Rapid determination of site-specific N, P, and K management for rice in a tidal swampland

Site-specific nutrient management (SSNM) for a rice (Oryza sativa L.)-growing domain is typically developed by first using the nutrient omission plot technique (NOPT) to determine yield responses with added nitrogen (N), with added phosphorus (P), and with added potassium (K) and then conducting an evaluation experiment to verify an SSNM practice developed from the NOPT results. We hypothesized that an effective SSNM practice could be more rapidly developed through concurrent NOPT experiments and evaluation of a preliminary best-bet SSNM practice derived from experiences in other rice-growing domains. Our study domain was rainfed lowland rice in an Indonesian tidal swampland without past NOPT experiments and without a verified SSNM practice. Concurrent NOPT and evaluation experiments were conducted in the wet season (WS) and dry season across 20-25 farmers' fields either directly or not directly influenced by tides. Rice yields and gross return above fertilizer cost for a preliminary SSNM practice were higher than for farmers' fertilizer practice in both seasons and for two fertilizer practices based on soil tests in WS. The inherent ability of SSNM to adjust fertilizer rates for an attainable target yield and time fertilizer applications to match crop demand contributed to the superiority of SSNM. In NOPT experiments, relative yields without added N, without added P, and without added K respectively averaged 0.70, 0.89, and 0.88 across seasons and tidal locations. These relative yields enabled preliminary SSNM fertilizer rates to be further adjusted for the rice-growing domain. Rice growers in domains without a verified SSNM practice can benefit, before NOPT experiments are completed, by using generic SSNM guidelines for timing fertilizer applications and adjusting fertilizer rates for a target yield. After completion of NOPT experiments, the fertilizer rates can be further adjusted based on measured yield responses with added N, P, or K.