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 (T (1): control-two times ploughing through harrow and cultivator, each followed by planking before sugarcane planting, T (2): deep tillage through disc plough (depth 25-30 cm) before planting followed by harrowing, cultivator and planking and T (3): 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 (M (1): 0.5 IW/CPE ratio and M (2): 0.75 IW/CPE ratio) at 7.5 cm depth of irrigation water, and four N levels (N-1-0; N-2-75; N-3-150; N-4-225 kg N/ha) in sugarcane crop. The higher mean SMBN (16.61 mg NH4-N/m(2)/day) during sugarcane ratoon crop was analysed as compared to plant crop (12.97 mg NH4-N/m(2)/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/m(2)/day vis-A -vis 17.00 mg NH4-N/m(2)/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/m(2)/day at 225 kg N/ha over 15.56 mg NH4-N/m(2)/day at N-0). Deep tillage and subsoiling (T (3)) at 0.75 IW/CPE ratio and 225 kg N/ha showed the highest mean soil respiration (158 mg CO2-C/m(2)/day). In sugarcane plant crop, at the highest N application (225 kg N/ha), M (1) (0.50 IW/CPE) showed the lowest available N, i.e. 160 kg N/ha vis-A -vis 186.00 kg/ha at 0.75 IW/CPE (M (2)) with conventional tillage (T (1)). 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-A -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.