Making corn and soybean replant decisions
May 7, 2019
Is it time to re-plant now or when is the right time you might ask? Now is the time when producers should be out in their fields assessing to determine if replanting is necessary. Various conditions can cause reduced corn stands; it is important to identify the cause before deciding whether to replant. The difficulty of these decisions can stem from predicting how the effectiveness of replant will be along with the combination of planting date and changing environmental conditions. Again, replant decisions are never easy and are ultimately determined by which decision provides the greatest net income. Each field will have its own set of circumstances that will influence the decision. Recent thunderstorms have wreaked havoc on localized area with lots of heavy rain causing flooded areas in fields that may cause stand losses. Small corn plants are not tolerant of flooding and may succumb to this condition in 1-3 days. Soybean shows slightly better tolerance to flooding but still will not tolerate these conditions for very long.
Corn seed is very sensitive to soil and soil water temperatures below 50°F during the first 48 hours after planting. Soil temperatures regulate whether seeds will germinate or not. The ground temperature needs to be 50°F for a corn seed to start the germination process. During the first 24 to 48 hours the seedling imbibes or absorbs water and swells. Cold imbibition, cold chill imbibition, or cold shock are all terms used to describe the same affects caused to seedlings. If temperatures are below 50°F, cells can rupture, which can lead to nonviable swollen kernels and aborted growth of the root and shoot. Cold temperatures will interfere with proper hydration that could lead to chilling injury and reduced yield. When temperatures remain above 50°F for the first 48 hours after planting, seeds can be expected to germinate. If the soil temperature dips below 50°F after the imbibition period, it usually isn't an issue as the seed will be taking in water through a slower process known as osmosis. Also, with cooler temperatures germination will be delayed but should occur.
Cold stress also can occur in soybean seed if the soil temperature falls below 50°F during the first 48 hours after planting. The germination stage of soybean consists first of a very fast uptake of water (imbibitional phase) followed by a much slower uptake of water (osmotic phase). Chilling during the first phase can cause severe problems because the imbibed water is needed to rehydrate the cotyledons and embryo to the point that cell membranes become functional. Cold temperatures interfere with proper hydration of those membranes. The imbibitional phase typically is not very long (less than 24 hours) and can occur with relatively little soil moisture since the seed is dry. Thus, getting a cold rain 0-24 hours after you plant can lead to chilling injury in soybean and lower stands. A key point to consider is that chilling injury on soybeans is likely to be greater if soil temperatures were cold (conservatively, less than 50°F) at planting rather than becoming cold 24 or more hours after sowing. The longer the seed is in the ground at warm soil temperatures before cold temperatures occur, the less likelihood there is of chilling injury. The bottom line is: You can consider planting soybeans if you think soil temperatures won't get cold (less than 50°F) for at least 24-48 hours after planting. If you planted two or more days before the cold rain, there should be no imbibitional injury due to cold temperature.
Feel free to call the office at Nichols Ag, O’Toole or Muscatine Ag and talk to one of our trusted advisors.