Using Deep Profile, Residual Nitrogen for Corn Production.

Nitrogen (N) and other plant nutrients costs growers between 76 and 200 percent more compared to a decade ago.  Meanwhile, increasing concerns regarding nutrient contamination of surface and groundwater resources have refocused attention on impairments attributed to N and phosphorus management in major row crops.  In previous studies, 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.  Corn is frequently grown as a rotational crop with cotton and may also benefit from residual soil N, particularly following seasons with below normal rainfall.  Additional information was needed on how to properly credit residual, carryover N with soil depth.  Field studies were conducted at 29 sites throughout the Upper Coastal Bend and Central Texas Blacklands from 2008-2012 to assess plant availability and corn yield response 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.  Ear leaf chlorophyll was measured at flowering.  Corn grain yields and test weights were not affected at 28 of the 29 sites when carryover N was credited to 60 cm, indicating efficient recovery of profile soil N.