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Fluid Journal : Fluid Journal 2005-2007
Winter 2005 Fluid Journal 2 Dalhart site Soil. The Dalhart site is located on a Dallam fine sandy soil about 9 miles northwest of Dalhart, Texas, on a 500- acre field with a center-pivot irrigation system. In 1999, the site was producing its fifth corn crop since being broken from native grass in 1995. N applied. The amount of N applied to the whole field (N1) at Dalhart was 315, 327, 266 and 233 lbs/A of N for the 1999, 2000, 2001, and 2002 corn crops, respectively. The amount of N applied to the corn residue after harvest on the southwestern half of the field (N2) was 88, 120, 110, and 50 lbs/A of N in 1998, 1999, 2000, and 2001, respectively. Grain yield. From 1999 to 2002, combine corn yields over each half of the pivot ranged from 203 to 233 bu/A and averaged 217 bu/A at the (N1) fertility level. At the (N2) fertility level, they ranged from 197 to 224 bu/A and averaged 210 bu/A. Residue. The amount of corn residue returned to the soil from 1999 to 2002 ranged from 8,873 to 12,120 lbs/A and averaged 10,184 lbs/A at the (N1) fertility level. At the (N2) level, it ranged from 7,020 to 11,385 lbs/A and averaged 9,469 lbs/A. Residue C concentration averaged 45 percent with a 4-year average above-ground residue C and N input to the soil of about 4,588 lbs C/A and 81 lbs/A of N (N1) and 4,271 lbs C/A and 91 lbs/A of N (N2) per year. N concentration of the residue averaged 0.83 (N1) and 1.00 (N2) percent. Texline site Soil. The Texline site is located on a gently sloping Conlen clay loam (N2 fertility level) and rolling Dumas clay loam (N1 fertility level) about 11 miles north of Texline, Texas, on a 400-acre field with center-pivot irrigation. In 1999, the cropped area was producing its fourth corn crop since being broken Fig. 1. Change in soil organic C (SOC) with time at Dalhart and Texline, TX in the 0 to 6 inch soil depth. Fig. 2. Change in total soil N (TSN) in the 0 to 6 inch soil depth with time at Dalhart and Texline, TX. Fig. 3. Soil NO3-N levels in native sod in 1999 and after corn harvest each year at Dalhart and Texline,TX.
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