Nitrogen Management in Rice: A Case Study in Best Management Practices.

Direct-seeded, delayed-flood rice (Oryza sativa L.) production, which is prominent in the southern US, has been the focus of N research for several decades. Nitrogen use efficiency in these production systems has been optimized to ensure that added fertilizers are used effectively and that producers remain profitable. When properly managed, the direct-seeded, delayed-flood production system that is common to the US has the highest fertilizer N recovery efficiency (FNRE) of any cereal crop in the world often times exceeding >75% recovery of the season-total N applied. During the last decade more research has been focused on the development of the N Soil Test for Rice (N-STaR) which is a site-specific soil-based N test for rice production. Consistent and high FNRE of applied N across a wide range of soils and crop rotations is an important factor, which can allow the development of a soil-based N test. Since the release of N-STaR, N rate applications have changed significantly, with the majority of fields receiving 25-60 kg N ha^-1, less N than the producer would have typically applied, while maintaining or increasing rice yields.  Recent work has focused on the development of in-season N sensors to determine if the preflood N application was used efficiently and whether or not rice yield could benefit from additional N at the beginning of reproductive growth. Preliminary results indicate that NDVI can be a useful tool for guiding in-season N applications to rice. The coupling of high FNRE, site-specific N fertilizer recommendations and the use of in-season N decision tools makes this an example of how research and extension have developed best management practices to maximize NUE and reduce the potential for N losses and the associated environmental impacts.