Accounting for High Nitrate in Well Water to Meet Crop Nitrogen Needs.

Drought can lead to reduced crop yields and elevated residual nitrate (NO₃) levels in the soil in cases in which nitrogen (N) was applied pre-drought.  This may be exacerbated on irrigated acres if groundwater high in NO₃ exists. The objective of this research was evaluate the practice of accounting for existing N in irrigation water toward crop needs and the subsequent impact on crop production and N levels in the soil profile. Five fertility treatments were evaluated: 1) control; 2)  N; and 3) N plus P not accounting for NO₃ in well water; 4) N; and 5) N plus P accounting for NO₃ in well water under subsurface drip and center pivot irrigation systems.  Nitrogen applications were significantly reduced without compromising lint yields when well water NO₃ was credited.  During the 2011 drought season, naturally occurring NO₃ in the well water provided more than 100% of crop N requirements.  As a result, residual soil NO₃ levels increased, leading to greatly reduced N fertilizer application entering the 2012 season. Accounting for NO₃ in well water, as well as residual soil NO₃, can provide substantial economic savings to producers.