There are few studies in natural ecosystems on how spatial maps of soil attributes change within a growing season. In part, this is due to methodological difficulties associated with sampling the same spatial locations repeatedly over time. We describe the use of ion exchange membrane spikes, a relatively nondestructive way to measure how soil resources at a given point in space fluctuate over time. We used this method to examine spatial patterns of soil ammonium (NH^+ _4) and nitrate (NO^− _3) availability in a mid-successional coastal dune for four periods of time during the growing season. For a single point in time, we also measured soil NH^+ _4 and NO^− _3 concentrations from soil cores collected from the mid-successional dune and from an early and a late successional dune. Soil nitrogen concentrations were low and highly variable in dunes of all ages. Mean NH^+ _4 and NO^− _3 concentrations increased with the age of the dune, whereas coefficients of variation for NH^+ _4 and NO^− _3 concentrations decreased with the age of the dune. Soil NO^− _3 concentration showed strong spatial structure, but soil NH^+ _4 concentration was not spatially structured. Plant-available NH^+ _4 and NO^− _3 showed relatively little spatial structure: only NO^− _3 availability in the second sampling period had significant patch structure. Spatial maps of NH^+ _4 and NO^− _3 availability changed greatly over time, and there were few significant correlations among soil nitrogen availability at different points in time. NO^− _3 availability in the second sampling period was highly correlated ( r = 0.90) with the initial soil NO^− _3 concentrations, providing some evidence that patches of plant-available NO^− _3 may reappear at the same spatial locations at irregular points in time.