Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 15, 2004
Publication Date: June 1, 2005
Citation: Skinner, R.H. 2005. Emergence and survival of pasture species sown in monocultures or mixtures. Agronomy Journal. 97:799-805. Interpretive Summary: The potential benefits of sowing several forage species together to increase the biodiversity of grazed pastures are becoming more and more evident. However, little is know about how seedlings of different species interact with each other during seedling establishment. In order to improve our ability to establish diverse pasture mixtures, we examined interactions during the first two months following sowing among four forage species (perennial ryegrass, orchardgrass, white clover, and birdsfoot trefoil) commonly grown in pastures in the northeastern U.S.A. Seeds were sown at two sites in central Pennsylvania that differ in their potential susceptibility to drought stress. The experiment was conducted during the spring of two years, the first of which was drier and warmer than normal while the second was relatively cool and wet. Seeds were sown as monocultures of each species or as mixtures containing either two or four species. Seedling emergence was lower in mixtures than in monocultures but mortality was also lower so that the number of species in a plot had no effect on the number of seedlings present two months after sowing. In the warm, dry year, survival of perennial ryegrass seedlings improved and plant size increased as the distance to the nearest neighboring seedling decreased. This study was able to show that seedlings interact with each other from the very earliest stages of development, affecting emergence, mortality and growth. In some cases, neighboring plants can have beneficial effects on each other, improving survival and growth under harsh conditions. However, in most cases there was a negative effect of neighbors on survival. A better understanding of interactions during establishment could improve our ability to obtain adequate stands under unfavorable environmental conditions.
Technical Abstract: Plant-plant interactions during seedling establishment can markedly affect the composition of pasture communities. This research examined the emergence, mortality and early growth of four forage species commonly found in temperate northeastern USA pastures. Species were selected based on functional group (grass vs. legume) and relative drought tolerance. Drought tolerant species included 'Penlate' orchardgrass (Dactylis glomerata L.) and 'Viking' birdsfoot trefoil (Lotus corniculatus L.), while drought sensitive species included 'Basion' perennial ryegrass (Lolium perenne L.) and 'Will' white clover (Trifolium repens L.). Seeds were sown as monocultures, as grass/legume binary mixtures and as a complex, four-species mixture. Mixture complexity had no effect on seedling emergence. However, legume mortality was significantly reduced in the complex compared with other mixtures in a year when high temperature and drought stress limited seedling establishment. In most cases, there was a negative effect of neighbors on survival as evidenced by reduced clustering in surviving compared to emerged seedlings and by a negative relationship between mortality rate and distance to the nearest neighbor. However, in a drought year, perennial ryegrass mortality decreased as distance to the nearest neighbor decreased, suggesting that survival was facilitated by the presence of neighbors. Even though mixture complexity had significant effects on seedling emergence and mortality, species composition in the binary and complex mixtures could be predicted based on emergence and survival of monocultures. It appears that seedling emergence information gleaned from monocultures can be a useful tool for predicting initial species composition of more complex mixtures.