Nitrogen Outputs from a Field-Size Agricultural Watershed
- Richard Lowrance *
Nitrogen outputs from a 0.34-ha field were measured for 1984 through 1987. The field consisted of Cowarts loamy sand (fine-loamy, siliceous, thermic Typic Hapludult) managed in a summer row crop-winter cover crop sequence. Outputs measured were subsurface flow, surface runoff, and denitrification. Monthly sampling of denitrification rates showed a high degree of temporal and spatial variability. Rates significantly increased with soil moisture and depth. Denitrification also increased after irrigation events. Nitrogen movement in subsurface flow was 97% NO3-N and was about 10 times that in surface runoff. Most subsurface flow and movement of N (77 kg NO3-N ha−1) occurred in December 1986 through February 1987 when 62 cm of precipitation fell in a 12-wk period (December 1986–February 1987) following fertilizer application. This period accounted for one-half the total subsurface nitrate movement for the 4-yr study. Even though no crop was harvested in 1985, subsurface outputs of N were low in winter of 1985–1986. Soil NH4-N levels were significantly higher after the year without a harvest, indicating that more of the N in crop residue was found in the soil pool.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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