RAINFALL SIMULATOR AND PLOT DESIGN FOR MESOPLOT RUNOFF STUDIES

There is need to evaluate the effects of agricultural production activ ities on sedimentation, pesticide, and nutrient losses under controlle d simulated rainfall on plots large enough (generally exceeding 50 m(2 )) to incorporate realistic slope lengths and dominant processes that control runoff and sediment yield from ''field-size'' areas. Therefore , a rainfall simulator system was developed for 600-m(2) plots (mesopl ots) to evaluate runoff (water and sediment) and agrichemical movement from fields for different tillage practices and chemical applications . The rainfall simulator applies water with irrigation sprinklers spac ed 3 m apart on two irrigation laterals arranged 14.6 m apart along th e plot length. Runoff and sediment were collected in a V-shaped trough and directed to a flume for measuring and sampling. Simulated rainfal l of 25 mm/h with a median drop diameter of 1.52 mm had a coefficient of uniformity of 91 over the plot area. Water was applied and sediment and runoff collected from two mesoplots for sir events over a corn-gr owing season.