Grass and Grass/Legume Mixes for Irrigated Pasture Using Organic Production Methods.

Selecting irrigated pasture mixes adapted to organic systems in the semi-arid West can be challenging. This study looked at grass and grass-legume mixes for irrigated pastures using organic production methods. Four grass mixes (tall fescue, hybrid wheatgrass/tall fescue/hybrid brome, orchardgrass/meadow brome/smooth brome, and orchardgrass/ meadow brome/Kentucky bluegrass) were established in duplicate in 2008. Half of the plots were interseeded in fall 2008 with each of four legumes (alfalfa, birdsfoot trefoil, sainfoin, and white clover). Also in fall 2008, the remaining plots were treated with 0, 11.2, or 22.4 Mg/ha of dairy compost (0.3% N) to compare the effects of compost versus legumes on yield and quality of the grass mixes. Mixes were harvested six times to simulate season-long, rotational grazing and evaluated for yield, crude protein, neutral detergent fiber (NDF), acid detergent fiber (ADF), and in vitro true digestibility (IVTD). Data from 2008 that looked at just the grass mixes showed that annual dry matter yields of tall fescue and HWG/TF/HB were 10,975 and 9,814 kg/ha, respectively, and averaged 19% higher than the other mixes. The dry matter yield per cutting of tall fescue also averaged 23% greater than those of the other grass mixes. Additionally, tall fescue had 120% higher dry matter yield at the last cutting in September than the other grass mixes. Conversely, crude protein of tall fescue (19.8%) averaged two percentage points lower than all other grass mixes. NDF, averaged across all species, declined (higher quality) throughout the growing season. Results from the 2009 growing season comparing the same grass mixes with legume and compost treatments will be presented.