Bermudagrass Forage Production As Affected By Rate and Timing of Nitrogen Fertilization.

Fertilizer prices have considerably increased in the last decade.  The price increase has prompted hay producers to rethink management practices to reduce input while maintaining yield production and quality of warm-season perennial grasses.  Nitrogen use efficiency (NUE) in warm-season perennial hay production systems in the south is usually less than 40% due to losses such as N volatilization under high temperature and humidity during the growing season (May to September).  Another issue with low NUE is that hay producers tend to use a single N application to reduce fuel costs.  Methods to improve NUE in bermudagrass (Cynodon dactylon) have not included temporal N applications throughout the growing season.  The objective of the study reported herein was to determine the effects of four levels of nitrogen fertilization and the timing of applications in yield, nutrient use efficiency and forage quality.  The study was conducted from 2012 to 2013 in a mixed bermudagrass field at the Mississippi State University’s Henry H. Leveck Animal Research Farm.  The soil map unit is a Marietta fine sandy loam (Fine-loamy, siliceous, active, thermic Fluvaquentic Eutrudepts).  The study was a randomized complete block replicated four times.  Four N treatments (0, 50, 100 and 150 lb Nac^-1) were temporally applied throughout the growing season.  Potassium, phosphorus, and lime were applied based in soil test recommendations.  Plots were 6 ft x 12 ft in size and harvested in a 28-30 day interval by removing a 52-inch swath from the middle of the plot with a Ferris commercial mower equipped with a bagging system.  Biomass subsamples were collected, ground to pass 1-mm and used for dry matter determination, nutrient content and forage quality.  Nitrogen applications during the greenup phase and after the first harvest impacted yield production and NUE throughout the season.  Higher yields were attained at high N fertilization, but NUE declined at higher yields.  Crude protein levels were impacted by the spatial N applications.  The study indicated that despite of the surplus of fertilizer additions, the majority of crop N uptake is still dependent on internal cycling.