DETERMINATION OF WHEAT NITROGEN STATUS WITH A HAND-HELD CHLOROPHYLL METER - INFLUENCE OF MANAGEMENT-PRACTICES

The nitrogen (N) status of wheat at specific growth stages has potential in predicting yield goals and supplemental N fertilizer requirements but there is a need for a simple and reliable method for field determination of wheat (Triticum aestivum L.) N status under different management schemes. This field study was conducted for two seasons (1989-90 and 1990-91) on a Norfolk sl (fine-loamy, siliceous thermic Typic Kandiudults) in east-central Alabama. Treatment variables were tillage, fungicide and N rate. Tillage treatments were disk/harrow or paraplow. Fungicide treatments were no fungicide or propiconazole (Tilt(R)) applied at Feekes growth stage (GS) 8. Nitrogen rates were a 0-N control and 45, 90, 134, or 179 kg N/ha applied in a two-way split with 22.5 kg N/ha applied at planting and the remainder applied in mid-February. Whole plant samples at GS 3 and 5, and flag leaf samples at GS 10.51 were analyzed for N; a hand-held meter was used to measure chlorophyll concentrations at these sampling times also. The most consistent yield response was to fungicide, especially at higher N rates, with increases ranging from 15 to 62%. Paraplowing also affected grain yield response to N application. Leaf chlorophyll meter readings were significantly correlated to tissue N concentration and grain yield. The best predictor of grain yield was N uptake at GS 5, however, multiple regression models that included chlorophyll meter readings and dry matter at GS 5 were comparable to N uptake as predictors of yield. Chlorophyll meter readings have potential to be combined with other simple measurements, e.g., dry matter determination and/or soil nitrate tests, to develop quick and reliable methods for predicting N fertilizer requirements for winter wheat.