A comparison of the effects of anhydrous ammonia and a solid ammonium nitrate fertilizer on herbage production from a pure perennial ryegrass sward

SUMMARY In a 2-year experiment anhydrous ammonia (82% N) and an ammonium nitrate fertilizer (34·5% N) were applied at three annual rates—100, 200 and 300 lb N/acre (112, 224 and 336 kg/ha)—on an S.24 perennial ryegrass sward. At each rate the two fertilizers were applied either as a single dressing in the spring or as five equal split dressings over the season. Total yields of herbage dry matter and of crude protein were determined by cutting the herbage at approximately the same stage of growth five times each year. On the basis of total yield and seasonal distribution of yield anhydrous ammonia was best applied as a single dressing in the spring, whereas ammonium nitrate was best applied as five equal split dressings over the season. However, in both years anhydrous ammonia applied as a single dressing gave smaller yields and a poorer seasonal distribution of production than did ammonium nitrate applied as five equal split dressings. The factors contributing to the lower yield level with anhydrous ammonia applications are discussed. It is concluded that anhydrous ammonia has no marked advantages over ammonium nitrate as a nitrogen fertilizer for intensively managed grassland.