A comparison of nitrogen fertilizers for spring and summer grass production

Three experiments were carried out in 1983-85 to compare split dressings of ammonium nitrate and urea with a single injection of aqueous ammonia for seasonal and total annual dry matter (DM) production. Total annual fertilizer nitrogen (N) applied was 360 kg ha¹ for a six-cut management. The solid fertilizers were applied in spring at different dates for the first cut and then after cuts 1 —4in the pattern 90,90,60,60,60 kg N ha¹. A winter injection of aqueous ammonia in the first year was replaced thereafter by early and late spring injections, the latter at 300 kg N ha¹ with 60 kg N ha ¹ as ammonium nitrate. Injection was to a depth of 100 mm at 30 cm spacing using a commercial applicator. The experiments were carried out on farms in a low rainfall area; the soils were sandy loams. Urea gave 3% less total DM production than ammonium nitrate (0middot;32±0middot;153 t ha-¹) and produced on average 7% less DM in the spring, and 12% less in dry conditions in early autumn of 1984. Lower production was associated with reduced uptake of N, which occurred at most cuts. From these experiments it is concluded that urea can be a suitable alternative to ammonium nitrate, and when used in spring must be about 20% cheaper per kg N. The performance of aqueous ammonia was variable. In the dry summer of 1984, when applied in early April with 60 kg N ha-¹ as ammonium nitrate it equalled the ammonium nitrate treatment in both spring and total production and was better (P< 0 ?05) in early autumn. In the same year, an early March injection was inferior (P < 0 05) in total DM production to ammonium nitrate. This early injection was also lower, but not significantly (P>005) in 1985, mainly because of lower spring production. A delayed, mid-April injection, plus ammonium nitrate, in 1985, gave even less spring growth and lower total production. A January injection, in 1983, showed poor persistency and is not recommended for sandy loam soils.