On-farm assessment of site-specific nutrient management for rainfed lowland rice in the Philippines

Rice yield in the drought-prone rainfed lowlands is constrained by low availability of nutrients and water. Fertilizer applications currently conducted by farmers may not match the crop demands nor be resource-use efficient. The objective of this study was to characterize the farmers' practices of nutrient management (FP) in rainfed lowland environments, and compare it with the site-specific nutrient management guideline by using decision-support software (Rice Crop Manager; RCM) in terms of rice yield and production cost. On-farm trials were conducted in northern Philippines in the wet seasons of 2011-2014. Average application rate of N, P and K in RCM was 82, 10 and 21 kg ha−1, respectively, while the application rate was 93, 11 and 18 kg ha−1 in FP (n = 93). Grain yield in FP, which ranged from 1.82 to 6.49 t ha−1, was significantly enhanced by RCM by 6% on average (4.48 vs. 4.22 t ha−1). The yield difference was mainly associated with the different N application regimes in RCM and FP. Average number of N applications was 1.94 in FP with 52% of total N applied during the first 15 days after transplanting while there were 2.63 applications in RCM with 29% applied during the first 15 days after transplanting and 44% at panicle initiation, respectively. Total cost for fertilizer was comparable or lower in RCM than FP, and hence the net income was increased by 154 US$ ha−1. The results of this study showed that site-specific nutrient management improved productivity and profitability in rainfed lowlands of the Philippines.