| A bromide (Br) transport study was conducted in a 2 ha potato field in Aberdeen, ID to monitor water and solute transport and to quantify stemflow, hill-furrow runoff, lateral moisture, solute transport and leaching, and plant Br uptake. The effects of irrigation depth (excess vs. optimum) and mode of solute application (spray application vs. chemigation) on solute transport and leaching were also investigated. Bromide application was followed by 8 sprinkler irrigations during the 119 day study in which water and solute transport were monitored using time domain reflectrometry and extensive soil sampling. Nonuniform moisture and Br distributions were observed from two-dimensional water and Br concentration plots. Factors contributing to this non-uniformity were runoff from hill and shoulder to furrow, preferential flow through open soil cracks, hill-furrow geometry causing two-dimensional solute transport, irrigation depth and mode of chemical application. Irrigation depth significantly affected Br transport and leaching, while solute application method was not as significant. Chemigation caused greater initial penetration and leaching of Br compared to spray application.; A two-dimensional deterministic model (Annandale, 1991) was then used to evaluate different irrigation and nitrogen (N) management options. The model was validated with reasonable success based on the data collected in Aberdeen, Idaho. Simulations were performed for different irrigation depths (deficit, 80% ET; optimum, 100% ET; and excess, 130% ET), irrigation intervals (less frequent, 7 to 10 days; and frequent 3 to 5 days), and chemigation frequencies (3 heavier vs. 6 lighter applications). Simulations were significantly affected by irrigation depth but not affected by chemigation frequency. The best results were obtained for optimum and frequent irrigation management option. Excess irrigation simulations resulted in the highest amount of leaching and lowest dry matter production due to lower N use efficiency. Sensitivity analysis showed a tradeoff in leaching between non-uniform chemical application (i.e. chemigation increased leaching) and non-uniform water application (i.e. increased runoff and reduced leaching). This tradeoff was demonstrated by simulations of high (center pivot) and low (solid set) intensity sprinkler irrigations. |
