The fate of urea applied at various intervals after the sowing of a wheat crop on a sandy soil in Western Australia

Abstract

Nitrogen at the rate of 77.28 kg/ha was applied as urea at seeding and two, four or eight weeks after seeding, to a wheat crop grown on a deep yellow sand. Measurements of the nitrogen contents in the top 91 cm of soil, plant nitrogen content and dry matter yields were made at regular intervals. All urea treatments gave marked yield increases, with later applications giving higher yields and higher recovery of applied nitrogen by plant tops. There was considerable movement of nitrogen down the profile studied and losses of nitrogen were greatest with earlier applications. However, the time taken for the level of nitrogen in the soil to fall to that of the control was similar for all times of application. Differences resulting from treatments appeared to be related to the stage of development of the plants at the time of application of urea, the later applications being made to plants with presumably better developed root systems, which took up the nitrogen more rapidly than plants receiving urea earlier. Grain yields were closely related to the nitrogen uptake into the plant tops. Leaching of applied nitrogen was more marked when urea was applied closest to seeding.