Stabilization of organic C in an Indo-Gangetic alluvial soil under long-term manure and compost management in a rice–wheat system

Figures & data

Table 1. Annual exogenous and plant-mediated C input in a rice–wheat system in unamended control plots and plots amended with fertilizer NPK, farmyard manure (FYM), vermicompost (VC), rice straw compost (RSC) and NPK plus FYM (INM). Numbers in parentheses indicate standard error.

Treatment	C input in rice (kg ha^−1)			C input in wheat (kg ha^−1)			Exogenous C (kg ha^−1)	Total C input (t ha^−1)
	Root	Rhizodeposition	Stubble plus leaf litter	Root	Rhizodeposition	Stubble plus leaf litter
Control	520.6^e(26.5)	281.1^e(2.1)	76.8^c(2.1)	564.7^d(15.2)	304.8^d(5.4)	50.8^c(5.4)	0	1.79^f(0.05)
NPK	665.8^d (20.8)	359.5^d(7.7)	93.1^b(7.7)	654.2^c(23.6)	353.3^d(3.2)	67.8^bc(3.2)	0	2.19^e(0.04)
INM	840.1^c(8.7)	487.3^c (9.2)	94.1^b(9.2)	746.2^bc(17.5)	432.8^c(3.8)	73.9^b(3.8)	7611(312)	10.29^c(0.35)
VC	963.4^b(20.2)	606.9^b(2.6)	130.7^a(2.6)	795.6^b(20.4)	501.2^b(9.2)	74.2^b(9.2)	5829(277)	8.94^d(0.32)
FYM	956.1^b(25.7)	602.3^b(3.4)	138.5^a(3.4)	905.1^a(7.9)	570.2^a(4.5)	93.2^a(4.5)	15159(244)	18.44^a(0.28)
RSC	1096.3^a(17.5)	690.6^a(1.9)	112.9^a(1.9)	923.3^a(20.1)	600.2^a(3.1)	96.5^a(3.1)	9483(191)	13.07^b(0.23)

Values within a column followed by different letters differ significantly (p < 0.05) by Duncan’s multiple range test.

Table 2. Chemical composition of farmyard manure (FYM), vermicompost (VC) and rice straw compost (RSC). Numbers in parentheses indicate standard error.

Constituent	FYM	VC	RSC
C (%)	37.51^a(1.01)	14.12^b(0.31)	35.32^a(0.64)
N (%)	0.99^b(0.03)	0.96^b(0.02)	1.48^a(0.04)
C/N ratio	37.92^a(0.26)	14.61^c(0.29)	23.89^b(0.20)
Lignin	11.56^b(0.29)	13.85^b(0.33)	27.27^a(0.65)
Cellulose	26.74^a(0.64)	24.84^b(0.62)	20.27^c(2.01)
Hemicellulose	24.04^a(0.57)	20.14^b(0.76)	22.65^ab(0.60)
Lignin/N	11.77^c (0.56)	14.43^b(0.23)	18.43^a(0.89)

Values within a row followed by different letters differ significantly (p < 0.05) by Duncan’s multiple range test.

Figure 1. Carbon accumulation (over fertilizer NPK) in soil at different profile depths after 10 years of management with farmyard manure (FYM), vermicompost (VC), rice straw compost (RSC) and integrated use of NPK and FYM (INM) and unamended control in a rice–wheat system. Vertical line bars show standard error. Bars labeled with different letters indicate significant (p < 0.05) difference by Duncan’s multiple range test.

Table 3. Soil organic carbon (SOC) concentration, bulk density and C stocks in the 60-cm profile after 10 years in a rice–wheat system in unamended control plots and plots amended with fertilizer NPK, farmyard manure (FYM), vermicompost (VC), rice straw compost (RSC) and NPK plus FYM (INM). Numbers in parentheses indicate standard error.

Treatment	SOC concentration (g k^−1)
	0–7.5 cm	7.5–15 cm	15–30 cm	30–45 cm	45–60 cm
Control	6.69^e(0.06)	6.54^e(0.08)	2.74^d(0.13)	2.46^a(0.06)	2.84^a(0.23)
NPK	7.33^d(0.18)	7.50^d(0.01)	2.82^d(0.02)	2.58^a(0.17)	2.87^a(0.21)
INM	8.90^c(0.05)	8.93^c(0.41)	3.09^c(0.17)	2.71^a(0.08)	2.78^a(0.16)
FYM	11.55^a(0.03)	11.68^a(0.12)	3.50^b(0.21)	2.48^a(0.18)	3.14^a(0.19)
VC	9.41^bc(0.17)	10.21^b(0.13)	3.76^a(0.03)	2.56^a(0.12)	3.04^a(0.03)
RSC	10.75^a(0.15)	11.12^a(0.29)	3.57^b(0.01)	3.09^a(0.08)	3.00^a(0.05)
Bulk density (Mg m^−3)
Control	1.32^b(0.03)	1.39^a(0.02)	1.88^ab(0.01)	1.88^ab(0.01)	1.88^ab(0.01)
NPK	1.35^a(0.01)	1.43^a(0.02)	1.89^a(0.03)	1.89^a(0.03)	1.89^a(0.03)
INM	1.31^b (0.05)	1.36^bc(0.02)	1.88^ab(0.02)	1.88^ab(0.02)	1.88^ab(0.02)
FYM	1.21^c(0.04)	1.34^c(0.05)	1.89^a(0.03)	1.89^a(0.03)	1.89^a(0.03)
VC	1.31^b(0.01)	1.37^b(0.05)	1.87^b(0.02)	1.87^b(0.02)	1.87^b(0.02)
RSC	1.29^b(0.03)	1.37^b(0.03)	1.92^a(0.04)	1.92^a(0.04)	1.92^a(0.04)
SOC stocks (t ha^−1)
Control	6.58^d(0.06)	6.82^e(0.08)	7.73^c(0.35)	6.93^b(0.17)	8.02^b(0.63)
NPK	7.42^c(0.18)	8.16^d(0.03)	7.99^c(0.05)	7.31^b(0.48)	8.14^b(0.64)
INM	8.75^b(0.05)	9.12^c(0.44)	8.87^b(0.49)	7.15^b(0.52)	7.86^b(0.44)
FYM	10.46^a(0.03)	11.74^a(0.12)	8.91^b(0.69)	7.02^b(0.49)	8.91^a(0.53)
VC	9.25^b(0.09)	10.49^b(0.13)	10.59^a(0.07)	7.21^b(0.35)	8.57^a(0.07)
RSC	10.48^a(0.14)	11.43^a(0.32)	10.28^a(0.03)	8.89^a(0.25)	8.65^a(0.17)

Values within a column followed by different letters differ significantly (p < 0.05) by Duncan’s multiple range test.

Figure 2. Response of coarse particulate (cPOC), fine particulate (fPOC) and mineral-associated organic C (MinOC) in 0–7.5 and 7.5–15 cm soil depths to 10 years management with farmyard manure (FYM), vermicompost (VC), rice straw compost (RSC), integrated use of NPK and FYM (INM) and unamended control compared to fertilizer NPK in rice–wheat system. Vertical line bars indicate standard error. Bars with different letters differ significantly (p < 0.05) by Duncan’s multiple range test.

Figure 3. Influence of 10 years of management with fertilizer NPK, farmyard manure (FYM), vermicompost (VC), rice straw compost (RSC), integrated use of NPK and FYM (INM) and unamended control in a rice–wheat system on distribution of soil organic C among physical pools, viz. coarse particulate (cPOC), fine particulate (fPOC) and mineral-associated organic C (MinOC), as proportion of soil organic C in 0–7.5 and 7.5–15 cm soil depths. Numbers inside the bars labeled with different letters for a given pool indicate significant (p < 0.05) differences between treatments by Duncan’s multiple range test. Vertical line bars show standard error.

Table 4. Non-hydrolyzable carbon (NHC) in 0–7.5 and 7.5–15 cm soil depths after 10 years in a rice–wheat system in unamended control plots and plots amended with fertilizer NPK, farmyard manure (FYM), vermicompost (VC), rice straw compost (RSC) and NPK plus FYM (INM). Numbers in parentheses indicate standard error.

Treatment	NHC stocks (t ha^−1)		NHC as proportion of SOC (%)
	0–7.5 cm	7.5–15 cm	0–7.5 cm	7.5–15 cm
Control	3.55^d(0.04)	2.44^d(0.01	53.9 ^cd(4.6)	35.8^c(2.1)
NPK	3.65^d(0.02)	2.45^d(0.01)	49.2^d(2.6)	30.1^c(1.9)
INM	5.07^c(0.05)	3.78^c(0.01)	57.9^c(6.2)	41.4^b(3.1)
FYM	7.91^a(0.01)	4.22^b(0.03)	75.6^a(1.7)	35.9^c(1.5)
VC	5.15^c(0.02)	5.32^a(0.01)	55.1^c(2.1)	50.7^a(1.2)
RSC	7.12^b(0.04)	6.74^a(0.09)	67.9^b(3.6)	57.9^a(1.3)

SOC: Soil organic carbon. Values within a column followed by different letters differ significantly (p < 0.05) by Duncan’s multiple range test.

Figure 4. Temporal trends of C mineralization in soils drawn from field plots (0–7.5 cm and 7.5–15 cm depth) amended with fertilizer NPK, farm yard manure (FYM), vermicompost (VC), rice straw compost (RSC), integrated use of NPK and FYM (INM) and unamended control for 10 years in a rice–wheat system. Points represent measured C mineralization and lines are fitted to the first-order kinetics model. Vertical line bars on points indicate standard error. Vertical line bars on the X-axis indicate least significant difference (p < 0.05) values for each sampling day.

Figure 5. Relationship between C mineralization potential (C₀) and coarse particulate (cPOC), fine particulate (fPOC) and mineral-associated organic C (MinOC) in 0–7.5 and 7.5–15 cm soil depths.

Table 5. Parameter (C₀ and k) estimates for the first-order kinetic model (Equation 3) fitted to cumulative carbon mineralization (Cmin) vs. time data for 0–7.5 and 7.5–15 cm soil depths in unamended control and plots amended with fertilizer NPK, farmyard manure (FYM), vermicompost (VC), rice straw compost (RSC) and NPK plus FYM (INM).

Treatment	0–7.5 cm
	Cmin (mg kg^−1)	C0 (mg kg^−1)	k (d^−1)	RMSE	R^2
Control	386^cd	504^cd	0.024^bc	4.7	0.996
NPK	376^d	483^d	0.026^bc	4.4	0.996
INM	409^c	516^c	0.026^bc	6.8	0.999
FYM	577^a	667^a	0.031^a	8.6	0.989
VC	472^b	632^b	0.025^bc	7.2	0.999
RSC	460^b	620^b	0.023^c	7.2	0.998
7.5–15 cm
Control	325^cd	409^c	0.027^b	5.1	0.996
NPK	292^d	359^d	0.031^a	4.1	0.997
INM	344^c	403^c	0.029^b	5.4	0.995
FYM	523^a	610^a	0.025^bc	7.4	0.997
VC	399^b	501^b	0.026^bc	5.9	0.999
RSC	387^b	497^b	0.023^c	6.8	0.999

C₀: Carbon mineralization potential (mg kg⁻¹); k: first-order rate coefficient (d⁻¹); RMSE: Root mean square error; R²: Coefficient of determination. Values within a column followed by different letters differ significantly (p < 0.05) by Duncan’s multiple range test.