Ammonia volatilisation from urea broadcast in spring on to autumn-sown wheat

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Abstract
Ammonia volatilisation from nitrogen (N) fertilisers applied at 100 kg/ha N in spring to autumn-sown wheat was measured using a continuous air flow enclosure method. Loss from the bare soil surface was 21 and 29% of urea-N when broadcast in two seasons. Loss from broadcast ammonium sulphate was less than 1% and from urea placed 25 mm in the soil was 1% of applied N. The loss when wheat plants were present averaged two thirds the loss from bare soil. The total loss from the same soil type but with a history of crop or pasture was the same but loss occurred more rapidly from the pasture soil. Ammonia loss was also measured in one season using a micrometeorological technique (integrated horizontal flux). Both the total loss after 9 days and the daily pattern of loss were the same as estimated by the enclosure technique. The hydrolysis of urea and surface soil pH changes in both systems were similar.