The Influence of Selected Management Practices on Soybean Soil-Plant Relationships.

Research was conducted in Columbia, Missouri, during the 1976 to 1978 growing seasons to determine the impact of selected management practices on the soil, plant, and water relationships of soybeans {Glycine max (L.) merr.}. Four different management practices for growing 'Williams' soybeans were established in a corn-soybean rotation experiment on a Mexico silt loam soil. A standard cultural practice (conventional tillage, early-May planting date, preemergence and postemergence application of a herbicide) was designated as a control. By changing the planting date, tillage method, or herbicide application, three other treatments were provided: June planting (as soon as possible after June 1), weedy planting (no postemergence herbicide), and no-tillage. No differences in the diurnal trends of xylem pressure potential, leaf conductance, and leaf temperatures were found among treatments. Mean plant water stress over the three years was greatest for the weedy treatment and least for the June planting. Mean xylem pressure potential was -1.30, -1.19, -1.14, and -1.05 MPa for the weedy, May planting, no-tillage, and June plantings, respectively. A similar treatment ranking was found when stress was based on leaf conductance and leaf temperature (0.16, 0.18, 0.21, 0.21 cm sec('-1) leaf conductance and 32.8, 32.5, 32.3, 32.2(DEGREES)C leaf temperature for the weedy, May planting, no-tillage, and June plantings, respectively). Differences in plant growth and seed yields among management practices were attributed to plant water stress. Mean yields for the three-year study were 1590, 1530, 1520, and 970 kg ha('-1) for the June planting, May planting, weedy, and no-tillage treatments, respectively. Despite their greater growth and favorable water relations, the no-tillage soybeans had the lowest yields of all treatments because of weed competition and sparse stands. Because of greater soil moisture reserves during pod-fill, June plantings had lower stress and slightly higher yields than other treatments. Limited early-season water use by the June planting, resulting from a shorter vegetative growth period and less canopy development, and favorable rains late in the season increased yields by providing soil moisture for use during pod-fill.