Phosphorus status of a Humic Gleysol after 10 years of cultivation under contrasting cropping practices

Cropping practices interactively affect soil P status. Previous studies mostly focused on cropping practices individually and limited assessments within the plow layer. This study assessed the P status of a Labarre silty clay (Humic Gleysol) profile after 10 yr cultivation under contrasting practices. Soils of 0-15, 15-30, 30-60, and 60-90 cm layers were sampled from a split-plot experiment comprising barley (Hordeum vulgare L.) monoculture and a 3-yr barley-red clover-timothy rotation both tilled with either chisel or moldboard plow as main plots, and receiving fertilizer P or liquid dairy manure as subplots. A modified Hedley sequential fractionation was used to characterize soil P status. Labile P pools were more affected than stable ones by cropping practices. The P fractions depended more on nutrient sources than cropping systems in the 0- to 30-cm soil layer, whereas the impacts were predominated by cropping systems in the subsoil. Compared to the manure, fertilizer P resulted in higher contents of Mehlich III extractable P, resin-P, NaHCO3-P and NaOH-P and lower contents of NaHCO3-P NaOH-P and H2SO4-P in the 0- to 30-cm layers. The rotation produced larger labile P fractions than the monoculture in the 30- to 60-cm layer. The impacts of the investigated cropping practices on labile P fractions extended deeper in the soil profile than the depth disturbed by primary tillage. Crop sequence, primary tillage and nutrient source had large effects on P status in the soil profile, of this clayey and poorly drained soil.