Flooding is often a problem in areas of the southern USA with high rainfall and impermeable soils. A field study was conducted on two poorly drained, slowly permeable soils, a Sharkey clay (veryfine, montmorillonitic, nonacid, thermic Vertic Haplaquept) and a Crowley silt loam (fine, montmorillonitic, thermic Typic Albaqualf), to determine the influence of prolonged flooding on the growth and seed yield of eight determinate soybean [Glycine max. (L.) Merr.] cultivars. Soybean was continuously flooded 3 cm above the soil surface at either the V4 or R2 growth stage for 2, 4, 7, or 14 d. Soil water pressures were monitored at four depths in the Sharkey profile. Flood duration effects on the soybean plant were manifested in yellowing and abscission of leaves at the lower nodes, stunting, and reduced dry weight and seed yield. Canopy height and dry weight decreased linearly with duration of the flood at both growth stages. The growth rates were 25 to 35% less when soybean was flooded at R2 than at V4. The additional 4 wk of vegetative growth after flooding allowed the soybean flooded at V4 to recover to a greater extent than the cultivars flooded at R2. A linear relation was found between seed yield and monthly average crop growth rates for the 4 wk following flooding. A linear decrease in seed yield with flood duration was also found. On the Sharkey clay, rates of yield reduction were 157 and 124 kg ha−1 d−1 of the flood for the soybean flooded at R2 and V4, respectively. On the Crowley silt loam, yield reduction rates were 101 and 53 kg ha−1 d−1 of the flood duration for the soybean flooded at R2 and V4, respectively. Crop susceptibility factors (CS) were determined by dividing the decline in yield by the unstressed control, where the 2‐d flooded soybean cultivars were considered the controls. Values of CS ranged from 0.0 to 0.6 and were linearly related to flood duration after 2 d. The slopes of the lines were 1.5 times greater for the flood applied at R2 than at V4, and 2.4 times greater with soybean grown on the Sharkey clay than on the Crowley silt loam. The determinate soybean cultivars were more susceptible to prolonged flooding during early reproductive growth than early vegetative growth and when grown on the clayey soil than on the silt loam.

Spatial variability of soil properties is important in determining pesticide behavior in soils. A study was conducted on a 4‐ha field to measure the spatial variability in sorption coefficients (K) for the herbicide metolachlor [2‐chloro‐N‐(2‐ethyl‐6‐methylphenyl)‐N‐(2‐methoxy‐1‐methylethyl)acetamide] and to correlate these K values to other soil properties. The soils in this field were Captina and Johnsburg (Typic Fragiudults). The rectangular field was sampled on a grid with 135 nodes. At each node, samples of the Ap, Bt, and Btx horizons were taken for determinations of water content at 10 and 1500 kPa, pH, particle size analysis, sorption coefficients (K), and organic matter content. Means, standard deviations, minimum values, maximum values, and coefficients of variation (CV) were determined on all properties. In addition, multiple linear regression analyses were performed to determine the maximum correlation between K and the soil properties. Soil organic matter content was the soil property most highly correlated with the adsorption of metolachlor in the surface soils (Ap). Adsorption was also significantly correlated with clay content, water content at 1500 kPa, and pH. Semivariograms were constructed for each horizon for the organic matter content and K. Semivariograms for organic matter indicated a range of spatial dependency of 110 m in the Ap and no spatial structure for the Bt and Btx horizons. The range for K was 110 m in the Ap and 42 m in the Bt with no spatial structure evident in the Btx horizon. The data for K and organic matter were normalized by dividing each semivariance by the mean squared for each parameter, which resulted in similar semivariograms in the Ap horizon. Contour plots of kriged values for normalized organic matter and normalized K in the Ap horizon were also similar.

No abstract

Extensive tillage during long periods of time affects soil productivity by altering soil properties. Quantitative measurements were made to determine the combined effects of duration of tillage and production of soybean [Glycine max. (L.)] and rice (Oryza sativa) on selected physical and chemical properties of a Crowley silt loam (fine, montmorillonitic, thermic Typic Albaqualf). Four adjacent fields were sampled which included a virgin prairie and three fields in cultivation for 1, 12, and 30 yr. Undisturbed soil cores were taken at 0.05‐m depth intervals to 0.15 m and analyzed for soil water retention at 10, 30, 50, 80, 100, 500, and 1500 kPa, bulk density and saturated hydraulic conductivity. Organic matter content, pH, and particle size were determined on disturbed samples. Compared with the cultivated soils, the prairie had higher organic matter contents. The 12‐yr and 30‐yr fields in cultivation had higher pH values and bulk densities but lower water retained at a given pressure than the prairie and 1‐yr field in cultivation. No differences were found with respect to particle‐size distribution. For a given soil property, values of CV were affected by time in production but not by depth. The CV was low in the prairie, increased in the 1‐ and 12‐yr fields and in the 30‐yr field was similar to values found in the prairie. The greatest changes in organic matter and bulk density occurred in the initial 12 yr of cultivation. The temporal variability of organic matter contents in the surface 0 to 0.05‐m interval was mathematically modeled with both constant and variable rate equations.

Knowledge of crop response to temporary waterlogging is important in the development of effective water management practices. A field study was conducted to determine the response of soybean rGlvcine max. (L.) Merr] grown on a poorly drained, clayey soil to temporary flooding at three growth stages. The four treatments were soybean flooded for seven consecutive days at either VI, V4 or R2 growth stages at a flood height of 0.03 m above the soil surface and a well-watered control. Flooding for seven consecutive days wetted but did not saturate the lower parts of the soil profile. This was attributed to the swelling by the montmorillonitic clay and subsequent sealing of the soil near the surface. In general, Eh and ODR decreased gradually during the flood, but 1045 increased as the soil dried upon removal of the flood. Canopy heights and dry weights of the flooded soybeans were dependent on plant growth stage at flooding and time of measurement but were lower than the control. When flooded at the VI or V4 growth stages, concentrations of N and K in the above-ground plants were lower than the control after the flood. Three weeks after the flood was removed higher concentrations of these elements were found. When flooded at R2, concentrations of N and K were lower than in the control. Few differences were found in the plant concentrations of Ca, Mg, Mn, Fe, Al, and Na in the plant due to the flood, but by the end of the growing season, concentrations of Mn, Fe and Al were higher in the R2 flooded soybeans than in the other treatments. Seed yield response of the soybeans depended upon plant growth stage at flooding. The soybeans were particularly sensitive to the seven days of continuous flood at the R2 growth stage. Values of relative seed yield were 88, 83, and 44 % of the well watered-control for the VI, V4 and R2 growth stages, respectively.Differences in seed yield were found with cultivar and with cultivar*flood treatment.