Using Subsurface Hydrology to Improve Nitrogen Use Efficiency.

Water availability and efficient use of nitrogen are critical to a sustainable and profitable crop production system.  At the ARS-USDA Optimizing Production Inputs for Economic Enhancement site (OPE3) in Beltsville, Maryland, two corn production fields about 4 ha each were studied over a four year period to evaluate nitrogen use efficiency under two different management practices.  One field, field B, used split application of nitrogen, receiving 30 kg/ha at planting and then about 120 kg N/ha at side-dressing when the corn was about 60 to 80 cm high.  The second field, field D, was under precision management -- receiving 30 kg N /ha at planting and then 0 to 140 kg N/ha as side-dressing (same time as field B).  The amount of N applied in field D, for each 10 m by 10 m cell, at side-dressing depended primarily upon crop yield history and the location of subsurface flow pathways, previously determined with ground-penetrating radar.  The hypothesis was that nitrogen was typically excessively applied – leaving considerable N to leach and move through the subsurface.  If subsurface flow pathways could be quantified then corn plants down gradient would be feed via subsurface channels.  Knowing where the subsurface flow channels existed allowed less N to be applied down slop along the subsurface flow pathways.  Results demonstrate the precision site generally received about 40% less nitrogen than the split N application site however there was no significant reduction in yields.  This work demonstrates that a knowledge of the hydrology can improve nitrogen use efficiency and thereby increase farm sustainability.