Effects of nitrogen deficiency and soil moisture stress on growth of pasture grasses at Samford, south-east Queensland. 1. Results of field experiments

Two field experiments were carried out at Samford during 1958, 1959, and 1960 using three grasses, nitrogen fertilizer, and supplementary irrigation. Attention was concentrated on grass growth during September to December, a period that is particularly important for livestock that have been grazed on poor quality feed during winter. Nitrogen deficiency was more important than soil moisture stress in limiting growth of grass under natural rainfall. Nitrogen fertilizer caused large increases in yield each year, and maximum yields above 10,000 lb of d y matter an acre were produced by uninterrupted growth up to December or January-four or five times the yields of the unertilized plots. Differences between the yields of the three grasses were small compared with the size of the nitrogen response. In the spring of 1960-61, which was the driest of the three seasons during this investigation, soil moisture stress reduced growth of nitrogen-fertilized Rhodes grass (Chloris gayana Kunth.) up to mid-December one-third. It was observed that fertilized Rhodes grass withdrew water more rapidly and to a greater depth than Rhodes grass without added nitrogen.