Living Mulches for Irrigated Corn and Soybeans in the Semi-Arid West.

Leguminous living mulches have been successfully integrated into corn cropping systems in the upper Midwestern United States.  This study evaluated the feasibility of adapting the practice under irrigation in the semi-arid West.  Specifically, different living mulch and annual crops were tested for performance and compatibility.  Corn for grain, corn for silage, and soybeans were planted into established stands of alfalfa (Medicago sativa), red clover (Trifolium pratense), white clover (Trifolium repens), birdsfoot trefoil (Lotus corniculatus), and a mix of red clover and birdsfoot trefoil.  Fertility treatments of 0, 84, 168, and 225 kg ha^-1 nitrogen without a living mulch were also applied to the corn crops.  These were used to generate nitrogen response curves and quantify nitrogen inputs of living mulches.  All living mulch plots received 84 kg ha^-1 nitrogen.  Added nitrogen benefits from legumes in corn silage plots were 54, 36, 35, 25, and 17 kg ha^-1 for alfalfa, white clover, birdsfoot trefoil, red clover, and the birdsfoot trefoil/red clover mix, respectively.  Corn silage yields in legume plots ranged from 17.2 to 20.4 Mg ha^-1.  In corn grain, nitrogen additions from legumes were 46, 55, 26, 23, and 21 kg ha^-1 for alfalfa, white clover, birdsfoot trefoil/red clover mix, birdsfoot trefoil, and red clover, respectively.  Yields ranged from 8.2 to 10.1 Mg ha^-1 in legume plots.  Soybean yields showed no response to the presence of living mulches (average 3.1 Mg ha^-1).  Crop aftermath, which is commonly grazed, was similar among legume treatments in the corn grain plots, while birdsfoot trefoil had the greatest fall yield at 282 kg ha^-1.  Preliminary results suggest that living mulch cropping systems may be a viable alternative under irrigation for producers in the West.