Search

Interest in integrated crop-livestock agroecosystems (ICL) has increased due to their versatility in management options, potential to offset increasing levels of atmospheric C and enhanced agronomic and ecosystem sustainability. Identifying agroecosystems that have the greatest potential for C sequestration requires an understanding of soil organic C distribution within aggregate fractions. Six soil aggregate C pools were physically isolated to evaluate the C sequestration potential of three ICLs and two continuous cotton (CTN) agroecosystems in the Texas High Plains. The proportions of the water stable aggregate fractions were used to calculate mean weight diameter, an indicator of soil stability. The first ICL (FRG_CTN) included paddocks of dryland perennial native grasses, a foxtail millet-cotton (Setaria italica [L.] P. Beauv. and FiberMax 9058F, respectively) rotation, and WW B-Dahl – Old World Bluestem [bluestem; Bothriochloa bladhii (Retz) S.T. Blake] under deficit irrigation (replacement of approximately 30% evapotranspiration). The second ICL (OWB_BER) included paddocks of deficit irrigated bermudagrass [bermuda; Cynodon dactylon (L.) Pers.] and bluestem and the third ICL (FRG_RC) included paddocks of irrigated bluestem and row crop production. Soil samples (0–5 and 5–20 cm) were collected in July 2010. In general, ICLs increased water stable macroaggregates providing a physical protective shell for SOC and increasing C sequestration potential. A strong correlation between SOC and mean weight diameter identified a critical SOC level of 5.5 Mg ha−1 for the greatest increases in mean weight diameter. Of the five agroecosystems evaluated, FRG_RC and OWB_BER ranked the highest in terms of mean weight diameter (130% larger), whole SOC (up to 45% more), and intra-aggregate microaggregate SOC (157% greater) relative to CTN production. Increased stability and reduced exposure of intra-aggregate fractions resulted in relatively greater intra-aggregate microaggregate SOC under perennial vegetation. The potential to serve as significant SOC accumulators may aid in offsetting increasing atmospheric C levels, and while specific to these semiarid soils, the identified critical SOC level can act as a target for producers to minimize and ultimately reverse soil degradation.

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.

Factors that affect wind erosion such as surface vegetative and other cover, soil properties and surface roughness usually change spatially and temporally at the field-scale to produce important field-scale variations in wind erosion. Accurate estimation of wind erosion when scaling up from fields to regions, while maintaining meaningful field-scale process details, remains a challenge. The objectives of this study were to evaluate the feasibility of using a field-scale wind erosion model with a geographic information system (GIS) to scale up to regional levels and to quantify the differences in wind erosion estimates produced by different scales of soil mapping used as a data layer in the model. A GIS was used in combination with the revised wind erosion equation (RWEQ), a field-scale wind erosion model, to estimate wind erosion for two 50 km 2 areas. Landsat Thematic Mapper satellite imagery from 1993 with 30 m resolution was used as a base map. The GIS database layers included land use, soils, and other features such as roads. The major land use was agricultural fields. Data on 1993 crop management for selected fields of each crop type were collected from local government agency offices and used to ‘train’ the computer to classify land areas by crop and type of irrigation (agroecosystem) using commercially available software. The land area of the agricultural land uses was overestimated by 6.5% in one region (Lubbock County, TX, USA) and underestimated by about 21% in an adjacent region (Terry County, TX, USA). The total estimated wind erosion potential for Terry County was about four times that estimated for adjacent Lubbock County. The difference in potential erosion among the counties was attributed to regional differences in surface soil texture. In a comparison of different soil map scales in Terry County, the generalised soil map had over 20% more of the land area and over 15% greater erosion potential in loamy sand soils than did the detailed soil map. As a result, the wind erosion potential determined using the generalised soil map was about 26% greater than the erosion potential estimated by using the detailed soil map in Terry County. This study demonstrates the feasibility of scaling up from fields to regions to estimate wind erosion potential by coupling a field-scale wind erosion model with GIS and identifies possible sources of error with this approach. Published by Elsevier Science B.V.