No abstract

Short‐term, split‐root experiments were conducted in a growth chamber with ‘Lee’ soybeans (Glycine max). The upper portion of the root medium was a limed, fertilized sandy loam surface soil; the lower portion was a nutrient solution. Calcium concentration of 0.25 ppm was sufficient to obtain maximum growth rates in a nutrient solution at pH 5.6. More than 2.5 ppm of Ca was required at a solution pH of 4.5, and 5 ppm of Ca was insufficient when the pH was 4.0. High concentrations of Mg [ratios of Ca/(Ca + Mg) of 0.1 or less] also reduced growth. Replacing half of the Mg with K at low ratios of Ca/total cations produced more rapid elongation than the Ca + Mg systems, but had no effect at the higher ratios. Aluminum in the nutrient solution reduced root growth when the ratio of activities of Al to Ca was greater than 0.02.

Measurements were made of both shoot and root growth on a corn (Zea mays L.) and a tomato (Lycopersicon esculentum Mill.) plant in a rhizotron. Root intensity at the transparent panel was estimated by two methods. It increased during the growing season for both species, but was always greater for corn. Estimates of root density and total root length were three times greater for corn than for tomato at the end of the growing season. Side walls and glass panels showed no concentrating effect on root growth.

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.