Sunn hemp biomass accumulation, regrowth, and nutritive value in response to harvest time and cutting height

The integrated crop-livestock systems of the northern High Plains are lacking in annual legumes that meet the nutrient demands of beef cattle when alfalfa (Medicago sativa) is in limited supply. We investigated the biomass accumulation, regrowth biomass, and nutritive value of sunn hemp (Crotalaria juncea) in response to initial harvest day and cutting height in irrigated and dryland studies in Wyoming. Net biomass accumulations in 105-day growing period were 4.4 tons acre⁻¹ under irrigation and 0.7 tons acre⁻¹ in dryland conditions. Initial harvest day after planting (iDAP) affected initial and regrowth biomass accumulation but did not affect net biomass accumulation in irrigated or dryland studies. Regrowth and net biomass accumulations were affected by cutting height in the irrigated study only. Nutritive value concentrations were significantly affected by iDAP in both irrigated and dryland studies. Under irrigation, net nutrient accumulation was not affected by iDAP but was significantly greater with a cutting height of 4.2 inches compared to 2.5- and 6-inch heights. In contrast, the dryland study, net nutrient accumulation was not affected by cutting height but was higher in 55–105 iDAP than 45 iDAP. In the irrigated study, a cutting height of 4.2 inches produced net accumulations higher in both biomass accumulation and nutritive value. In the dryland study a harvest time of 55–105 iDAP produced the highest net accumulation regardless of harvest time or cutting height. Sunn hemp can be harvested once or twice in a 105-day growing season to produce biomass and essential nutrients for livestock feeding.