Yield and soil nutrient balance of sugarcane (Saccharum officinarum) plant ratoon system under integrated nutrient management

A field experiment was conducted during 2002 to 06 to find out suitable integrated nutrient management prac- tice for sustenance of soil health and productivity in sugarcane ( Saccharum officinarum L.) plantratoon cropping system for two cropping cycles. Integrated nutrient management strategies involving combinations of inorganics (NPK) + organic nutrient sources (FYM, pressmud, vermicompost, green manuring and trash incorporation) were tested against inorganic fertilizer (NPK) alone laid out in randomized block design with four replications. Results revealed that supply of nutrients to sugarcane plant through combined use of 120-60-40 kg N-P-K/ha + FYM (25% N) + Azotobacter + phosphate solubilizing bacteria (PSB) 2.5 kg/ha each and integrated use of 150-60-40 kg N-P- K/ha + trash 5 tonnes/ha incorporation with cellulolytic culture 1 kg/tonne of trash + Azotobacter + PSB in ratoon gave the highest cane yield of 99.8 and 92.1 tonnes/ha under plant and ratoon cane, respectively. The treatment also showed significant improvement in soil health at the end of crop cycle by 47.9% substantial increase in soil organic carbon (0.88 to 1.05%), 165.2% increase in soil microbial biomass-C (213 to 297 mg C-CO /kg soil) and 2 128.6% enhancement in soil microbial biomassN (3.7 to 4.8 mg N-NH /kg soil) over initial value (0.71%, 112 mg 4 C-CO /kg soil, and 2.1 mg N-NH /kg soil). Besides integrated nutrient management modules resulted in significant 2 4 increase in the contribution of soil microbial-C to soil organic C varying from 2.38 to 3.03% against 1.58% of initial value. Soil physical properties were also enhanced as bulk density reduced from 1.57 to 1.42 Mg/m3, water stable aggregates swelled from 0.345 mm to 0.482 mm diameter under integrated nutrient management modules at ra- toon harvest. This practice was proved to be the most profitable (B: C ratio 1.94 and 2.90) for sugarcane plant and ratoon crop, respectively. Availability status of major nutrients (NPK) in soil after harvest of ratoon crop recorded a positive balance due to application of various treatments over the initial status.