Spatial Distribution and Chemical Speciation of Soil Phosphorus in a Band Application

There is limited information on how manure and inorganic fertilizer application in a concentrated band impacts the solubility, mobility, and transformation of the phosphate compounds in Canadian prairie soils. A combination of resin membrane probes, sequential chemical extraction, and synchrotron based techniques were used to reveal the spatial distribution and chemical speciation of soil phosphorus (P) when inorganic fertilizer P or manure is placed in the soil in a band under field conditions. This study was performed at Central Butte and Dixon, SK, Canada. Monoammonium phosphate blended with urea was applied at a rate of 54 kg N ha(-1) and 12 kg P ha(-1) at Central Butte (Brown Chernozem) and solid cattle manure was applied at rate of 60 t ha(-1) yr(-1) at Dixon (Black Chernozem). Fertilizer application increased the total and labile P supply at the center of the band and was mainly confined to a relatively small area within about 5 cm of band regardless of slope position. The X-ray absorption near edge structure (XANES) spectroscopy directly identified different forms of soil P, while chemical extraction results provided indirect support that there are differences in the forms of P in the band center as related to in the landscape position and fertilization type. The XANES analysis results showed that different P retention mechanisms take place depending on both landscape position and fertilizer type. For the inorganic fertilizer application made in calcareous upslope positions, a significant amount of apatite and adsorbed P species were observed at center and near-band and only apatite was present at large distances from the band; adsorbed P species dominated at all distances from the band at downslope positions. The solid cattle manure applied soil contained dicalcium phosphate (DCP) and organic P at center and near-band at both slope positions but adsorbed P and calcium phosphate further away at upslope positions and adsorbed P further away at downslope positions. The XANES results also indicated that the movement of organic P was limited as this species was always localized near the band.