Assessing the Necessity of Surface‐Applied Preplant Nitrogen Fertilizer in Rice Systems

Abstract

California rice (Oryza sativa L.) growers typically use two forms of preplant N fertilizer: aqua NH 3 applied 7 to 10 cm below the soil surface (subsurface N) and surface-applied N. Th e rational for applying about 25% of the total N rate to the surface is to provide a readily available N source for young rice seedlings; however no research has been done to verify this. On-farm fi eld studies were conducted over a 3-yr period (12 site-years) with the specifi c objectives of determining when rice begins to use subsurface N and to compare the effi ciency of surface and subsurface applied N. Rice seedlings began accumulating subsurface N within 2 wk aft er sowing at some sites. When a portion of the N rate was applied to the surface, early season plant biomass and N uptake was higher than when all of the fertilizer-N was applied subsurface. In contrast, grain yields were higher when all of the N fertilizer was applied subsurface. Averaged across all sites, the fertilizer-N recovery effi ciency of surface-applied N was 38% compared to 53% when only subsurface N was applied. As aqua NH 3 is less expensive than NH 4 + based fertilizers and the application of surface N requires an additional fi eld operation, there is no justifi cation to recommend the practice of applying surface N fertilizer in these rice systems. Instead, all of the preplant N should be applied subsurface as aqua NH 3 .

Greenhouse Gas Emissions and Management Practices that Affect Emissions in US Rice Systems

“…On the basis of a review of mostly Asian rice fields by Akiyama et al (2005), the IPCC (Eggleston et al, 2006) determined the default N 2 O emissions from continuously flooded rice fields to be 0.003 kg N 2 O‐N kg −1 N applied. Assuming a typical fertilizer N rate of 170 kg N ha −1 for US rice fields (Linquist et al, 2009), this would amount to 0.51 kg N 2 O‐N ha −1 season −1 , which is six times higher than reported here. Lower N 2 O emissions in US rice systems relative to Asian rice systems may be due to better water control, which ensures that fields remain flooded when desired.…”

Nitrate Leaching in Californian Rice Fields: A Field- and Regional-Scale Assessment

“…On average, 40% (range, 31–52%) of fertilizer N was taken up by the rice crop, similar to what has been reported for rice by others (Ladha et al, 2005). Based on the N difference method, Linquist et al (2009) found that 49% of the N applied was recovered in California rice systems; however, N recovery based on the 15 N‐dilution method is on average 11% higher than that suggested by the N difference method (Ladha et al, 2005). During the course of the year, 36.5 to 38% of the applied fertilizer N was lost.…”

“…Although the N rate is typical for California, the method of application differs. In most cases, 70 to 80% of the N is applied as aqua‐ammonia about 7.5 cm below the soil surface (Linquist et al, 2009). The remaining fertilizer N is usually applied to the soil surface before planting as a blended fertilizer containing P and K as well as some N (usually as ammonium sulfate or ammonium phosphate).…”

Nutrients and Sediments in Surface Runoff Water from Direct-Seeded Rice Fields: Implications for Nutrient Budgets and Water Quality

“…Typically in Asia, rice is transplanted and fertilizers are applied into flooded water; however, the general trend in Asian rice systems is toward direct seeding (Rao et al, 2007). In direct water‐seeded systems such as those found in California, much of the fertilizer N is injected into the soil as aqua‐NH 3 before planting (Linquist et al, 2009). Some N and the P and K fertilizers are usually applied to the soil surface at the same time and may or may not be incorporated into the surface soil.…”