If fescue pastures are high in summer annual grasses, such as crabgrass or foxtail, nitrogen efficiency for tall fescue growth will be low. The summer annual grasses that are growing vigorously in August will take up most of the available nitrogen, leaving little for the fescue. The summer annuals die with the first killing frost, leaving very poor quality feed while the nitrogen is immobilized (unavailable) in the slowly decaying weeds. Therefore, nitrogen fertilization for stockpiling should be limited to pastures with a vigorous fescue sod that is relatively free of summer annual grassy weeds.
Many producers are reluctant to apply nitrogen, believing that the percentage of legumes will be reduced the next season. While this is true for spring-applied nitrogen, it is not true for late-summer nitrogen applications. White clover contributes some nitrogen to fescue during the fall; its growth and nitrogen production slows greatly in the cooler and shorter days of the late summer. Apply nitrogen even when you have up to 30% of the stand composed of legumes. If the stand is over 30% legumes, nitrogen should be used during the fall rather than saved for winter.