Fifteen years of wheat yield, N uptake, and soil nitrate–N dynamics in a biosolids-amended agroecosystem

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 25 km 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 R2 > 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.