Stand Age, Precipitation, and Temperature Effects on Forage Yield

Abstract

The effects of seasonal distribution of precipitation on forage yield are often confounded by stand age. Forage yields of Russian wildrye (Psathyrostachys junceus), green needlegrass (Stipa viridula), crested wheatgrass (Agropyron desertorum), and intermediate-pubescent wheatgrass (Agropyron intermedium-trichophorum) were determined from 6 separate studies, each of 6 years duration, from 4 locations in the northern Great Plains. Stepwise multiple regression showed that forage yield of all 4 species was significantly (P<0.01) related with April and May precipitation and stand age. Forage yield of Russian wildrye was significantly (P<0.05) related with April mean monthly temperature and degree days (accumulation of daily mean air temperature above a given threshold temperature) accumulated until the end of May or June; however, yields of the other 3 species were not significantly related with April, May, or June mean monthly temperatures nor degree days accumulated until the end of May or June. The highest forage yield per centimeter of precipitation occurred either the second or third year after establishment; then yield decreased asymptotically and by year 5 or 6 was only 75% of maximum for green needlegrass and 40-50% for the other grasses. Economic evaluation of seeding forages must include the influence of stand age on forage yield.