Soybeans are a tap root crop. This is a not a good example of a tap root. This is a no-till field following corn in 2014. Part of the field is fine, but in spots where heavy rain accumulated the top 4 inches of soil has turned to a brick.
This picture is obviously up side down, but you get my point. The effect of soil conditions on soybeans was evident 6 weeks ago, even in well drained loamy soils. But, you had to look close to find it.
These weak roots from a different field taken back in June are suffering from rhizoctonia root rot. The root problems have led to similar stunting symptoms and reduced stands as the first field shown above.
While corn has on average appeared to improve, soybeans have faded due to the same tight soil problems which plagued the corn crop. That is because the peak demand for nutrient and water uptake in soybeans is now. In a corn crop the poor spots are hidden from view by the good spots, but the soybean crop is reverse. The poor spots become more evident.
The number one solution is simple. More rotation is required. More wheat and fibrous rooted cover crops are needed. Soybeans contribute zero to soil quality. The temptation to deep rip these poor soybean fields after harvest must be resisted. Steel's contribution to long term soil quality is not much better than the soybean.
To add insult to injury, soybean aphids are back. I took this picture 3 weeks ago and at that time hot spots were extremely scattered. That has changed. Folks to the north of us have been spraying for several weeks. Now practically all fields from St Marys through St Pauls have aphid numbers at threshold, which is 1000 aphids per plant. The reason 250 aphids and increasing is quoted as a trigger is that it gives you time to organize a spray program. By the time you get there, hopefully the numbers are still less than a 1000. Predator numbers have been extremely low to date which only gives us another reason to pull the sprayer out one more time.