Phosphorus-related properties in the profiles of three Italian soils after long-term mineral and manure applications

摘要

The long-term evolution (44 years) of phosphorus (P) in 1-m profile of three reconstructed soils (0-80 cm = sandy, SDY; clay, CLY; and peaty, PTY; 80-100 cm = native layers) typical of the Po Valley (northern Italy) has been studied in a factorial experiment with farmyard manure and mineral fertilizer. Calcium, magnesium, aluminium, and iron concentrations were determined as total (Ca-T, Mg-T) and pseuto-total (Al-PT and Fe-PT) amounts and as extractable forms by Mehlich-3 (M3) and ammonium oxalate (Ox) extracting solutions. The P distributions in total P (TP), organic P (P-org), H2SO4 P (P-H2SO4), and the more mobile NH4F P (P-NH4F) and NaOH P (P-NaOH) were also measured. As expected soil type always influenced P sorption related soil properties. Ca-M3/Ca-T ratios indicated the presence of easily dissolved/released Ca in PTY while Al and Fe dominated in CLY and PTY soils as crystalline and poorly crystalline oxides forms. Treatments affected the pseudo-total Al and Fe with higher contents in manure than mineral, whereas mineral induced higher oxalate/total ratios of both Fe and Al than manure and untreated. Treatment affected the P content with a pattern strongly influenced by soil type and depth. Despite the comparable P balance between mineral and manure, P forms were generally higher in amended plots than mineral fertilized. Manure increased P-H2SO4 down to 50 cm in CLY and down to 80 cm in SDY and PTY. High values of P-NaOH were also induced by manure throughout the 0-80 cm of SDY. The occurrence of leaching process has been indicated by the general change in some P sorption related properties and P forms found in the native layers. In particular, both stable (i.e. TP) and labile forms (i.e. P-NaOH) increased following 44 yr of fertilization. The phenomenon occurred not only in the overfertilized SDY but also in CLY and PTY where the P balance was negative. Long-term factors influencing the mobility of P within the soil profile are due not only to excessive P inputs, but also the forms of P fertilizer applied.