Should I harvest soybean for forage or grain?
By Roger Borges, Professor of Agronomy, University of Wisconsin-Madison, Extension Soybean and Small Grain Specialist , 608-262-7975 rborges@wisc.edu
During dry years, Wisconsin soybean growers frequently ask if they should make forage out of their soybean crop. To answer this question, growers must consider their own needs for forage, the price prospects for forage versus grain yields, the development stage of the crop, the limitations imposed by the pesticides used in the field, and logistics. The 2003 forage supply in Wisconsin is very low for three reasons: small carry over from 2002, significant winterkill losses on alfalfa fields and drought in summer. Forage prices are expected to be higher than normal throughout the winter. Because of the forage shortage Wisconsin growers are looking for other feed sources.
When should I harvest to maximize the tonnage and protein content of soybean forage?
Studies conducted by the University of Wisconsin Agronomy Department in the late ‘80s showed that soybeans can make forage similar in quality to alfalfa. However, it is critical to observe the proper development stage of the soybean in order to maximize its feed value. Early in the growing season, soybean has high digestibility. Later in the growing season, tonnage will be greater.
For instance, at R7 growth stage (when the first pod naturally turns brown) soybeans are likely to produce about three times more tonnage than at R1 (when soybean starts to flower). So, how can growers decide on the best compromise between quality and quantity? Fortunately, the green soybean grains can make up for the loss of tissue quality. The grain is rich in high quality, easily digestible protein. Assuming a normal year, during the grain filling phase, the soybean grain would grow from 1 to 1.5 bushels an acre per day. The fast growth will tend to compensate for loss of tissue quality until the soybean plant starts to senesce. So, the optimum soybean forage quality/quantity compromise is typically reached just before the plants start to turn and drop leaves. Conversely, the lowest quality will be achieved at R5 growth stage (just before the plants start filling the seeds). At R5 the vegetative part of the soybean plant already lost some of its digestibility and the grain is still not there to boost the protein content.
Adapted from Hintz et. al., 1992.
What to expect from a drought stressed field
Soybean plants on severely stressed fields may die prematurely. Typically plants will turn color and defoliate in certain spots while the rest of the field is still green. A few strategies could be used to maximize the quality and quantity of the soybean forage produced. Depending on the shape, size and geographic distribution of the “bad” spots, the grower might consider cutting those spots first. That would give the “green areas” a chance to fill the seeds a little further and perhaps take advantage of future rains.
Soybeans may be chopped and fed directly to the cattle. It is also suitable for silage. However, the recommended method is to ensile corn and soybean mixed. Corn will provide most of the sugars needed to support the fermentation process and soybeans will raise the average protein content of the silage compared with corn alone silage. Soybean plants at seed filling that have been under drought stress since the beginning of the podding phase might produce one to two tons per acre of dry matter. Making soybean hay is also a possibility, but it tends to be a dusty hay. Soybean forage is highly palatable and readily accepted by ruminants.
Do I need to consider which and when pesticides were applied in the soybean field?
YES! Pesticide labels describe the minimum number of days between spraying and harvesting (or feeding) soybeans. Make sure to check and apply the label information on the products used in your field.
References
http://www.uwex.edu/ces/crops/uwforage/SoybeanForage.htm
Hintz, R.W. and K.A. Albrecht 1994. Dry Matter Partitioning and Forage Nutritive Value of Soybean Plant Components. Agron. J. 86:59-62.
Hintz, R.W., K.A. Albrecht, and E.S. Oplinger. 1992. Yield and Quality of Soybean Forage as Affected by Cultivar and Management Practices. Agron. J. 84:795-798.
Sheaffer, C.C., J.H Orf,., T.E. Devine, and J.G. Jewett. 2001. Yield and Quality of Forage Soybean. Agron. J. 93:99-106.
