Intermittent Flooding and Organic Fertilizer Improve Biological Phosphorus Cycling and Crop Yield in a Low‐Fertility Tropical Rice Cropping System

Manipulating the water regime and applying organic fertilizer can conserve water, reduce greenhouse gas emissions, and improve soil quality in rice cultivation. However, rice yields depend on soil phosphorus (P) availability, which fluctuates with water and fertilizer manipulations on the low‐fertility soils that characterize many tropical rice cropping regions. We conducted a field experiment to determine the effects of water regime and fertilizer source on rice yield and associated P dynamics in a low‐P tropical soil under a double‐cropping system in Panama. Water regime (continuously vs. intermittently flooded) and fertilizer source (mineral fertilizer [NK, NPK, and none] or composted cow manure) were manipulated in a randomized complete block split‐split plot design. We used the Diagnostic and Recommendation Integrated System (DRIS) to determine nutrient limitation of rice yield. Organic fertilizer increased plant P uptake, soil available P, microbial P, and phosphomonoesterase activity, but the changes were greater under intermittent flooding than continuous flooding. In the first cropping period (dry season), plant growth was limited by P availability, and yields were greater with combined NPK + organic fertilizer (6.6–6.8 t·ha −1 ) compared with NPK only (4.9–6.2 t·ha −1 ). In the second cropping period (rainy season), plant growth was limited by nitrogen, and yields were greater under continuous flooding than intermittent flooding unless organic fertilizer was added (i.e., a significant water regime × fertilizer interaction). These findings demonstrate that organic fertilizer can maintain P availability and yield in water‐conserving rice production systems with intermittent flooding in low‐fertility systems. This is of particular importance given the challenges faced by resource‐poor farmers on low‐fertility soils in the face of unpredictable water availability and rainfall responses to climate change.