Department of Plant Sciences

Irrigated rice (Oryza sativa L.) and 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 at 56 sites in six key irrigated rice-wheat domains 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 rice and two wheat crops. Compared with the current farmers’ fertilizer practice (FFP), average grain yields increased from 5.1 to 6.0 and 4.2 to 4.8 Mg/ha for rice and wheat crops, respectively, while plant N, P, and K accumulations increased by 12 to 20%. Improved timing and/or splitting of fertilizer N increased N recovery efficiency from 0.20 and 0.17 kg/kg in FFP plots to 0.30 and 0.27 kg/kg in SSNM plots in rice and wheat crops, respectively. The agronomic N use efficiency was 63 to 83% greater with SSNM than with FFP. The gross return above fertilizer cost (GRF) was 13-14% greater with SSNM than with FFP. Future SSNM 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.