Chlorophyll meter as a tool for forecasting wheat nitrogen requirements after application of herbicides

Abstract

Because limited information is available about the validated use of a chlorophyll meter for predicting nitrogen requirements for optimum growth and yield of wheat after application of herbicides, field experiments were carried out in the winter seasons of 2011/2012 and 2012/2013 under different weed and N fertilization treatments. Five weeded treatments, application of herbicides 25 days after sowing (DAS), hand pulling once at 55 DAS and a weedy check were combined with four N application rates. Weeds were completely absent in the non-fertilized plots, either with metribuzin or hand pulling as well as in isoproturon-treated plots fertilized with 190 or 285 kg N ha⁻¹. The grain yield was similar in the treatments of isoproturon × 190 kg N ha⁻¹, isoproturon + diflufenican × conditional N treatment (113.9) or 190 kg N ha⁻¹, hand pulling × conditional N treatment (104.8) or 285 kg N ha⁻¹ and metribuzin × 190 kg N ha⁻¹. Under weeded practices, conditional N treatment recorded the maximum nitrogen use efficiency and almost equaled the grain protein content of the 190 kg N ha⁻¹ application rate. N application based on SPAD readings saved about 40.0% and 44.8% N with isoproturon + diflufenican or hand pulling, respectively, compared to the recommended rate (190 kg N ha⁻¹) without noticeable yield loss.

Keywords:

• wheat
• herbicides
• chlorophyll meter
• nitrogen use efficiency

Acknowledgements

The author would like to express his deepest gratitude to Prof Dr. Mohamed El-Bially whose comments and suggestions made an enormous contribution to this research. We would like to acknowledge the Faculty of Agriculture, Ain Shams University, for providing the financial support. Also, we thank the anonymous reviewers for their helpful comments on the manuscript.