Keywords: fertiliser recommendations, grassland, nutrient management, soil fertility, fertilisers, manures.
Providing fertiliser recommendations for grassland is challenging due to the variety and complexity of livestock production systems ranging from extended grazing to fully housed ‘zero grazing’ systems. Many farms use multiple grazings and cuttings and there is a wide range of field conditions and grass growth potential. Nutrients recycled at grazing and nitrogen (N) fixed by clover add another layer of complexity and the quantity of grass production is dependent on livestock stocking rates and concentrate use, and can be considerably lower than growth potential.
Nevertheless, many decades of research, principally since the 1940s, provide a sound basis for good nutrient management advice, covering the maintenance of soil fertility and the application of nutrients to maintain critical levels of soil nutrient reserves and stimulate the required response in grass growth in terms of grass energy, protein and dry matter (DM) yield. It is also important that nutrient management is integrated so that account is taken of the supply of major and micronutrients from soil, feed, clover, manure and manufactured fertiliser to ensure adequate grass growth and animal health.
There is some evidence from cultivar trials that nitrogen use efficiency and grass DM yields achieved from modern grass varieties have improved significantly in recent decades and there is only limited data on the ability of modern clover varieties in mixed swards to fix N. Recent field experiments conducted by ADAS and Rothamsted Research North Wyke indicate that the DM yield response of modern grass varieties to applied N may have increased since the 1980s and there are indications that modern grass/clover swards can fix at least 100-150 kg N/ha/yr during the growing season. There is also new data on the amount of potash (K2O) taken off in cut grass and new developments in phosphorus (P) recommendations that take account of the P sorption capacity of different soils.
New grassland recommendation systems need to take account of and maximise the impact of recent research findings while also remaining relevant to modern livestock production systems. The challenge is to synthesise research into recommendations that are provided at an appropriate level of precision and are also easy to understand, accessible and recognisable so that farmers can relate them to their own systems. Only then will uptake and use of recommendations increase to further contribute towards improved nutrient use efficiency in grassland production.
J P Newell Price, ADAS Gleadthorpe, Meden Vale, Mansfield, UK.
M Lobley, University of Exeter, Exeter, UK.
J R Williams, ADAS Boxworth, Cambridge, UK.
28 pages, 7 figures, 2 tables, 12 plates, 41 references