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The objectives of this rainfall simulation study were to determine 1) what relationships exist between both total dissolved solids (TDS) and orthophosphate-phosphorus (PO4-P) in surface runoff and the bulk soil electrical conductivity (ECb) measured by time domain reflectometry (TDR) in the top layer of soil, 2) how rates of added P for Nicollet soil affect top soil layer ECb, and TDS and PO4-P in surface runoff, under the soil surface cover condition with and without an energy-absorbing screen, and 3) how the hydrologic conditions including volumetric water content as determined by TDR are affected by the treatments mentioned above. The soil used, allowed to partially air dry in the laboratory, was sifted through a 2.5 mm sieve and then thoroughly mixed. Two plastic runoff pans with a 3490 cm2 rainfall collection area were used. The treatments of 0, 50, 125, 300, and 600 ppm (on a dry weight of soil basis) of added monobasic amonium phosphate (MAP) were dissolved in water and sprayed on the soil as it tumbled in a mixer. The soil was incubated in plastic containers for a period of 30 days. From the chosen bulk density of 1.1 g/cm3, calculated amounts of soils were packed into runoff pans in three 2.54-cm layers, for a total soil depth of 7.6 cm. Two TDR probes per pan were inserted into soil 1 cm below the soil surface. Simulated rainfall was applied at an intensity of 6.5 cm/h for 64 min to the packed soil pans, either with or without the screen cover. The results indicated that ECb in the top soil layer (mixing zone) was linearly related to both TDS and PO4-P concentrations in surface runoff samples taken over time during runoff, when the soil received added P at rates of 125, 300, and 600 ppm. Statistical analyses indicated that decreases in ECb and PO4-P or TDS as a function of time during runoff might be expressed as power function. Added P significantly increased the ECb value in the top layer of soil as well as TDS and PO4-P concentrations in runoff. Whether the soil pans did or did not have a screen cover did not affect ECb in top soil layer or TDS or PO4-P concentrations in runoff water. But the screen cover significantly decreased the volume of surface runoff water, and therefore the loss of PO4-P and TDS in surface runoff.