Profitability and environmental benefits of irrigated grass-legume mixtures in comparison with synthetic fertilizer use in Wyoming

High fertilizer prices coupled with environmental effects of fertilizers have created serious concerns among scientists and the general public. Studies were conducted to evaluate the (a) environmental and economic benefits of replacing nitrogen (N)-fertilized grass with grass-legume mixtures and (b) implications of phosphorus (P) and potassium (K) application on forage crops.;Results from the study showed that total annual forage yields were generally high in legume monocultures than their respective mixtures. Forage mixtures produced similar yields as grass monocultures receiving N. Application of N increased forage yield in grass monocultures but the half recommended rate (56 kg N ha-1) produced similar yield as the full rate (112 kg N ha-1). Forage nutritive value of legumes was high which resulted in improved nutritive value of meadow bromegrass-legume mixtures relative to meadow bromegrass monocultures.;The 30% alfalfa + 70% meadow bromegrass and 50% alfalfa + 50% meadow bromegrass mixture treatments and legume monocultures (alfalfa, sainfoin, and birdsfoot trefoil) were profitable one year after establishment. Application of N to meadow bromegrass was, however, not profitable.;Soil water depletion and total soil microbiota were not influenced by grass and legumes monocultures as well as grass-legume mixture treatments. The uptake of N by plants was high and resulted in low residual soil nitrate-N. Efficiency of N use and recovery were not influenced by N application but applying half the recommended N rate resulted in 35% more efficiency in N use.;Generally, application of P and K did not improve growth and forage nutritive value. High root:shoot ratio resulted in low P and K uptake.;Grass-legume mixtures, especially the 30:70% mixtures have shown promise as viable alternatives to N application to meadow bromegrass monocultures under irrigation in Wyoming.