Fig. 3. Effect of trickle irrigation (Tr), overhead sprinkler irrigation (Ov), trickle irrigation plus controlled-release fertilizer (TrF), and overhead sprinkler irrigation plus controlled-release fertilizer (OvF) on nitrate N concentration in leachate in soil columns during a 2-yr study. Records during the experiment of precipitation and air and soil temperatures and records of percent soil moisture in overhead and trickle irrigation treatments are presented. * = significant at P 0.05; NS = not significant.