Effect of previous urine application on ammonia volatilisation from 3 nitrogen fertilisers

An enclosure method was used to measure the daily volatilisation losses of ammonia (NH 3 ) from 3 fertilisers (urea, diammonium phosphate, and ammonium sulphate). These fertilisers were broadcast on pasture in spring at a rate of 3 g/m 2 N (30 kg/ha). The NH 3 loss was measured in the absence or presence of sheep urine applied 1 week before the fertiliser. The surface soil pH was monitored in situ using a flat surface glass electrode. The cumulative loss of NH 3 ‐N over an 11‐day period from non‐urine‐treated and urine‐treated soil was 0.22 and 0.80 g/m 2 for urea, 0.07 and 0.30 g/m 2 for diammonium phosphate, and less than 0.01 and 0.03 g/m 2 for ammonium sulphate respectively. After urea application, maximum fluxes of 0.08 (on Day 3) and 0.31 g/m 2 per day N (on Day 2) occurred in the absence and presence of urine pretreatment respectively. Maximum fluxes occurred within 1 day of diammonium phosphate application, and were 0.03 and 0.09 g/m 2 per day in treatments without and with urine respectively. The daily pattern of ammonia loss from both fertilisers was related to soil pH changes. Although previous application of urine significantly promoted NH 3 volatilisation from urea and diammonium phosphate, modifications to N fertiliser management practices were not considered necessary. It was estimated that only a small proportion (6%) of the soil surface would receive urine each day, even under the intensive grazing systems frequently used in spring.