Leaching of dissolved phosphorus and carbon and phosphorus fractionation in drainage: effects of soil type, chemical characteristics and amendments

Abstract Purpose Losses of phosphorus (P) and carbon (C) from livestock farming impair downstream water quality, requiring a better understanding of their leaching processes. The aim of the study was to examine how leaching of P (total dissolved P – TDP; dissolved reactive P – DRP; dissolved organic P – DOP) and dissolved organic C (DOC) was affected by soil type, chemical property and amendment. Methods Leaching experiments with simulated rain were conducted on five different mineral and organic soils before and after a manure or mineral fertilizer application, respectively. The soils were: Fluvisol, Stagnosol, Umbrisol, Histosol (Ruptic), and Histosol. Profile-long soil columns were used, and chemistry of soil and water samples were studied. Results Before the P addition, the Histosol (Ruptic) soil with high P and organic matter contents but low sorption in the subsoil had significantly greatest flow-weighted mean concentrations (FWMCs) of TDP (315 versus 33‒48 µg L ‒1 ), DRP (215 versus 5‒26 µg L ‒1 ), DOP (101 versus 19‒33 µg L ‒1 ) and DOC (46 versus 8‒25 mg L ‒1 ) in drainage water among all soils. Leaching of DOC varied more than TDP, DRP and DOP across most soils. The manure application significantly elevated FWMCs-TDP in three soils than before the application and led to greater FWMCs-TDP in all soils and FWMCs-DOC in most soils than mineral fertilizer did. The ratios of DRP to DOP and to TDP were significantly correlated to whole-profile degree of P saturation (DPS) of the soils (R 2 > 0.9, p < 0.05). Conclusion Sorption/desorption characteristics of subsoils greatly affected concentrations and loads of P and DOC in drainage, as well as the ratios of DRP to DOP and to TDP. Therefore, sorption/desorption characteristics and DPS of subsoils should be included in the work of assessing dissolved P and DOC leaching and developing nutrient mitigation measures.