Studies on Development of High Productive Grazing System and Nitrogen Dynamics on Tropical-Subtropical Pasture

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The study was conducted firstly to clarify the potential carrying capacity of giant stargrass was evaluated under different stocking rates in intensive rotational grazing system. Secondly, the nitrogen dynamics through fertilization was estimated under different stocking rates with 15N tracer methods. The followings are the major results.1)Grazing trials were conducted to estimate a potential carrying capacity of giant stargrass based on the results which the optimum cutting frequency is 4-6 weeks and the effective nitrogen application level is 0.5 Nkg/a after cutting or grazing in giant stargrass grazing pasture. High pasture availability and good quality forage to bring about the effective animal production were produced by using relatively heavy stocking rates of 6-8 heads/ha.2)Annual ryegrass(Lolium multiflorum Lam.) was overseeded to heighten a nutritive production on the low productive giant stargrass pasture during short winter in this district. Pasture utilization and daily dry matter intake on the pasture overseeded with ryegrass were higher than pure giant stargrass. Average pasture availability and utilization at heavy stocking rate was higher than at light stocking rate even in winter.3)The fate of ^<15>N-labeled fertilizer nitrogen applied was estimated under two stocking. ^<15>N recovered by harvested part(same as intake part) was 10-43% through the year, and which value was higher under heavy stocking rate(6.4 heads/ha). ^<15>N recovered in soil was higher under light stocking rate(3.2 heads/ha).From the research, it can be concluded that the carrying capacity of giant stargrass pasture, managed effectively was doubled with increasing pasture and animal production comparing with the present traditional grazing system.