When are soybeans mature?
Soybean yield is derived from plants per acre, pods per plant, seeds per pod, and weight of seeds. Of these components, plants per acre is the one most controlled by the producer through seeding rate.
Assuming a reasonable or acceptable plant population density that will result from planting high quality seed at a pre-selected rate into usually ideal conditions for emergence, this leaves pods per plant, seeds per pod, and weight of individual seeds as the yield components controlled by the plant and its environment.
These latter three soybean yield components are sometimes lumped into two basic ones-seeds per acre (combines pods per plant and seeds per pod) and seed size, which is usually expressed as seeds per pound.
The goal of a soybean producer is to maximize the number of seeds per acre and weight of individual seeds to realize maximum yield potential of a particular variety. The controlling factor in this effort is usually water, assuming proper soil fertility and control of pests and weeds. Lack of optimum water at pod set and during seed fill will result in decreased yields because of fewer and smaller seed.
A producer’s capability to irrigate should ensure that the maximum number of pods are set, that the maximum number of seed per pod develop, and that the seed that are developed will attain their maximum size for a given variety. Thus, the critical decisions involved in irrigation management for soybeans are when to start and when to stop in order to achieve the maximum number of seed and the maximum weight of individual seeds.
The decision of when to start irrigating soybeans can be easily determined, especially since early-season rainfall in the Midsouth is usually adequate to maintain necessary soil moisture.
So, irrigating early- and normal-planted soybeans is rarely if ever necessary before they start blooming, which is R1. In fact, for early-planted soybeans, there is ample evidence that starting irrigation before R3 or beginning podset is not required when rainfall during vegetative development is normal. Also, both R1 and R3 are easily determined.
Remember, the critical yield components of soybeans are number of seeds per acre and weight of individual seeds. Thus, it is my opinion that the hardest decision is when to stop or terminate soybean irrigation so that the high seed load established by early irrigations will attain maximum weight per seed. The importance of attaining maximum seed size to achieve maximum soybean yield is presented here.