Stand Age, Precipitation, and Temperature Effects on Forage Yield

Larry M. White
1985 Journal of range management  
Abstnct The effects of seasonal distribution of precipitation on forage yield are often confounded by stand age. Forage yields of Russian wildrye (Psathyrostachys juncag), green needlegrass (S@MI vir-*r), created whaQrassr(A@vpyrcm dsertorra), and hltermediate pubesctnt wheatgrass (Agropyron int mnedium-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
more » ... yield of all 4 species was significantly (PCO.01) related with April and May precipitation and stand age. Forage yield of Russian wildrye was significantly (KO.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 itiuence of stand age on forage yield. Methods are needed to determine potential forage yield of seed range grasses without having to test each species for 5 to 10 years at numerous locations. Kilcher and Heinrichs (1974) found that forage production the first year after establishment was 2 to 3 times greater than their 7-year average. Except for Russian wildrye (Psathyrostachys junceus), forage species tested by Currie and Smith (1970) yielded the most forage during the third year after establishment. Russian wildrye required 5 years to reach its highest forage production. Kilcher (1980) suggested that when ranking a species forage production potential, the first harvest year data be ignored and only data for the following 5 consecutive years be used. Six years seems to be an excessively long requirement for evaluation of forage species. A number of researchers have found forage production was highly correlated with seasonal precipitation. Stitt (1958) noted that forage yield of a number of grass species had higher correlations (r = 0.88) with April through May precipitation than with April through June precipitation (r = 0.54). Smoliak (1956) found forage yield of native range had higher correlation (r = 0.86) with May through June precipitation than with precipitation during any other period over a 20-year period. However, Thomas and Osenbrug (1959) reported forage yields of a mixture of bromegrasscrested wheatgrass (Bromus inermis-Agropyron desertorum)for 8 years were not significantly ((m.05) correlated (r = 0.53) with April through June precipitation. They found that the range of daily temperature combined with precipitation was needed to significantly ((X0.05) correlate (I = 0.84) with forage yields. Lawrence and Heinrichs (1968) found, over a 15-year period, that precipitation received during the previous September (r = 0.55)
doi:10.2307/3899330 fatcat:2asoq2qrhfbztb6fcx6oa3qp4i