Agricultural phosphorus (P) loss, which is highly variable in space and time, has been studied using the hot spot/hot moment concept, but increasing the rigor of these assessments through a relatively newer “ecosystem control point” framework may help better target management practices that provide a disproportionate water quality benefit. Sixteen relatively large (0.85 ha) subsurface drainage plots in Illinois were used as individual observational units to assess dissolved reactive P (DRP) concentrations and losses within a given field over four study years. Three plot‐months were identified as DRP control points (one export and two transport control points), where each plot‐month contributed >10% of the annual DRP load from the field. These control points occurred on separate plots and in both the growing and nongrowing seasons but were likely related to agronomic P applications. Elevated soil test P, especially near a historic farmstead, and soil clay content were spatial drivers of P loss across the field. The nongrowing season was hypothesized to be the most significant period of P loss, but this was only documented in two of the four study years. A cereal rye (Secale cereale L.) cover crop did not significantly reduce DRP loss in any year, but there was also no evidence of increased drainage P losses due to freezing and thawing of the cover crop biomass. This work confirmed annual subsurface drainage DRP losses were agronomically small (<3% of P application rate), although the range of DRP concentrations relative to eutrophication criteria still demonstrated a potential for negative environmental impact. The control point concept may provide a new lens to view drainage DRP losses, but this framework should be refined through additional within‐field studies because mechanisms of P export at this field were more nuanced than just the presence of tile drainage (i.e., a transport control point).

Nitrate is the main form of nitrogen associated with water contamination; the high mobility of this species in soil justifies the concern regarding nitrogen management in agricultural soils. Therefore, the objective of this research was to assess the effect of companion cation on nitrate displacement, by analyzing nitrate transport parameters through Breakthrough Curves (BTCs) and their settings made by numerical model (STANMOD). The experiment was carried out in the Soil and Water Quality Laboratory of the Department of Biosystems Engineering, "Luiz de Queiroz" College of Agriculture in Piracicaba (SP), Brazil. It was performed using saturated soil columns in steady-state flow condition, in which two different sources of inorganic nitrate Ca(NO₃)₂ and NH₄NO₃ were applied at a concentration of 50 mg L^-1 NO₃^-. Each column was filled with either a Red-Yellow Oxisol (S1) or an Alfisol (S2). Results are indicative that the companion ion had no effect on nitrate displacement. However, nitrate transport was influenced by soil texture, particle aggregation, solution speed in soil and organic matter presence. Nitrate mobility was higher in the Alfisol (S2).

With current environmental concerns and the need to understand the processes that govern the movement of water and solutes in soil, studies are needed to facilitate more efficient use of agriculture inputs, thereby mitigating the impact of agriculture on groundwater contamination. The objective of this study was to characterize nitrate transport parameters, through the development of breakthrough curves (BTC) for steady state transport of calcium nitrate and potassium nitrate solution, at a concentration of 50 g m^-3 NO₃^-, through columns of disturbed and undisturbed soil from two tropical soils; Yellow Oxisol and Anfisol. The experiment was conducted in the Laboratory of Soil and Water Quality, Department of Biosystems Engineering "Luiz de Queiroz” College of Agriculture, Piracicaba - SP. The nitrate transport parameters were obtained by a numerical fit using the STANMOD software. The results are indicative that nitrate displacement is linked with the soil characteristics and that there was more rapid leaching through the Anfisol for the calcium nitrate, and for potassium nitrate, there were only differences in the values of the transport parameter P ​​between disturbed and undisturbed samples.