Counting Fired Leaves: A Potential Method for Evaluating Nitrogen Sufficiency In Grain Sorghum.

Despite the application of recommended nitrogen rates, grain sorghum may still experience nitrogen deficiencies in many production areas.  Nitrogen loss due to ammonia volatilization, denitrification, immobilization and leaching are reoccurring issues in many cropping systems and soils.  Producers have the option to apply additional nitrogen during the growing season if loss is observed.  However, if loss is experienced, the issue becomes whether or not additional nitrogen is needed, and if so, how much. Two methods are currently available to producers for assessing the nitrogen status of grain sorghum during the growing season: plant analysis and optical sensors.  Both can be used to determine the N status of the plant during the season.  However, plant analysis can be both costly and time-consuming.  Optical sensors are very time-efficient, but require a large financial investment.  These two methods may not be an economical option for sorghum producers in the United States and developing countries.  Producers in developing countries especially, need a method of evaluating the N status of grain sorghum that is cost and time-effective as well as simple to perform.  Using these parameters, a method of counting fired leaves to evaluate nitrogen status was developed. Research was conducted during 2010 and 2011 at multiple locations in Kansas to define the relationship between the percentage of fired leaves, grain yield, and leaf nitrogen content of grain sorghum.  The percentage of fired leaves was found to have a strong correlation with grain yield and was a good indicator of nitrogen status under most conditions.