The effects of grazing with and without excretal returns on the accumulation of nitrogen by ryegrass in a continuously grazed upland sward

Abstract

With ati average slocking rate of 15 sheep ha ', soil nitrate-N, but nol total N (Kjeldahl) nor bulk density, was increased during the winter of the second year as a result of excretal returns. AbstractRates of N accumulation were studied on sheep grazed grass swards maintained at a constant height of 5 cm for two growing seasons (1985 and 1986) and receiving no N fertilizer using a tiller tissue turnover technique. Grazing with normal excretal returns resulted in an 85-10570 increase in the estimated rates of N accumulation by laminae compared with similarly grazed swards where excretal returns were prevented. Generally, increases in tiller numbers in plots receiving excreta were mainly responsible for the increased rates of N accumulation, rather than increased rates of N accumulation per tiller. Rates of N remobilization from laminae and senescence (flux of N to standing-dead litter pool) per tiller, and rales of leaf extension and leaf appearance/ disappearance were unaffected by excreial returns, in urine patches increased tiller numbers and increased rates of accumulation per tiller both resulted in greater estimates of N accumulation compared wilh tillers not visibly affected by excreta. However, at any one time only about 1 I' M. of the plot area was affected by excreta and increases in N accumulation in excreta patches could not account for the overall plot increases in rates of N accumulation.The increased tillering in plots receiving excreta may have increased exploitation of the soil N.

Long-term fencing improved soil properties and soil organic carbon storage in an alpine swamp meadow of western China

“…So, higher soil nitrogen contents may be related to higher soil microbial biomass carbon in fenced meadow. However, excretal returns of dung and urine from grazing animals can also result in the accumulation of soil nitrogen (Thomas et al 2006). As well as increasing soil nitrogen, fencing also results in increased soil total phosphorus and available phosphorus (Wu et al 2009).…”

Review. Impact of grazing on plant communities in forestry areas

“…This in turn favours the maintenance of a pool of rapidly mineralisable organic nutrients close to the soil surface (Floate, 1981;Chapin et al, 1995), which translates into increased pasture production (Williams and Haynes, 1995). The greater concentrations of nutrients in the vegetation of grazed than in non-grazed systems supports the idea that grazing accelerates the recycling of nutrients (Detling, 1988;Thomas et al, 1990). This might be due, however, to other factors such as enhanced uptake of nutrients by defoliated plants (Ruess, 1984), an increase in nutrient availability due to increased microbial activity associated with higher humidity and soil temperature (Jones and Woodmansee, 1979;Parton and Risser, 1980), or the different ages or phenological stages of plants when the modifications to their structure occur (Binnie and Chestnutt, 1994).…”

Detailed studies of grazed swards — techniques and conclusions

“…The effects of grazing animals on N fluxes in unfertilized upland grass swards were investigated by Thomas et al (1990), who combined leaf and tiller turnover measurements with N determination in individual plant parts to measure the accumulation of N. Measurements were made in swards with excretal returns and swards where excretal return was prevented. The study showed that excreta can substantially increase the rates of accumulation of N by grass laminae through direct (increased N supply) and indirect (increased tiller number) effects at moderate stocking rates with poor apparent recovery of N.…”