Abstract
Site-specific nutrient management (SSNM) can be an alternative to a recommendation for uniform fertilizer use across a rice (Oryza sativa L.) production system within a country or region of a country. We developed a web-based decision support tool named Nutrient Manager for Rice (NMR), which used principles of SSNM to calculate fertilizer N, P, and K rates for individual fields based on a target yield set for each field. It also used expected growth duration of the rice variety, crop establishment method, and age of transplanted seedlings to calculate days after rice establishment for each of three applications of fertilizer N. NMR enabled P rates to match estimated removal of P with harvested grain and crop residue for the target yield set for each field. We compared field-specific fertilizer recommendations from NMR with uniform application of fertilizer provided by an existing blanket fertilizer recommendation for irrigated inbred rice (BFR) and farmer’s fertilizer practices (FFP) in on-farm trials conducted in 74 irrigated rice fields across three growing seasons in the Cauvery Delta, Tamil Nadu, India. Grain yield was 0.6–0.7 Mg ha−1 higher (P ≤ 0.05) with NMR than FFP in two of the three seasons, even though total fertilizer cost was comparable or less with NMR. Yield was comparable for NMR and BFR, but NMR reduced fertilizer N and P rates and total fertilizer cost compared to BFR. Use of NMR rather than BFR also had less risk of financial loss for a farmer. The likelihood of financial loss with a switch from FFP to BFR averaged 31%. It reduced to 18% with a switch from FFP to NMR. NMR facilitated the calculation of field-specific fertilizer N, P, and K management practices, which increased fertilizer use efficiency without loss in rice yield compared to a recommended uniform fertilizer management across fields.
Highlights
The management of fertilizers can be critical for profitable rice farming in Asia because fertilizers are typically the second largest input cost after labor
Our study showed the capability of Nutrient Manager for Rice (NMR) to lower total fertilizer cost and increase Partial factor productivity of added N (PFP) of added N compared to BFR, even though yield was not significantly higher for NMR than BFR (Table 2)
Precise field-specific fertilizer management on small landholdings with NMR rather than uniform application of fertilizer across a wide production area could for the conditions in our study reduce total fertilizer cost, increase partial factor productivity of added N, and reduce the likelihood of financial loss for an individual farmer
Summary
The management of fertilizers can be critical for profitable rice farming in Asia because fertilizers are typically the second largest input cost after labor. Rice fields in Asia tend to be small (often less than one hectare) and frequently variable in soil nutrient status; yet rice farmers in Asia are often provided with a recommendation using a uniform blanket dose of fertilizer N, P, and K for all fields within a geographical or administrative area. Such recommendations ignore variations across fields in supply of essential nutrients from the soil (Dobermann et al 2003) and variations in crop management practices, which can influence the needs of the rice crop for fertilizer and the yields obtained in farmers’ fields (Witt et al 2007). The use of blanket nutrient recommendations across a rice production area can lead to low nutrient use efficiencies and leakages of nutrients to the environment (Singh et al 2015)
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