Productivity, profitability and nutrient balance as influenced by diversification of rice (Oryza sativa)-wheat (Triticum aestivum) cropping system

A field experiment was conducted during 2004–2005 and 2005–06 at Sabour, Bihar to diversify the existing rice (Oryza sativa L.) - wheat (Triticum aestivum L. emend. Fiori & Paol.) cropping system. Among the 14 rice-based cropping systems tested, rice-potato (Solanum tuberosum L.)-onion (Allium cepa L.) + maize (Zea mays L.) relay cropping gave the highest mean rice-equivalent yield (30.66 t/ha/year), followed by rice-garlic (Allium sativum L.) - maize (30.35 t/ha/year) and rice-potato-onion (27.95 t/ha/year). The highest net returns of Rs 96,581/ha/year were realized from rice-garlic-maize, which were on a par with that of rice-potato-onion + maize relay cropping (Rs 92,837/ha/year). However, the benefit: cost ratio was highest (1.73) in rice-berseem [Trifolium alexandrinum (L.) Juslen.] - maize + cowpea [Vigna unguiculata (L.) Walp.], both grown for fodder. The highest water-use efficiency (37.01 kg rice-equivalent yield/ha/mm) was recorded with rice-garlic-maize system. The rice-potato-onion + maize relay cropping proved the most effective in producing highest calorific value (61,155 K calories/ha) and showed the maximum land-use efficiency (94.8%). The same cropping system removed the maximum quantity of N (371.6 kg/ha), P (110.4 kg/ha) and K (451.4 kg/ha), followed by rice-berseem -maize + cowpea (F), having corresponding values 352.0, 88.2 and 361.0 kg/ha/year. Heavy removal of NPK by rice-berseem-maize+cowpea (F) resulted in maximum negative balance of nitrogen (152.9 kg/ha), phosphorus (31.4 kg/ha) and potassium (304.6 kg/ha/year). Potassium balance was negative in all the cropping systems, indicating that K was the most removable nutrient by the crops, which results in mining of soil K and thus calls for adequate K fertilization.