Manipulating Plant Geometry to Improve Microclimate and Grain Yield.

Crop production in dryland areas is low not only because of the low and highly variable amounts of precipitation, but also because only a relatively small portion is used for transpiration. As aridity increases, the units of transpiration required to produce a unit of dry matter also increases because of higher vapor pressure deficits (VPD). In drylands, growers usually practice reduced plant populations and skip row configurations with zero or minimum tillage for a better utilization of precipitation and available soil water. But decreased plant population can reduce water use efficiency (WUE) and transpiration efficiency (TE) because it exposes more leaf area per plant to the wind and sunlight and provides less shading of soil surface. A greenhouse study was conducted in 2013 at West Texas A&M University, Canyon, Texas to compare difference in VPD, grain yield and yield components, WUE and TE between clumped (3 plants) and evenly spaced planting (ESP) geometries in grain sorghum with the same plant populations. Plants were grown at high and low water levels with lid covered, straw mulched and bare surfaces. Data loggers were used to measure the air temperature and relative humidity (RH) within the crop canopy at different growth stages. VPDs within the clumps were consistently lower than those for ESP indicating that clumps improved the microclimate. Straw mulch significantly increased WUE, grain yield and harvest index as compared to the bare surface. Although potential yield increases from growing plants in clump are limited, they could be worthwhile because no additional inputs are required.