Losses of Nitrogen in Surface Runoff in the Blackland Prairie of Texas1
- D. E. Kissel,
- C. W. Richardson and
- Earl Burnett2
Our objective in this study was to determine NO3−-N and total N losses in surface runoff from Houston Black clay, a swelling clay soil with a relatively low infiltration rate. The study was carried out on duplicate 4-ha watersheds cropped to a rotation of grain sorghum (Sorghum bicolor [L.]), cotton (Gossypium hirsutum [L.]), and oats (Avena sativa [L.]), all fertilized at recommended rates of N application. The loss of NO3−-N varied considerably during the study, depending on events before each runoff-producing storm. Concentrations of NO3−-N were usually highest just after fertilizer application when the soil was near field capacity and lowest when large amounts of water infiltrated into dry soil immediately before runoff. During runoff-producing storms just after fertilizer application, the concentrations were lowest in the initial runoff and highest near the end of the runoff event. To compute NO3−-N losses with reasonable accuracy on these soils, the shape of the entire NO3−-N concentration curve needed to be well defined.
In general, the results of this study indicate that a small and probably insignificant amount of N is lost to surface waters when crops are fertilized at recommended N rates in the Texas Blackland Prairie. For the entire 5-year study, the mean concentration of NO3−-N in runoff was 2.9 and 2.3 ppm NO3−-N for the duplicate watersheds. The mean total loss of NO3−-N was 3.2 kg ha−1 year−1. Losses of sediment associated N were about 5 kg N ha−1 year−1.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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