MAXIMIZING SUGARCANE YIELD BY INCREASING PLANT-POPULATION DENSITY, MINIMIZING NO3-N LEACHING AND IMPROVING SOIL ORGANIC-MATTER IN DIFFERENTCROP ROTATIONS

In a field experiment conducted during 1992-95 at Lucknow, India, suga rcane was planted in rows 60 and 90 cm apart in three crop rotations ( rice-sugarcane-ratoon? Sesbania aculeata for green manure-sugarcane-ra toon, and cowpea-sugarcane-ratoon) with 0, 150 and 300 kg N ha(-1) as urea either with or without farmyard manure (FYM) at 10 t ha(-1). Suga rcane yields were significantly greater in the Sesbania rotation than in the other because of a larger N uptake. N uptake of the crop was si gnificantly affected by soil organic carbon, and available N and K con tents. Ratoon yields? however, were largest in the cowpea sequence fol lowed by the rice rotation, probably due to a prolonged residual effec t of cowpea and rice root residues. The residual effect of a Sesbania green manure was negligible as demonstrated by the low NO3-N content o f the soil profile after sugarcane harvest compared to the other two c rop sequences. The total cane productivity (main sugarcane plus ratoon ) was greater (156 t ha(-1)) in the cowpea rotation than the Sesbania (152 t ha(-1)) and rice (140 t ha(-1)) rotations.