Relationship between soil test phosphorus and phosphorus release to solution in three soils after long-term mineral and manure application (original) (raw)

2016, Agriculture, Ecosystems & Environment

Continued fertilizations have led to soil phosphorus (P) concentrations that exceed those required for optimal plant growth. In this study, P accumulation and leaching were investigated in 1-m profile of three reconstructed soils (sandy, SDY; clay, CLY; peaty, PTY) typical of the Po Valley (northern Italy) following long-term (44 years) farmyard manure and mineral applications and untreated. Soil test P was determined by extracting with ammonium oxalate (P Ox), Mehlich-3 (P M3) and Olsen (P Ols) solutions, whereas soil P release was estimated by water extraction (P H2O). Two single-point sorption indices (PSI 19.4 and PSI 50) were used to assess the P sorption capacity in these soils. The relationship between extractable P forms and water P was also modelled as a segmented line. Soil test P resulted as being affected by type of soil, treatment and depth. Farmyard manure increased the P forms by 7.7-fold that of untreated down to 50 cm in CLY and PTY, and 28-fold untreated down to 90 cm in SDY, thus indicating both accumulation and leaching of P. The P sorption indices were affected by type of soil, treatment and depth. P accumulation was also confirmed by increments of PSI 50 in the manure-treated deeper layers, likely due to increased organic matter and/or precipitation and coprecipitation of P with carbonates in these soils. Although mineral fertilization also increased extractable P it was with lower magnitude than manure on P leaching and P sorption indices. From the segmented lines between P H2O and extractable P, the presence of change points in CLY and PTY revealed P H2O concentrations above the environmental threshold values. In the light-textured SDY soils, the low P sorption capacity and absence of change points evidenced high P leaching and potential contamination of surface and ground waters, in particular when manure was used. 2016 Elsevier B.V. All rights reserved.