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

Authors: SHORTNACY, LAUREN - Tuskegee University; Eberle, Carrie; PAISLEY, STEVE - University Of Wyoming

Submitted to: Crop, Forage & Turfgrass Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/16/2023
Publication Date: 5/1/2023
Citation: Shortnacy, L.K.W., Eberle, C.A., Paisley, S. 2023. Sunn hemp biomass accumulation, regrowth, and nutritive value response to harvest time and cutting height. Crop, Forage & Turfgrass Management. 9(1). Article e20215. https://doi.org/10.1002/cft2.20215.
DOI: https://doi.org/10.1002/cft2.20215

Interpretive Summary: Legume crops benefit crop and livestock agriculture through nitrogen fixation and nutritive, high quality animal feed. There are few annual legumes that are grown during the summer season and meet the nutrient demands of beef cattle when alfalfa hay is in limited supply. Crotalaria juncea (sunn hemp) is a warm season, annual legume that produces high amounts of biomass, fixes nitrogen, and provides high quality livestock feed. Here we investigated the effect of first cutting date and height on yield, regrowth, and feed quality of Wyoming grown sunn hemp in irrigated and dryland conditions. In the irrigated study a first harvest cutting height of 4 inches produced greater biomass accumulation and higher nutritive accumulation than 2 and 6 inch cutting heights. The date of the first cutting did not have an effect on the full season biomass yield or nutritive accumulation. In the dryland study a first cutting of 55-105 days produced the highest biomass yield and higher nutritive accumulation regardless of cutting height. Average full season (105 days) yield from combined first and second cuttings was 2.8-4.4 tons per acre under irrigation and 0.7 tons per acre in dryland conditions. These research findings will benefit producers interested in using sunn hemp as a forage crop and extension educators, researchers, and ag consultants interested in adopting sunn hemp into a cropping rotation or feed ration.

Technical Abstract: 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 is in limited supply. We investigated the biomass accumulation, regrowth biomass, and nutritive value of Crotalaria juncea (sunn hemp) in response to harvest time and cutting height in irrigated and dryland studies in Wyoming. Average full season (105 days) biomass accumulations were 6.4-9.9 Mg ha-1 under irrigation and 1.6 Mg ha-1 in dryland conditions. Primary harvest time affected primary and regrowth biomass accumulation but did not affect cumulative full season biomass accumulation in irrigated or dryland studies. Regrowth and full season biomass accumulations were significantly affected by cutting height in the irrigated study only. Nutritive value concentrations were significantly affected by primary harvest in both irrigated and dryland studies. Under irrigation, primary harvest time was not significant in its effect on total nutrient accumulations over a full growing season, but cutting height was significant with a cutting height of 10.8 cm accumulating more nutrients compared to the 6.4 and 15.2 cm. The opposite was seen in dryland studies with primary harvest time being significant and cutting height insignificant. In the irrigated study a cutting height of 10.8 cm produced full season accumulations higher in both biomass accumulation and nutritive value. In the dryland study a harvest time of 55-105 days after planting produced the highest full season accumulation regardless of harvest time or cutting height.