Evaluation of yield and nutritive value of forage sorghums with different irrigation or fertilization rates

Authors: GRISHAM, ABBEY - University Of Wisconsin; AKINS, MATTHEW - University Of Wisconsin; REMICK, ELIZABETH - University Of Wisconsin; SU, HUAWEI - University Of Wisconsin; Coblentz, Wayne

Submitted to: Popular Publication
Publication Type: Popular Publication
Publication Acceptance Date: 5/11/2017
Publication Date: 6/15/2017
Citation: Grisham, A., Akins, M.S., Remick, E., Su, H., Coblentz, W.K. 2017. Evaluation of yield and nutritive value of forage sorghums with different irrigation or fertilization rates. Popular Publication. Project Reports 2016. Midwest Forage Assn. St. Paul, MN.

Interpretive Summary:

Technical Abstract: Dairy heifers require moderate quality forages to maintain adequate body weight gains (1.7 to 1.8 lbs/day). Corn silage is a high-energy forage (70-75% TDN); however, older dairy heifers (900 to 1200 lbs) require only 60-62% TDN. When corn silage is used as a main part of the diet, excessive weight gains and body condition can result, particularly when compared to heifers offered lower-energy diets that include high-fiber forages. Excess bodyweight and condition potentially leads to calving difficulties and metabolic problems that lower milk production and profitability for dairy producers. Sorghum and sorghum-sudangrass have moderate nutritive value (higher fiber, lower starch) and provide an alternative for reducing excessive weight gains. The objectives of this study were to evaluate the yield and nutritive value of various forage sorghum, sorghum-sudangrass, and sudangrass varieties with different rates of irrigation (Hancock Agricultural Research Station) or nitrogen application (Marshfield Agricultural Research Station). Sorghums were able to produce similar forage yields to corn with reduced irrigation and nitrogen fertilization in Wisconsin. Based upon these data, sorghums can produce similar forage to corn with 50% or less irrigation; however, the well distributed rainfall events in 2016 may have limited moisture stress for sorghums and corn. Years with more pronounced dry periods may prove that sorghums are even more beneficial compared to corn when there is an increased need for irrigation. Yield responses to nitrogen fertilization declined with additional nitrogen. It appears that a rate of 50-100 lbs total N/acre produced a maximum yield with smaller increases at 150 lbs N/acre. Producers should consider previous crops that may provide N credits (legumes), and adjust for N needs accordingly. The sorghum forages evaluated in this study would meet dairy heifer energy needs more closely than corn silage. With the high forage yield potential and better responsiveness to irrigation and a lower requirement for nitrogen fertilizer, producers could use these forages to reduce input costs while still maintaining an adequate forage inventory.