Illinois has been plagued with frequent, heavy rains for the past thirty days. Planting was delayed, soybeans had to be replanted and some farmers had to take preventative planting. These frequent rains have kept the soil saturated and ponded water in fields—to the point that some fields truly looked like ponds. Excess soil water caused by heavy rains and flooding is detrimental to soybeans.
Saturated soils, whether ponded or not, have little or no oxygen in the soil. Soybean roots require oxygen to respire and they get that oxygen from the soil. Because water contains very little oxygen, respiration is reduced in waterlogged soils. And the longer the soil remains saturated, the greater the crop damage and potential for yield losses.
Soil texture, conditions, landscape and presence of drainage impact how much water soil will hold and for how long. Also, the warmer the conditions, the faster oxygen is depleted and the more quickly plants become stressed. And oxygen is depleted faster with larger plants growing in ponded conditions.
If soils are waterlogged for 1 to 2 days, yield losses are minimal—as long as plants are small and air temperatures cool to moderate. However, saturated or ponded conditions lasting for 4 days or more cause significant yield reductions. If the waterlogging lasts for 6 or 7 days or more, plants probably won’t survive.
So if fields were ponded, what are your next steps? First, note how long the field was ponded—was it 2, 5 or 8 days? Second, once the water recedes and soils drain, you have to wait a couple days to see if the plant will recover. If stem tissues remain healthy and white, the plants will recover. However, if they turn brown and necrotic, they will probably die off.
Of course, after the water recedes and if the plant survives flooding, root and stem rots can infect the plant. Phytophthora root and stem rot is the most likely culprit because wet soil conditions and warm temperatures encourage this disease. Fungicide treatments will be ineffective as this stage.
Last, saturated soils reduce nitrogen fixation and root nodules may die due to lack of air. Lack of nitrogen fixation results in yellowing and slowed growth.
Did you experience extensive water ponding in June and, if so, how did your soybeans fare?
Agronomist Dr. Daniel Davidson posts blogs on agronomy-related topics. Feel free to contact him at firstname.lastname@example.org or leave a comment below.