Soil Microbial Biomass Nitrogen, In Situ Respiration and Crop Yield Influenced by Deep Tillage, Moisture Regimes and N Nutrition in Sugarcane-Based System in Subtropical India

A field experiment during 2010–2014 was conducted at Indian institute of Sugarcane Research, Lucknow, with three tillage practices (T1: control—two times ploughing through harrow and cultivator, each followed by planking before sugarcane planting, T2: deep tillage through disc plough (depth 25–30 cm) before planting followed by harrowing, cultivator and planking and T3: subsoiling at 45–50 cm, and deep tillage through disc plough/mouldboard plough (depth 25–30 cm) followed by harrowing, cultivator and planking before planting), two soil moisture regimes (M1: 0.5 IW/CPE ratio and M2: 0.75 IW/CPE ratio) at 7.5 cm depth of irrigation water, and four N levels (N1-0; N2-75; N3-150; N4-225 kg N/ha) in sugarcane crop. The higher mean SMBN (16.61 mg NH4–N/m2/day) during sugarcane ratoon crop was analysed as compared to plant crop (12.97 mg NH4–N/m2/day). Suboptimal moisture regime (0.5 IW/CPE) in plant crop reduced SMBN at all the stages of growth as compared to optimum moisture regime (0.75 IW/CPE). Mean SMBN at 0.5 IW/CPE was observed as 16.22 mg NH4–N/m2/day vis-à-vis 17.00 mg NH4–N/m2/day at 0.75 IW/CPE. The increasing levels of N up to 225 kg/ha increased SMBN at all the stages in both the soil depths, i.e. 0–15 and 15–30 cm (17.60 mg NH4–N/m2/day at 225 kg N/ha over 15.56 mg NH4–N/m2/day at N0). Deep tillage and subsoiling (T3) at 0.75 IW/CPE ratio and 225 kg N/ha showed the highest mean soil respiration (158 mg CO2–C/m2/day). In sugarcane plant crop, at the highest N application (225 kg N/ha), M1 (0.50 IW/CPE) showed the lowest available N, i.e. 160 kg N/ha vis-à-vis 186.00 kg/ha at 0.75 IW/CPE (M2) with conventional tillage (T1). Deep tillage increased production of millable canes which could be increased to 100,830/ha in sugarcane plant crop and 106,710/ha in ratoon crop. Mean sugarcane and sugar yields in plant crop was 68.97 and 8.28 t/ha vis-à-vis 83.67 and 10.03 t/ha in ratoon crop, respectively. Sugarcane plant crop showed 21.52 % increase in cane weight (774.75 g) due to adoption of deep tillage and subsoiling. Thus, it could be concluded that subsoiling at 45–50 cm depth followed by deep tillage at 20–25 cm depth once before planting of sugarcane with scheduling of irrigation at 0.75 IW/CPE soil moisture regime and 150 kg N/ha sustained soil microbial biomass N and in situ soil respiration besides increasing sugarcane and sugar yields in plant–ratoon system.