Cropping system influences on extractable water for mono- and double-cropped soybean

Abstract

For rain-fed agriculture in the southeastern United States, efficient soil water use when double-cropping is essential. Water use by soybean [ Glycine max (L.) Merr.] following winter wheat ( Triticum aestivum L.) is, however, poorly documented. Winter wheat may deplete soil water, thus limiting subsequent soybean yield. Cropping system variables, such as soybean planting date and row spacing, may also affect water use. Therefore, a 4-year field experiment in northeastern Mississippi was conducted on Leeper ( Vertic Haplaquept) and Catalpa ( Fluvaquentic Hapludoll) silty clays. The objectives were to (1) determine the influence of soybean planting date, cropping system (monocropped versus double-cropped), and row spacing on extractable water (similar to available water) for soybean, and (2) identify a production system to improve the use of extractable water over a growing season. In mid- to late-May (the first soybean planting date), “Centennial” soybean in 38- or 76-cm rows was planted either between rows of standing wheat or in bare (monocropped) plots. After the wheat was harvested and the straw chopped, soybean was planted into bare soil or planted no-till into wheat stubble in mid-June for the second planting and in early July for the third. Soil water content was measured with a neutron probe from soybean emergence to maturity. Differences between each water content profile and a dry profile (constructed using the lowest recorded water content at each depth) were regarded as extractable water. Neither soybean planting date nor cropping system, as a main effect, exerted much influence on extractable water for soybean. As interacting factors later in the season, however, they were important. Plots with soybean in 38- rather than 76-cm rows contained more extractable water throughout the 1982 and 1983 seasons, and yielded over 9% more seed. Canopies closed about 20 days sooner with narrow rows than with wide rows. These full canopies protected and shaded the soil surface, probably reducing crusting and decreasing water losses by evaporation. We concluded that double-cropped soybean in 38-cm rows planted either into standing wheat in late May or into wheat stubble not later than mid-June utilized extractable water efficiently in silty clay soils in northeastern Mississippi.