Microbial phosphorus pools in a long-term organic farming system in Scott, Saskatchewan

Abstract

Organic farmers across Saskatchewan face widespread phosphorus (P) shortages. Due to the lack of inputs in organic systems, organic farmers must rely on mechanisms like crop rotation and naturally-occurring arbuscular mycorrhizal fungi (AMF) for plant P supply. Crops that are not colonized by AMF (non-mycorrhizal) can decrease colonization of a following crop. An experiment was carried out to look at varying P pools in four cropping sequences under organic management, and also to determine if mustard (non-mycorrhizal) was delaying the colonization of wheat following it. Soils from the four cropping sequences were measured for inorganic P (Pi), AMF spore density (SD), phospholipid fatty acid analysis (PLFA, for AMF biomarker counts), and alkaline phosphatase activity (ALPase, related to AMF metabolic activity). Plants were measured for AMF colonization and P content and uptake of above-ground biomass. A lack of significant difference in AMF activity indicated that mustard was not depressing colonization. The combination of low Pi levels, no inputs, and crop rotation were most likely creating optimal conditions for AMF colonization.