Tillage-Induced Stratification of Soil Phosphorus Forms.

In many regions, conservation tillage practices such as direct drilling or no-till have replaced conventional tilling practices such as mouldboard plowing, to reduce soil erosion, improve water conservation and increase soil organic matter.  However, tillage can have marked effects on soil properties, specifically nutrient redistribution or stratification in the soil profile.  The objective of this research was to examine soil phosphorus (P) forms and concentrations in a long-term conservation tillage (direct drilling) and mouldboard plowing (to 20 cm depth) study established on a fine sandy loam (Orthic Humo-FerricPodzols) in Prince Edward Island. From 1985 until 2001 the cropping sequences were wheat-barley followed by soybean-barley. In 2001, tall fescue was established.  All plots received P fertilization and lime according to soil test recommendations soil samples were collected from the 0 to 60 cm soil depth in 2003. No significant differences in total P or total organic P concentrations were detected between the tillage systems at any depth. However, preliminary analysis with ³¹P NMR spectroscopy showed differences in P forms between 5 and 30 cm depth, right at the depth of plowing.  All samples contained a wide range of P forms, including the inorganic P forms orthophosphate and pyrophosphate and the organic P forms phytate, scyllo-inositol P, DNA and unidentified orthophosphate monoesters and diesters.  Samples from the ploughed fields had higher concentrations of orthophosphate, while those from the direct-drilled fields had higher concentrations of phytate.