Estimating the Availability of Nitrogen in Poultry Manure through Laboratory and Field Studies
- Carolyn C. Bitzer and
- J. Thomas Sims *
Excessive applications of poultry (chicken, Gallus gallus domesticus) manure in some cropping systems have resulted in nitrate contamination of groundwater. To determine the application rates necessary for optimum crop growth and minimal nitrate leaching, estimates of the availability of N in poultry manure are necessary. This research investigated, under laboratory and field conditions, an approach that could be used to predict available N in poultry manure. In the laboratory study, 20 manures were incorporated with a Kalmia sandy loam (Typic Hapludults) at rates estimated to provide 100 mg predicted available N (PAN) kg−1 soil, where PAN = 80% Ni + 60% No and Ni = (NH4-N + NO3-N), No = (Total N − Ni). Actual available N, defined as Ni initially extractable by 2 M KCl, plus N mineralized during a 140-d nonleached incubation study, ranged from 54 to 118 mg N kg−1 soil. A field study was also conducted at two locations comparing three poultry manures, applied at rates of 0, 90, 180, and 270 kg PAN ha−1, with ammonium nitrate (AN) applied at the same rates. Irrigated corn (Zea mays L.) was grown at both sites during 1985 and soil, plant, and yield data were obtained. Nitrogen content of ear leaf samples at mid-silking was significantly less, at both sites, for the three manures than for AN. No significant differences in grain yields were observed between N sources at site one, but average yields (across N rate) were significantly less with two of the poultry manures (PM-7, PM-11), relative to AN, at site two. Postharvest soil samples (0–100 cm) were obtained from the control (0N) and 270 kg PAN ha−1 rates of all N sources. Residual Ni was less than 10 mg kg−1 for all treatments and depths; however, significantly higher (P = 0.08) NO3-N levels were found with AN at the 60 to 80 depth cm at site two and at the 80 to 100 cm (P < 0.05) depths at sites one and two. The field study was repeated at the same sites in 1986 to assess the residual N value of manure applied in 1985. Based on ear leaf N and grain yields, residual available N from manures was determined to be less than 45 kg N ha−1. The second year decay constant for PM was estimated, by comparison with AN yields, to be 0.11 and 0.06 at sites one and two, respectively.
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