Response of oats to nitrogen and defoliation

Abstract

Field and glasshouse trials were conducted to examine the growth responses of oats to defoliation and nitrogen fertilizer. In a field crop, nitrogen increased tillering early in the growth of the crop and slowed the rate of decline in tiller density in the spring. A dressing of nitrogen after a midwinter defoliation failed to increase the regrowth rate of the crop until early spring. The severity of the defoliation had little effect on the regrowth rate, with subsequent differences in yield being due largely to differences in residual dry matter. In glasshouse experiments, the parts of the plant responded differently to defoliation. The roots stopped growing almost immediately; did not recommence active growth for approximately two weeks, but generally maintained their dry weight during this time. The leaf sheaths declined in dry weight for seven days after defoliation, but then recovered their pre-defoliation weight after a further three days. The growth rate of the leaf laminae was apparently unaffected by the defoliation. Plants with a high nitrogen availability recovered faster after defoliation. The more severe the defoliation, the longer the plant took to recover, but once active growth recommenced, there was no difference between the growth rates of plants defoliated to different degrees. The prevailing climatic conditions also influenced the time to recommence active growth. A second defoliation imposed before the plants had replaced the weight lost by the leaf sheaths after an earlier defoliation reduced the subsequent regrowth. situation is discussed.