Conservation tillage and residue management improves soil properties under a upland rice-rapeseed system in the subtropical eastern Himalayas

Poor soil properties and low soil moisture content (SMC) are major limitations for cultivating a second crop after the rainy season rice (Oryza sativa L.) in the uplands of the Eastern Himalayas. Information on impact of conservation tillage and residue management (RM) to alleviate soil constraints is limited in the region. Thus, a field study was conducted in a rice-rapeseed (Brassica campestris Var. Toria) system under rainfed conditions with two tillage systems (CsT-conservation and CT-conventional) and five RM practices (100% NPK fertilizer, 50% NPK; 50% NPK + in-situ rice residue retention [ISRR, 5 Mg ha(-1)], 50% NPK + weed biomass [WB, 10 Mg ha(-1)] fresh weight basis (FW)]; 50% NPK + green manuring [GM, 10 Mg ha(-1) FW]), and their impact on soil quality parameters were assessed after 3 years. Significantly lower bulk density and penetration resistance (0-15 cm) and higher water infiltration rate were recorded under CsT than CT. The soil water holding capacity (WHC) and SMC in rapeseed were significantly higher under CsT than those under CT at 0-15 cm and 15-30 cm depths. The WHC and SMC were the maximum under 50% NPK + GM/WB and the minimum under sole application of 50% NPK. After 3 years, there were 5.7% higher available nitrogen (N), 7.3% phosphorus (P), and 3% potassium (K) (kg ha(-1)) in 0-15 cm depth under CsT than those under CT, respectively. Similarly, SOC stock (0-30 cm), soil microbial biomass carbon (SMBC), and dehydrogenase activity (DHA) under CsT were significantly higher than CT. Application of 50% NPK + WB/GM/ISRR registered significantly higher available NPK, SMBC, and DHA in soil than those under 50% and 100% NPK. Thus, CsT along with 50% NPK + WB/GM/ISRR are recommended for improving soil properties under the rice-rapeseed system of the region.