Browsing by Subject "soil water"
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Item Effects of Woody Vegetation Removal on Soil Water Dynamics in a South Texas Shrubland(2013-07-30) Mattox, April MarieEcosystem changes from grassland to shrubland in the Rio Grande Plains are thought to have negative effects on the hydrology of the region. The increase in woody plants, known as woody encroachment, may alter the amount of water moving beyond the root zone of plants. Water moving beyond the root zone is referred to as deep drainage, and has potential to become aquifer recharge. A vegetation manipulation project was designed to understand the effects of woody vegetation removal on soil water dynamics in the recharge zone of the Carrizo-Wilcox aquifer of south Texas. The primary objective of the project was to determine the potential to increase groundwater recharge through woody vegetation removal. To understand the effects of vegetation removal on various soil textures we studied changes in soil water, rooting depth, and the role of water redistribution by woody vegetation. Woody vegetation was removed using common methods of cut-stump and roller chop across three soil types. Soil water contents and changes were measured using neutron moisture meter to a depth of 180 cm. Average rooting depth was determined across three soil types. Soil and stem water stable isotopes were used to understand soil water movement. Rooting depth was determined to between 140 and 160 cm for all soil textures. Soil water content and changes were analyzed at three depth increments: 0-60, 60-120 and 120-180 cm. ANOVA analysis showed that there was no treatment response in average soil profile water in the sandy or sandy loam soils. There was a significant decrease in soil profile water for clay loam soil in response to roller chopping. Changes in soil profile water were the greatest in the sandy roller chopped soils. Below 120 cm, three months had significant differences in change in soil water in the sandy roller chop plot. During dry conditions, Honey mesquite shifts water use to deeper in the soil profile. In clay loam soils under dry conditions there is evidence of water being moved up from below 2 m soil depth to drier shallow soils. Roller chopping in sandy soils is the vegetation removal treatment and soil type most likely to result in water moving beyond the root zone. Although treatments had significant effects on soil moisture dynamics that interacted with soil type, we did not find support for deep drainage effects over the Carrizo-Wilcox aquifer from woody vegetation removal.Item Responses of Grain Sorghum to Profile and Temporal Dynamics of Soil Water in a Semi-arid Environment(2014-02-24) Bell, Jourdan MDevelopment of efficient irrigation strategies is a priority for producers faced with water shortages. Managed deficit irrigation attempts to optimize water use efficiency (WUE) by synchronizing crop water use with reproductive stages. Soil water use and yield of grain sorghum [Sorghum bicolor (L.) Moench], on a Torrertic Paleustoll in the Texas High Plains, USA, were evaluated during the 2010 to 2012 growing seasons under three sprinkler irrigation strategies: full (FI), deficit (DI), and managed deficit irrigation (MDI). Soil water contents were measured weekly at 0.20-m intervals from 0.10 to 2.30 m depth using a neutron moisture gage. Irrigation for the FI treatment was scheduled when root zone water (0 to 1.6 m) was depleted to 50% of the potential plant available water (PPAW). The DI treatment was irrigated at 50% of FI. The MDI treatment was irrigated at 75% of FI between growing point differentiation and half-bloom, 50% of FI after half-bloom, and less than DI prior to growing point differentiation. Fully irrigated sorghum grain yields averaged 3.7 Mg ha^(-1) greater (p < 0.001) than deficit irrigated sorghum in all years. Seasonal crop water use under MDI averaged 29 mm greater than DI. Concomitant with increased water use principally during the reproductive period, MDI yields averaged 1.6 Mg ha^(-1) greater than DI, which was significant in 2010 and 2012 (p ? 0.006). The WUE of FI sorghum was significantly greater than MDI in 2012 (p = 0.003) and DI in 2010 and 2012 (p ? 0.001). In 2011, crop water uptake was restricted to above 0.6 m when water contents deeper in the profile were less than 42% PPAW. In 2010 and 2012, seasonal crop water uptake in the profile below 1.0 m was small (<14 mm) and did not appreciably increase in response to imposed soil water deficits. The rooting zone for evaluating plant water status and hence irrigation scheduling depended on initial profile water contents and possibly root density deeper in the profile. Results suggest that WUE?s of grain sorghum are not compromised under MDI compared with FI in most cropping seasons.Item Shrink-Swell Dynamics of Vertisol Catenae under Different Land Uses(2012-02-14) Dinka, Takele MitikuBecause of the dynamic nature of shrinking and swelling of soils that are classified as Vertisols, partitioning of rainfall into infiltration and runoff in a Vertic watershed is more temporally and spatially unique than in most other watersheds. Hydrology models that account for realistic representation of crack dynamics are rarely used because the spatial and temporal patterns of cracking across a catena and under different land uses are poorly understood. The objectives of the study were to 1) determine if variability in soil cracking on a Vertisol catena, having the same soil and land cover, could be explained by shrink-swell potential of the soil and changes in soil water content; 2) characterize the temporal and spatial variability of the shrinkage of a Vertisol under different land uses; and 3) determine the relationship between specific volume and water content of soils, particularly between saturation and field capacity. The research was conducted in Vertisol catenae of the Houston Black and Heiden soil series. The catenae were located within the USDA-ARS Grassland, Soil and Water Research Laboratory, Riesel Texas. Soil samples were taken to characterize the general properties of the soils. In situ bi-weekly measurements of vertical soil movements and soil water contents were made over a two-year span. Because shrink-swell potential was high at most landscape positions, soil water content was the primary factor driving the spatial and temporal variability of soil shrinking and swelling. The measured relationship between the amount of soil subsidence and water loss generally agreed with what would be theoretically expected. Maximum soil subsidence was 120 mm in the grazed pasture, 75 mm in the native prairie, and 76 mm in the row cropped field. Shrinkage of the whole soil was not equidimensional, and the study generally indicates more horizontal shrinkage than vertical shrinkage. Laboratory analysis showed an appreciable change in volume of soils between saturation and field capacity, suggests a layer of soil layer can subside up to 4% while drying from saturation to field capacity, which indicates the common laboratory measure of shrink swell potential does not capture the complete shrink-swell behavior of soils.