Phosphorus fertility in rice systems
Most rice growers in the Sacramento Valley apply P fertilizer to their rice crop. Approximately 30 kg P ha-1 is applied annually. The P fertilizer is usually mixed with N (and sometimes K) and applied and mixed into the soil surface just before planting. Currently used soil P tests are not accurate in determining a potential grain yield response to rice if P fertilizer is added. Since legislation has been passed requiring rice growers to stop burning their rice straw, most farmers incorporate the rice straw into the soil. We hypothesize that this change in management practice has resulted in more available P passing through the labile organic P fractions which the currently used soil P tests do not measure. In this study on-farm trails have been set up around the Sacramento Valley to identify rice response to P. Sites have been identified with contrasting straw management practices (burn, incorporate and fields under organic management). Soils from these trials will be analyzed using traditional soil P tests as well as be subjected to a P fractionation to identify sources of plant available P.