Corn & Soybean Replant


Corn & Soybean Replant

Most farmers have finished planting for the first time but may be looking to replant. Replanting corn can be a difficult decision. Young plants can recover especially if the damage is above ground. However, below ground damage from insects, disease, compaction, saturated soils, or fertilizer injury are more difficult for corn to recover. With the cold nights lately and cloudy days, sometimes sunshine and warmer temperatures allow your crops to recover, making that decision easier to make. First, determine how widespread the damage is and how healthy the plants are that are remaining on the whole field. Aerial Drones can help cover a large area but you still need to inspect the remaining plants to determine their health. 

Dr Robert Nielson, Purdue University offers these suggestions on corn replant decisions. Most modern corn varieties are fairly tolerant of both low and high populations. Based on 10 years research, populations ranged from 23,500 to 40,000 seeds per acre. Based on those yields and the cost to replant, populations above 23,500 are acceptable based on Dr. Nielson’s research. Dr. Nielson based his recommendations on $3.50 corn per bushel and $240 per acre to replant. Most farmers want perfect stands but it does not always pay based on potential profit per acre. 

 Yield potential is difficult to estimate in replanted fields due to so many factors to consider including weather, insect, disease, and timing. With warmer weather, seed germinate faster so the best strategy is to plant the seed amount needed to reach a targeted population. Farmers may want to consider using a shorter maturity corn to match up with the existing corn if spot replanting. Late planted long maturity corn is more suspectable to some late season foliar diseases like gray leaf spot, northern corn blight, etc. 

The next question is do you totally replant by destroying the original stand or fill in with some extra seed? Filling in seed by planting next to an existing stand causes shading and puts the new seed at a disadvantage. If the stand loss is less than 25%, filling in corn may be attempted. Expect some competition and higher moisture at harvest. Often, filling in corn is done in drowned out areas or certain areas where the corn stand is really thin. Terminating an existing stand is also difficult due to lack of acceptable herbicides, especially traited herbicide tolerant corn varieties. Many companies offer free replant but not all. The cost of seed can range from zero up to $120 per acre. Fuel, labor and equipment costs also must be considered along with additional herbicides, insecticides, fungicides, and possibly higher drying cost. 

On soybeans, at what point do you replant soybeans? Most farmers are planting 180-200 thousand seeds per acre. An Ohio State University study found that soybeans at 85-100 thousand seeds per acre may yield as much as the higher soybean populations. The caveat is that the plants have to be evenly spaced in the field so that the soybeans plants can branch out. With large gaps or patchiness, replanting is a safe bet. Once soybeans have at least 1-2 trifoliate leaves, they can tolerate replanting as long as they are not completely cut off. Soybeans have more flexibility than corn in replanting. Double crop soybeans are often planted after wheat, so soybeans have time to grow and put on pods. However, on all crops, adequate moisture is the key to making grain. 

On wheat, early planted wheat (around fly free date) is at least 7-10 days, possibly 2 weeks ahead of schedule for harvest. With adequate moisture and warm winter weather, the wheat harvest should be good as long as the wheat is healthy. Several early planted wheat fields are already starting to turn. If wheat comes off early, many farmers will want to plant double crop soybeans. 

What about the straw? Some farmers chop it and leave it on the field. It is best to spread it out evenly behind the combine to reduce to much chaff in one spot. Lots of chaff promotes insects, slugs, and voles. While some farmers may want to keep the straw to increase soil organic matter, most SOM comes from the roots, not the straw. Baling it off can be beneficial for getting the double crop soybeans or cover crops to grow faster. Ideally, at harvest, leave several inches of stubble to keep the soil in place. Chaff and chopped straw tends to have a toxic (allelopathic) effect on growing crops. Straw and chaff have a high carbon:nitrogen (C:N) ratio which means the microbes need extra soil nitrogen to decompose and stabilize the organic matter. Enjoy your summer!