Crop residue management to reduce GHG emissions and weed infestation in Central India through mechanized farm operations

Figures & data

Figure 1. Base map of farm trial sites (Source: Google Maps [44]).

Table 1. Details of experimental treatments.

Treatments	Treatment abbreviations	Details of tillage and weed management
		Tillage	Weed management
Current farmers’ practice	FP	Burning of previous crop residues followed by four episodes of soil tillage, including two passes of cultivator and rotavator. Sowing of crop using normal seed- drill.	Rice: application of bispyribac-Na, 25 g ai ha^-1 at 30 to 35 DAS followed by hand weeding if required.
			Wheat: application of 2,4-D, 1 kg ai ha^-1 at 30 to 35 DAS in wheat.
			Greengram: only one hand weeding.
Conservation agriculture with improved weed management practices	CAW	Crop residue of previous crop uniformly spread and kept as such. Crop sowing done with happy seeder. No other tillage operation carried out.	Rice: application of pyrazosulfuron, 25 g ai ha^-1 at pre-emergence followed by spray of bispyribac-Na, 25 g ai ha-^1 at 18 DAS.
			Wheat: clodinofop + metsulfuron 60 + 4 g ai ha^-1 at 30 DAS followed by one hand weeding if required.
			Greengram: Application of imazethapyr 100 g ai ha^-1 at 20 DAS followed by one hand weeding if required.
Conservation agriculture without any weed management practices.	CA	Crop residue of previous crop was uniformly spread manually or mechanically and the anchored residue was kept as such. A happy seeder (with nine tines) was used to sow the crops. No other tillage operation was carried out.

Table 2. Coefficients used for preparation of emissions inventory from crop residue burning.

Crop	Production-to-residue ratio (R)	Dry matter-to-crop ratio (D)	Dry matter burned in fields % (B)	Burning efficiency (E)
Rice	1.76^a	0.85^a	0.8^b	0.89^a
Wheat	1.75^a	0.83^a	0.25^a	0.86^a
Total pulses	1.50^d	0.71^a	0.25^c	0.68^a

a [45].

b [9].

c [46].

d [47].

Table 3. Emission coefficients for residue burning of various crops.

Parameters	Emission coefficients (g kg^−1)
	Rice	Wheat	Greengram
PM2.5	8.3	7.6 ± 4.1^a	3.9
PM10	9.1	5.7^b	8.05
SO2	0.18	0.4^b	0.216
CO2	1177	1787 ± 35^c	1130
CO	93	28 ± 20^c	86.3
NOx	2.28	1.7 ± 1.68^c	0.7
N2O	0.48 ± 4.45^c	0.74 ± 0.46^c	0.74 ± 0.46^d
NH3	4.1	1.3^b	1.3
CH4	9.59	3.55 ± 2.66^c	4.56
NMVOC	7	7^d	7
EC	0.51	0.16 ± 0.07^c	0.47
OC	2.99	0.29 ± 0.12^c	0.7
PAH	0.005^e	0.0037^e	0.00117^d

Modified from [13].

All emission coefficients are taken from [48] except the following:

a [49], where a value of 8.3 was taken for best estimates;

b [47];

c [50];

d per the authors’ best estimate, where EF values were unavailable, EF values for other crops were used;

e [51].

Table 4. Lower heating value of various crop residues.

Crop	Lower heating value (MJ kg^−1)	Ref.
Rice	16.02	Ravindra et al. [13]; Koopmans and Koppejan [52]
Wheat	12.38
Greengram	12.38

Table 5. Maximum crop residue load recorded in farmers’ fields before straw burning.

Crop cultivated	Year	Previous crop	Area (ha)	Maximum residue load (t ha^−1)	Residue burned (t)
Rice	2017	Greengram	2	1.35	0
	2018	Greengram	2	1.47	0
Wheat	2017–2018	Rice	2	6.71	13.42
	2018–2019	Rice	2	5.97	11.94
Greengram	2018	Wheat	2	5.00	10.00
	2019	Wheat	2	5.00	10.00
Total					45.36

Table 6. Emissions of greenhouse gas and air pollutants from burning of rice and wheat crop residues in farmers’ fields (values are sums of residues from five farmers).

Particulars		Emissions (kg)
		Rice		Wheat		Total (2 years)
		2017	2018	2017–2018	2018–2019
GHG emissions	CO2	9557.24	8497.94	4503.24	4449.63	27,008. 05
	CH4	77.87	69.24	8.95	8.84	164.90
	N2O	3.90	3.47	1.86	1.84	11.07
	*GWP (CO2e)	12,665.49	11,261.68	5282.60	5219.71	34,429.49
Air pollutant emissions	PM2.5	67.40	59.93	19.15	18.92	165.40
	PM10	73.89	65.70	14.36	14.19	168.15
	SO2	1.46	1.30	1.01	1.00	4.77
	CO	755.16	671.46	70.56	69.72	1566.90
	NOx	18.51	16.46	4.28	4.23	43.49
	NH3	33.29	29.6	3.28	3.24	69.41
	NMVOC	56.84	50.54	17.64	17.43	142.45
	EC	4.14	3.68	0.40	0.40	8.63
	OC	24.28	21.59	0.73	0.72	47.32
	PAH	0.04	0.04	0.01	0.01	0.09
	Total (air pollutants)	1035.01	920.3	131.42	129.86	2216.61

* GWP (CO₂e) was estimated using Equation (3)(3) $$\text{EGHG}={\mathrm{ }\text{ECO}}_2+{\mathrm{ }\text{ECH}}_4\times {\mathrm{ }\text{GWPCH}}_4+{\text{EN}}_2\mathrm{O}\times {\text{GWPN}}_2\mathrm{O}$$(3) with GWP values of 25 for CH₄ and 298 for N₂O.

Figure 2. Theoretical energy potential (TEP) of crop residue burning under farmers’ practice.

Figure 3. Two year pooled weed density and weed dry biomass under various crops.

FP - Farmer Practice; CAW - Conservation agriculture with improved weed management practices; CA - Conservation agriculture without any weed management practices; no. - number; g - gram; sq. m - square meter

Table 7. Weed parameters observed under different treatments.

Weed parameters	Treatments	Rice		Wheat		Greengram
		2017	2018	2017–2018	2018–2019	2018	2019
Weed density (weeds m^−2)	FP	56.2^B	66.4^B	100.6^B	110.6^A	56.2^B	50.6^B
	CAW	24.3^C	26.5^C	17.2^C	18.9^B	33.2^C	29.9^C
	CA	132.2^A	134.8^A	166.7^A	123.1^A	128.8^A	115.9^A
	LSD (p = 0.05)	10.7	4.8	12.8	13.5	6.5	5.9
Weed dry biomass (g m^−2)	FP	93.3^B	54.1^B	63.4^A	65.8^A	57.1^B	51.4^B
	CAW	34.6^C	35.2^C	12.7^B	14.2^B	34.2^C	30.8^C
	CA	168.5^A	145.1^A	66.3^A	70.8^A	118.9^A	106.8^A
	LSD (p = 0.05)	9.0	9.9	7.5	5.6	5.6	5.0

Weed data were subjected to square root transformation $\left(\sqrt{X+0.5}\right).$

FP - Farmer Practice; CAW - Conservation agriculture with improved weed management practices; CA - Conservation agriculture without any weed management practices; LSD - Least Significant Difference; Letters A, B and C indicates treatment means are significant at 5% level of significance and means with the same letters are not significantlly different; g - gram; m - meter.

Figure 4. Weed control efficiency (WCE) of recommended herbicides in various crops.

FP - Farmer Practice; CAW - Conservation agriculture with improved weed management practices; WCE - Weed control efficiency

Table 8. Crop yield parameters under different treatments.

Yield attributes	Treatments	Rice		Wheat		Greengram
		2017	2018	2017–18	2018–19	2018	2019
Grain yield (t ha^−1)	FP	3.8^B	3.4^B	4.0^B	4.0^B	0.9^B	1.0^B
	CAW	4.6^A	4.1^A	4.9^A	4.8^A	1.3^A	1.3^A
	CA	2.9^C	2.4^C	4.0^B	3.7^B	0.5^C	0.5^C
	LSD (p = 0.05)	0.4	0.2	0.5	0.3	0.3	0.2
Straw yield (t ha^−1)	FP	6.7^B	6.0^B	7.1^B	7.0^B	1.4^B	1.0^B
	CAW	8.1^A	7.1^A	8.5^A	8.4^A	1.9^A	1.3^A
	CA	5.1^C	4.2^C	7.0^B	6.6^B	0.7^C	0.5^C
	LSD (p = 0.05)	0.6	0.3	0.8	0.6	0.5	0.3

FP - Farmer Practice; CAW - Conservation agriculture with improved weed management practices; CA - Conservation agriculture without any weed management practices; LSD - Least significant difference; Letters A, B and C indicates treatment means are significant at 5% level of significance and means with the same letters are not significantlly different.

Figure 5. Percentage reduction in crop yields under farmers’ practice (FP) over conservation agriculture with improved weed management practices (CAW).

Table 9. Economic analysis of the cropping systems.

Crop	Treatments	CoC (Rs./ha)	Reduction in CoC over FP (%)	Gross return (Rs./ha)	Benefit–cost ratio
Rice	FP	30,438	–	73,304	2.4
	CAW	23,188	23.8	88,596	3.8
	CA	20,588	32.4	56,162	2.7
Wheat	FP	31,158	-	75,488	2.4
	CAW	22,988	26.2	91,425	4.0
	CA	21,038	32.5	74,325	3.5
Greengram	FP	29,758	-	44,649	1.5
	CAW	23,058	22.5	62,469	2.7
	CA	21,728	27.0	23,958	1.1

CoC: Cost of cultivation; Rs.: Indian rupees.

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