A Model of the Leaf Extension Rate of Tall Fescue in Response to Nitrogen and Temperature

Abstract

The leaf extension rate (LER) of tall fescue (Festuca arundinacea Schreb.) was studied in the field under various nitrogen and temperature regimes. The LER was closely related to temperature when N was not limiting plant growth. Two distinct relationships between the LER and the temperature were obtained, one for vegetative growth and one for the reproductive period. These relationships, described by a Gompertz function, were exponential at temperatures below 8 °C and linear at temperatures above 8 °C. They made possible the calculation of an optimal LER corresponding to non-limiting N conditions for plant growth. The strong influence of the temperature on the LER was still observed under N limiting conditions. The N status of the swards was described by the ratio between the actual N content (Nactual) and the optimal N content (Noptimal). The Noptimal was defined as the N content experienced at a non-limiting level of N nutrition but without N luxury consumption. The Noptimal, expressed as a function of dry matter yield, declined during growth. The effect of the N status of the swards on the LER was analysed by calculating the ratio between the actual LER and the optimal LER, and relating it to the ratio between Nactual and Noptimal. It was shown that these two ratios were highly correlated.