Conventional irrigation experiments and rainfall distribution‐yield studies have indicated that insufficient water during flowering and pod‐fill stages frequently limits yields of soybeans (Glycine max (L.) Merr.). In this 3‐year experiment, field plot covers were used to control rainfall and water stress was imposed on plants at various stages of growth to determine more specifically the critical periods for irrigating soybeans for maximum yields. Soil water regimes ranged from a limited supply (10% available soil water) to adequate water (50% available) during the entire growing season. More bean production was obtained from water applied after full bloom than earlier. The pod‐fill stage, from August 15 to September 20 for ‘Bragg’ soybeans at Thorsby, Alabama, was the critical time for adequate water for maximum yields. Yields from adequately watered soybeans were 540 to 1,040 kg/ha, or 24 to 55%, greater than where water was limited throughout the growing season. Highest yield obtained under the best water regime was 3,320 kg/ha. Conditions limiting yields were not obvious.

Synopsis Potassium applications increased yield of seed cotton, size of bolls, and fiber micronaire values, but decreased lint percentage. K content of plants increased in proportion to rate of K applied. Old leaves plus perioles gave the best indication of the K status of the plant. Fiber quality was best at lower rates of K.

Synopsis Effective rooting depth decreased as soil moisture level increased. A high percentage of the roots was found in the surface 12 inches of soil for all species regardless of soil moisture level. Soil moisture extraction was used with reasonable accuracy to estimate effective rooting depth.

Soybean (Glycine max (L.) Merrill) yields in the past have varied considerably from year to year in the southeastern United States. Many factors are important in soybean production, but water stress at critical growth periods appears to be one of the most frequently limiting factors. Soybeans were grown on a Lucedale fine sandy loam soil to determine the effects of three soil water regimes at two row widths and three plant population levels on water use, rate of plant growth, and bean yield of two varieties. Water use rates by soybeans were influenced more by soil water regime than by row width or variety. Average rates during the season ranged from 0.05 to 0.84 cm/day, depending on the amount of available water in the soil. Variety had the greatest influence on plant height. Final plant heights ranged from 10 to 15 cm greater for ‘Bragg’ than for ‘Hampton 266.’ Heights were increased by irrigation and plant population level, but were not affected by row width. Average bean yields were influenced more by irrigation or variety than by row width or plant population. Average bean yields by soil water regimes were 2,020, 2,420, and 2,490 kg/ha for no irrigation, intermediate, and high irrigation, respectively. Bragg averaged 2,420 kg/ha and Hampton 266 averaged 2,150 kg/ha. Row width and plant population showed little influence on average bean yields.

Land spreading of dairy manure is effective both in disposing of waste and in utilizing plant nutrients in the manure. This study was conducted to determine the residual effect of manure after three annual applications at rates of 0, 22.5, 45, 90, 180, and 270 metric tons/ha were each incorporated into two soils. Plots were double‐cropped each of those 3 years with pearl millet [Pennisetum americanum (L.) K. Schum ‘Gahi I’] and rye (Secale cereale L. ‘Wren's Abruzzi’). During the residual phase of the experiment, plots were double‐cropped with rye and corn (Zea mays L. ‘Funks 5757’) for a period of 4 years. Residue from high application rates of dairy cattle manure increased yields of corn on both Dothan loamy sand (Plinthic Paleudults) and Lucedale sandy loam (Rhodic Paleudults) for 4 years after the manure was applied. On the Dothan soil high rates of manure adversely affected rye growth. Most years, the residue increased N uptake in both crops on both soils. The high rates of manure increased pH to a depth of over 100 cm on the Dothan soil. Potassium accumulated in the subsoil to the 100‐cm depth. Phosphorus was increased to the 60 to 75‐cm soil depth. Magnesium also moved into the subsoil, but there was little movement of Ca below the surface 30 cm. The effect on pH, K, P, and Mg movement was much smaller on the Lucedale soil than on the coarser‐textured Dothan soil. The high rates of manure increased soil pH and soil contents of K, Mg, and P and increased the cation exchange capacity of soils. These factors contribute toward higher crop yields on manure‐treated plots. Response to dairy manure may be measured for 4 years or more after high rates of manure applications have been stopped.