|STALLINGS, ANNA - Auburn University|
|WOOD, CHARLES - University Of Florida|
|GUERTAL, ELIZABETH - Auburn University|
|WEAVER, DAVID - Auburn University|
Submitted to: Journal of Plant Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/19/2016
Publication Date: 1/17/2016
Citation: Stallings, A., Balkcom, K.S., Wood, C.W., Guertal, E.A., Weaver, D.B. 2016. Nitrogen mineralization from 'AU Golden' sunn hemp residue. Journal of Plant Nutrition. 40(1):50-62.
Interpretive Summary: ‘AU Golden’, a new sunn hemp cultivar released by Auburn University, has the potential to provide substantial amounts of nitrogen (N) to subsequent crops that could reduce recommended application rates of synthetic N fertilizers. However, one typical problem associated with legumes involves timing N release from legumes with the N uptake needs associated with the following crop. ARS researchers at the National Soil Dynamics Laboratory in Auburn, AL in cooperation with scientists from Auburn University conducted a mineralization field trial to measure N and carbon (C) release amounts from sunn hemp residue produced after 60 d for three planting dates (May, June, and July) at two locations in Alabama. Sunn hemp released N very quickly with up to 64% released within two weeks after termination. June and July planted sunn hemp released N slower compared to May planted sunn hemp, which may have been related to more biomass production associated with the later planted sunn hemp. Carbon remaining was comparable for the May and June plantings (~55%) at both locations, but C amounts remaining during the July planting were much greater and different (73.7 vs. 87.9%) across northern and southern locations, respectively. These results illustrate that termination of the sunn hemp must occur closer to planting of the following crop to take advantage of N mineralization from the residue. Termination that occurs too early increases the potential that N released from the residue will be lost and unavailable to the following crop, which limits the effectiveness of using sunn hemp in the crop rotation.
Technical Abstract: The tropical legume sunn hemp (Crotalaria juncea) cultivar ‘AU Golden’ has the potential to provide substantial amounts of nitrogen (N) to subsequent crops that could reduce recommended application rates of synthetic N fertilizers. Nitrogen fertilization problems via legumes are often due to asynchronization between legume N mineralization and N uptake by a subsequent crop. A mineralization field trial was conducted to measure mass decomposition and N and carbon (C) amounts remaining from sunn hemp residue produced after 60 d for three planting dates (May, June, and July) during the 2013 growing season at the Tennessee Valley Research and Extension Center (TVS) in Belle Mina, AL and Wiregrass Research and Extension Center (WGS) in Headland, AL. Three incubation periods corresponded to each planting date and ranged from 60 to 120 d. Decomposition and N release at the WGS location exceeded that at the TVS location. Sunn hemp released up to 64% of its total N, sometimes within two weeks following termination. Residue from June and July plantings contained 50.0% and 61.1% N at WGS and 41.5% and 66.5% N at TVS by the end of their respective incubation periods compared to residue from the May planting, which contained 21.1% N at WGS and 47.8% at TVS. Carbon remaining was comparable for residue from the May and June plantings at both locations, but C amounts remaining from the July planting were greater and amounts (73.7 vs. 87.9%) varied across TVS and WGS, respectively. In order to create a more synchronous relationship between ‘AU Golden’ residue N mineralization and uptake by the succeeding crop, termination must be delayed until approximate planting of the following crop.