Long-term fertilizer and manure amendments have resulted in the accumulation of P in surface soils in intensively managed agricultural fields in the Midwestern U.S. Phosphorus losses from these agricultural fields have been an environmental issue due to its negative impact on aquatic ecosystems. Sediment loss in surface runoff has been frequently discussed as a primary transport path of P, and many scientists downplayed subsurface loss via tile drainage networks in the Midwestern agricultural systems. Concentrations of dissolved reactive P (DRP) and total P in dranage ditches can range from just detectable to many tenths of a mg /L in tile lines. Furthermore, the contribution of colloidal and particulate P can be as high as ~45% during high flow events. These concentrations and loads of P are more than enough to lead to eutrophication and algal production in downstream water bodies. As part of the Hypoxia Action Plan, the Midwestern states in the U.S. have recently developed a nutrient loss reduction strategy to reduce P losses from both point and non-point sources. There has been a great interest in understanding the mechanisms of subsurface P transport processes through tile lines. It was hypothesized that the subsurface accumulation of P in the intensively managed agricultural soils is contributing to the P loss from tile lines. Mollisols enriched in organic C, clays and metal oxides could effectively retain P but it is not clear how and how much P has transported through subsoils because of the poorly drainage characteristic. We explored the soil P speciation and physiochemical properties of P colloids in tile waters using experimental geochemistry is conjunction with zetasizer, dynamic light scattering, synchrotron based X-ray diffraction, nuclear magnetic resonance spectroscopy, and P K-edge X-ray absorption near edge structure spectroscopy. In this presentation, the depth sequence distribution of P, its reactivity and speciation and the colloidal Fe controlled subsurface P loss in the intensively managed agricultural soils in the Midwestern U.S. will be discussed.