Nitrate leaching from grazed grassland lysimeters: effects of fertilizer input, field drainage, age of sward and patterns of weather

Abstract

Drained and undrained grassland lysimeter plots were established in 1982 on a clay loam of the Hallsworth series at a long-term experimental site in south-west England. The plots were continuously grazed by beef cattle, and received fertilizer at either 200 or 400 kg N ha -I per annum to the existing permanent sward, or at 400 kg N ha-' to a new sward, reseeded to perennial ryegrass following cultivation. Drainage water was monitored at V-notch weirs and sampled daily for the analysis of nitrate-N. Seven years of data are presented (five years for the reseeded swards). On the drained plots a large proportion of the rainfall was routed preferentially down large pores to the mole drains, whilst on the undrained plots, drainage was mainly by surface runoff. The average quantities of nitrate N leached per year were 38.5,133.8 and 55.7 kg ha-' from the old sward that received 200 and 400 kg N ha-', and from the reseed that received 400 kg N ha-' fertilizer, respectively. Ploughing and reseeding resulted in a two-fold reduction in leaching, except during the first winter after ploughing, and twice as much leaching occurred after a hot, dry summer as after a cool, wet one. Nitrate concentrations in drainage from either drained or undrained plots were rather insensitive to rainfall intensity, such that concentration was a good predictor of nitrate load for a given drainage volume. The drainage volume determined the proportion of the leachable N that remained in the soil after the winter drainage period. Initial (peak) concentrations of nitrate N ranged, on average, from 55 mg dm-3 for the drained old sward that received 400 kg N ha-' fertilizer, to 12 mg dm-3 for the undrained sward at 200 kg N ha-' fertilizer input. Concentrations of nitrate N in drainage from similar, unfertilized plots rarely exceeded 1 mg dm-3. The results suggest that manipulating the nitrate supply can lessen leaching and that the route of water through soil to the watercourse determines the maximum nitrate concentration for a given load.

Mitigating climate change: the role of domestic livestock

“…The key principle is to maximize the uptake of nutrients by the pasture plants. Factors such as the amount of manure applied (Scholefield et al, 1993) and the intensity of grazing (Ryden et al, 1984) are known to influence nitrogen leaching and were included in a model developed by Hansen et al (2000) to compare organic v. conventional farming. However, due to lack of data, such models are not yet at a stage of development though to be able to deal with all the processes involved.…”

A lysimeter study of the fate of15N‐labelled nitrogen in cow urine with or without farm dairy effluent in a grazed dairy pasture soil under flood irrigation

“…In intensively grazed dairy pasture systems, although the amount of NO3--N leached is affected by inputs of N fertilisers and organic waste effluents (Scholefield et al 1993;Di et al 1998aDi et al ,b, 1999Ledgard et al 1999a;Silva et al 1999;Monaghan et al 2000), the largest contribution comes from the N returned from the animal urine (Ball et al 1979;Ryden et al 1984;Field et al 1985;Silva et al 1999;Di & Cameron 2000, 2002b. In a grazed pasture, between 60-90% of the N ingested by the grazing animal is returned to the pasture in the urine and dung and more than 70% of the N returned is in the urine (Haynes & Williams 1993;Jarvis et al 1995).…”

Treating grazed pasture soil with a nitrification inhibitor, eco‐n™, to decrease nitrate leaching in a deep sandy soil under spray irrigation—a lysimeter study

“…Recent studies have shown that in a grazed pasture system, direct leaching losses of NO 3 -from applied fertiliser nitrogen (N) or farm dairy effluent (FDE) are relatively small compared with the leaching losses from animal urine patches (Scholefield et al 1993;Di et al 1998Di et al , 1999Di et al , 2002Silva et al 1999;Ledgard et al 1999;Di & Cameron 2002b;Monaghan et al 2002).…”