Nitrogen Management in Rice under Suboptimal Soil conditions

In Mid-South rice (Oryza sativa, L.) production, nitrogen (N) fertilizer management for pureline varieties is most often recommended as a single preflood (SPF) or two-way split (2WS) application in a direct-seeded, delayed-flood system. Most of the N fertilizer is typically applied at the four- to six-leaf stage onto dry soil, and the second application, if necessary, into the floodwater during early reproductive growth stages (referred to as midseason). Environmental factors frequently prohibit growers from applying early N fertilizer under optimal dry soil conditions. A study was conducted to determine the best N fertilization management practices to utilize in rice when faced with suboptimal (dry or wet) soil conditions, or an established flood at the early tillering rice growth stage.Two locations, one a silt loam soil at the Rice Research and Extension Center (RREC) near Stuttgart, AR, and the other a clay soil at the Rohwer Research Station (RRS) near Rohwer, AR, were used to evaluate N fertilizer treatments to the pureline cultivar ‘Diamond’. Treatments included a control receiving no N, SPF and 2WS treatments applied to dry and wet soils, and several treatments using single and multiple N applications into an established flood. Base N fertility rates at each location were determined using the Nitrogen Soil Test for Rice (N-STaR) recommendations of 112 kg N ha-1 for SPF on the silt loam and 212 kg N ha-1 on the clay. Total N uptake, canopy height, grain yield, and milling yield were among the plant parameters measured at both sites. Due to a treatment by location interaction data were analyzed independently by site, which is not surprising since season total N rates for silt loams and clay soils differ significantly. On the silt loam soil, N treatments applied to dry soil according to standard recommendations (SPF and 2WS), applied to wet soil with elevated N rates, and those applied in multiple applications into the flood (“spoon-fed”) were the highest yielding treatments, while standard N rates applied to wet soil and single applications of high N rates into an established flood had statistically lower yields. On the clay soil, N treatments applied in a SPF or 2WS application to dry or wet soil, SPF (early) applied during flood initiation, and three of the four spoon-fed treatments were among the highest yielding. The lowest yielding treatments on the clay soil were the 4x52 spoon-fed late and SPF applications applied late (i.e., 7 to 10 days post flood) into the established flood. The different soil textures, accompanying cation exchange capacities, and flood establishment/management may help to partially explain the differences in results among treatments between the two locations. This study shows alternative N management strategies exist for achieving optimum grain yields with extra N fertilizer when faced with wet soil conditions or an established flood at beginning tillering or preflood-N application time