Three manures were compared with urea as sources of nitrogen for corn (Zea mays L.) on a different field site in each of 3 yr. The manures and their average [Formula: see text]–N:total N ratios were as follows: liquid poultry manure (LPM), 0.89; liquid dairy cattle manure (LCM), 0.53; and solid beef cattle manure (SBM), 0.09. The manures were applied at rates of 100, 200 and 300 kg total N ha −1 . An additional LCM treatment of 600 kg total N ha −1 was also included. For comparison with the manures as N sources, urea was applied at rates of 50, 100 and 150 kg N ha −1 . The yield response data were examined on the basis of a previously suggested model which predicted that all of the [Formula: see text]–N and part (e.g., 10–20%) of the organic N in manures are available for crop growth in the field. Regression analyses of paired yield data sets of urea and LCM or urea and LPM indicated that only 75–80% of the [Formula: see text]–N fraction applied in these manures was equivalent to urea-N. Thus, it was concluded that the model did not take into account net N immobilization and possibly N losses through denitrification following application. It was concluded also that N release from the organic N fraction of SBM differed substantially from that for the other manures. This conclusion was supported by greenhouse data which indicated that net N immobilization occurred for the first crop shortly after SBM was applied but this was followed by net N mineralization for a second crop as manure decomposition continued. Soil NO 3 − concentrations in mid-June generally increased with the urea, LPM and LCM sources of N at the higher rates of application in the field. Lower soil NO 3 − concentrations with SBM reflected the lower availability of N. Key words: Corn, manure N availability, Zea mays L.
