What is physiological maturity: Physiological maturity is defined as the time when dry matter accumulation in the kernels or seeds ceases, in other words the grain stops "filling." Black layer formation at the tip of the kernel is a good indicator of physiological maturity in corn and grain sorghum. For soybeans, physiological maturity has been reached when one normal pod on the main stem has reached its mature pod color. For sunflower, physiological maturity has been reached when the bracts turn brown. After physiological maturity, the crop will no longer respond to irrigation or rainfall.
Water requirements: Given the situation of high irrigation costs and time of year, a review of crop water requirements may be in order. Although irrigation costs are very high, it will be necessary to irrigate until the crop is near physiological maturity to realize the greatest potential. Effective rooting depth will be critical for calculating the final irrigation. If temperatures stay hot into early September, maintaining plant health will be crucial to reaching and surpassing your expected yield goals. Well-timed and carefully managed late-season irrigation will pay dividends for the efforts put forth.