USING A CHLOROPHYLL METER TO PREDICT NITROGEN-FERTILIZER NEEDS OF WINTER-WHEAT

Although it has been shown that the nitrogen (N) concentration of wint er wheat (Triticum aestivum L. em Thell) at Feeke's growth stage 5 (GS 5) can be used to assist in making more accurate spring N fertilizer recommendations, the need remains to find a more convenient and accura te means for predicting N fertilizer needs of wheat. We conducted seve n N fertilizer response experiments over two years in central and sout heastern Pennsylvania to determine if chlorophyll meter readings of wh eat leaves at GS 5 could predict whether a significant, positive grain yield response to N fertilizer would be obtained. The chlorophyll met er readings at GS 5 were more accurate (correctly predicting response to N fertilizer in 24 Of 25 treatments for a 4% error rate) than GS 5 plant N concentration (20% error rate). There were too few treatments with a positive response to N fertilizer to be able to determine if ch lorophyll meter readings could be used to accurately predict N fertili zer rates needed for economic optimum yield.