Location: Dairy Forage ResearchTitle: Sorghum-sudangrass responses to nitrogen and tillage following polyphenol-containing legumes, alfalfa, reed canarygrass, and kale
Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/12/2017
Publication Date: 9/7/2017
Citation: Grabber, J.H., Yost, M.A., Coulter, J.A., Sullivan, M.L. 2017. Sorghum-sudangrass responses to nitrogen and tillage following polyphenol-containing legumes, alfalfa, reed canarygrass, and kale. Agronomy Journal. 109:2050-2062.
Interpretive Summary: The nitrogen-use efficiency of crop rotations on dairy farms must be improved to decrease input costs for fertilizer and to avoid leaching of nitrate to groundwater. Polyphenols are natural substances that bind to other plant components including proteins that are rich in nitrogen. Low concentrations of polyphenols in forage legumes are desirable for improving the protein-use efficiency, growth, and milk production of livestock. We conducted this study to see if low concentrations of polyphenols altered the cycling of nitrogen in short-term crop rotations where one-year old stands of forage legumes were killed and followed for two years with a nitrogen-demanding crop, namely sorghum-sudangrass. This short-term rotation study also evaluated how different types of forage crops (i.e. legumes vs. non-legumes) influenced the production of sorghum-sudangrass grown on tilled and untilled soil amended with varying amounts of nitrogen fertilizer. We found that polyphenols did not influence the short-term cycling of nitrogen and growth of sorghum-sudangrass and concluded that additional field studies are needed to assess the long-term benefits and limitations of growing polyphenol-containing forages in crop rotations. Our study revealed that first-year sorghum-sudangrass grown after forage legumes such as alfalfa produced greater yields and required 40% less fertilizer nitrogen during the growing season than sorghum-sudangrass grown after non-legumes such as grasses or kale. We also found that tillage increased yields of sorghum sudangrass grown after grasses, and it increased yields and reduced nitrogen fertilizer requirements of second-year sorghum-sudangrass grown in all tested crop rotations. Adjusting fertilizer nitrogen rates for sorghum-sudangrass according to crop rotation and tillage practices also reduced the risk of nitrate leaching from soil. Implementation of our findings will improve profitability and reduce risk of nitrate contamination of groundwater by farms growing nitrogen-demanding crops such as sorghum-sudangrass for livestock feed.
Technical Abstract: The collective effects of protein-binding polyphenols (PBP), preceding forage type, tillage, and fertilizer N on soil NO3-N production, N uptake, and dry matter yield (DMY) of N-demanding crops such as sorghum-sudangrass [SS, Sorghum bicolor (L.) Moench x S. sudanese Piper] are poorly understood. These factors and response variables were evaluated in Wisconsin by growing SS for 2 years with 2 harvests yr-1 using no-tillage or conventional-tillage and fertilizer N rates of 0, 33, 67, 112, or 220 kg N ha-1 harvest-1 following 1-yr stands of birdsfoot trefoil (Lotus corniculatus L.) containing condensed tannins (CT), o-quinone producing red clover (Trifolium pratense L.), alfalfa (Medicago sativa L.), reed canarygrass (Phalaris arundinacea L), and kale (Brassica oleracea L.). Herbage PBP was associated with reduced in vitro soil NO3-N accumulation, whereas herbage nitrogen yield (NY) primarily affected in situ soil NO3-N accretion and N uptake and DMY of SS. The DMY of first-year SS (SS1) following legumes exceeded that following kale in both tillage systems, but rotational benefits of grass equaled legumes when conventional tillage was used. To maximize net return, SS1 required 75 kg N ha-1 harvest-1 following legumes and 125 kg N ha-1 harvest-1 following nonlegumes. Depending on tillage system and harvest, SS2 required 50 to 130 kg N ha-1 harvest-1 to maximize net return. To optimize DMY and profitability of SS following short-term forages, producers should grow legumes to maximize NY before SS production, use conventional tillage following reed canarygrass, and adjust N rates according to crop sequence and tillage practices.