Effects of Ammonium Sulfate On Seedling Rice Growth, Grain Yield, and Nitrogen Recovery.

Seedling rice growth on high-charged, montmorillonitic soils, representative of the majority of rice hectarage in Mississippi, can be slow.  Research evaluated the effects of starter fertilizer application {ammonium sulfate (AMS)} on seedling growth and grain yield (GY) for two rice cultivars (‘Cocodrie’ and ‘XL723’) on a Sharkey (very fine, smectitic, thermic, Chromic Epiaquerts) clay soil in 2007 and 2008 at the Delta Research and Extension Center near Stoneville, MS.  Starter AMS resulted in no increases in plant height or GY.  Total dry matter (TDM) was increased 28% in 2008 when starter N was applied.  Total N uptake (TNU) was also greater in 2008 when starter N was applied.  In 2008, plant recovery of ¹⁵N-AMS was approximately 3.5 times greater than in 2007 when measured at the five-leaf stage.  The recovery percentage of ¹⁵N-AMS reached its maximum at heading (HD) in both years.  Maximum recovery averaged approximately 15% in 2007 and 8% in 2008.  The hybrid XL723 had approximately 1% greater N concentration at the five-leaf rice growth stage, produced approximately 25% greater yield than Cocodrie in both years, and in 2007, recovered the greatest amount of starter N, thus providing evidence that heterosis is a means by which greater GY and N use efficiency can be obtained.  This study revealed that to more consistently increase growth and GY, studies should be conducted that investigate more effective starter fertilizer application strategies, including starter fertilizer N source, rate, and placement in proximity to the root zone.