Effects of irrigation and grazing systems on steer performance and plant response in an old world bluestem pastures
Bezanilla, Gerardo Arturo
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Irrigation is the single most expensive input on improved summer pasture. Ranchers in the Texas High Plains extensively use water pumped from the Ogallala Aquifer for this purpose. Old World bluestem grasses (OWB) are an example of improved grasses that possess good potential for beef and hay production. Our objective was to investigate different alternatives for beef production using an improved forage. A combination of continuous and 3-pasture grazing system, and 2 rates of irrigation (0 and 75 mm ha') were used as treatments and applied to three repetitions of a WW-B.Dahl pastures. Steer performance (average daily gain and beef production per ha) and grass response (standing crop) were measured during two consecutive summers. Yearling steers with an initial weight of 200 kg were individually weighed every 28 days from early June to early September of 1999 and 2000. Clippings were done to determine standing crop of pastures. About 75 mm of water were applied throughout each grazing season using a central pivot irrigation system. Pastures were fertilized before the beginning of the grazing season. A put-and-take method used in 1999 was changed to a set-stocking rate in 2000.. No interactions were found between the three factors studied (irrigation, grazing system, and grazing period) on animal performance on both years. In 1999, steers on irrigated pastures gained more weight than those on non-irrigated plots regardless of grazing system and period. ADG did not differ between grazing systems. However, ADG of the first-1999 grazing period varied from the last two. The last 2 periods did not differ. During 2000, ADG was not affected by irrigation, grazing system, or grazing period. Beef production per ha was different between rates of irrigation and between grazing periods regardless of the system observed in 1999. The first grazing period of irrigated pastures of 1999 produced the highest gains per ha and per period regardless of grazing system. More beef per ha was produced on the continuously grazed pastures compared to the rotational grazed pastures during the second year of the trial. Beef production per ha was unchanged through the three grazing periods of 2000. Overall in both years, continuous irrigated pastures yielded the best gains per animal, and also per unit of area. The non-irrigated rotational grazing system was the treatment with the lowest performance. No interactions were detected in standing crop in 1999. Irrigated pastures always had higher standing crop than non-irrigated. In regard to the grazing systems, continuous vs. rotational grazed pastures did not differ in standing crop. When the 3 grazing periods of 1999 were compared, the first and the third were different. The second period was similar to the first and third period on standing crop in 1999. In 2000, standing crop during the grazing periods remained constant. When compared within irrigation rate, the continuous system produced the most and proved to be better than the rotational. When compared within the continuous grazing system, irrigated pastures were better than non-irrigated. Comparisons within rotational systems showed no significant difference between rates of irrigation.