Wednesday, November 7, 2007
271-21

Root Distribution of Temperate Forage Species Subjected to Water and Nitrogen Stress.

R. Howard Skinner, Bldg. 3702, USDA-ARS, USDA/ARS Pasture Sys. Lab, Curtin Road, University Park, PA 16802-3702 and Louise H. Comas, Penn State University, University Park, PA 16802.

Root production can be important in determining forage yield during moisture and nutrient stress because enhanced rooting depth can increase access to water and nutrients found deeper in the soil profile. We examined rooting characteristics of 19 species (8 grasses, 5 legumes, and 6 forbs) that are common in northeastern pastures. Species examined covered a range of tolerances to defoliation frequency, drought, and nitrogen availability. Eight week-old plants were transplanted into PVC pots (15 cm diameter, 50 cm deep). One week after transplanting, 50% of the leaf area of each plant was removed. Roots and shoots of each species were harvested 7 d after clipping when plants were 10 wks old. A second set of plants were harvested three weeks later. The experiment was replicated in 3 greenhouse sections. When roots were harvested at the second harvest, root systems were dissected into fine, coarse, and tap roots. All roots less than 1 mm were considered fine roots, serving primarily in the acquisition of soil resources rather than storage or structure. Stolon biomass was pooled with stems for stolon-producing species and rhizome biomass was pooled with coarse and tap roots for rhizome-producing species. This report will present data on the ability of forage species to reallocate carbon within the root system in response to water and nitrogen stress. Data from the pot study will be compared against field results to determine if inherent species differences in root distribution can explain rooting differences observed in multi-species forage mixtures.