Agronomic and economic evaluation of site-specific nutrient management for irrigated wheat in northwest India

Similar to other regions of Asia, irrigated wheat (Triticum aestivum L.) yield increases in Punjab, India, have slowed in recent years. Future yield increases may occur in smaller increments through fine-tuning of crop management mainly by accounting for the large spatial and temporal variation in soil characteristics. On-farm experiments were conducted from 2002-03 to 2004-05 on 56 irrigated wheat farms (hereafter referred to as 'sites') in six key irrigated rice (Oryza sativa L.)-wheat regions of Punjab to evaluate an approach for site-specific nutrient management (SSNM). Site-specific N-P-K applications were calculated by accounting for the indigenous nutrient supply, yield targets, and nutrient demand as a function of the interactions between N, P, and K. The performance of SSNM was tested for two wheat crops. Compared with the current farmers' fertilizer practice (FFP), average grain yield increased from 4.2 to 4.8 Mg ha(-1), while plant N, P, and K accumulations increased by 12-20% with SSNM. The gross return above fertilizer cost (GRF) was about 13% greater with SSNM than with FFP. Improved timing and/or splitting of fertilizer N increased N recovery efficiency from 0.17 kg kg(-1) in FFP plots to 0.27 kg kg(-1) in SSNM plots. The agronomic N use efficiency was 63% greater with SSNM than with FFP. As defined in our study, SSNM has potential for improving yields and nutrient use efficiency in irrigated wheat. Future research must build on the present approach to develop a more practical way for achieving similar benefits across large areas without site-specific modeling and with minimum crop monitoring.