Tuesday, November 6, 2007
205-4

Soil Nitrate Profiles for Southern High Plains Center-pivot-Irrigated Fields.

Adinarayana Reddy Malapati, Texas Agric. Exp. Stn, 1102 E FM 1294, Lubbock, TX 79403 and Kevin Bronson, Texas A&M University, Texas A&M Univ.Agric. Exp.Sta, 1102 E FM 1294, Lubbock, TX 79403.

Nitrate (NO3) contamination of the Ogallala aquifer is a problem in the Texas High Plains, especially in counties south of Lubbock.  The source of this NO3 is not clear.  Leaching of residual soil NO3 in cropped fields is a possibility, but this may take many decades to reach the 32 to 93 m depths of the Ogallala groundwater.  We present soil profile NO3 data from eight cotton fields from five counties across the Southern High Plains.  Soils were sampled to 0.9 m in four depth increments.  Mean 0 – 0.9 m soil NO3 for the eight sites was 99 kg N/ha, but ranged from 22 kg N/ha to 228 kg N/ha.    Nitrate was relatively low in the 0-15 cm layer, averaging 17 kg N ha-1.  We also analyzed irrigation well water NO3 in each of 11 Texas High Plains counties.  Well water NO3 ranged from 2.7 mg N/ L in Hale county to 12.8 mg/L in Lynn county.  Using the Web Soil Survey (USDA-NRCS) we analyzed soil profile and county scale well water data by soil map unit.  Soil NO3-N ranged from 50 kg N/ha on Amarillo fine sandy loam (Paleustalf), 0-1 % slopes to 130 kg N/ha on Pullman clay loam (Paleustoll), 0-1 % slopes.  Deep soil sampling and consideration of all sources of N can help protect possible NO3 contamination of the Ogallala aquifer.

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