Effect of rice (Oryza sativa) stubble and nitrogen on performance of tobacco (Nicotiana tabacum) in rice-tobacco cropping system

A field experiment was conducted during the winter (rabr) seasons of 2001-04 to evaluate the effect of different pre-treatment practices to hasten rice (Oryza sativa L.) stubble decomposition and of nitrogen levels on perfor- mance of FCV tobacco (Nicotiana tabacum L.) in rice-tobacco cropping system in the rainfed Vertisols. The high- est mean yields of green, cured and bright leaf of tobacco and grade index were recorded with sprays of 4% urea + cellulose degraders (Cellulomonas sp.) on stubbles and incorporation into the soil, which was 16.5, 11.6, 20.7 and 20.0% more, respectively compared with those of the stubbles incorporated without pre-treatment. Sprays of 4% urea + cellulose degraders also increased the leaf-equivalent yield of tobacco, system productivity, profitability, net returns and benefit : cost ratio; the leaf-lamina nitrogen, potassium and nicotine, and reduced sugars, and the sugars : nicotine ratio compared with those of other stubble pre-treatments. Soil-available N and P were signifi- cantly higher with sprays of 4% urea + cellulose degraders and application of 21.8 kg P/ha, respectively as com- pared with other stubble-decomposition methods. The bright leaf yield of tobacco and grade index were compa- rable with 45 and 60 kg N/ha to tobacco and significantly superior to 30 kg N/ha. Higher leaf-equivalent yield of to- bacco, system productivity, profitability, net returns and benefit : cost ratio were obtained with 60 kg N/ha, closely followed by 45 kg N/ha. Benefit : cost ratio was higher with 45 kg N/ha. Leaf lamina concentrations of nitrogen and nicotine increased while sugars, and sugars : nicotine ratio decreased with increase in the level of N from 30 to 60 kg/ha. The soil-available N increased by 6.4% with 60 kg N/ha in comparison with 30 kg N/ha during the 3 years. Nitrogen dose of 45 kg N/ha proved adequate for tobacco when rice stubbles were pre-treated with sprays of 4% urea + cellulolytic bacteria Cellulomonas sp. in rice-tobacco cropping system.