Soil organic matter and NPK status as influenced by integrated use of green manure, crop residues, cane trash and urea N in sugarcane-based crop sequences

A field experiment was conducted at Lucknow (26•5°N, 80•5°E, 120 m above mean sea level), India, during 1992–1995 to compare biomass productivity and crop yields in Sesbania aculeata (as green manure)-sugarcane-ratoon and rice-sugarcane-ratoon rotations at 0, 150 and 300 kg ha−1 N through urea to sugarcane, and 0, 75, 150 and 225 kg N ha−1 applied to the subsequent ratoon crop with and without trash mulch. The Sesbania-sugarcane-ratoon rotation added 14•48 t ha−1 biomass to the soil compared with 4•81 t ha−1 by the rice-sugarcane-ratoon rotation because Sesbania yielded a significantly greater biomass (11•12 t ha−1) than did the residual rootmass of rice (1•68 t ha−1) and sugarcane (2•64-3•83 t ha−1). Soil organic carbon, however, tended to decline after green manuring with Sesbania but gradually increased after incorporation of rice-root residues. Trash mulching of the ratoon crop upgraded the level of soil organic carbon and mineral-N status compared to no mulching. Sugarcane yields were significantly higher in the rice-sugarcane-ratoon rotation than in the Sesbania-sugarcane-ratoon rotation. A multiple linear regression model; Y = 8•075 + 0•675 (PN) − 22•45(OC) + 0•671(P); R2 = 0•965, showed that cane yields (Y) were influenced significantly by N uptake (PN), soil organic carbon (OC) and available P (P) status.