Sustainable Soil Management through Organic Amendments and Legume Inclusion in Intensive Sudan Grass Cropping Systems

Abstract

The study evaluated the effects of fertility levels, organic nitrogen sources, and cropping sequences on soil physico-chemical and biological properties in a Sudan grass-based forage system on Gangetic alluvial soils at Varanasi, India, during 2015–16 and 2016–17. A split-plot design with three replications was employed, comprising two fertility levels (100% and 75% recommended dose of fertilizers, RDF) integrated with four organic nitrogen sources (20 and 40 kg N ha⁻¹ through farmyard manure or vermicompost) in the main plots, and three cropping sequences (Sudan grass–Berseem, Sudan grass–oats, Sudan grass–barley) in the subplots. Soil pH, electrical conductivity, and organic carbon remained statistically unaffected by fertility levels, organic sources, and cropping sequences over the two-year period, reflecting the buffering capacity of the alluvial soil and the short experimental duration. In contrast, soil microbial biomass carbon (SMBC) and available macronutrients (N, P, K) and sulfur responded significantly to organic nitrogen sources, with 40 kg N ha⁻¹ through vermicompost consistently recording the highest SMBC (171.4 and 186.2 µg g⁻¹) and available NPKS relative to lower organic doses and farmyard manure. Reducing mineral fertilizer from 100% to 75% RDF did not significantly affect SMBC or available N, K, and S, though available P was slightly but significantly higher under 100% RDF in both years. The Sudan grass–Berseem sequence produced significantly higher available soil N and, in the second year, higher SMBC than cereal-based sequences, indicating the beneficial role of legume inclusion in nitrogen enrichment and stimulation of soil microbial activity. Overall, the results demonstrate that integrating reduced mineral fertilizer rates with higher doses of vermicompost, coupled with Sudan grass–Berseem rotation, can enhance soil biological health and nutrient availability without compromising key chemical properties in alluvial soils under intensive forage production. However, the observed trends in soil organic carbon and biological properties reflect short-term responses, and longer-term field experiments are required to confirm sustained soil carbon sequestration and long-term sustainability outcomes.