Urea as a fertilizer. Ammonia evolution and brairding of wheat

Abstract

1. Moderate percentages of urea are widely and successfully used in compound fertilizers but the use of large proportions may be accompanied by two disadvantages:(a) the loss of nitrogen as ammonia from surface applications,(b) the occurrence of toxic effects when urea and seeds are drilled together in soil. This paper shows that both these effects are consequences of the rapid hydrolysis of urea to ammonia and carbon dioxide.2. The effect on brairding of the presence of urea and of ammonium sulphate drilled with wheat seeds, and the loss of ammonia from top-dressings of the compounds on bare soils have been studied on a range of soils. Phytotoxicity was most pronounced in those conditions in which ammonia evolution was greatest. Thus, in a sandy soil, from which about 75% of the nitrogen of a top-dressing of urea was evolved as ammonia in our conditions, more than 15 lb. nitrogen as urea per acre reduced the braird of wheat seeds; while in a clay soil, from which only 10% of a top-dressing was lost as ammonia, up to 60 lb. nitrogen as urea per acre could be added before braird was reduced. Intermediate results were obtained with three more soils and ammonia evolution and brairding were always closely parallel.