Evaluation of long-term conservation agriculture and crop intensification in rice-wheat rotation of Indo-Gangetic Plains of South Asia: Carbon dynamics and productivity

Abstract

In the context of deteriorating soil health, stagnation of yield in rice-wheat cropping system (RWCS) across Indo- Gangetic plains (IGP) and environmental pollution, a long term field experiment was conducted during 2009-2016 taking four crop scenarios with conservation agriculture (CA), crop intensification and diversified cropping as intervening technology aiming to evaluate the sustainability of the systems. Scenario 1 (S1) represented conventional farmers' practice of growing rice and wheat with summer fallow. In scenario 2 (S2) and scenario 3 (S3), legume crop was taken along with rice and wheat with partial CA and full CA, respectively. Conventional RWCS was replaced with rice-potato + maize- cowpea cropping system with partial CA in scenario 4 (S4). The S3 scenario registered highest total organic carbon (TOC) stock of 47.71 Mg C ha^-1 and resulted in significant increase of 14.57% over S1 (Farmer's practice) in 0-30 cm soil depth after 7 years of field trial. The S4 scenario having intensified cropping systems recorded lowest TOC of 39.33 Mg C ha^-1 and resulted in significant depletion of 17.56% in C stock with respect to S3 in 0-30 cm soil depth. The TOC enrichment was higher in S2, S3 and S4 scenario in the surface soil (0-10 cm) compared to S1. At lower depth (20-30 cm), the TOC enrichment was significantly higher in S2 (12.82 Mg C ha^-1) and S3 (13.10 Mg C ha^-1 soil) over S1 scenario. The S2 and S3 scenario recorded highest increased allocation of TOC (3.55 and 6.13 Mg C ha^-1) to passive pool over S1. The S2 (15.72 t ha^-1), S3 (16.08 t ha^-1) and S4 (16.39 t ha^-1) scenarios recorded significantly higher system rice equivalent yield over S1 (10.30 t ha^-1). Among the scenarios, S3 scenario had greater amount of total soil organic carbon, passive pool of carbon and higher system rice equivalent yield, thus, is considered the best cropping management practice to maintain soil health and food security in the middle IGP.

Keywords: AlkP, alkaline phosphatase activity; C stock, carbon stock; CA, conservation agriculture; CMI, carbon management index; CT, conventional tillage; Carbon budgeting; Carbon fractions; Carbon stock; Conservation agriculture; Crop yield; DHA, dehydrogenase activity; FDA, flouroscein di acetate activity; IGP, Indo Gangetic plains; MBC, microbial biomass carbon; NT, no tillage; OC, organic carbon; RWCS, rice wheat cropping system; S1, scenario 1; S2, scenario 2; S3, scenario 1; S4, scenario 4; SOC, soil organic carbon; TOC, total organic carbon.

Fig. 1

Monthly total rainfall, mean monthly maximum and minimum temperature prevailing during the experimental period.

Fig. 2

Cropping systems with their dates of sowing, harvesting and residue management practices followed in different scenarios from 2009 to 2012. PTR: puddle transplanted rice; ZT-DSR: zero till direct seeded rice; NPTR: non puddle transplanted rice; CT- conventional tillage. *Nursery seeding for transplanted rice was done on the same day as on DSR was sown. In case of transplanted rice 30 days old seedling was used for transplanting.

Fig. 3

Cropping systems with their dates of sowing, residue management practices followed in different scenarios from 2013 to 2016. PTR: puddle transplanted rice; ZT-DSR: zero till direct seeded rice; MTNPR: machine transplanted non puddle rice; CT- conventional tillage. *Nursery seeding for transplanted rice was done on the same day as on DSR was sown. In case of transplanted rice 30 days old seedling was used for transplanting

Fig. 4

Total active (AP) and passive pool (PP) (Mg C ha⁻¹ soil) of soil organic carbon in 0–30 cm depth soil as affected by different tillage and crop management practices followed under four scenarios. Different small letters denote significant difference among the values of C stock, AP and PP between the scenarios. The vertical lines above the bars represent the standard deviation. S1 (TPR-CTW): conventional till puddled transplanted rice- conventional tille wheat; S2 (TPR/MTNPR + R-ZTW + R-CTMB + R): conventional till puddled transplanted rice/machine transplanted non puddle rice with residue- zero till wheat with residue- conventional till mung bean with residue; S3 (ZTDSR + R-ZTW + R-ZTC/ZTMB + R): zero till direct seeded rice with residue-zero till wheat with residue-zero till cowpea/zero till mung bean with residue; S4 [NPTPR/ZTDSR + R-CT(P + M)/ZTM + R-ZTC/ZTM + R]: non puddle transplanted rice/zero till direct seeded rice with residue-conventional till potato and maize intercrop/zero till mustard with residue-zero till cowpea/zero till maize with residue. Scenario details are given in Table 2, Fig. 2, Fig. 3.