Effects of nitrogen and phosphorus fertilizers and gypsum on a Danthonia caespitosa-Stipa variabilis grassland. 1. Response to fertilizer application over four successive years

Abstract

The effect of nitrogen and phosphorus fertilizers and gypsum was assessed over four years on a Danthonia caespitosa-Stipa variabilis grassland, growing on the semi-arid Riverine Plain in south-eastern Australia. Fertilizers were applied annually and gypsum once only. The treatments were combined factorially. Seasonal production of total dry matter and individual species, and nitrogen and phosphorus contents of the plant tops, were measured. Forage production increased in response to the additives in years in which the annual rainfall varied from well below to near average. They accentuated the normal pattern of a spring peak, but also gave lesser increases in production in winter and autumn. Summer production was not measured because of the absence of effective summer rainfall. Nitrogen and phosphorus fertilizers and gypsum all contributed to the increased production, and the combination of the three additives produced the greatest yield. Over all seasons the yield of grassland treated with nitrogen plus phosphorus plus gypsum averaged 250 per cent of the control, or approximately 1500 kg ha-1. The main contributors to increases in yield were D. caespitosa, S. variabilis, annual herbs, and legumes. The perennial grasses were particularly favoured by nitrogen fertilizer whereas the yield of legumes was suppressed. The yield of legumes increased greatly in response to phosphorus fertilizer. With the exception of two species, all plants which increased in yield are acceptable to sheep. Nitrogen and phosphorus contents were above the minimum requirements for domestic herbivores.