A single field experiment was conducted in southwestern Arizona (Yuma Valley) in an irrigated cotton production system on a Holtville clay soil (montmorillonitic (calcareous), hyperthermic Typic Torrifluvents). Experimental objectives were 1) to characterize the spatial and temporal variability of solute leaching within relatively uniform field conditions, and 2) to develop an assessment of the worst-case leaching potential of solutes within the system. Bromide (Br-) was used as a biologically conserved tracer to facilitate leaching potential measurements. A system of four mainplots were established equidistantly within a 16 ha field of Pima (Gossypium barbadense L., var. S-6). Within each mainplot area,1 m² subplots were further identified, to which 20 g KBr was applied uniformly on the soil surface in a solution form (500 ml total volume), for light incorporation. Subplot areas were given KBr applications separately at six separate times in the growing season. Soils from respective subplots were then sampled at distinctly separate times following applications of specified amounts of irrigation water after the application of the KBr to the subplot area. Mainplot arrangements were structured to provide information regarding spatial variability among areas of the field sampled at a given date of sampling, and subplots were intended to provide a measure of the degree of variability encountered over time, as a function of the dates of KBr application and subsequent irrigation water applications. Soil samples were taken to a depth of 120 cm, by 30 cm increments from each subplot area at an appropriate sampling date. Soil samples were dried, ground, and analyzed for Br^- and NO₃^--N concentrations for each 30 cm depth increment. Amounts of irrigation water and fertilizer N applied were recorded. The crop nutritional status was monitored by the use of NO₃^--N analysis of petioles throughout the season. Estimates of plant uptake of total N were made at seasons end. Results revealed a very high degree of variability both spatially and temporally with regard to the solute measurements and leaching estimates. These results have implications regarding the methodology appropriate for any monitoring of agricultural production systems and their potential for solute leaching. However, patterns of movement were consistent in terms of limits of the leaching of solutes, as measured with Br^-. The Br^- data indicated minimal movement below a depth of 60 cm following an application of 25 cm/ha (10 acre inches) of irrigation water. The pattern of the N nutritional status (from petiole NO₃--N analysis) maintained adequate levels all season, and revealed a well managed N fertilization program in terms of both rate and timing of applications. Greatest degrees of leaching potentials of NO₃-N appeared to be in the earlier stages of crop development when plant needs and uptake capacities are low, and resident levels of NO₃ -N may be high from pre- or early-season applications of fertilizer N. The results reinforce the need to utilize estimates of residual soil NO₃^--N, reduce pre-season N fertilizer applications, follow actual crop N nutritional patterns (petiole testing), and to utilize split applications of fertilizer N in-season in accordance to crop development and petiole analysis results. Therefore, this experiment demonstrates means by which fertilizer N inputs can be utilized for maximum agronomic and economic efficiency, and with minimal potential for environmental damage.