Growing Sorghum and Corn in Clumps As a Strategy to Improve Microclimate, Grain Yield and Harvest Index.

Photosynthesis is the major process in plants using solar radiation and carbon dioxide (CO₂) concentration, but it is affected by the availability of soil water, wind speed, air temperature, relative humidity, and vapor pressure deficit (VPD). A corn (Zea mays L.) field study and a 2-yr grain sorghum (Sorghum bicolor L. Moench) greenhouse study were conducted in the Texas High Plains to compare VPD, grain yield, yield components, transpiration efficiency (TE), and water use efficiency (WUE) for clump and evenly spaced planting (ESP) geometries. Thermal images were taken for the field study and the air temperature and relative humidity (RH) within the plant canopy were measured at different growth stages for both studies. Canopy temperatures (corn) and mean VPDs (corn and sorghum) were consistently lower for clumps than those for ESPs indicating that clumps improved the microclimate. Compared to ESPs, clumps increased relatively the grain yield, and significantly the harvest index (0.48 vs. 0.43 for sorghum and 0.56 vs. 0.54 for corn). Grain transpiration efficiency (TEg) was significantly higher for clumps (2.5 kg m^-3) than for ESPs (2.3 kg m^-3) for sorghum. Similarly, WUE (grain) was greater for clumps (1.8 vs. 1.7 kg m^-3 for ESPs) for corn. Our results suggest that growing sorghum and corn plants in clumps can be a useful strategy under dryland conditions because it may improve the microclimate thereby increasing grain yield and harvest index with no additional inputs.