A four-year-field trial with animal manures: I. Nitrogen balances and yields

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Abstract
Data are presented for a 4-year field experiment with various rates of both dry and liquid manures, and two levels of irrigation. Yields of sudangrass and barley forages were increased at moderate rates of manures, but higher rates decreased yields. Effects of the rate of irrigation water on yields were not significant. Leaching of NO-3 was correlated with rates of manures applied. Increased drainage volumes decreased NO-3 concentrations of leachate only at the high rates of manures, but increased mass emissions of NO-3 for all manure treatments. A N balance in which the sum of accumulation in the organic matter, in crop removal, and in leaching losses was subtracted from the total N input in manures and irrigation water to obtain unmeasured losses, indicated that volatilization losses were small unless large excesses of manure were applied. The measured mineralization of the N added in dry dairy manure and in liquid feedlot manure agreed well with mineralization calculated from decay series. The relationships between forage yields and amounts of N leached as NO-3, and between yields and calculated rates of N mineralization, were studied. The N in the dry dairy manure, which averaged 1.6% N on a dry weight basis, was about 45% available the first year after application, whereas the N in the liquid feedlot manure, which averaged 4.5% N on a dry weight basis, was about 75% available. The problems of conducting experiments with animal manures as N sources, and the implications of calculated mineralization rates, are discussed.