Optimizing Grain Sorghum Seeding Rates for Anticipated Hydrologic Conditions.

Excessive plant populations can exacerbate soil moisture limitations and result in lower yields, stalk rot diseases and lodging in grain sorghum.  Selection of optimum seeding rates is further complicated by spatial and temporal variability of pre-season soil moisture and in-season precipitation. We initiated a study to evaluate grain sorghum yield in response to increasing seeding rates and contrasting soil moisture conditions in the central and northern Blacklands of Texas. Trials were imposed at five locations in the central and northern Blackland Prairie of Texas. At each field, treatments were arranged in a randomized complete block design with three replications of five treatments. Treatments comprised five seeding rates (87,186; 127,144; 161,453; 201,816; and 232,493 seeds per hectare). Row spacing was 76.2 cm at all locations except for Thrall, which was at 96.5 cm spacing. Plots were four rows wide and extended the entire length of row for each selected field (about 300 m). Prior to planting, soil was sampled to a depth of 0.30, 0.60, 0.91, and 1.22 m to quantify total and available soil moisture at planting. Plant emergence at Thrall averaged 90% of the target seeding rate. Similar results were observed at other locations. Total and plant available moisture within the upper (0.30 m) soil profile at planting did differ (p < 0.05) among locations. The Buckholts location had 0.11 m of total water in the 0 – 0.30 m depth of soil depth compared to 0.14 m at the Farmersville location. Soil profile moisture was generally greater for northern locations compared to southern locations, reflecting rainfall patterns during the winter and early spring.