GRASS, LEGUMES, AND GRASS-LEGUME MIXTURES: YIELD, NUTRITIVE VALUE, AND SOIL WATER USE

Forages play a major role in Wyoming’s economy. However, forage yields in the state have been dwindling and below the national average over the past few years. A field study was conducted from 2013 to 2015 in Sheridan, WY to evaluate grass-legume mixture seeding ratios and nitrogen (N) fertilizer rates for improved forage yield and nutritive value and efficient soil water use. In 2014, forage dry matter (DM) was highest (5980 kg ha) in meadow bromegrass receiving the highest N rate (100% meadow bromegrass + 112 kg N ha). In general, forage DM in mixture treatments were relatively lower than their respective sole stand treatments in 2014. An opposite trend in forage DM was observed in 2015. The highest yield (8580 kg ha) was observed in 25% alfalfa + 25% birdsfoot trefoil + 50% meadow bromegrass treatment. Average forage yield was higher in 2015 (6854 kg ha) than 2014 (4611 kg ha). Soil water depletion (SWD) between April 4 and August 15, 2015 ranged from 301 to 318 mm. Birdsfoot trefoil monoculture (100% birdsfoot trefoil) depleted the highest amount (318 mm) of soil water. Water use efficiency (WUE) ranged between 44 kg DM mm water (100% sainfoin; 50% sainfoin + 50% meadow bromegrass treatments) to 74 kg DM mm water (30% alfalfa + 70% meadow bromegrass treatment). Nutritive value of the legumes was higher than meadow bromegrass and this resulted in higher nutritive value in meadow bromegrass-legume mixtures than sole meadow with or without N application. Forage crude protein (CP) in birdsfoot trefoil was as high as 231 and 296 g kg in 2014 and 2015, respectively which was almost similar to that of sole alfalfa (286 and 292 g kg in 2014 and 2015, respectively). These results showed that birdsfoot trefoil either grown in mixtures with alfalfa and meadow bromegrass or as monoculture has the potential as a good substitute for alfalfa in Wyoming. With the added benefits of non-bloating and resistance to the alfalfa weevil, birdsfoot trefoil will be suitable as a forage crop both for grazing and haying for Wyoming producers, and perhaps for neighboring states.