Effect of RyZup Smartgrass™ 40SG on Annual Ryegrass Production.

Vigorous early fall growth and late maturity have made annual ryegrass a popular forage crop.  In Mississippi, approximately 40 to 50% of warm-season pastures are planted in annual ryegrass to minimize winter feeding.  With increases and fluctuations in fertilizer prices over the last 5 years, producers have reduced nitrogen applications considerably, affecting forage production and quality.  The main objective of the study was to examine the effects of nitrogen and RyZup Smartgrass™ 40SG (RZ) on forage biomass production of annual ryegrass.  The experimental design was a randomized complete block in a 2x8 factorial arrangement replicated four times.  Two nitrogen sources [Urea-ammonium nitrate solution (32%) (UAN) and ammonium nitrate (AN)] were used in the experiment.  The study consisted to eight treatments of RZ and nitrogen sources applied at 56 or 112 kg ha^-1 in split applications.  Marshall annual ryegrass was planted at a seeding rate of 33.6 kg ha^-1 on a prepared seed bed.  Plot size was 1.82 m x 3.35 m.  RyZup Smartgrass™ 40SG was applied at a rate of 23.1 mL ha^-1 using a CO₂ backpack sprayer.  Plots were harvested to a 7.5 cm stubble height when 50% of the plots have reached a height of 20 to 30 cm.  Treatments were applied 2 days after each harvest to allow plant recovery.  Plots were harvested using a sensation mower, removing a 1.05 m swath from the center of the plot, to minimize border effect.  Subsamples were collected for dry matter determination.  Chlorophyll readings were taken prior to each harvest to correlate with nitrogen content in the tissue.  Chlorophyll readings were taken using the Red NDVI GreenSeeker (NTech Industries, Ukia, CA).  Data was analyzed using the General Linear Model of SAS and mean separation was done using the least significant difference (LSD) at α = 0.05. There were no significant yield differences among the nitrogen sources.  Nitrogen applications of 28 kg ha^-1 alone or with RZ had significantly higher yields.  A single application of RZ alone at the beginning of the season or after each harvest had lower yields than the control.  Unseasonably warmer temperatures in the spring might have decreased the effect of RZ in forage production.