OPTIMAL SPACING OF SURFACE-BANDED NITROGEN ON FESCUE

A recommended N application method for approximately 0.2 million ha of tall fescue (Festuca arundinacea Schreb.) grown in Kansas is topdress banding in early spring. Optimal spacing of N fertilizer bands increa ses N use efficiency, thereby reducing expenditures for fertilizer and the potential for environmental contamination. The objective of this study was to develop and test a model to determine optimal spacing of surface-banded N from tall fescue dry matter measured on plots fertili zed with single bands. A major assumption in the development of the mo del was: the yield at any point between two fertilizer bands is the su m of yield responses from adjacent bands. In 1985 tall fescue yields m easured at various distances from single bands of N fertilizer (applie d at rates of 30, 60, 90, and 180 kg ha(-1)) were used to develop the model. The yields on another set of plots fertilized in a complete fac torial arrangement at rates of 60 or 180 kg N ha(-1), with band spacin gs of 25 and 50 cm, were used to test the model in 1984 and 1985. Meas ured and model-predicted yields indicated that optimal band spacing wa s near 25 cm. The model predicted a decrease in optimal band spacing w ith increasing N rates. The fitted regression of measured yield on pre dicted yield had a slope and an intercept not significantly different from one and zero, respectively, indicating a good fit between measure d and modeled yields. This research provides a practical tool to predi ct fertilizer band spacings that maximize fescue yields at N rates bet ween 30 and 180 kg N ha(-1).