Determination of wheat nitrogen status with a hand‐held chlorophyll meter: Influence of management practices¹

Contribution of USDA‐ARS in cooperation with the Alabama Agricultural Experiment Station. This research was supported by the Alabama Farmer's Federation Wheat and Feed Grain Check‐Off Program.

Abstract

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®) 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.

Notes

Contribution of USDA‐ARS in cooperation with the Alabama Agricultural Experiment Station. This research was supported by the Alabama Farmer's Federation Wheat and Feed Grain Check‐Off Program.