Understanding N dynamics in biosolids-amended agroecosystems can help avoid over-application and the potential for environmental degradation. We investigated 15-years of biosolids application to dryland-wheat (Triticum aestivum L.) grown on Weld loam soils (fine, montmorillonitic, mesic Aridic Paleustolls) located about 25km east of Brighton, CO, USA, questioning what is the relationship between cumulative grain yield and N uptake (N removal) and biosolids or N fertilizer rates and how many times biosolids or N fertilizer are applied? How are wheat-grain production and N uptake intertwined with residual soil NO₃-N? We found that biosolids or N fertilizer rates plus the number of applications of each material produced planar-regression (3D) models with 15-years of grain yield and N uptake data (all R ² >0.93). To evaluate how yield or N uptake impacted residual soil NO₃-N, we completed linear regressions on yield, N uptake, and soil NO₃-N. We then correlated the slopes where P <0.10 for the yield and soil NO₃-N and the N uptake and soil NO₃-N. A significant negative relationship was found for biosolids application for each of these comparisons while the N fertilizer results were inconsistent. For the biosolids treatments, as yield or N uptake increased, residual soil NO₃-N decreased. Our findings show that planar-regression models could aid biosolids beneficial-use management programs when considering agroecosystem N dynamics.