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Publication Date
1981
Description
Using the acetylene reduction assay, field studies in recent years have investigated the variation in N fixation in grazed systems, and some of the principles involved in the interaction with available soil N have been described. This experiment extends this work to include the effect of grazing management on the factors influencing N fixation. Two self-contained sheep-grazed units, one a 10-paddock rotationally grazed system and the other set stocked, were established on a high-fertility ryegrass-white clover pasture, with a basic stocking rate of 22 sheep/ha. Over the 1975-1978 period, both units were monitored for pasture growth, N fixation, and associated herbage and soil parameters. Annual N fixation under set stocking was 10% higher than under rotational grazing. The difference, which occurred during the dry summer-autumn period, reflected a greater ability of the set-stocked pastures to respond to short-term alleviation of moisture stress. Legume growth rate was the principal factor controlling N fixation in both systems. Available soil N appeared to he of greater significance in controlling N fixation under rotational grazing. This finding was consistent with the generally lower herbage N03-N levels found under set stocking. These differences were attributed to differences in sward structure and physiological stress between the two grazing systems.
Citation
Brock, J L.; Hoglund, J H.; and Fletcher, R H., "Effects of Grazing Management on Seasonal Variation in Nitrogen Fixation" (1981). IGC Proceedings (1981-2023). 5.
(URL: https://uknowledge.uky.edu/igc/1981/seection4/5)
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Agricultural Science Commons, Agronomy and Crop Sciences Commons, Plant Biology Commons, Plant Pathology Commons, Soil Science Commons, Weed Science Commons
Effects of Grazing Management on Seasonal Variation in Nitrogen Fixation
Using the acetylene reduction assay, field studies in recent years have investigated the variation in N fixation in grazed systems, and some of the principles involved in the interaction with available soil N have been described. This experiment extends this work to include the effect of grazing management on the factors influencing N fixation. Two self-contained sheep-grazed units, one a 10-paddock rotationally grazed system and the other set stocked, were established on a high-fertility ryegrass-white clover pasture, with a basic stocking rate of 22 sheep/ha. Over the 1975-1978 period, both units were monitored for pasture growth, N fixation, and associated herbage and soil parameters. Annual N fixation under set stocking was 10% higher than under rotational grazing. The difference, which occurred during the dry summer-autumn period, reflected a greater ability of the set-stocked pastures to respond to short-term alleviation of moisture stress. Legume growth rate was the principal factor controlling N fixation in both systems. Available soil N appeared to he of greater significance in controlling N fixation under rotational grazing. This finding was consistent with the generally lower herbage N03-N levels found under set stocking. These differences were attributed to differences in sward structure and physiological stress between the two grazing systems.
