Snow catch and soil water recharge in standing sunflower residue

Sunflower (Helianthus annuus L.) is an economically viable crop for dryland rotations in the central Great Plains. Sunflower's ability to extract large amounts of soil water can depress subsequent crop yields unless significant soil water recharge occurs, The objectives of this study were to measure the effects of differences in standing sunflower stalk height and population on snow deposition and subsequent overwinter soil water recharge. Observations of snow depth and overwinter soil water recharge were made at seven sites near Akron, CO, over three winters. Sunflower stalks were laid flat after harvest, or left standing at approximately 18 or 28 in. Stalk population varied from approximately 10 600 to 26 100/acre. Silhouette factor (stalk height x diameter x population) ranged from 0 to 111 sq in./1600 sq in. Soil types in the study areas were Rage silt loam (fine, smectitic, mesic Pachic Argiustoll) or Weld silt loam (fine, smectitic, mesic Aridic Paleustoll). Increasing stalk height (and silhouette factor) increased snow catch and soil water content during the winter, but amounts of increase varied depending on wind speed and snow amount. With near-average snowfall amounts and number of drifting storms, soil water recharged linearly with increasing silhouette factor, thereby increasing stored soil water by nearly 5 in. where silhouette factor was 80 sq in./1600 sq in. Maintaining standing sunflower residue during the winter and spring following sunflower harvest can provide critically needed soil water recharge by increasing depth of snow deposition.