June 17, 2014
University of Minnesota Extension specialists are out with some tips for managing corn and beans that are sitting in saturated soils. Some the top things to know about flooded corn and soybeans are:
•Young corn can survive flooded conditions lasting for about 2 days under warm temperatures (at or above mid-70 degree F) to 4 days under cooler temperatures (at or below mid-60 degree F). Survivability also is influenced by how much of the plant was submerged and how quickly the water recedes.
•Corn plants that survived flooded conditions should show new leaf development within 3 to 5 days after water recedes.
NOT LOST: A soybean field is flooded by heavy rain and runoff. They can survive is they are not underwater too long.
•Nitrogen loss is a big worry. In sandy soils or heavily tile-drained soils it is possible to move urea or nitrate as much as a foot for each inch of rain. Movement is only approximately five to six inches for each inch of rain in a clay loam or silt loam soil.
•In fine-textured soils, water saturated conditions cause N lost through denitrification. Denitrification rates increase after about a day under oxygen-depleted conditions that result when soil pore space is filled with water. Under these conditions, soil microbes utilize nitrate for respiration, and N is released as a bi-product in gaseous forms that are lost to the atmosphere. For each day the soil remains saturated with water under warm soil temperatures, it is possible to lose as much as 5% of the nitrate-N in the soil. In coarse-textured soils or soils intensively tiled, N loss occurs mostly by leaching below the root zone or into tile lines.
•Nitrogen uptake by corn from emergence through the V6 (six leaf collar) stage only represents about 5% of the total plant uptake. However, starting at about the V8 (eight leaf collar) stage, there is rapid accumulation of N by the plant, with about 60% of the total N uptake occurring between V8 and silking. Thus, it is important that N-deficient areas are detected early, and that supplemental N is sidedressed on these areas as soon as possible.
•Soybeans can survive underwater for a week or more under ideal conditions. Generally, soybeans tolerate 48 hours under water quite well, but flooding for 4 to 6 days can reduce stands, vigor, and eventually yield.
•Soybean yield losses are seldom noted in fields flooded for 48 hours or less. Four days or more of flooding stresses the crop, delays the plants' growth, and causes the plants be shorter with fewer nodes. Flooding for six days or more can depress yields significantly, while flooding for a week or more may result in significant (or entire) losses of stand.
•Some of the main indirect effects of flooding on soybean yields are: 1) root diseases, 2) N deficiency, 3) and other plant nutrient imbalances. Caring for recuperating soybean stands should focus on reducing crop stresses where possible. For example, cultivation should be considered to increase soil aeration and herbicide stress should be minimized or postponed where possible.
For more details, see the complete article online.
Sources; Jeff Coulter, U of M Extension corn agronomist; Seth Naeve, U of M Extension soybean sgronomist; Dean Malvick, U of M Extension plant pathologist; and Fabian Fernandez, U of M Extension nutrient management specialist
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