Nitrogen Rate and Timing Effects On the Yield of Tall Fescue Stockpiled for Winter Grazing.

Stockpiled tall fescue can provide economical winter feed for grazing livestock in the transition zone of the United States.  Late summer nitrogen (N) fertilization is a primary factor affecting yield of cool-season pastures allowed to accumulate herbage for deferred grazing.  Long-term weather data indicates that below normal precipitation during the stockpiling period (Jul to Oct) can be expected in one out of every five years.  This means that a considerable risk exists that nitrogen fertilizer could be applied without the normally expected increase in dry matter accumulation.  As the cost of nitrogen fertilizer increases, there is a heightened interest in fertilization strategies that minimize financial risk.  The objective of this study was to evaluate the effect nitrogen rate and application timing on the yield of stockpiled tall fescue.  The experimental design was randomized complete block with a two-factor factorial treatment arrangement and five replications.  Four nitrogen rates ranging from 0 to 135 kg ha^-1 were applied either in Aug, Sep, or one-half in Aug and one-half in Sep to an established tall fescue sod located near Blackstone, VA.  Growth was allowed to accumulate until mid-Dec when plots were harvested.  Averaged over years, N fertilization increased dry matter yield regardless of application date (P < 0.05).  Yields ranged from 2100 to 4000, 3800, and 3600 kg DM ha^-1 for the Aug, Sep, and split N applications, respectively.  Applications of N made in Aug and Sep increased yield in a linear manner, while the split application resulted in a quadratic response.  The split N application resulted in dry matter production similar to or slightly higher than Aug application up to approximately 105 kg N ha^-1.  Dry matter production dropped off above 105 kg N ha^-1 when applied as a split application.  These data indicate that applying moderate rates of nitrogen as a split application with one-half in August and one-half in September had a minimal effect on total dry matter accumulation and at the same time provided the flexibility of withholding the second application if weather conditions were not conducive for plant growth.