Carbon mineralization in soil as influenced by crop residue type and placement in an Alfisols of Northwest India

Figures & data

Table 1. Initial characteristics of the soil used for the incubation study.

Soil property	Mean
pH (1:2 soil:water)	8.06
EC (dS m^−1; 1:2 soil:water)	0.21
Total carbon (%)	0.65
Oxidizable organic carbon (%)	0.45
Available N (kg ha^−1)	130
Available P (kg ha^−1)	15.73
Available K (kg ha^−1)	183.4
Total N (%)	0.14
Bulk density (Mg m^−3)	1.67

Table 2. Initial chemical characteristics of the crop residues used for the study.

Residue type	Total C (%)	Total N (%)	C/N ratio
Rice	26.86 ± 0.64^c	0.617 ± 0.03^c	43.59 ± 1.07^d
Wheat	38.75 ± 0.16^a	0.619 ± 0.02^c	62.67 ± 2.62^a
Maize	39.32 ± 0.05^a	0.766 ± 0.03^c	51.38 ± 1.65^c
Mungbean	39.04 ± 0.09^a	2.517 ± 0.01^a	15.51 ± 0.01^e
Rice + wheat^†	32.81 ± 0.45^b	0.62 ± 0.01^c	53.13 ± 1.50^c
Maize + wheat^†	39.03 ± 0.40^a	0.69 ± 0.01^c	57.02 ± 1.04^b
Rice + wheat + mungbean^†	34.88 ± 0.52^ab	1.25 ± 0.02^b	40.59 ± 0.85^d
Maize + wheat + mungbean^†	39.03 ± 0.28^a	1.30 ± 0.03^b	43.19 ± 0.70^d

^†The residues were mixed in equal proportions on a dry weight basis (values followed by different lower-case letters are significantly different at P < 0.05 according to Duncan’s multiple range tests for separation of mean). For all variables, n = 3 ± standard error of mean.

Figure 1 Changes in cumulative carbon mineralization (µg C g⁻¹ soil) on different days under different residues incorporated in soil. Vertical bars indicate ± standard error of the mean of the observed values.R_i: Rice, incorporated into the soils. W_i: Wheat, incorporated into the soils. M_i: Maize, incorporated into the soils. RW_i: Rice + wheat, incorporated into the soils. MW_i: Maize + wheat, incorporated into the soils. RWMb_i: Rice + wheat + mungbean, incorporated into the soils. MWMb_i: Maize + wheat + mungbean incorporated into the soils. Control: only soil.

Figure 2 Changes in cumulative carbon mineralization (µg C g⁻¹ soil) on different days under different residues surface-applied to the soil. Vertical bars indicate ± standard error of the mean of the observed values.R_i: Rice, incorporated into the soils. W_i: Wheat, incorporated into the soils. M_i: Maize, incorporated into the soils. RW_i: Rice + wheat, incorporated into the soils. MW_i: Maize + wheat, incorporated into the soils. RWMb_i: Rice + wheat + mungbean, incorporated into the soils. MWMb_i: Maize + wheat + mungbean incorporated into the soils. Control: only soil.

Table 3. Cumulative C mineralization (µg C g⁻¹ soil) in soils amended with different residues after 106 days of incubation.

		Decomposition kinetics model
Treatment	C mineralization (µg C g^−1 soil)	C0 (mg g^−1)	k (day^−1)	R^2
Rs	366.06 ± 15.47	0.340 ± 0.038	0.121 ± 0.009	0.94
Ri	413.70 ± 12.01	0.403 ± 0.030	0.076 ± 0.002	0.98
Ws	548.61 ± 13.75	0.501 ± 0.027	0.073 ± 0.005	0.94
Wi	666.77 ± 10.87	0.664 ± 0.023	0.042 ± 0.001	0.97
Ms	574.39 ± 9.05	0.560 ± 0.021	0.041 ± 0.002	0.98
Mi	556.56 ± 8.45	0.528 ± 0.019	0.041 ± 0.002	0.97
RWs	538.89 ± 11.80	0.488 ± 0.008	0.065 ± 0.003	0.93
RWi	610.02 ± 9.29	0.605 ± 0.042	0.040 ± 0.001	0.96
MWs	659.64 ± 11.94	0.622 ± 0.034	0.050 ± 0.002	0.96
MWi	549.12 ± 7.89	0.515 ± 0.003	0.044 ± 0.001	0.88
RWMbs	605.27 ± 16.09	0.554 ± 0.012	0.081 ± 0.004	0.93
RWMbi	640.41 ± 16.89	0.599 ± 0.052	0.075 ± 0.008	0.94
MWMBs	682.75 ± 13.58	0.544 ± 0.021	0.065 ± 0.004	0.96
MWMbi	600.10 ± 13.89	0.568 ± 0.042	0.070 ± 0.009	0.94
T15 [Control (only soil)]	121.59 ± 14.75	0.123 ± 0.024	0.029 ± 0.001	0.97
P values
Type	<0.001
Placement	<0.001
Time	<0.001
Type × placement	<0.001
Time × type	<0.001
Time × placement	<0.001
Time × type × placement	<0.001

Estimated mean values of the model parameters are presented. C₀, potentially mineralizable C and k, decomposition rate.

Rs: Rice, surface-applied. R_i: Rice, incorporated into the soils. Ws: Wheat, surface-applied. W_i: Wheat, incorporated into the soils. Ms: Maize, surface-applied. M_i: Maize, incorporated into the soils. RWs: Rice + wheat, surface-applied. RW_i: Rice + wheat, incorporated into the soils. MWs: Maize + wheat, surface-applied. MW_i: Maize + wheat, incorporated into the soils. RWMbs: Rice + wheat + mungbean, surface-applied. RWMb_i: Rice + wheat + mungbean, incorporated into the soils. MWMbs: Maize + wheat + mungbean, surface-applied. MWMb_i: Maize + wheat + mungbean, incorporated into the soils. Control: Only soil. For all treatments, n = 3 ± standard error of mean.

Figure 3 Changes in rate of carbon mineralization (µg C g⁻¹ soil) on different days under different residues incorporated into the soil. Vertical bars indicate ± standard error of the mean of the observed values. R_i: Rice, incorporated into the soils. W_i: Wheat, incorporated into the soils. M_i: Maize, incorporated into the soils. RW_i: Rice + wheat, incorporated into the soils. MW_i: Maize + wheat, incorporated into the soils. RWMb_i: Rice + wheat + mungbean, incorporated into the soils. MWMb_i: Maize + wheat + mungbean incorporated into the soils. Control: only soil.

Figure 4 Changes in rate of carbon mineralization (µg C g⁻¹ soil) on different days under different residues surface-applied to the soil. Vertical bars indicate ± standard error of the mean of the observed values.R_i: Rice, incorporated into the soils. W_i: Wheat, incorporated into the soils. M_i: Maize, incorporated into the soils. RW_i: Rice + wheat, incorporated into the soils. MW_i: Maize + wheat, incorporated into the soils. RWMb_i: Rice + wheat + mungbean, incorporated into the soils. MWMb_i: Maize + wheat + mungbean incorporated into the soils. Control: only soil.

Figure 5 Changes in cumulative C mineralization in soils amended with mixed residues of rice, wheat, maize and mungbean after the 106-day incubation.

Table 4. Statistical parameters to evaluate the observed and predicted cumulative C mineralization.

Treatment	MRE	ME	RMSE	CD	CRM	EF
Rs	0.130	2.25	25.418	0.959	0.009	0.949
Ri	0.081	3.98	17.414	0.908	0.014	0.984
Ws	0.132	8.40	36.919	0.859	0.024	0.951
Wi	0.151	12.73	32.766	0.855	0.032	0.978
Ms	0.153	7.99	27.580	0.873	0.024	0.978
Mi	0.164	10.24	30.378	0.860	0.033	0.970
RWs	0.156	9.70	42.821	0.856	0.029	0.931
RWi	0.181	12.85	40.502	0.838	0.036	0.958
MWs	0.157	12.28	38.486	0.852	0.031	0.966
MWi	0.248	17.27	54.649	0.778	0.054	0.889
RWMbs	0.151	11.09	41.315	0.831	0.028	0.947
RWMbi	0.144	11.82	40.598	0.828	0.028	0.957
MWMBs	0.233	76.49	84.729	1.05	0.177	0.846
MWMbi	0.159	12.37	39.205	0.812	0.032	0.955
Control (only soil)	0.214	3.16	6.713	0.821	0.049	0.969

CD: Coefficient of determination. CRM: Coefficient of residual mass. EF: Modeling efficiency. ME: Mean residual error. MRE: Mean relative error. RMSE: Root mean square error.

Rs: Rice, surface-applied. R_i: Rice, incorporated into the soils. Ws: Wheat, surface-applied. W_i: Wheat, incorporated into the soils. Ms: Maize, surface-applied. M_i: Maize, incorporated into the soils. RWs: Rice + wheat, surface-applied. RW_i: Rice + wheat, incorporated into the soils. MWs: Maize + wheat, surface-applied. MW_i: Maize + wheat, incorporated into the soils. RWMbs: Rice + wheat + mungbean, surface-applied. RWMb_i: Rice + wheat + mungbean, incorporated into the soils. MWMbs: Maize + wheat + mungbean, surface-applied. MWMb_i: Maize + wheat + mungbean, incorporated into the soils. Control: Only soil.