A Soil-N Uptake Monitoring (SUM) system was used to determine water and N uptake dynamics of perennial peanut, bermuda grass, and citrus and competition for uptake between citrus and other species. Large (32 L) PVC columns were filled with a Candler sandy soil. Treatments included were 1) citrus (CIT); 2) perennial peanut (PP); 3) bermuda grass (BG); 4) CIT+BG; 5) CIT+PP; 6) bare soil (Control). Nitrogen applied as KNO3 (year1) or CaNO3 (year2) at biweekly intervals at an annual rate of 26 g N/column. Perennial peanut and bermuda grass were clipped every 8 and 4 weeks respectively. After an uptake period of 14 days residual N was leached and collected using 3 porevolumes of water combined with a partial vacuum (12 cbar). Nitrogen uptake (Nupt) was determined by comparing N recovery for a specific treatment with control as follows: Nupt= Ncont x Vcont – Ntrtm X Vtrt; where N= N concentration in leachate, V= volume of leachate, and “cont” refers to soil columns without plants. The SUM system performed excellent and overall N recovery from controls was consistently high with averaged values of 100.1+/- 2.1%. Overall biweekly uptake rates were 161, 180, 436, 294 and 485 mg N per column, for CIT, PP, BG, CIT+BG, and CIT+PP, respectively. Both BG and PP showed pronounced N uptake cycles as related to clipping and its effect on canopy size and uptake capacity. Assuming that species compete for N uptake if the sum of the N uptake of monoculture systems was greater than that of the mixed systems it was estimated that competition reduced citrus uptake by 15 and 51% for PP and BG, respectively. It is therefore concluded that Bermuda grass strongly competes for both water and nutrients and its presence near young trees may thus hamper initial citrus growth.