26 28 23 Nitrogen (N) use efficiency of rice grown in Arkansas. ---1992--- ---2000--- ---2006--- Total Rice Acres§ 1,380,000 1,410,000 1,400,000 Total N Fertilizer Applied (lbs)§ A 197,340,000 204,450,000 288,400,000 Average N fertilizer Applied (lbs/ac)§ 143 145 206 Total Rice Yield (lbs)§ 7,590,000,000 8,615,100,000 9,660,000,000 Percent N in Rice Grain† 1.3 Total N Removed in Grain (lbs)§ 98,670,000 111,996,300 125,580,000 N Removed from Soil (lbs)‡ 47,361,600 53,758,224 60,278,400 N Removed from Fertilizer (lbs)§ B 51,308,400 58,238,076 65,301,600 Efficiency (%) [B/A] X 100 26 28 23 §http://www.nass.usda.gov †http://plants.usda.gov/NPK/main ‡ Calculated using a factor of 0.48; determined from multiple N fertility trials in Arkansas. 150 31

Increasing NUE in Rice Reduce Two Major Loss Mechanisms Volatilization and Nitrification/Denitrification Urease and nitrification inhibitors Quickly applying flood water to achieve anaerobic conditions Maintaining flood water to keep anaerobic conditions

Rice Root Density Yoshida and Hasegawa (1982) Because of the extensive root system of rice, the crop is able to accommodate for not being able to take up NO3 via mass flow