Deep, Residual Nitrogen Supports Grain Sorghum Yield.

Though nitrogen (N) is essential for the production of grain sorghum, escalating costs, volatility in market pricing, and increasing concerns regarding nutrient contamination of limited water resources require attainable improvements in management. Previous studies planted to corn in the Central Blacklands and upper Gulf Coast regions in Texas demonstrated that grain yields and test weights were not affected at 29 of 30 sites when carryover N was credited to 60 cm, an efficient recovery of profile soil N. Only 23% of sites in Texas planted to cotton showed a yield response to supplemental N fertilizer where residual soil N levels ranged from 34 to over 181 kg/ha to a depth of 1.22 m. Grain sorghum grown as a rotational crop with cotton on approximately 1.3 million hectares per year in Texas may also benefit from residual soil N to 60 cm, especially following a dry season. Field studies were conducted at 19 sites throughout the Upper Coastal Bend and Central Texas Blacklands from 2008-2012 to assess the response of grain sorghum yield to residual soil nitrate-N to 60 cm. Deep profile sampling was used to identify study sites with a range of residual soil N levels. Supplemental N was applied to achieve soil test recommendations based on residual nitrogen at 0 to 15-, 0 to 30-, and 0 to 60-cm. Experimental units were arranged in randomized complete block designs and replicated five times. Uppermost leaf chlorophyll measured at flowering was not different when carryover N was credited to 60 cm. Likewise, grain yields were not affected at 17 of the 19 sites when carryover N was credited to 60 cm, indicating efficient recovery of carryover soil N by plants.