Spring Drought Effects on Rangeland Forage Yield from Clayey Ecological Sites in Western South Dakota

Understanding the historical influence of seasonal precipitation, especially spring precipitation, and stocking rate on forage yield would be desirable for planning purposes. The objectives of this study were to examine the historical precipitation pattern and how it influenced forage yield on pastures that were stocked at light, moderate, and heavy stocking rates for 15 years at the Cottonwood Range and Livestock Research Station in western South Dakota. Weather data from 1909 to 2004 at the station were analyzed to determine the frequency of occurrence of below (≤75 of mean), normal, and above normal (\u3e125% of mean) spring precipitation (April, May, June). Additional data from the station provided for an examination of the relationships between weather and forage yield from pastures grazed at three stocking rates. Forage yield and precipitation data were collected from 1945 to 1960 from pastures continuously grazed from May to November at 0.25, 0.40, and 0.60 AUM/acre. Analysis of variance was used to test influence of spring precipitation (spring drought and non-spring drought) and stocking rate (light, moderate, and heavy) on forage yield. Below normal, normal, and above normal spring precipitation occurred 29, 48, and 23% of the time, respectively. Forage yield in spring drought years was 420 lb/ac less (P \u3c 0.01) than in non-spring drought years. Lightly stocked pastures had 38 and 71% more (P \u3c 0.01) forage than moderate and heavily stocked pastures. Spring droughts reduced forage yield (P \u3c 0.01) in light, moderate, and heavily stocked pastures by 20, 27, and 35%, respectively. Forage yield from lightly stocked pastures during spring droughts was similar to heavily stocked pastures in non-spring drought years. Our study indicates that spring precipitation should guide stocking rate decisions made during the growing season. Light and moderate stocking rates reduce the impact of spring drought on forage yield more than heavy stocking rates