Uptake, cycling and fate of nitrogen in grass-clover swards continuously grazed by sheep

Abstract

S U M M A R YComponents of the N cycle were studied at Hurley, UK, in 1985-87. In grass-clover {Lolium perenne and Trifolium repens) swards, grazed at three intensities, low total inputs of N were associated with low outputs and losses of N. Nevertheless, the flows (intake and excretion) of N through animals were substantial and gave rise, at the higher intensities of grazing, to an acceptably high agricultural output per hectare. This was considered evidence of a fast and efficient recycling of N between plants, animals and soil. The release of N to the environment (as nitrogenous gases and nitrate) was substantially less from the grass-clover swards than from a grass sward fertilized with 420 kg N/ha, and this was at the expense of only 20% loss in production. The mechanisms which might account for the high efficiency of utilization and recycling of N in grass-clover swards are discussed in the context of the balance of the supply of C and N to plant and soil biomasses under grazing. The results confirm that optimizing agricultural output in grass-clover swards has little adverse effect on the environment, but the importance to this end of sustaining a large proportion of N-deficient grass in grass-clover swards is emphasized.

Nitrogen fixation in Australian dairy systems: review and prospect

“…, similar to that observed in the UK (Parsons et al 1991;Andrews et al 2007) and NZ (Woodfield and Clark 2009), although Jarvis (1993) suggested that in the UK, dairy pastures were typically much lower in both clover content (<10%) and the amount of N 2 fixed (10 kg ha -1 year -1 ). These low clover contents are likely to be suboptimal in terms of dairy production (Woodfield and Clark 2009) as well as N 2 fixation and thus efforts to increase N 2 fixation should be rewarded with increased milk production efficiency.…”

“…Generally to minimise losses of N via denitrification, leaching or NH 3 volatilisation a 'tight' N cycle is required, necessitating the maintenance of some N limited grass to 'mop up' available N (Parsons et al 1991). However, it is generally thought that a system with slightly N-deficient grass may limit feed quantity and quality and is not considered optimised in terms of animal production (Eckard 2001).…”

Produção animal em gramíneas de estação fria com fertilização nitrogenada ou associadas com leguminosa, com ou sem fertilização nitrogenada

“…Isto tem levado a um aumento do interesse pelo uso de leguminosas, devido a seu baixo impacto, mas reduzindo o rendimento dos sistemas pastoris. Tais benefícios podem ser encontrados em ambos os sistemas, simplesmente pela redução, sobretudo da fertilização nitrogenada, e assim, possivelmente, da produtividade do sistema (PARSONS et al, 1991). Uma exceção é a Nova Zelândia (NZ) onde uma pastagem consorciada bem manejada, freqüentemente tem produções de forragem entre 10 -15t de MS/ha/ano (DALY, 1990).…”

Ammonia volatilization and soil nitrogen dynamics following fall application of pig slurry on canola crop residues

“…There is a short window of time between the average harvest date of canola (15 September) and the latest date for PS fall application to land (1 October) in Québec. This means that slurry is usually applied on recently harvested crop residues, which may slow down the infiltration of slurry into the soil and lead to greater NH 3 volatilization losses than when slurry is applied on a bare soil (Parsons et al 1990). Rapid incorporation of slurry following application has been shown to reduce volatilization of ammonia .…”