Soil compaction is a major factor which influences root growth and crop yields. Studies were conducted to determine the influence of different factors on mechanical impedance and to determine the influence of mechanical impedance and other soil factors on root growth. Regression models for dependent variables, soil strength and root growth, vs. the independent variables, soil type, soil depth, clay content, bulk density, voids, and water content were computed using the maximum R2 improvement by stepwise regression. The models for soil strength and root growth varied with soil type, soil depth, and/or clay content. The soils used were a Miles fine sandy loam, Udic Paleustalf and an Abilene clay loam, Pachic Argiustoll. Soil strength for both soils studied and at all depths was influenced by bulk density, voids, and clay content. The overall equational models accounted for 75% of the variability in soil strength and 76% of the variability in root growth. Root growth in both soils and at all depths was significantly influenced by soil strength, volumetric water content, voids, and clay content. The critical strength in bars, defined as the probe pressure at which root elongation stopped, was a function of % clay. The critical strength ranged from 60 to 70 bars in coarsetextured to 25 bars in clay soils. These data provide a better understanding of the influence of mechanical impedance on root growth, and a basis for determining the need for use of deep tillage to minimize the adverse effects of excessive soil strength or compaction.

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In field experiments, P‐induced Zn deficiencies were observed in field corn in 1958 and in sweet corn, tomatoes and field corn in 1959. In greenhouse experiments with Red Kidney beans (Phaseolus vulgaris), severe P‐induced Zn deficiencies occurred with P fertilization. Zinc absorption was increased by Zn fertilization and decreased by P fertilization. Phosphorus uptake was increased with P fertilization and decreased by Zn fertilization. When both Zn and P were applied, the uptake of both Zn and P were reduced.

Soils of the Texas Rolling Plains have poor structure, low soil organic matter contents, and low water holding capacity. Alternative farming practices must be explored to conserve and improve this natural resource. An 11‐yr (1979‐1989) field experiment was conducted at the Texas A&M University Research Station at Munday to determine the effects of tillage (reduced vs. conventional) and residue management (with vs. without residue) on grain yields of continuous grain sorghum [Sorghum bicolor (L.) Moench] and continuous wheat (Triticum aestivum L.) under dryland and irrigated conditions. A grain sorghum—wheat rotation (double‐crop) under reduced tillage was included in the irrigated study. Yields of reduced‐tillage grain sorghum in dryland and irrigated studies were as high or higher than yields of conventional‐tillage grain sorghum. Removal of surface residues in irrigated grain sorghum caused a significant decrease in yields. In contrast, reduced‐tillage systems and surface residues caused reductions in yields for dryland and irrigated wheat, which may be the result of decreased plant populations caused by poor seed‐to‐soil contact when planting through surface residues and N deficiency caused by immobilization. The average yield of irrigated wheat or grain sorghum using reduced‐tillage double‐cropping (2 and 3 Mg ha−1, respectively) was lower relative to wheat (3.5 Mg ha−1) and grain sorghum (4.6 Mg ha−1) grown continuously under conventional tillage.

Economic returns from crops require establishment of a good plant stand. Soil crusting reduces seedling emergence and stands of many crops throughout the world. One of the most important crops adversely affected by crusting is cotton (Gossypium hirsutum L.). The force exerted by germinating plants such as cotton often determines the seedling's ability to rupture and emerge from under the soil crust. However, the force exerted by an emerging cotton seedling has not been determined. Studies were conducted in the laboratory to determine and better understand the emergence force of cotton seedlings. The force exerted by cotton seedlings under different soil moisture conditions and temperatures was determined using a force transducer. The transducer mv output, which is a linear function of the force exerted against the transducer button, was continuously monitored with a mv recorder. Emergence force was a linear function of volumetric soil moisture, number of seedlings, and cross‐sectional area of the emerging hypocotyls. The size of the hypocotyl was a function of soil moisture and temperature. Maximum diameters of the cotton hypocotyl at 22, 27, 32, and 40 C were 0.32, 0.41, 0.34, and 0.26 cm, respectively, and the maximum forces exerted were about 350, 600, 400, and 200 g, respectively. The time required for maximum exertion by the seedling was dependent upon temperature, ranging from 40 to 48 hours at 32 C and 50 to 60 hours at 27 C. These findings suggest that planting methods, planting dates, and cultivar improvement may offer possible ways to minimize or circumvent crusting effects and increase emergence.