CHLOROPHYLL METER PREDICTS NITROGEN STATUS OF TALL FESCUE

The nitrogen (N) status of a crop can be used to predict yield and sup plemental N fertilizer requirements, and rapid techniques for evaluati ng the N status of crops are needed. A study was conducted to determin e the feasibility of using a hand held chlorophyll meter (SPAD 502, Mi nolta Co, Ltd., Japan) to monitor N status of tall fescue (Festuca aru ndinacea Schreb,). Four diverse tall fescue genotypes were grown at th ree locations in Alabama and fertilized at four N-rates from 0 to 336 kg ha(-1). A similar experiment was conducted in the greenhouse using soil from the same field sites. Chlorophyll meter readings (SPAD) were taken, and extractable chlorophyll content, tissue N concentration an d dry matter yield were determined at harvest. SPAD, extractable chlor ophyll content, tissue N concentration, and dry matter yield increased quadratically (0.67 < R(2) < 0.99) with increasing N fertilization in both experiments. All genotypes responded similarly to applied N, wit h some differences in magnitude. Relationships between SPAD meter read ings and extractable chlorophyll and tissue N concentrations were line ar with (r)2 > 0.95. An additional independent variable, the square ro ot of the inverse of SPAD, lowered the residual mean square by 11 and 16%, respectively, for tissue-N and chlorophyll concentrations, but di d not increase the R(2). This would be preferred for predictive purpos es. Tissue N concentrations at higher N-rates were sufficient for maxi mum yield which occurred at 290 and 248 kg N ha(-1) for greenhouse and field, respectively, but were lower than previously reported sufficie ncy values. The chlorophyll meter is an easy and efficient method of d etecting tall fescue N status.