Dry Conditions and Yield Predictions

We know what happens when soybeans are planted in dry conditions, they simply cannot germinate. That has not been the case this past spring, but now we are looking at some hot weather in the forecast. This year’s planting conditions made for a slow start on soybeans and they are relatively shorter than what we are used too, so how will soybeans respond?

Until recently we did not receive a lot of moisture in many parts of Illinois. That, coupled with a tough May, did not allow for much soybean growth. During vegetative growth, soybeans can withstand moisture stress relatively well, but shorter plants and less canopy coverage can affect several things during the reproductive stages:

A shorter plant that has not closed its canopy can let a lot of sunlight reach the soil. Ninety degree plus days can stress the plant enough to reduce nodulation. This decreases nitrogen fixation and compounds stress on the soybean plants; adding surplus nitrogen rarely helps alleviate this stress. Adequate nodulation can be measured at flowering by checking roots; 7-14 nodules on the tap root is ideal.

Right now, May planted soybeans are reaching the R2 growth stage, this is full bloom. Drought conditions during this time will cause the plant to abort flower production. A sure sign of stressed soybeans is when the leaves flip over to reflect more sunlight and conserve moisture. As much as stress can cause a soybean to abort flowers, new blooms can form and produce when moisture needs are met. Pod abortion can also happen during the R3 stage if conditions persist. Although late season rains are often much desired by most growers because new flowers can successfully set pods up to the R5 stage.

The biggest impact on yield for soybeans is a drought after the R5 stage when the number of pods per plant is reduced and additional flower set is no longer an option. In the R6 stage, seed size can be impacted. At this stage, the plant has green seed set in the pods, but growth is not yet finished, which results in the seed maturing before pods finish filling. Drought stress after these stages will not cause a reduction in yield. You can check for R7 stage when one pod on the main stem has reached mature pod color.

There are several ways to help alleviate moisture stress in soybeans, with irrigation being the simplest. When irrigation is not an option, finding a way to conserve moisture is the best management tactic. This can be done with reduced tillage systems and leaving residue to cover the soil. Keeping soil fertility up and healthy as well as reducing compaction can also aid in moisture retention.

When it comes to drought conditions, soybeans can handle stress a lot better than corn. Their ability to produce new seed when times are tough is truly unique. Genetics keep getting better with lots of research and development shifting to soybeans in most recent years. A lot of that research is geared towards increasing yields for more profitability, but agronomics like drought tolerance do not get overlooked.