Abstract:
Many studies have shown reducing or eliminating tillage to leave crop residues on the soil surface in dryland areas increases soil water. This allows shortening the fallow periods and in some cases annual cropping. Limited work, however, has been conducted on manipulating plant geometries to increase water use efficiency and grain yields, and to reduce risk of crop failure. Low plant populations are used in water deficient areas to conserve stored soil water for use during the grain filling period. Favorable conditions early can lead to tillering in crops such as corn (Zea mays L.) and grain sorghum (Sorghum bicolor L. Moench). Also, equally spaced plants in rows with low populations are often 20 to 30 cm or more apart and are subject to high amounts of radiation and wind. Recent studies in the Southern High Plains have shown that growing plants in clumps at the same population as in rows with equidistant spaced plants is a promising strategy. The hypothesis is based on several assumptions that are supported by the literature. First, aboveground biomass produced is a function of water use during the growing season and properly spaced clumps will utilize available water similar to plants in rows. Second, the maximum harvest index (HI) is species related and decreases with increasing water stress. Third, tillers become water-stressed sooner than the main stalk and many senesce before forming enough leaves to form a panicle, and even when they produce grain, the HI is lower than for main stalks. Fourth, plants in clumps have a more favorable microclimate because of mutual shading, higher humidity, and less wind. Data will be presented to illustrate that this strategy reduces early season vegetative growth leaving more soil water for grain filling. The strategy performs best when crop residues are present to suppress evaporation.