Leaf area index, light penetration, and carbohydrate reserves during growth of Kentucky 31 tall fescue (Festuca arundinacea Schreb.)

The interrelationship between dry matter production, leaf area index (LAI), light penetration through the canopy and carbohydrate reserve fluctuations during regrowth under different growth stages and cutting managements of Kentucky 31 tall fescue were studied in three field experiments during spring and summer.

Stages of growth (vegetative to reproductive) had marked influence on LAI development and distribution at various layers above the ground. Also there were marked influences of stage of growth on the relationships between dry matter production and LAI. Stage of growth also affected the regrowth after different frequencies and heights of defoliation. During reproductive growth in spring, LAI showed a marked reduction due to senescence and shading of lower leaves after head emergence. During vegetative growth in summer, LAI tended to attain steady, ceiling values, associated with complete light interception. Previous management of sods affected the maximum values attained at this stage. Higher ceiling LAI’s were observed in the swards previously managed as hay as compared with the pasture swards.

Light penetration profiles were affected by LAl distribution at various layers above the soil There were differences between light interception by different canopy layers at a given time. Lower leaf layers were more efficient than the upper ones in light interception. Previous management of the swards also affected the ability of canopies to intercept incident light. Changes in extinction coefficients of the canopies with time during regrowth were apparent. Results indicated a continuous, change in extinction coefficients of the grass canopy, with height within the canopy at a given time, and with time at a given height above the ground.

Carbohydrate reserves fluctuated during regrowth, and frequency and height of defoliation affected the levels and magnitude of these fluctuations. Results confirmed the apparent participation of carbohydrate reserves in regrowth and showed the existence of a dynamic balance of energy status of the swards. Carbohydrate content of tillers was minimum when the rate of LAI development and dry matter production were maxima, but it increased rapidly when rates of dry matter production and LAI development decreased.

The interrelationships between these factors during regrowth of tall fescue are discussed.