CSI: Crop Soy Investigation

With the growing season rapidly progressing, it’s coming down to the final push for producing a top soybean crop. It’s amazing how soybean yields come down to a few weeks in August. My grandfather always said August rains make beans. Unlike corn, where rain at several key growth stages is important to produce good yields.

Bean yields can be summed up by how many pods produce beans and how much each bean weighs. Many parts of Illinois have received adequate rainfall over the last few weeks that will help support beans as they enter pod-fill stages. With rainfall comes a recharged soil profile and a charged soil solution that will help move key nutrients into the root zone.

Now is a very critical time to be out scouting soybean fields for potential issues, as well as yield potential. It’s important to identify what growth stage each bean field is currently in to understand how the environment impacts soybean plants moving forward.

While scouting soybean fields, take note of anything that looks odd or not right. It may be important to collect a tissue or soil sample to better understand an issue that is showing up as a nutritional deficiency.

Key Lookouts

Soybean Development stages:

Image: Nordby, Dawn. Pocket Guide to Crop Development: Illustrated growth timelines for corn, sorghum, soybean, and wheat. Publication C1389, University of Illinois Extension, Copyright 2004, Board of Trustees, University of Illinois

Table: How a Soybean Plant Develops. Iowa State University. Publication SR 0053.

Bloom formation: Field studies have shown that a given soybean plant could potentially abort an upwards of 75 percent of blooms, therefore some kind of stress or limiting factor is always holding a soybean back. It’s good to scout a field and make flower counts to understand how many field blooms actually end up producing a pod. It will be a lot less than you think.

This information is valuable to understand yield potential, but also to start understanding what the limiting factor was causing bloom loss. The more we can understand soybean growth and development in a given field setting, the better prepared we will be to make decisions in the futures. Always remember, stress or combinations of stress cause flowers and tiny pods to abort. The more you can do to minimize or even eliminate stress, the more pods, and yield, the plant will produce.

Growth stages R3-R4: Reproductive stages for pod formation or elongation from bloom in the upper canopy. This is the optimum stage to apply a fungicide to protect the soybean plant as it goes into pod fill. And if any nutrients are short, they can be applied at the same time.

Growth Stages R5-R6: Reproductive stages for pod fill. During this stage, rapid remobilization of nutrients is taking place to develop and fill as many pods as possible. This is when a soybean plant will have decided how many beans will develop in each pod.

During all the pod development and fill stages, watch out for any herbicide damage (yellow or brown) or insect feeding (spider mites, bean leaf beetles, stink bugs, grasshoppers,. etc.).

Since not all beans are created equal, now’s a great time to understand how your fields filled the row or canopied and when the row closed over. As there are several different bean plant structures and row configurations, it’s important to observe your current product lines along with local or regional plots to see which product will work for your farm and your fields moving forward.

CCA Todd Steinacher is an agronomist at AgriGold. He works with growers to better manage their nitrogen and weed control needs, along with understanding the best way to estimate cost to generate a strong ROI. He is a 2017 Illinois Soybean Association CCA Soy Envoy.