Nitrate leaching following autumn and winter application of animal manures to grassland

Abstract

Abstract. Under a UK Government consultation procedure announced in 2001, it was proposed that measures agreed within already designated Nitrate Vulnerable Zones (NVZ ‘s) would be extended to include a considerably increased area of England, Wales and Scotland. Since existing NVZ ‘s in the UK have included relatively little grassland, it is important to examine how nitrate losses from grassland areas, especially from animal manures, one of the major potential sources of nitrate loss, can be minimized. Experiments were carried out on freely draining grassland soils at four sites (Devon, Hampshire, Shropshire and N Yorkshire) representative of a wide range of climatic and farming conditions across lowland England, over a four year period, 1990/91 to 1993/94. Slurry was applied to experimental plots over a range of times (including June and then monthly, from September to January) at a target rate of 200 kg N ha–1. Nitrogen leaching over the four years ranged from 0 to >50% of applied slurry N, with the largest losses occurring following applications in the September to November period. The use of a nitrification inhibitor with slurry applied in November failed to provide consistent reduction in nitrate leaching. A strategy to reduce the risk of N leaching from manures applied to freely draining grassland soils must take account of the characteristics of the manure, in particular its N content, the application rate and the amount of excess rainfall following application. The experimental results suggest that slurry applications to freely draining grassland, in September, October and November should generally be avoided, the rationale for this being dependent on the amount of excess rainfall subsequent to application. Farmyard manure represents a lower risk and does not justify the restrictions on application timing that appear to be necessary with slurry.

Nitrate leaching in agriculture to upper groundwater in the sandy regions of the Netherlands during the 1992–1995 period

“…However, in situations where swards were grazed by cattle, nitrate leaching was 5 to 6 times greater, exceeding the leaching losses normally observed from arable land (Ryden et al, 1984). Especially grazing (Sauer and Harrach, 1996) and slurry application (Smith et al, 2002) in late summer and early autumn enhances nitrate leaching. In grassland, leaching losses of fertilizer N are essentially confined to the winter succeeding the summer in which the fertilizer was applied (Dowdell, 1982).…”

Nitrate leaching from liquid cattle manure compared to synthetic fertilizer applied to grassland or silage maize in the Netherlands

“…It is however necessary to evaluate the design of these experiments, as often the application time and LCM rates are poorly synchronized with the grassland N uptake capacity. In some studies, LCM, or largely similar liquid manure types, were intentionally applied at the end of the growing season, to assess the nitrate leaching risk over winter (Carey et al 1997;Smith et al 2002).…”

Assessing the impact of Nitrate Vulnerable Zones in England on nitrate loss from agricultural land

“…These could result in some nitrate loss (e.g. Jackson and Smith, 1997;Smith et al, 2002) as was reflected in the MANNER model results. In addition, on the basis of NVZAP criteria (Defra, 2002) only about 9% of agricultural land would be classed as 'sandy or shallow', and therefore subject to closed periods for manure application.…”