The high rates of urine‐N deposited during grazing offers the potential for considerable N loss through volatilization, leaching, and denitrification. A field experiment was conducted to evaluate the magnitude and pathways of N transformations and losses under warm, moist conditions. Urine was applied to 3‐m 2 plots in a ryegrass ( Lolium perenne L.)‐white clover ( Trifolium repens L.) pasture at 300 or 600 kg N/ha. These rates simulate the urine affected area of sheep and cattle, respectively. Ammonia volatilization, inorganic N in the soil profile, symbiotic nitrogen fixation (by acetylene reduction assay), and herbage N yields were measured over 53 days. Four days after application from 30 to 35% of the added N could not & accounted for as either soil mineral N or volatilized NH 3 ‐N. Ammonia‐N evolution was rapid only for the first 2 days, and I5 to 18% of the N was volatilized as NH 3 . Profile NH 4 ‐N was completely nitrified by 21 days. Considerable amounts of the applied N was lost from the 0 to 45 cm profile by 53 days. Since rainfall and irrigation exceeded estimated evapotranspiration, leaching of NO 3 ‐N is the probable loss mechanism. The apparent recovery of N in herbage was 37 and 22% of that added. Acetylene reduction was substantially less in the urine‐treated swards. From 30 to 35% of the urine‐N was not accounted for as inorganic N early in the experiment; immobilization and rapid leaching of urine below 45 cm are probable loss mechanisms. The experiment indicated that in a warm, moist environment, typical of late spring‐early summer in New Zealand, more than half of the N in urine voided by sheep or cattle can be lost, and that an intensively grazed grass‐legume system is far from a closed system, or cycle, with respect to N.
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Ball et al. (1979) studied this question.