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Grain yields and water‐use efficiencies were compared for conservation bench terraces, bench terraces, and common systems of dryland production of winter wheat (Triticum aestivumL.) and grain sorghum (Sorghum bicolor[L.] Moench). Grain production and water‐use efficiency were highest on a bench terrace cropped in continuous grain sorghum. Conservation bench terraces and continuous grain sorghum grown on sloping land also had higher water‐use efficiences and grain production than the common dryland systems of wheat‐sorghum‐fallow on graded terraces and continuous wheat or wheat‐fallow on sloping land. The management factors greatly influencing water‐use efficiencies were crop selection and land leveling to conserve potential runoff.

Eliminating or reducing storm runoff in the Southern Great Plains can increase soil‐water storage, decrease erosion, and increase crop yields. The primary objectives of this study were (i) to examine the potential of furrow dikes as a conservation practice to retain runoff and increase crop yields, and (ii) to examine the effects of furrow diking on sorghum [Sorghum bicolor(L.) Moench] and sunflower (Helianthus annuusL.) production. Analyses of 28 yr of runoff records show furrow diking has the potential to retain 25 to 30 mm of runoff annually. The maximum annual runoff retention by diking observed during the 14 crop years of research (three separate experiments conducted between 1980 and 1985) was 111 mm. The maximum increase in sorghum yield measured as a result of diking was 2.46 Mg/ha. Conditions responsible for maximum yield responses of sorghum to diking were: (i) annual cropping, (ii) large rainfall/runoff events occurring prior to or early in the growing season, and (iii) limited growing season precipitation. Diking increased annual cropped sorghum yields on graded and contour furrow treatments by 49 and 14%, respectively, whereas water use efficiencies were increased by 25 and 16%. Yields and water use efficiencies from diked treatments on graded and contour furrows were as great as yields and water use efficiencies from a leveled minibench treatment, indicating that from a crop production standpoint, furrow diking was as effective as land leveling in retaining runoff and increasing crop yields. Sunflower yields were increased significantly by diking during 1 yr out of 3 when sunflower was grown after 76 weeks of fallow, whereas sorghum yields were not affected by diking after fallow. Decreasing row spacing from 1.0 to 0.75 m resulted in a significant increase in the 3‐yr avg yield of sorghum and sunflower of 1.0 and 0.14 Mg/ha, respectively, when grown after fallow, indicating that considerable opportunity for improving summer crop production may exist simply by changing to a narrow row spacing. A regression equation relating runoff from graded furrows to runoff from contour flat‐tilled graded terraces showed increased runoff from graded furrows, particularly from small storms.

The results of previous studies with a straw mulch in place during fallow and the growing season of grain sorghum (Sorghum bicolorL. ‘Moench’) suggested that having the mulch in place during the growing season increased the use efficiency of growing season rainfall. The objective of this study was to evaluate the contribution of a growing season straw mulch to growth, yield, grain quality, water use, and water‐use efficiency of grain sorghum. Before sorghum was planted in 1977, 1978, and 1979, areas of Pullman clay loam (fine, mixed, thermic Torrertic Paleustolls) were irrigated twice, irrigated once, or not irrigated to simulate high, medium, and low levels of water storage in soil during fallow. After sorghum emergence, wheat (Triticum aestivumL.) straw was placed on the surface at rates of 0 (check), 2, 4, or 8 metric tons/ha. Differences in sorghum response to the high and medium water levels were slight because the second irrigation resulted in relatively little additional water storage in the slowly permeable soil even though the soil was not filled to capacity. Sorghum with the high and medium water levels grew taller, yielded more, and used water more efficiently than sorghum with the low water level at planting. In general, sorghum responded more to soil water content at planting than to mulch rate during the growing season. When significant responses to mulch rate were obtained, they resulted mainly from mulch on the low water level plots. For the 3 years, the growing season mulch at 8 metric tons/ha increased water‐use efficiency 19% over the no‐mulch treatment, which was less than expected, based on earlier experiments and observations. Apparently, shading from the plant canopy largely substituted for the beneficial effect of a mulch during the growing season. When a mulch is present during both the fallow and the growing seasons, a major effect with respect to water conservation and crops production, therefore, is to enhance water storage in soil during fallow.

For oilseed sunflower (Helianthus annuusL.) to develop as a competitive crop on the drylands of the Southern High Plains, information is needed concerning the effects of various agronomic practices on sunflower production in this area. The objectives of the research were to determine the effects of seeding date, plant population, and soil water content at time of seeding on dryland sunflower seed yield, water‐use efficiency (WUE), and oil concentration and quality. The study was conducted from 1975 through 1979 on Pullman clay loam (fine, mixed, thermic Torrertic Paleustoll). Seeding date had the greatest effect on seed yield and WUE and reflected the effects of seasonal precipitation patterns. Yield response to increased soil water content at seeding was 0.70 kg seed/m3water. Plant populations in the range of 2.5 to 4.5 plants/m2resulted in similar seed yields and WUE , but high populations (>3.5 plants/m2) tended to increase oil concentration. Seeding date significantly influenced oil concentration and quality with April seedings having a 50 to 80 g/kg greater oil concentration than July seedings. Oleic acid concentration in sunflower oil decreased, and conversely, linoleic acid concentration increased as seeding dates became later. Thus, by manipulating seeding dates, oil of a quality suited to a particular need (margarine, cooking or salad oil) may be produced. Yield potential was enhanced when soil water content at seeding was increased, indicating that sunflower is adapted for use on water conservation systems or after fallow where additional soil water may be available.