Flood Damaged Soybeans

Much of the province received welcome showers over the weekend. A few areas were hit with heavy rains that caused flooding in low lying areas. In most cases water drained away quickly but standing water could still be found in some fields two days after the rain. See picture #1.

 June 1 004 Flooded soybeans on June 1st, 2015 at Ridgetown, ON.

How long can soybeans survive flooding? The length of time soybeans will survive depends on temperature, cloud cover, and growth stage. If the beans are small and conditions are cool as well as being cloudy soybeans can survive up to a week completely submerged. Under more average summer weather they may survive for as little as 2 days.  Warmer temperatures and sunlight speeds up plant respiration using up available oxygen. Flooding can be divided into two categories. 1) Water logging when the roots are under water and 2) complete submergence when the whole plant is under water. Water logging is more common and often causes yield loss across a larger portion of the field. Yield losses may be minimal if the field is only water logged for 2 days or less.  If the field is water logged for more than 4 days yield losses can be significant. Some research has shown that water logging can reduce soybean yield up to 43% during the vegetative growth stages and 56% during the reproductive stage. Yield losses are the result of reduced growth, nitrogen fixation, photosynthesis, and diseases. There are a number of diseases that can take advantage of the wet conditions including phythophthora, rhizoctinia, and pythium, amoung others. Soil type also impacts the amount of damage. Flooded clay soils suffer more than silt loam soils when flooded (Scott et al, 1989). During the V4 growth stage, flooding resulted in a yield loss of 1.8 bu/ac per day on a clay soil and 0.8 bu/ac per day on a silt loam soil . The impact of flooding during later growing stages was considerably higher.

Plant survival from submergence can be assessed within a couple of days after the water drains. Generally, by the time conditions are dry enough for a possible replant it’s clear if the plants have survived. New growth will be evident if the plants have survived.

Scott, H.D., J. DeAngulo, M.B. Daniels, L.S. Wood. 1989. Flood duration effects on soybean growth and yield. Agron J. 81:631-636.