Application of chlorimuron and imazaquin at 0.28 kg ai/ha to field-grown sicklepod at early bloom and early fruit stages in 1984 and 1985 almost eliminated seed production. In addition, none of the seed produced following these treatments were capable of emergence during a 4-week period following acid scarification. Glyphosate applied at 0.28 kg ai/ha at early bloom decreased seed production 84% but did not affect seedling emergence in 1984, and precluded production of seed capable of emergence in 1985. Glyphosate applications at the early fruit stage reduced the number of seed that emerged 93 and 90% in 1984 and 1985, respectively. Application of 2,4-DB at 0.28 kg ai/ha and 2,4-D at 0.56 kg ai/ha at early bloom did not affect seed production or emergence in 1984 but almost eliminated production of seed capable of emergence in 1985. Applications of 2,4-DB and 2,4-D at the early fruit stage decreased the number of seed that emerged 99 and 52% in 1984 and 46 and 57% in 1985, respectively. Herbicide applications at the late fruit stage were generally less effective than earlier applications in reducing seed production and emergence.

Current environmental concerns justify renewed evaluation of crop management strategies that offer promise for maintaining or increasing productivity while reducing environmental impacts. Field studies were conducted using weed‐free conditions to determine the effects of corn (Zea mays L.) leaf orientation on light interception, vegetative and reproductive development, and grain yields. ‘DeKalb 689’ was handseeded in north‐south rows to achieve populations of 22 000 and 33 000 plants/acre. Controlled seed positioning in the soil was used to attain across‐row and with‐row leaf orientations, while conventional planting provided random leaf orientation. Light interception, intraspecific competition among corn plants, and grain yield were affected by leaf orientation and plant population. At selected row positions 8 wk after planting, light interception for across‐row leaf orientation exceeded random and with‐row orientations by up to 10 and 25%, respectively, while light interception for the high plant population exceeded the low population by up to 15%. Across‐row and random leaf orientations produced 8% greater leaf area than with‐row orientation. Greater intraspecific competition was indicated for the high plant population due to lower leaf area, leaf biomass, and stalk biomass per plant than the low population. Grain yields were greater at the high than the low plant population for all leaf orientations. At the high plant population, across‐row leaf orientation yielded 10 and 21% more than random and with‐row orientations, respectively. Therefore, across‐row leaf orientation at the high plant population should provide more rapid canopy closure, enhance crop competition with weeds, and reduce dependence on herbicides while enhancing grain yields. Research Question Manipulation of the corn canopy to enhance light interception through greater light penetration and more uniform distribution offers the potential for reducing intraspecific competition and increasing grain yield. Regulating corn leaf orientation by controlling seed placement in the soil may provide a means to achieve these results. The objectives of this research were to determine the effects of corn leaf orientation on light interception, intraspecific competition, and grain yield. Literature Summary At high productivity levels, the primary ecological factor limiting corn yield is light. By improving light‐use efficiency of the crop canopy, it should be possible to increase grain yields. Corn yields have been increased by physical manipulation of the leaf angle, by selecting plants with increased leaf angle, and by using aluminum reflectors to increase light flux. These methods permit greater light penetration and provide more uniform distribution of light over greater leaf area. Orientation of corn leaves can be influenced by seed placement in the soil and may offer an effective means for increasing light interception, reducing intraspecific competition, and enhancing the rapidity of canopy closure. Row orientation and plant population have been show...

Yield and yield components of ‘Braxton’ soybeans [Glycine max(L.) Merr.], Maturity Group VII, were measured for differing irrigation regimes and intrarow spacings. Soybeans were planted in 0.91 m rows in mid‐May, 1980 and 1981 on a Cecil sandy loam soil (clayey, kaolinitic, thermic Typic Hapludults). Prior to the V3 growth stage, plots were thinned to achieve intrarow spacings of 61,76,102, 152,305, and 457 mm in 1980 with spacings of 43 and 51 mm added in the 2nd year. Soil water regimes were full‐season irrigation (FSI), irrigation beginning at bloom (BI), and no irrigation (NI). Beginning at R4, plants from a 0.5‐m section of row were removed at 10‐ to 14‐day intervals for determination of seed growth rate and effective filling period. Yield components (pod number, seed number, seeds per pod, and single seed weight) were determined at R7 or maturity. Final seed yields were determined by harvesting bordered rows following end trimming. Seed yields for the 2 years, averaged over all spacings, were 3023,2876, and 1322 kg/ha for the FSI, BI, and NI higation treatments, respectively. While yields were increased significantly with irrigation, no significant difference in yield was measured between FSI and BI treatments. Yields among plant spacings were not significantly different for any irrigation treatment either year with the exception that the yield of the 457‐mm spacing of the BI treatment was significantly reduced in 1981. Seed number was highly correlated with seed yield, whereas single seed weight was not significantly correlated with yield. Increases in seed number under the irrigation treatments were due to increases in both pod number and seed per pod. Seed growth rate was increased and effective filling period was decreased by irrigation. We concluded that intrarow spacings up to 457 mm had little influence on yield. Even though rainfall was low during vegetative growth prior to bloom in both years, full‐season irrigation gave no yield advantage over bloom irrigation.

Relay intercropping of wheat (Triticum aestivum L.) and soybean [Glycine max (L.) Merr.] allows for earlier soybean planting than in conventional doublecropping systems, but shading and other influences of the wheat crop may be detrimental to intercropped soybean development. The purpose of this study was to determine the effect of relay intercropping on soybean growth and yield. Intercropped soybean, planted 19 (1989) or 14 (1990) days before wheat harvest, was compared with a control treatment (same no‐till planting pattern and date, but no wheat) on a Cecil sandy loam (clayey, kaolinic, thermic Typic Hapludults) soil. Intercropping had a greater influence on soybean growth in 1989, when there was more shading by the wheat canopy and also when the period between soybean planting and wheat harvest was longer, than in 1990. In both years, the greatest effects of intercropping on growth occurred early in the season, when intercropped plants were taller but had smaller stem diameters, less leaf area, and less aboveground dry weight, as compared with control plants. Photosynthetic rates of upper canopy leaves were reduced by intercropping for 2 wk after wheat harvest in 1990. This was associated with an increase in specific leaf area in intercropped plants. Lateseason growth, including that of reproductive parts, was similar for intercropped and control treatments, and there were no detectable effects of intercropping on final yield components or yield in either year. In environments where the period of overlap between the wheat and soybean crops is relatively short, negative effects of relay intercropping on early soybean growth may not result in yield reductions.

Aluminum toxicity is a deterrant to the growth of plants in acid soil. Little is known of the initial site or sites of AI injury in plant roots nor of the sequence of events that characterize AI toxicity. The objective of this study was to document some effects of short-term exposure to AI in two wheat (Triticum aestivum L.) cultivars, Eagle and Atlas 66. Root elongation in Eagle was much more susceptible to concentrations of 0.02 to 1.85 mM AI than was root elongation in Atlas 66. A 2-h exposure to 0.19 mM AI drastically inhibited root elongation in Eagle, whereas a 48-h treatment with 0.19 mM AI had little effect on root elongation in Atlas 66. Exposures of Eagle seedlings to 0.19 mM AI for 4 h caused a 32% inhibition in subsequent incorporation of 3 H-thymidine into DNA, with the degree of inhibition increasing with duration of exposure to AI. In Atlas 66, there was a 10% reduction in incorporation of radioactivity into the DNA fraction for all the AI pretreatments, ranging from 2 to 48 h. Exposure of Eagle roots to AI for 2 h showed this same 10% reduction in incorporation of radioactivity into DNA. For both cultivars, there usually was a 10 to 20% decrease in 3 H-thymidine uptake by whole roots after 0.19 mM AI pretreatment periods of 2 to 12 h as compared with control plants not receiving AI. The extent of inhibition was fairly constant and was not correlated with duration of AI pretreatment for either cultivar. There was a similar depression of 3 Mthymidine uptake in root tips of Eagle after 4 to 12 h of AI pretreatment. The reduction of 3 H-thymidine uptake in both cultivars resembled the depression of 3 H-thymidine incorporation into DNA in Atlas 66 but not in Eagle. This work suggests that AI has two effects on susceptible cultivars: a rapid inhibition of root elongation followed by an inhibition of DNA synthesis. Another effect of AI on both the tolerant and the susceptible cultivar, that of depression of 3 H-thymidine uptake, also was seen.