A rainfall simulation study on the relationships between soil test P versus dissolved and potentially bioavailable particulate phosphorus forms in runoff

摘要

Runoff from clayey soils often contains abundant particulate phoshorus (PP); part of which may solubilize in surface waters. Monitoring losses of potentially bioavailable forms of PP is expensive; calling for other ways to predict them. Such predictions could be based on soil loss and available soil P indices; e.g.; agronomic P status. To study correlations between P pools in runoff versus soil P saturation (by Mehlich 3 extraction; DPSM3) and acetate soil test P (PAc); 15 clayey soils of south Finland were subjected to laboratory rainfall simulation. Runoff from these simulations was analyzed for concentrations of suspended soil (TSS); dissolved molybdate-reactive P(DRP); total P(TP); and; as normalized to soil loss; potentially bioavailable formsof PP: desorbable (anion exchange resin-extractable; AER-PP/TSS) and redox-labile PP (bicarbo-nate-dithionite-extractable; BD-PP/TSS). Correlation coefficients (r2) between DPSM; and DRP; AER-PP/ TSS; and BD-PP/TSS equaled 0.92; 0.77; and 0.45; respectively. Runoff P forms were also correlated to soil PAc with r2 values of 0.84; 0.56; and 0.58 for DRP; AER-PP/TSS; and BD-PP/TSS; respectively. Prediction of soil loss-normalized concentrations of potentially bioavailable PPby the agronomic PAc test was considered possible. However; such predictions have a high degree of uncertainty; evidenced by comparison to published field data. Acceptably accurate predictive equations would require a large material as a basis for their construction; and soils should probably also be grouped according to other soil properties that would account for variation in P sorption capacity.