Effects of Standing Wheat Residue on Soil Water Storage and Herbicide Spray Deposition

Standing winter wheat (Triticum aestivum L.) residue can capture snow, reduce soil erosion and water evaporation, and increase the following crop yield in semi-arid environments. After wheat harvest, there is approximately a 10-month period until the next crop is planted, during which controlling weeds is important to reduce soil water use. Although standing residue provides many benefits in a cropping system, it can intercept herbicide spray droplets and decrease its efficacy. This research is focused on improving agronomic recommendations of wheat residue variety that can enhance soil moisture by trapping snow and calculating subsequent corn (Zea mays L.) yield and also evaluating the impact of standing residue on herbicide spray deposition. The effect of standing residue on soil water content was tested among five wheat varieties representing hollow-stemmed winter wheat (HSWW) with tall, short, strong, or weak stem; or solid-stemmed winter wheat (SSWW). ‘Warhorse’ (SSWW) and ‘Settler CL’ (HSWW) had the lowest yield in 2017, which was a dry year. The residue of Warhorse did not persist longer in the field compared to the other varieties. Warhorse did not show an advantage over HSWW in enhancing soil moisture during years with average precipitation during corn growing season, and corn yield was not greater. Standing residue also had an impact on herbicide spray deposition. To evaluate herbicide spray deposition, three heights of wheat stubble, four nozzle types, and three application directions were tested. The spray classifications of the four nozzles used in this experiment were fine, medium, coarse, and ultra-coarse as determined using laser diffraction. Wheat stubble greater than 70 cm tall decreased spray deposition 37%, while 30-35 cm tall stubble decreased 23%. The AIXR nozzle was less prone to spray deposition differences among all application directions. TTI nozzle had the least amount of spray deposition when used traveling perpendicular to the wheat rows. TTJ and XR had better spray deposition at angular application direction. Applicators should consider traveling in an angular direction to the wheat rows for improved droplet deposition across spray nozzle types. Advisor: Cody F. Creec