later. The largest green bean yield was consistently attributed to FMP application (Figure 3-8). Soil sample analyses also revealed that while all three fertilizer P sources had caused a similar increase in soil contents of available P during the course of experimentation, only the use of FMP resulted in the maintenance of

exchangeable Ca and Mg and pH in the treated topsoil (Figure 3-9). It is concluded that the supply of Ca and Mg (contained in FMP) in addition to P, improved nutrient supply and was beneficial to the root environment of coffea robusta on this acid soil, to the extent that yields in FMP treatments were larger than those in DAP and SSP treatments.

P sources No P DAP FMP SSP 0

1

2

3

4 pHKCl

5

6

7

0

10

20 30 40 Available P (mg kg-1)

50

3

0

1 2 Exchangeable Mg (cmol kg-1)

3

No P DAP FMP SSP 0

1 2 Exchangeable Ca (cmol kg-1)

Before experiment

After 5 years

Fertilizer nutrient application: 300 N + 300 K2O + 100 P2O5 (50% in May + 50% in July) as DAP (diammonium phosphate), FMP (fused magnesium phosphate), and SSP (single superphosphate) (kg ha-1 yr-1).

Figure 3-9 Effect of fertilizer P nutrient sources applied to coffea robusta on a ferralitic soil derived from basalt in Dak Lak Province before (1997) and after five years of experimentation (2001). (NISF, BALCROP Annual Report 2002)

.

52 Combined SSP and FMP fertilization usually benefits crop performance on the upland soils in Vietnam; this is attributed to a more gradual release of P from these sources and the beneficial effect of other nutrients such as S, Ca, and Mg. On acidic upland soils, the alkaline character of FMP not only balances the acidic character of SSP, but may also cause a liming effect, thus reducing the P-fixation potential of these soils. On alkaline soils, combined FMP and SSP fertilization increases the solubility of phosphorus in FMP, while the high Si content of FMP supports the formation of Al3+ compounds, which can reduce alkaline toxicity. Consequently the combined application of SSP and FMP can bring about yield increases on acid as well as alkaline soils. Combined SSP and FMP fertilization resulted in paddy yields increase of 9.2% (0.37 t paddy ha-1) compared with FMP alone, and 5.8% (0.24 t paddy ha-1) when compared with SSP alone. Combined SSP

and FMP fertilization also gave similar results in groundnut, increasing yield by 10.3% (0.19 t ha -1 ) compared with separate applications of FMP and SSP. The effects of fertilizer omission on coffea arabica on ferralitic soils in Phu Tho Province were observed over three years (Figure 3-10). The omission of Ca, Mg, and S from a FN+FYM application (=100) resulted in substantial reductions in yields that averaged about 25%, 33% and 36% respectively when calculated over the observation period. When micronutrients Zn, B, and Cu were omitted from the FN treatment, reduction rates of 21%, 36% and 24% were recorded. The average green bean yield of coffea arabica was reduced by ~54% in treatments that received only FYM (no fertilizer nutrients). This example underlines the importance of fertilizer nutrients – macro-, secondary, and micronutrients – in maintaining crop production on the highly-weathered upland soils of Vietnam.

FN+FYM-N FN+FYM-P FN+FYM-K FN+FYM-Ca FN+FYM-Mg FN+FYM-S FN+FYM-Zn FN+FYM-B FN+FYM-Cu FYM only -60

-50 -40 -30 -20 -10 0 Yield reduction in green bean yield (%) Figure 3-10 Three-year average reduction (%) of green bean yield of coffea arabica due to the omission of fertilizer N, P, K, Ca, Mg, S, Zn, B, and Cu nutrients from a full fertilizer with farmyard manure application (FN+FYM=100) on ferralitic soils in Phu Tho Province, 1998–2000. (NISF, BALCROP Annual Reports 1999, 2000 and 2001)

53 In a similar fertilizer omission experiment on a rice–rice–maize system on the alluvial and degraded soils of the RRD over six years, it was observed that paddy yields were reduced progressively over time (Figure 3-11). On alluvial soils, yield reduction due to the omission of fertilizers Ca, Mg, and S was generally larger in the 2 nd rice crop (summer rice, 18–20% reduction) than in the 1 st rice crop (spring rice, ~15% reduction). This indicates that the nutrient supplied in the 10 t FYM crop-1 ha-1 is not sufficient to compensate for the omission of fertilizer Ca, Mg, and S on these soils. On degraded soils, the omission of fertilizer Mg caused the largest yield

reduction (24–26%) in spring rice. The omission of fertilizer S caused a yield reduction in summer rice in Year 6 (24%) that was substantially greater compared to Year 1 (9.5%). Similarly, the omission of fertilizers Ca and Mg caused yield reductions in summer rice that were larger in Year 6 than in Year 1 (Figure 3-11). Although yield reductions caused by the omission of fertilizers N, P, and K in these experiments were comparatively greater, it is clear from these results that the omission of ‘secondary’ nutrients in fertilizers can cause yield reductions of >1 t paddy ha -1 in the intensified rice systems of Vietnam, regardless of soil fertility conditions and soil reserves of Ca, Mg, and S.

Figure 3-11 Paddy yield reduction (%) of spring and summer rice due to the omission of fertilizer N, P, K, Ca, Mg, and S nutrients from a full fertilizer with farmyard manure application (FN+FYM=100) on alluvial and degraded soils of the RRD, 1996 and 2001. (NISF, BALCROP Annual Reports 1997–2002)

54 In the same nutrient omission trial on degraded soils, dry matter (DM) accumulation, measured at three growth stages of spring and summer rice and winter maize during the 2001/2002 crop rotation, reveals the impact of Mg and S on biomass production and crop development. Differences between full nutrient supply (FN+FYM) and omission plots were largest at harvest. Clearly, the omission of fertilizer K has a spectacular effect on DM production, increasingly noticeable throughout the cropping sequence (Figure 3-12). The omission of K reduced DM of spring rice, summer rice and winter maize at harvest by ~5, 7.3 and 12.2 t ha-1 respectively, compared with treatments that received the FN+FYM application. In contrast, DM reductions due to fertilizer Mg and S omission were smaller, but were still significant enough to cause grain yield reductions of >1 t ha-1. The omission of fertilizer Mg reduced DM of the three crops (at harvest) by 2.9, 2.7 and 3.3 t ha-1, while the omission of S reduced DM by 2.4, 3.1 and 3.7 t ha-1 respectively (Figure 3-12).

In a fertilizer N, P, K, Ca, Mg, S, Zn, B, and Cu nutrient omission trial on coffea robusta grown on ferralitic soils of Dak Lak Province from 1996 to 2001, the omission of fertilizers Mg, S, and Zn each caused yield reductions averaging 0.7–0.8 t green bean ha-1 yr-1 compared with the FN+FYM treatment (Figure 3-13). Although the reductions are much smaller than those arising from the omission of fertilizer N, P, and K, these results reinforce the point that the application of secondary nutrients and micronutrients in fertilizers does have an impact on crop productivity. In all the above cases, the supply of nutrients from fertilizers and FYM was combined. In general (and this is to be expected), the efficiency of fertilizer nutrient use decreased due to the addition of FYM. This effect was found to be largest in the case of fertilizer micronutrient use when compared with macronutrient during an experiment conducted with coffea robusta on ferralitic soils derived from basalt in Dak Lak Province between 1996 and 2000 (Figure 3-14).

t ha-1 Spring rice

16 14 12 10

Summer rice

Winter rice J B

B

FN

J

FN+FYM

G

FN-K

G

FN-Mg

Ñ

FN-S

J

8 6 4 2

J B Ñ G G

J B Ñ G G

Ñ G

B Ñ G

J B Ñ G

J B Ñ G

G

G J B Ñ G G

G

J B Ñ G G

0 Til. FN:

PI

Har.

Til.

PI

Har.

J B Ñ G G

G

7—9L Tas. Har.

Spring rice = 120 N +90 P2O5 +120 K2O + 200 CaO + 40 MgO + 33 S (kg ha-1); Summer rice = 90 N +60 P2O5 + 90 K2O + 200 CaO + 40 MgO + 33 S (kg ha-1); Winter maize = 180 N +120 P2O5 +150 K2O +200 CaO +40 MgO + 33 S (kg ha-1);

FN+FYM: FN + 10 t FYM crop-1 ha-1

Figure 3-12 Effect of fertilizer N, P, K, Ca, Mg, and S nutrient applications with and without K, Mg, S, and farmyard manure (FYM) on dry matter accumulation at three growth stages of spring and summer rice (tillering [Til.], panicle initiation [PI], harvest [Har.]) and winter maize (7–9 leaves [7–9L], tasseling [Tas.], harvest [Har.]) grown in a rice–rice–maize system on degraded soils of the Red River in Northern Vietnam, 1996–2001/2002. (NISF, BALCROP Annual Report 2002)

55 Yield (t green bean ha-1) 6 5 4

-P treatments

-N treatments J B

J B

J B

J B

J B

J B

E

E

E

G

G

3 2

E G

E G E G

1

J B E G

J B

J B

J B

J B

J B

E G

E G

E G

E G

E G

G

0 -K treatments

6 5 4 3 2

J B E

J B

J B

-Ca treatments

J B

E G

G E G

1

J B

J B

E

E G

J E B G

J E B G

J B E G

J B E G

J B E G

J E B G

G

E G

0

5 4

-S treatments

-Mg treatments

6 J E B G

J B E G

J E B G

J B E G

J B E G

J E B G

J E B G

J B E G

J B E G

J B E G

J B E G

J E B G

3 2 1 0

5 4

-B treatments

-Zn treatments

6 J B E G

J E B G

J B E G

J E B G

J B E G

J E B G

J E B G

J E B G

J E B G

J E B G

J E B G

J E B G

97

98

99

'00

'01

3 2 1 0 96 -Cu treatments

6 5 4

J E B G

J E B G

J E B G

J E B G

J E B G

B

FN

J

FN+FYM

G

FN-[fert]

E

FN+FYM-[fert]

J E B G

3 2 1 0 96

97

98

99

'00

'01

FN: 300 N + 100 P2O5 + 300 K2O + 300 CaO + 50 MgO + 60 S + 12 Zn + 12 Cu + 5 B (kg ha-1 yr-1). FN+FYM: FN + 10 t FYM ha-1 yr-1

Figure 3-13 Effect of fertilizer nutrient with and without N, P, K, Ca, Mg, S, Zn, K, Mg, S and FYM application on green bean yield of coffea robusta on a ferralitic soil derived from basalt in Dak Lak Province, 1996–2001. (NISF, BALCROP Annual Reports, 1997–2002)

56 Fertilizer efficiency (kg green bean kg-1 fertilizer nutrient) 60 FN 50

50

FN+FYM

40 34.2

18.717.5

20 10

32

28.3

30

9.9 9.2

9.8 8.5

9

9.5 6.4

10.8 7.7

9.2

1.2 0.9 0 N

P2O5

K2O

CaO

MgO

S

Zn

B

Cu

Figure 3-14 Efficiency of fertilizer N, P, K, Ca, Mg, S, Zn, B, and Cu nutrient use (kg green bean kg-1 fertilizer nutrient applied) with and without farmyard manure (FYM) based on average annual green bean yield of coffea robusta grown on ferralitic soils derived from basalt in Dak Lak Province, 1996– 2000. (NISF, BALCROP, Annual Reports 1997–2001)

Conclusions As a result of the insights gained throughout the course of the Balanced Fertilization for Better Crops in Vietnam (BALCROP) project, the principles of BF are today more widely practiced in Vietnam’s agriculture than in the past. Improvements have been observed not

only with regard to the rates and ratio of fertilizer NPK consumption, but also in terms of fertilizer use in relation to soil characteristics (Table 3-14). Throughout Vietnam, the benefits of BF have been demonstrated on farms i n numerous locations involving representative soils and typical cropping systems (Figure 3-15).

Table 3-14 Rates and ratios of fertilizers used for rice in North Vietnam. Soil type Alluvial soils, Red River Alluvial soils, Thai Binh River Grey-degraded soils Sandy soils in coastal areas

Year under survey

N

P2O5

K2O

1992

76.2

26.4

2.0

100:35:3

1998

109.5

54.8

47.5

100:50:43

-1

kg ha

N:P2O5:K2O

1992

87.1

40.0

2.0

100:46:2

1998

94.6

62.9

39.5

100:66:42

1992

69.5

36.6

13.0

100:53:19

1998

95.7

36.6

69.0

100:38:72

1992

79.7

39.3

14.0

100:49:18

1998

83.6

37.3

44.6

100:45:53

57 Crop 0.83

Summer soybean

1.75 1.83

Spring soybean

2.24 1.51

Groundnut

3.04 1.19

Groundnut

1.68 0.45

Winter maize

4.21 2.8

Winter maize

3.45 3.28

Maize

3.81 3.39

Early rainy season rice

5.01 2.79

Early rainy season rice

3.48 2.98

Summer rice

4.78 1.89

Spring rice

3.38

2.52

Pepper

4.42 1.81

Coffee

3.64 1.07

Tobacco

1.52 2.51

Tea

2.81 0.7

Soybean

1.48 1.84

Groundnut

2.21 3.73

Sweet potato

6.93 6.72

0

Winter maize

0

1

2

3

4

5

6

7

77.4

Sugarcane

89.3

16.4

Cassava

24 6.48 9.48

Orange 0

10

20

30

40

50

60

70

80

90

Yield (t ha-1) NP

NPK

Figure 3-15 Effect of balanced NPK application as compared to farmers’ practice (NP) on yield of 22 selected crops grown on major soil types in Vietnam, 1991–2001.

58 When BF was compared with FP in onfarm demonstrations in Northern Vietnam during the years 2000 and 2001, crop

yields increased by up to 222% while net profit gains of > US$600 ha -1 were achieved (Figures 3-16 and 17).

Application rate (kg ha-1)

Crop Nutrient

Alluvial soils Nam Dinh Province

5.37 6.05

Spring rice

3.58 4.35

Summer rice

11.19

Winter potato

15.49

0

5

10

15

20

Spring groundnut

Summer rice

Winter potato

FP

BF

FP

BF

FP

BF

FYM

0k

8k

8k

8k

17 k

18 k 150

N

38

64

109

77

127

P2O5

93

93

46

93

83

90

K2O

25

82

97

59

131

100

CaO

0

278

-

-

-

-

25

Yield (t ha-1)

Application rate (kg ha-1)

Alluvial soils Hai Dzuong Province

5.37 6.05

Spring rice

5.03 5.64

Summer rice

17.25

Winter potato

21.38

0

5

10

15

20

Nutrient

Spring groundnut

Summer rice

Winter potato

FP

BF

FP

BF

FP

BF

FYM

8k

8k

8k

8k

14 k

14 k 150

N

127

127

102

102

127

P2O5

44

87

36

67

46

90

K2O

50

83

50

83

66

120

25

-1

Yield (t ha )

Application rate (kg ha-1)

Acid sulfate soils Hai Phong Province

4.14 5.54

Spring rice

4.44 5.86

Summer rice

14.59

Winter potato

20.23

0

5

10

15

20

Nutrient

Spring groundnut

Summer rice

Winter potato

FP

BF

FP

BF

FP

BF

FYM

5k

8k

1k

5k

8k

13 k 150

N

115

120

110

90

140

P2O5

38

90

15

60

0

90

K2O

0

60

0

90

15

120

25

-1

Yield (t ha ) FP

BF

Figure 3-16 Effect of balanced fertilization (BF) as compared to farmers’ practice (FP) on yield of typical crops and cropping sequences in Northern Vietnam, 2000. (NISF, BALCROP Annual Report 2001)

59 Crop Alluvial soils Hai Dzuong Province

5.37 6.05

Spring rice

5.03 5.64

Summer rice

17.25

Winter potato

21.38

Acid sulfate soils Hai Phong Province

4.14 5.54

Spring rice

4.44 5.86

Summer rice

14.59

Winter potato

20.23

Alluvial soils Ha Tay Province

5.36 5.98

Spring rice

5.27 5.63

Summer rice 1.2 1.6

Winter soybean

Degraded soils Bac Giang Province

4.8 5.18

Spring rice 1.54 1.7

Summer soybean

3.8 4.12

Late summer rice

11.6

Winter potato

13.9

Ferralitic soils Phu To Province

7.97 9.56

Tea (fresh) 0

5

10

15

20

0.35

Coffee arabica

1.13

0

0.5

1

25

Ferralitic soils Phu To Province 1.5

Yield (t ha-1) FP

BF

Figure 3-17 Effect of balanced fertilization (BF) as compared to farmers’ practice (FP) on yield of typical crops and cropping sequences in Northern Vietnam, 2001. (NISF, BALCROP Annual Report 2002)

60 Here within the framework of the BALCROP project, plant nutrition based on applied sciences has been introduced to a wide variety of crops and crop systems on representative soils located on farmers’ fields in Vietnam. Details of major experiments conducted during Phase I and II of BALCOP are presented in the following sections. The recorded fertilizer nutrient omission experiments in ricebased systems and coffee may be viewed

as the first long-term fertilizer trial involving six nutrients and FYM in Vietnam and the whole of SE Asia. The results achieved provide the foundation for implementing Phase III of the project which anticipates to establish balanced fertilization as a common practice throughout Vietnam in a network involving farmers, extension workers, scientists, and decision-makers during 2003–2005.

US$ 5000 FP

BF

4000

3000

2000

1000

0

-1000 OFD1

OFD2

OFD3

OFD4

Coffee

Tea

OFD1 = Spring rice - summer rice - winter soybean on alluvial soil of the RRD in Ha Tay province OFD2 = Spring rice - summer soybean - late summer rice - winterpotato on degraded soil in Bac Giang province OFD3 = Spring rice - summer rice - winterpotato on alluvial soil of the Thai Binh river in Hai Dzuong province OFD4 = Spring rice - summer rice - winterpotato on acid sulphate soils in Hai Phong province Coffee = Coffea arabica on ferralitic soil in Phu Tho province Tea = Tea on ferralitic soil derived from clay scale in Phu Tho province

Figure 3-18 Effect of balanced fertilization (BF) as compared to farmers' practice (FP) on net income of typical crops and cropping sequences in Northern Vietnam, 2001. (NISF, BALCROP Annual Report 2002)