PIG SLURRY APPLICATIONS - EFFECTS ON BIOAVAILABLE PHOSPHORUS AND CATION CONCENTRATION IN SOIL SOLUTION [French]

摘要

Bioavailability of soil phosphorus and cation concentration (Ca++, Mg++, K+ and Na+) in the soil solution were analysed in soil samples taken from an experimental field designed to study the denitrification of nitrogen contained in pig slurry. The experimental set-up, located in Brittany (western France) on an acid soil, comprised a control plot that did not receive pig slurry, and four plots which all received pig slurry at the same rate. The experimental design was cropped with Lolium perenne. The mean rate of slurry application was about 1 000 m(3).year(-1).ha(-1) and of phosphorus 1 400 kgP.year(-1).ha(-1). Soil samples were taken each year in three soil layers 0-20, 20-40 and 40-60 am just before each first campaign of slurry application. The main results observed were the following: (i) on a yearly scale, phosphorus included in slurry must be considered to be as available as phosphorus derived from wafer-soluble P fertilizers; (ii) organic matter in the slurry decreases the phosphate-fixing capacity of soils; as a consequence the risk of eutrophization of surface wafer is increased when soil particles containing available soil P enter into contact with surface waters; (iii) the Dyer method with 2% citric acid extraction, currently used in France to analyse 'available soil P' in non calcareous soils, overestimates it by dissolving calcium/magnesium phytate in soils that recently received pig slurry; (iv) at the rates of application utilized in this experiment, even in this acid soil where the initial fixing capacity was high, a P migration took place below the ploughed layer. However, the increase of P-fixing capacity with depth will generally limit the leaching of P into ground wafer.