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

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.

Keywords:

• ammonia volatilisation
• urea
• ammonium sulphate
• wheat
• continuous flow enclosure
• integrated horizontal flux
• mass balance
• micrometeorological methods
• fertilisers