What Happens To The Essential Macro-Elements in Stockpiled Tall Fescue Leaves in Winter?

Missouri leads the nation in tall fescue production (˜17 million acres) and is second in feeder calf production (Missouri Farm Facts 2004). While Missouri is second only to Texas in cow-calf operations, the size of Missouri farms is drastically different from those in Texas. Missouri's continued success in feeder calf production depends on providing cattlemen with cost effective methods of improving earnings. One way of reducing production costs is the use of stockpiled forage. Stockpiling or saving fall growth of tall fescue pastures allows the forage to accumulate for delayed autumn and winter grazing. The hardy nature of tall fescue and its ability to maintain growth with the onset of cooler temperatures in late fall make it excellent forage for stockpiling. This technique reduces the amount of harvested and stored feed required by a herd in winter as well as the costs associated with winter feeding.

Tall fescue is a resilient cool season grass that persists with little or no management but forage yields can be enhanced by fertilization. Several researchers have shown forage yield increases from 35 to 61% with late summer and fall applications of nitrogen fertilization. However, the efficient use of pasture in grazing systems not only depends on the amount of forage produced but also on the concentrations of mineral nutrients in the forage. Studies in Tennessee and West Virginia found that macronutrient concentrations in tall fescue leaves declined through the winter months. In fact, by late winter and early spring, concentrations of phosphorus (P) and magnesium (Mg) were often below levels recommended for lactating beef cows. This poses a problem for beef herds that calve in late winter and early spring.

Beef cattle production in Missouri and in a large portion of the U.S. is based on tall fescue pastures. Much of the tall fescue in Missouri is typically grown on soils with a low pH and low in plant available phosphorus (Bray I P). Our early studies have shown that P fertilization of low P soils increased both P and Mg concentrations of tall fescue leaf tissue in early spring, and greatly increased total forage production. Therefore forage production on such soils may impact the nutrient concentrations of stockpiled tall fescue leaves. However there are no reports of P fertilization on possible improvement of macronutrient quality of stockpiled tall fescue. The objective of this research was to improve the macronutrient concentrations of stockpiled tall fescue during winter and early spring with P fertilization.

Concentrations of P, Mg, and calcium (Ca) in leaves of stockpiled tall fescue were higher with P fertilization than those of the untreated controls. After the second year's application of fertilizer, the 25 lbs P/acre treatment maintained leaf P and Mg concentrations above the critical 0.2% required by lactating beef cows during late winter and early spring. The leaf concentrations of phloem mobile macronutrients showed a decline from October to February with the exception of nitrogen (N), which reached the lowest concentration in January. The decrease in leaf concentrations of mobile elements like P, Mg, N, and potassium (K) may be the result of nutrient remobilization from leaves to roots during the late fall and early winter a plant strategy to provide support for next springs growth.

The physiological nature of the perennial grass, tall fescue, may have an impact on the nutrient concentrations of the stockpiled forage during the winter months. Producers should take this into account when utilizing stockpiled tall fescue for late winter grazing. With the P and Mg concentrations of tall fescue not treated with P fertilization dropping well below the requirements for lactating beef cows, there would be a greater chance for nutritional disorders to arise. Phosphorus fertilization increased P, Mg, Ca, and to some extent K and N concentrations of stockpiled tall fescue leaves. Therefore, tall fescue growing in established pastures with low soil P are very responsive to P fertilization.