Soybeans are moving from flower to pod development and fill. So, what’s happening?

As our soybeans are currently in the reproductive stages – most around R3 or later – many producers are done with their trips across the field with herbicides, fungicides and/or insecticides. The crop is now in Mother Nature’s hands, right? Or is it? I won’t argue the value of a million-dollar rain at the right time, but what if it doesn’t rain? What if it is excessively hot, or excessively humid? What if there were ways to lessen nature’s negative effects on our crops when things aren’t ideal? Many of these questions have answers when we consider plant hormones and the importance of maintaining the optimal hormonal balance.

First off, let’s be clear; I’m not saying we offset the effects of less-than-ideal conditions. But I am suggesting is there are ways to lessen the negative effects Mother Nature sends our direction.

This all begins when we control two plant hormones – abscisic acid (ABA) and ethylene. We all have seen the effects of ABA in our fields, especially this time of year. When you look out at your soybean field as the day progresses, the field begins to show a silver tint as leaves are flipping and curling up because of the heat. This is an ABA response by the plant – it closes the stomata to help preserve water. This can help the plant survive, but when this occurs, your photosynthetic activity stops as the plant can no longer bring in additional CO2 to continue to make sugars. These sugars are essential for the plants’ survival and grain filling.

As ABA continues to keep the stomata closed, reactive oxygen species (ROS), or free radicals, begin to increase in the plant. As stress continues, these free radicals damage and destroy plant cells, and the production of excessive stress ethylene begins, causing cell death. Ethylene is a gas given off by the dead cells that not only affects the cells it is produced in, but also speeds up cell death in neighboring cells. The more cells that die, the more ethylene is produced and makes cell death even faster. This continues in a snowball, rolling effect.

As a survival mechanism, plants allocate valuable energy to controlling the effects of these damaging levels of ethylene rather than using this energy to fill grain. So, the big question is, what can we do to control these two hormones?

Ideally, we precondition plants to deal with stress by ensuring we have a strong root system and all our plants’ nutritional needs are met. When we get into situations that limit the transpiration of water, thus limiting the transport of cytokinin to the upper part of the plant, a foliar application of cytokinin can help offset the negative effects of ABA and ethylene.

Adding a cobalt-containing product that can be absorbed such as Stoller’s Keylate Cobalt can block ACC oxidase in the plant. ACC oxidase is an enzyme that catalyzes the precursor to ethylene production. By blocking the plant’s ability to produce ethylene, its negative effects can be reduced or eliminated. When we do this, we essentially help the plant more efficiently deal with Mother Nature’s curveballs.

As a result, the plant can use its energy resources to hold onto more seeds and increase the overall seed size. If we limit late season stresses and increase the seed size by a minimal 0.05 of a gram per seed, an average 50-bushel yield now becomes 65-plus bushels. Seed size is the third and final component of yield, and it is often the most critical as small differences have huge yield implications. Controlling and limiting ABA and ethylene late in the season is a factor in increasing seed size and attaining top yields.

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About the Author: Rob Jarek