Clomazone is an effective herbicide widely used for preemergence grass control in rice. However, use of clomazone on sandy textured soils of the western Texas rice belt may cause serious rice injury. When labeled for rice in 2001, sandy textured soils were excluded. Laboratory experiments were conducted to determine the effect of soil characteristics and water potential on plant-available clomazone and rice injury. A centrifugal double-tube technique was used to determine plant-available concentration in soil solution (ACSS), total amount available in soil solution (TASS), and Kd values for clomazone on four soils at four water potentials. A rice bioassay was conducted parallel to the plant-available study to correlate biological availability to ACSS, TASS, and Kd. TASS was significantly different in all soils at the 1% level of significance. The order of increasing TASS for the soils studied was Morey Edna Nada Crowley which correlated well with soil characteristics. Two field experiments at three locations were conducted in 2002 and 2003 to determine the optimum rate range that maximizes weed control and minimizes crop injury across a wide variety of soil textures and planting dates. At Beaumont, Eagle Lake, and Ganado, TX, preemergence application of 0.41 to 0.56, 0.38 to 0.43, and 0.36 to 0.42 kg ha-1 clomazone, respectively, provided optimum weed control with minimal rice injury. Data suggests that clomazone is safe to use on rice on sandy textured soils. Injury may occur, but, rates suggested from this research will minimize injury and achieve excellent weed control. As a result, amendments to the herbicide label will allow clomazone use on sandy textured soils giving rice producers more flexibility and access to another effective herbicide.

Clomazone is an effective herbicide widely used for preemergence grass control in rice. However, use of clomazone on sandy textured soils of the western Texas rice belt may cause serious rice injury. When labeled for rice in 2001, sandy textured soils were excluded. Laboratory experiments were conducted to determine the effect of soil characteristics and water potential on plant-available clomazone and rice injury. A centrifugal double-tube technique was used to determine plant-available concentration in soil solution (ACSS), total amount available in soil solution (TASS), and Kd values for clomazone on four soils at four water potentials. A rice bioassay was conducted parallel to the plant-available study to correlate biological availability to ACSS, TASS, and Kd. TASS was significantly different in all soils at the 1% level of significance. The order of increasing TASS for the soils studied was Morey Edna Nada Crowley which correlated well with soil characteristics. Two field experiments at three locations were conducted in 2002 and 2003 to determine the optimum rate range that maximizes weed control and minimizes crop injury across a wide variety of soil textures and planting dates. At Beaumont, Eagle Lake, and Ganado, TX, preemergence application of 0.41 to 0.56, 0.38 to 0.43, and 0.36 to 0.42 kg ha-1 clomazone, respectively, provided optimum weed control with minimal rice injury. Data suggests that clomazone is safe to use on rice on sandy textured soils. Injury may occur, but, rates suggested from this research will minimize injury and achieve excellent weed control. As a result, amendments to the herbicide label will allow clomazone use on sandy textured soils giving rice producers more flexibility and access to another effective herbicide.

Typescript (photocopy) / xxv, 179 leaves : ill. (part col), maps ; 30 cm / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Soil Science, 1982

Thesis (Ph.D.) -- University of Adelaide, Dept. of Soil Science, 1982. / Typescript (photocopy).

Thesis (M.Ag.Sc.)--University of Adelaide, 1939. / Typewritten. Includes bibliographical references.

Evaporation synergy is the phenomenon in which two porous medium textures that share a common vertical boundary experience a higher cumulative evaporation than either homogeneous texture can produce. Studies that have been conducted to date address this phenomenon in relatively fine and coarse sands but not in finer textured soils where viscous forces play a major role. The purpose of this study was to determine which of the 66 combinations of soil textures would exhibit evaporation synergy and develop a conceptual model of the conditions necessary for synergy. The numerical modeler HYDRUS was used to investigate all soil texture combinations and generate evaporation rates and cumulative evaporation amounts for each system. In addition, two combinations of soils were selected as laboratory experiments based on the HYDRUS predictions: one that exhibited synergy (Loamy Sand & Silt Loam) and one that did not (Loamy Sand & Sandy Clay). The laboratory data supported the HYDRUS predictions for evaporation synergy and non-synergy. The conditions necessary for evaporation synergy were developed from the numerical and physical models��� predictions and results. The two textures must experience different air-entry values to create lateral and vertical pressure gradients, the fine must possess a high enough hydraulic conductivity to allow water to move to its surface before it reaches its own air-entry value and possess the capillarity to maintain liquid film flow to its surface, and the viscous forces within the coarse must be low enough for water to be pulled from itself to the fine. It was also determined that the evaporation rate of a bi-texture decreases as a series of constant-rate steps until the fine enters S2 evaporation and is associated with a stepwise recession of the drying front in the coarse media. The duration of each step appears to be associated with the lateral distance from which water can be extracted within the coarse media. / Graduation date: 2013

No description available.

Field scale variability of soil texture can influence crop yield and movement of soil water in the field. The objective of this study was to investigate the spatial structure of soil texture in relation to the variability of nitrate-N leaching using geostatistics. Soil textural fractions showed strong spatial autocorrelations from surface to 60 cm depth. Random variability of soil texture increased with depth. Soil water content, as well as total carbon, total nitrogen and soil organic carbon of top 15 cm, also showed spatial autocorrelations similar to soil texture. Elevation, relative slope position and vertical distance to channel network showed significant influence on the distribution of soil texture. Soil texture at 90 cm depth correlated best with cumulative percolated water and cumulative nitrate leached in field lysimeters. Our results showed that soil layers with low hydraulic conductivity control the water and nitrate movement through the soil profile.

Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 145-156).

Thesis (M.S.)--Mississippi State University. Department of Electrical and Computer Engineering. / Title from title screen. Includes bibliographical references.