The later you plant soybean, the later the maturity needed to reach maximum growth potential. This is most important in a food plot. Soybean unlike other crops have many different maturity groups. If you plant a southern variety in the north, it will mature much later than cultivars grown in that region and may get frosted on before fully mature. Farmers do not want that. If you plant a northern variety in the south, it will only get a foot or two in height and mature much earlier never reaching maximum potential. In my opinion, you should make the most out of your summer plot by utilizing the entire growing season until frost. I usually broadcast wheat into the soybeans prior to leaf drop and wait for rain to sprout the wheat. This leaves growing wheat in standing soybean stubble for both cover and food.