Weather factors affecting 22 years of tallgrass prairie hay production and quality.

Tallgrass prairie annual hay production and chemical composition (N, P, K, CA) data from n 23-year study conducted by H.J. Harper, Oklahoma State University, from 1929 through 1951 were correlated with corresponding monthly and seasonal temperature (mean, maximum and minimum, and absolute maximum and minimum), precipitation, wind, spring and fall growing season freeze dates, current and previous year’s harvest dates, and previous year’s yield. Multiple regression analyses were used to determine the weather variables and multiple regression equations which nccounted for the greatest percentage of variation in PMUri hay production and nutrient concentrations. Equations with 4 independent weather variables for all months prior to the date of hay harvest produced high Rz values for production (82%), and N (SO%), P (81%), K (81%) and CA (91%) concentrations. In general temperature values, especially in the fall of the previous year and Jmuary and mid-summer of the current year, recounted for more of the variation in all response variables than did any other kind of weather variable, such as precipitation, wind, or freeze dnte. Equations with 4 independent weather variables for those months prior to June produced only a moderate Rz value (48%) for production, but produced high R2 values for N (76%), P (74%), K (74%) and Ca (7%) concentrations. Relationships deserving additional research are suggested. Temporally and spatially, Oklahoma exhibits a unique variety of weather due to the location of the state on the North American continent. Oklahoma’s climate is controlled by various air masses (i.e., warm and humid maritime Tropical from the Gulf of Mexico, continental Tropical from the arid southwest, continental Polar from northern Canada, and continental Arctic from the north polar regions) vying for positions over the state. The weather characteristics of a given area depend upon the frequency and timing of occurrence of these air masses. The frequencies of air mass dominance vary significantly from year to year with the result Oklahomans can usually predict with confidence only that next year’s weather will be different from this year’s weather. In any given year, the state can experience temperatures and precipitation characteristics of the more humid climate to the east or the more arid characteristics to the west. Ranchers and other rangeland managers are acutely aware weather conditions cause rangeland forage production to vary widely from year to year. The annual variations in growing conditions make it difficult to predict or interpret vegetational responses to grazing and range improvement practices. Oklahoma also offers a significant east-west gradient in elevation, precipitation, and soil types and a north-south temperature gradient influencing the relative abundance of subtropical and temperate-origin flora. This makes it difficult to extrapolate research results from one area to another within the state. Consequently, the accuracy of interpretations of Oklahoma’s weather-vegetation relationships and dependability of resulting management recommendations are greatly influenced by the length of a data collection period and the particular mix of weather types within that period. Authors are professor of range science, associate professor of geography, and professor of statistics, Oklahoma State University, Stdlwater 74078. Jeff Powell ! s presently professor of range management, Department of Range Management, Umversity of Wyoming, Laramie 82071. This article is a contribution of the Oklahoma Agricultural Experiment Station as Journal Article No. 4445. Appreciation is expressed to David Engle and Anne Ewing, Oklahoma State University, for their review and suggestions in preparation of this manuscript. Manuscript accepted 27 January 1986. 354 Thus, Oklahoma experiences a mix of weather types unlike those which have been studied using similar methods. We used the variability within Oklahoma’s climate to determine the relationships between selected weather factors and tallgrass prairie hay data assembled over 23 years. Harper (1957) collected the database on hay production and nitrogen, phosphorus, potassium and calcium concentrations from 1929 through 195 1. This is the longest rangeland time series available in Oklahoma.