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This work was aimed at (1) comparing the effect of experimental supplementation of water and soil nutrients (N, P, K, Ca and Mg) on the relative numbers of soil microarthropods in a coastal desert ecosystem, (2) evaluating the effect of time (seasons) as an interacting factor, and (3) describing the phenological patterns of the main taxa. We tested the hypothesis of no-treatment effects, The work was done in Lagunillas (30 degrees 06’ S, 71 degrees 21’W, North-Central Chile), where two 1 ha-experimental plots were established in 1987. The plots differed in plant cover, soil characteristics and depth of an impermeable layer of calcium carbonate (hardpan). The study included a wet and a dry annual cycle. Time (seasons) was the most important factor in determining the numerical response of soil microarthropods; but differences in treatment effects between plots suggest that the depth of the hardpan layer may have played a role. The interaction water x time was significant for the prostigmatid mites and collembolans, but not for the remaining taxa. For the two and a half years of the study, we were unable to detect significant responses to the nutrient treatments. This lack of response might have been due to the low artificial water input or to the resilience of the system.