Yield and water use efficiency of different plant populations of dryland corn and sorghum
Two field experiments were conducted at the Tidewater Agricultural Research and Extension Center, in Suffolk, Virginia, during summer 1994, on a Uchee loamy sand (fine, loamy, siliceous, thermic Arenic Hapludult) with relatively low water holding capacity. The objective was to determine the effect of plant population on yield, water use, and water use efficiency, of one cultivar of corn (Zea mays L.) and two cultivars of sorghum (Sorghum bicolor (L.) Moench). Plant population treatments for corn were 37, 49, and 62 thousand plants ha⁻¹ of cultivar Pioneer 3140 on a 91- cm inter-row spacing. For sorghum, treatments were factorial combinations of plant populations of 54, 109, 158, and 202 thousand plants ha⁻¹ and cultivars Dekalb-48 and Southern States 1212 on a 46-cm inter-row spacing. Experimental plots were laid out in randomized complete blocks with four replications. Soil water measurements were taken non-destructively at 10-day intervals after planting and at 20-cm intervals to a depth of 1.7 m in the center of each plot, using a Sentry AP-200 moisture probe. Overall mean grain yield for com was 3909 kg ha- l . For sorghum, it was 4800 kg ha-] for cultivar Dekalb-48 and 4740 kg ha⁻¹ for cultivar Southern States-1212. Soil water measurements showed that soil water stress occurred during tasseling of corn at 75 to 83 days after planting. This stress occurred just prior to the boot stage for sorghum at 60 to 68 days after planting. Crop water use, averaged over all treatments, was 494 mm for corn and 424 mm for sorghum. For corn, plant population did not influence grain yield and crop water use. Water use efficiency ranged from 0.748 to 0.873 kg m³. For sorghun1, there was no interaction between plant population and cultivar. Grain and dry matter yield, crop water use, and water use efficiency were similar for both the cultivars. Significant plant population effects were obtained for both sorghum cultivars. Grain and dry matter yield were depressed at the lowest plant population. Water use efficiency for sorghum increased non-linearly with increase in plant population from 0.944 to 1.354 kg m³.