Aged biochar affects gross nitrogen mineralisation and nitrogen ...
Aged biochar affects gross nitrogen mineralisation and 15 nitrogen recovery: a N study in two contrasting soils Shamim Mia, Feike A. Dijkstra and Balwant Singh Centre for Carbon, Water and Food School of Life and Environmental Sciences Introduction
Materials and Methods
Biochar, a form of recalcitrant carbon (C), has shown to be a sustainable tool for climate change mitigation through C-sequestration in the soil. Simultaneously, its unique properties, i.e., large specific surface area and charge, can contribute to soil fertility improvement and agricultural productivity. After soil application, biochar properties change with formation of surface functional groups, that contribute to cation exchange capacity (CEC). However, the biochar mediated effects on nutrient cycling in soil may be dynamic, possibly driven by both biochar properties that change over time and the soil properties that regulate the ageing process. Biochar, when aged in the soil, may Dermosol Tenosol increase nitrogen (N) retention at the cation exchange sites. In addition, interactions between soil-aged biocharsoil organic matter (SOM) may also affect gross nitrogen mineralisation CEC=8.6 CEC=2.5 (GNM) due to SOM stabilisation or stimulation of microbial activity, Clay=29% Clay=8% particularly when this is enhanced by increased P bioavailability. Sand =51% Sand =82%
Biochar field study
Research question Are GNM and 15N recovery affected by aged biochar and P in different soils?
Silt=20%
15N
15N
injection (2 g m-2)
tracer study
Treatments: (a) soil type (Dermosol and Tenosol), (b) biochar application rate (0 and 20 t ha-1) and (c) phosphorus treatment (0 and 10 kg ha-1). Tracer: (15NH4)2SO4 with 98% enrichment, application rate: 20 kg ha-1 Harvesting: At 0, 48 hrs and 28 days after tracer addition
Soil and plant analysis Soil: Available N and P, CEC, and pH 15N
signature: Soil extracts, plants and soils at (0-6 cm) and (6-15 cm) depth
Silt=10%
15N
recovery and GNM calculation: Two pools isotopic dilution model.
Results
6
-1
ab
4 abc abc 3 c
bc
bc c
2
10
10
A 8
B a
0
8
a
a
6 b
b
4
2
2
0
0
+B
Dermosol
-B
ab
b
6
4
-B
1
a
pH
5
Cation exchange capacity (cmolc kg-1)
a
-1
Gross mineralisation rate (mg N kg soil day )
The biochar field was started in January, 2013, including two different soil types (Dermosol and Tenosol) at The University of Sydney. A grassland was established with eight clover species and three grass species.
+B
Tenosol
-B
+B
Dermosol
-B
+B
Tenosol
Fig.1 Soil properties after 21 months of biochar application. (A) cation exchange capacity and (B) soil pH +P -P +P -P -B +B Dermosol
-P
+P -B +B Tenosol +P
-P
Fig. 2 Mean gross N mineralisation rate in the two experimental soils with biochar and phosphorus treatments. Error bars represent one standard error. Explanation of abbreviations: –B: no biochar, +B: with biochar, -P: without phosphorus addition, +P: with phosphorus addition.
Key findings Biochar decelerated GNM in the clayey Dermosol while it was accelerated in the Tenosol when P was also applied. Biochar-induced effects on 15N recovery is soil specific. Aged biochar can increase N use efficiency in the sandy soil but such effect may not be visible in the soils with high clay content.
200 a
a
a
15 Total N recovery (mg m-2)
ab 150
bc cd d
d
100
50
a
a
ab
a
ab b
ab
b
0 -P
+P
-B
+P
-P +B
Dermosol
-P
+P
-B
+P
-P +B
Tenosol
Fig. 3 Mean total (upper bars) and soil 15N recovery (lower bars) in the two experimental soils with biochar and phosphorus treatments. Treatment abbreviations are given in Figure 1.
Fig. 4 Illustration shows 15N recovery in different fractions in the soil- plant systems. It also shows the possible mechanisms for greater retention of 15NH4+ in the Tenosol.
Acknowledgement- The University of Sydney and Department of Agriculture, Fisheries and Forestry, Australian Government.
Contact email- [email protected]
Materials and Methods
Biochar, a form of recalcitrant carbon (C), has shown to be a sustainable tool for climate change mitigation through C-sequestration in the soil. Simultaneously, its unique properties, i.e., large specific surface area and charge, can contribute to soil fertility improvement and agricultural productivity. After soil application, biochar properties change with formation of surface functional groups, that contribute to cation exchange capacity (CEC). However, the biochar mediated effects on nutrient cycling in soil may be dynamic, possibly driven by both biochar properties that change over time and the soil properties that regulate the ageing process. Biochar, when aged in the soil, may Dermosol Tenosol increase nitrogen (N) retention at the cation exchange sites. In addition, interactions between soil-aged biocharsoil organic matter (SOM) may also affect gross nitrogen mineralisation CEC=8.6 CEC=2.5 (GNM) due to SOM stabilisation or stimulation of microbial activity, Clay=29% Clay=8% particularly when this is enhanced by increased P bioavailability. Sand =51% Sand =82%
Biochar field study
Research question Are GNM and 15N recovery affected by aged biochar and P in different soils?
Silt=20%
15N
15N
injection (2 g m-2)
tracer study
Treatments: (a) soil type (Dermosol and Tenosol), (b) biochar application rate (0 and 20 t ha-1) and (c) phosphorus treatment (0 and 10 kg ha-1). Tracer: (15NH4)2SO4 with 98% enrichment, application rate: 20 kg ha-1 Harvesting: At 0, 48 hrs and 28 days after tracer addition
Soil and plant analysis Soil: Available N and P, CEC, and pH 15N
signature: Soil extracts, plants and soils at (0-6 cm) and (6-15 cm) depth
Silt=10%
15N
recovery and GNM calculation: Two pools isotopic dilution model.
Results
6
-1
ab
4 abc abc 3 c
bc
bc c
2
10
10
A 8
B a
0
8
a
a
6 b
b
4
2
2
0
0
+B
Dermosol
-B
ab
b
6
4
-B
1
a
pH
5
Cation exchange capacity (cmolc kg-1)
a
-1
Gross mineralisation rate (mg N kg soil day )
The biochar field was started in January, 2013, including two different soil types (Dermosol and Tenosol) at The University of Sydney. A grassland was established with eight clover species and three grass species.
+B
Tenosol
-B
+B
Dermosol
-B
+B
Tenosol
Fig.1 Soil properties after 21 months of biochar application. (A) cation exchange capacity and (B) soil pH +P -P +P -P -B +B Dermosol
-P
+P -B +B Tenosol +P
-P
Fig. 2 Mean gross N mineralisation rate in the two experimental soils with biochar and phosphorus treatments. Error bars represent one standard error. Explanation of abbreviations: –B: no biochar, +B: with biochar, -P: without phosphorus addition, +P: with phosphorus addition.
Key findings Biochar decelerated GNM in the clayey Dermosol while it was accelerated in the Tenosol when P was also applied. Biochar-induced effects on 15N recovery is soil specific. Aged biochar can increase N use efficiency in the sandy soil but such effect may not be visible in the soils with high clay content.
200 a
a
a
15 Total N recovery (mg m-2)
ab 150
bc cd d
d
100
50
a
a
ab
a
ab b
ab
b
0 -P
+P
-B
+P
-P +B
Dermosol
-P
+P
-B
+P
-P +B
Tenosol
Fig. 3 Mean total (upper bars) and soil 15N recovery (lower bars) in the two experimental soils with biochar and phosphorus treatments. Treatment abbreviations are given in Figure 1.
Fig. 4 Illustration shows 15N recovery in different fractions in the soil- plant systems. It also shows the possible mechanisms for greater retention of 15NH4+ in the Tenosol.
Acknowledgement- The University of Sydney and Department of Agriculture, Fisheries and Forestry, Australian Government.
Contact email- [email protected]
