Last month I wrote that “wet spring weather is the gift that keeps on giving”. My concern was that soil compaction and root diseases that resulted from challenging spring and early summer weather would make our grain crop plants more vulnerable to dry weather if conditions changed in summer and early fall. Unfortunately, August precipitation was less than needed to maintain corn and soybean yield potential in several parts of Missouri. The last two weeks of August were dry enough to decrease crops yields throughout Missouri.
In a normal year, September precipitation has minimal effect on soybean yield except for double cropped soybean after wheat and in some portions of the Missouri where delayed planting is part of a drought avoidance strategy. But, this year I estimate that nearly one million acres of soybean were planted after July 1. Many of these acres have soybean plants that have not matured and would have greatly benefited from normal September precipitation. For good to excellent soybean yields, about 1.2 inches of rain are required each week during grain-fill. Normal September precipitation is greater than 4 inches in most regions of Missouri, except the southeast, so normal would have been welcome.
The following graph presents precipitation amounts for September in five counties distributed among soybean production areas of Missouri. Unfortunately, dry weather continued through the entire month of September. The weather station at Albany (Gentry County) received more than 3 inches of rain on a single day early September. But after that event, NW Missouri was as dry as the rest of the state. Northeast Missouri, including Audrain County, has remained especially dry. This region is more vulnerable to drought stress because soils in a large portion of the region contain a clay-pan that restricts water drainage in spring and reduces root depth throughout the growing season.
With the delayed maturity of many Missouri soybean acres, normal September precipitation could have repaired some of the damage caused by dry August weather. But, Mother Nature did not cooperate. Four of the five weather stations I selected received less than one-third the normal precipitation in September. The 3+ inch rainfall at Albany was so intense that much of it did not soak into soil. After that event, the weather station received only 0.36 inch of rain. Farmers that planted soybean in July understood their crop was at risk from several challenges. But, the degree of drought in August in September was highly unusual and impossible to predict.
Soybean yields from fields harvested so far have been reasonably high. But, these fields were ones that had been planted in a timely manner. Soybean harvest season will continue for longer than normal because of the wide range in planting dates. Fields harvested in mid to late October will be from fields most affected by our dry late summer and fall.
An additional concern is wheat planting. Farmers should be preparing fields for fall planting of wheat. Although soybean harvest might be delayed, many corn fields have been harvested. Unfortunately, soils are so dry that wheat seeds will not germinate until rain returns. Dry soil is not harmful to wheat seed and seeds will sit in dry sol until sufficient water is available to initiate germination. But, we need a substantial rainfall event, not just a small one. Soil is too dry to support wheat seedling growth throughout the soil profile. A small rain may wet the soil where seed has been placed, but not the area where roots grow. A potential concern is that a return to dry weather shortly after germination could kill young newly sprouted seeds.
Unless normal rain amounts return, water conversation strategies are in order. Although soils are quite hard and depth control may be difficult it is recommended to avoid tillage or limit tillage to conserve soils of precious water. Allowing residue to remain on the surface will help reduce water evaporation and may stabilize soil water if rain amounts are small after planting. As dry as it is, chasing moisture with drill depth may be nearly impossible to accomplish. Stay with an ideal planting depth of 1” to 1.5”, it is recommended to not plant over a 2” depth.
REVISED: October 9, 2015