Management options for drought-stressed soybeans
If possible, it’s best to hold off on making any decisions about cutting soybeans for hay until the plants are moving into seed fill (R5 to R6). Beginning seed fill (R5) is the optimal time to cut beans for hay in order to retain digestible nutrients. However, holding off until this stage of growth may not be possible if plants in the vegetative stage are dropping half or more of their leaves already. If too many leaves are dropped, the plants have reduced value as a hay crop. Producers may need to make the decision to cut for hay while the plants are still in the vegetative stage, before the R5 stage, and before the soybeans lose too many leaves.
click image to zoomPhoto by Stu Duncan, K-State Research and ExtensionDrought-stressed, soybeans were baled in this field in Marion County last year. Soybean plants that still have 30 percent of their leaves can produce 0.75 to 1.25 tons (dry matter) of hay per acre, with about 13 percent protein and 48 percent in-vitro dry matter digestibility. The more leaves a plant has, the more hay tonnage it will produce.
Like most legumes, soybean hay quality is fairly good, ranging from 15 to 20% protein.
Soybean hay quality is roughly comparable to mature alfalfa. Once soybeans reach full pod and seeds begin to swell, quality begins to decrease because soon after this stage, leaf yellowing and leaf drop are initiated. In addition, the highest quality part of the plant is the leaf, and the least palatable portion is the stem, which will often be left as waste if fed directly to cattle in a bale. Grinding the hay or ensiling the soybean will increase the total dry matter consumed by the animal.
The “gray area” is where there are plants with 30 to 50 percent of leaves still remaining. Those have the capability of filling pods if it rains and of making a soybean harvest that is worth more than the price of the hay. But that's a pretty big “if” in parts of Kansas this year, given how spotty the rains have been and how long the crop has been subjected to triple-digit temperatures.
The producer’s decision this year will depend partly on when the soybeans were planted. Soybeans that were planted June or early July are probably still young enough to withstand drought stress for several more weeks without dropping leaves. Soybeans planted in May or early June will be more vulnerable to rapid leaf loss at this time of year.
By the early reproductive stage, the effects of prolonged heat and drought are critical. Under drought conditions, soybeans in early reproductive stages will have increased flower and pod abortion. In later reproductive stages, prolonged drought will cause pods to be small, with fewer and smaller (or shriveled) seeds than normal.