Managing corn and soybean fields submerged by recent heavy rains

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.      

The heavy rains have continued and have resulted in isolated areas of severe ponding in parts of the state. This problem has left growers struggling with the question of whether or not to replant water damaged stands and how to manage fields that have yet to be planted.

Assessing plant viability

The first step is to determine whether plants survived being under water or in saturated soil. Seed that has germinated but not emerged is also susceptible to excessive water damage. In corn, most of the plant mortality will be in localized low areas of the field that were subjected to standing water. The survivability of plants or seedlings under water is dependant on temperature, growth stage, variety, soil type, nutrient status and other factors but is generally in the 24 to 96 hour range. In cool temperatures, plants will survive longer as respiration slows. Conversely, when temperatures warm up, plants consume oxygen quicker, and submerged plants will not survive as long. In cool conditions, corn can survive four days submerged. With soil temperatures warmed up in the upper 70s, submerged corn may survive for only 24 hours. Fortunately, the cool temperatures experienced throughout much of Michigan while plants were submerged has likely increased the chances for stand recovery where the duration of flooding was not excessive. In soybeans, soilborne disease such as pythium and phytopthora can result in plant mortality beyond those areas that were under water. In assessing a soybean stand, for more fertile soils, a minimum of 80,000 to 100,000 living plants per acre are needed to approach the full yield potential of the field. In poorer soils, 100,000 plants per acre are needed. In situations with less than the minimum number of plants remaining, the cost of replanting should be weighed against the expected increase in yield to determine if replanting will be economically feasible.

Generally, the time it takes for submerged soil to dry out enough to get equipment on for replanting, is usually time enough to make a determination whether or not plants have survived. However, it can be difficult to determine survivability when plants are covered with soil and plant residue left behind by receding water. In these cases, split a plant lengthwise through the stem. The growing point should be relatively firm and white or cream colored. Darkening or softening of the growing point indicates a nonviable (dead) plant. A step by step worksheet (MSU E Bulletin # E-1961) to guide producers through a replant decision is available through local MSU Extension offices.

How late can I plant/replant and still expect a reasonable chance of maturing grain?

There is still time to replant drowned out corn or soybeans with varieties having appropriate maturities in Michigan. If the rains continue and field operations are delayed until the end of May, growers may want to consider planting an earlier maturing, short season hybrid. The lower half of the Lower Peninsula will on average, accumulate 2000 to 2200 growing degree days from June 1 to first frost. This is sufficient to mature 80-90 day corn and soybeans with a group II or less maturity classification. It is not recommended to plant corn after June 15. The rule of thumb most commonly applied to lost yield potential for delayed planting is one bushel per acre per day after May 10, and up to 2 bushels per acre per day after June 1. Soybeans can generally be planted up to the end of June, although yields will likely be reduced commensurate with the later planting date.

Considerations for replanting into existing stands

When replanting flooded out areas that still have some viable plants, it is usually best to tear up the existing stand and start over with an even-emerging stand. This may require you to manage the area differently than the non-flooded parts of the field with regard to activities based on plant growth stage such as weed control and time of harvest. Other considerations in flooded out areas include potential weed problems from weed seed brought in by encroaching waters, herbicide residue washed in from adjacent fields, loss of herbicide control from excessive leaching or erosion, loss of nitrogen through denitrification or leaching and increased incidence of phytophthora and other root disease. Nodule function in soybeans is also reduced in saturated soil. However, nodule activity resumes to normal levels once the soil dries out. Scout fields closely for these factors and use a PSNT soil test to determine nitrogen losses.

Other considerations for late planting/replanting

Following are other considerations with late planting that I have compiled including some from Bob Nielsen at Purdue University and Jim Beuerlein at Ohio State.

Bt corn hybrids. For most Michigan corn production systems, economic benefits from the use of transgenic Bt corn hybrids resistant to corn borers are more likely to occur with delayed plantings, especially when there is earlier planted corn in the vicinity. Consequently, growers may want to consider switching some of their late-planted intended non-Bt corn acreage to Bt hybrids as insurance against the higher risk of infestation by late brood corn borers.

Previous herbicides applied. Before replanting, review potential label restrictions associated with previously applied herbicides.

Seeding rates. There is no need to consider changing seeding rates for corn simply because planting is delayed. Optimum seeding rates for most growers’ fields range from 28,000 to 33,000 seeds per acre. Lower rates (low to mid-20’s) are suitable for fields with yield levels historically near or below 100 bushels per acre. Unlike corn, soybean has a great propensity to compensate or “flex” when plant populations vary. Therefore, the optimal planting population range is wider for soybean than it is for corn. Determining the minimal scale of that optimal soybean planting population range will optimize profitability and still maintain yield. As a starting point, begin with a planting population of 175,000 seeds per acre for drilled systems and 130,000 seeds per acre for 30 inch rows and then adjust down or up from there based upon field productivity, planting date, and planting conditions. When planting late, resulting soybean plants will be smaller than earlier planted soybeans. To compensate for the potential yield decrease of smaller plants due to late planting, increase your planting population by 20%.

Seeding depth. The key factor that should be used for determining seeding depth for corn is the importance of adequate and uniform soil moisture in the seed furrow. Some might say this is a moot point given the current soggy soil conditions. Remember, though, how quickly Mother Nature can change and how quickly shallow-placed seed can find themselves in bone-dry soil. A seeding depth of 1.5 to 2.5 inches for corn and 1.0 to 2.0 for soybean is acceptable over a range of soil conditions. Shallower depths for corn are risky if rains stop altogether and surface soils begin to dry rapidly.

Field tillage operations. Remaining pre-plant field operations should be scrutinized carefully to determine whether they are truly necessary. With today’s modern corn planters, there is little reason to overly-prepare a field to create a picture-perfect seedbed. In delayed planting situations, every day wasted overworking a field is a day lost to planting and represents lost yield potential. Furthermore, unnecessary tillage operations on soils that may be marginally wet increase the risk of creating tire and tillage compaction layers that can haunt root development and corn health later if excessively dry conditions suddenly become the norm.

Planter sidewall compaction. Another concern to watch for is the potential for significant root restriction by severe sidewall compaction when a rapid shift from wet to dry conditions occurs. If at all possible, avoid planting fields when soil moisture conditions favor the smearing of furrow sidewalls by the coulters or double-disc openers of the planter. The potential yield loss from planting in fields that are too wet far outweighs the potential yield loss from delaying planting until field conditions are suitable. Planting in wet conditions often results in sidewall compaction of the seed furrow. This causes poor seed to soil contact which has several negative consequences including: reduced germination and poor stands; uneven emergence which reduces yield due to plant-to-plant competition; and, restricted root growth which compromises the plant’s ability to withstand moisture stress later in the growing season. In addition, the limited rooting can result in phosphorus deficiency even though soil test phosphorus levels are adequate. This occurs because the plant uses all of the phosphorus that is immediately available within the seed furrow. The roots of these plants will appear thickened and gnarled – a visual sign of compaction. After a period of time, the roots may break through the compacted sidewalls and explore more of the soil. As this occurs, the phosphorus deficiency may be overcome and the plant will begin growing normally again. However, the sidewall smearing and compaction is likely to have set the crop back by a week or more as it tries to overcome the inhospitable soil environment.

Nitrogen fertilizer applications. Because the recent flooding will likely delay planting until the end of May or early June, growers may want to consider backing off on their intended nitrogen fertilizer application rates due to the expected lower yield of the late-planted corn. The rule of thumb most commonly applied to lost yield potential for delayed planting is one bushel per acre per day after May 10, and up to 2 bushels per acre per day after June 1. Consider using a pre-sidedress soil nitrate test to further fine-tune your nitrogen application rates.

Starter fertilizer. Where soil phosphorus and potassium soil test levels are adequate or better and tillage is other than pure no-till, consider eliminating starter fertilizer use for the remainder of this season’s corn planting. Soil temperatures at planting from here on (should) be more than adequate for rapid corn germination and early seedling growth, thus greatly diminishing the value of starter fertilizer. Eliminating starter fertilizer will not only reduce your costs, but will save some time during the planting operation. No-till corn, however, will likely continue to benefit from starter fertilizer applications, especially the nitrogen component, for planting throughout the remainder of the month.

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