In search of sustainable agricultural systems for the Llano Estacado of the U.S. Southern High Plains
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Crop production on the Llano Estacado of the Texas High Plains has used precipitation and supplemental irrigation with water pumped from the Ogallala aquifer at rates that have far exceeded recharge for many years. Over 20% of the U.S. cotton (Gossypium hirsutum L.) crop is produced currently in this once vast grassland. Most of this cotton is produced in monoculture systems that are economically risky and contribute to wind-induced erosion and depletion of ground water resources. Although large numbers of cattle are found in this region, little integration of livestock and crop production exists. Integrated crop-livestock systems could improve nutrient cycling, reduce soil erosion, improve water management, interrupt pest cycles, and spread economic risk through diversification. Two whole-farm scale systems compared (1) a cotton monoculture typical of the region; and (2) an alternative integrated system that included cotton, forage, and Angus-cross stocker beef steers (initial body weight 249 kg). Steers grazed the perennial warm-season grass 'WW-B. Dahl' old world bluestem [Bothriochloa bladhii (Retz) S.T. Blake] in sequence with rye (Secale cereale L.) and wheat (Triticum aestivum L.) from January to mid-July when they were sent to the feedyard for finishing. Grass seed were harvested from bluestem in October. Cotton in the alternative system was grown in a two-paddock rotation with the wheat and rye. Cotton was harvested from both systems in October. At the end of 5 years, the alternative system reduced needs for supplemental irrigation by 23% and for nitrogen fertilizer by 40% compared with the conventional cotton monoculture. Fewer chemical inputs including pesticides were required by the alternative system. Soil with perennial grass pasture was lower in predicted soil erosion and was higher in soil organic carbon, aggregate stability, and microbial biomass than soil where continuous cotton was grown. Profitability was greater for the alternative system until cotton lint yields reached about 1500 kg ha-1 for the continuous cotton system. Differences between the systems became larger as depth to ground water increased. Systems that are less dependent on supplemental irrigation and less consumptive of non-renewable resources and energy-dependent chemical inputs appear possible, but further improvements are required to ensure sustainability of agricultural systems for the future in the Texas High Plains.
