Managing Residual Nitrogen for Grain Sorghum Production.

Residual soil nitrogen (N) levels were considerably elevated in several key row crop production areas of Texas.  A 7-year study investigating N management in cotton indicated that residual N levels ranged from 34 to over 181 kg/ha to a depth of 1.22 m. Only 23% of study sites showed a yield response to supplemental N fertilizer. Grain sorghum is commonly used as a rotational crop with cotton and though it has a different root structure than cotton, grain sorghum also may benefit from residual soil nitrogen.  However, there is limited information about how to properly credit residual N from different soil depths.  First-year field studies were initiated in the Blacklands and Coastal Bend regions of Texas to evaluate the response of grain sorghum to residual soil N.  Supplemental N was applied to achieve soil test recommendations based on residual soil NO₃-N at 0 to 15-, 0 to 30-, and 0 to 60-cm.  Yields at most locations were limited by a relatively dry mid season.  Reducing N fertilizer applications for grain sorghum based on residual soil NO₃-N to 60 cm did not affect grain yield.