Adequate moisture is one of the most important factors that can help achieve optimum yield potential. With high summer temperatures and low relative humidity, soils can have a difficult time maintaining adequate soil moisture. Water stress during specific growth stage can lead to a decrease in yield potential.
Irrigation at the most important times (growth stages) can increase soybean yield potential and reduce the risk of yield losses to drought. Adequate water is essential during the most critical times of pod development (R3-R4) and seed fill (R5-R6). Unless soil moisture levels are extremely low, irrigation or high amounts of rain during vegetative growth are not beneficial and may stimulate vegetative growth, which may potentially lead to yield reduction. It may also produce lodging, which can substantially decrease yields. Irrigation application until soybean reaches maturity can help maximize yield potential.
Irrigation after physiological maturity does not help add additional yield potential. Irrigation should begin by bloom and continue until seeds are fully developed which may require additional moisture to maximize seed weight and yield potential.
Lack of moisture during seed development can significantly reduce yields as much as 10 bushels per acre. Lack of moisture from beginning of flowering through beginning of seed (R1 through R5) growth stages can reduce number of total pods/plant and reduce the average number of seeds/pod. Lack of moisture between R5 and R6 can result in smaller seeds.
Termination of irrigation depends on weather, available moisture, and soybean product. Although water requirements decrease as plant is closer to maturity, maintaining proper soil moisture is essential to minimize stress and help maximize yields. Continue maintaining good soil moisture until R6 stage, as seeds reached maximum weight. At R6 if good soil moisture is present, no additional irrigation is needed.
Soil moisture can be monitored by1 hand-free methods, mechanical or electrical devices and daily and weekly sums of soil moisture use can be estimated using ET data from a weather station.