The short-term fate of urea applied to barley in a humid climate. I. Experiments

Abstract

The fate of 15N labelled urea and potassium bromide applied to a mole-tile drained silt loam soil, sown to barley, was investigated using microplots and small weighable lysimeters. Two irrigation treatments, corresponding to normal and high rainfall conditions, were imposed on the lysimeters. After 35 days approximately 90% of the applied nitrogen (N) was recovered from the lysimeters, in the soil, plants and leachate, indicating gaseous losses were not large. Approximately 50% of the urea N was hydrolysed within 3 days of application, and a similar percentage was present as organic N in the soil after 20 days. Six per cent of the fertilizer N was leached from the normal lysimeters and 14% from the wetter lysimeters. In contrast, 76% of the applied bromide was leached from the wetter lysimeters. Plant uptake into shoots and roots of fertilizer N was 32% and 22% of that applied in the normal and wetter lysimeters respectively, leaching losses being largely at the expense of plant uptake. Native soil N was also measured. It is suggested that process-oriented studies of the kind described can assist in the interpretation and extrapolation of results from conventional fertilizer, trials, particularly when used to develop simple mechanistic models.