https://hdl.handle.net/10388/16746

Soil test phosphorus (STP) represents the amount of phosphorus that is available for crop uptake. In surface soil, STP is also correlated to the potentially mobile fraction that interacts with runoff. It is desirable to maintain available phosphorus in the soil to ensure sufficiency for crop needs and to avoid excessive phosphorus that can result in labile P moving off-field with snowmelt and rainfall runoff, resulting in the eutrophication of lakes and reservoirs. There is a lack of knowledge about the causes in variation and distribution of STP across farm field landscapes in western Canada. At the same time, there is a need to take into consideration the spatial variation of available phosphorus in the field when making site - specific nutrient management prescriptions. In this thesis research, soil labile phosphorus forms, soil properties, crop yield, phosphorus uptake and concentrations in simulated snowmelt phosphorus were assessed in samples taken across the landscape from four farm fields in southern Saskatchewan. Soil labile P was found to be more consistently and strongly influenced by landscape position (upper < mid < lower) in landscapes with greater slope gradients such the site located near Central Butte SK with knob and kettle topography. In contrast, sites with gently undulating landscapes and with minimal slope such as those located near Clavet and Outlook SK had soil P levels that were more influenced by differences in crop yield, soil properties, land management and fertilizer application patterns across the landscape. Headlands were identified in this study as areas where excess soil labile P may be encountered due to overlap when P fertilizer is applied. Landscape position was associated in some cases with variation in soil P sorption capacity, and snowmelt P concentrations were not significantly related to landscape position. The assessments of labile soil P used in this thesis research: modified Kelowna extractable P and anion resin exchangeable P were found to be suitable predictors of runoff risk in the landscape. Observed higher crop yield and crop P uptake and removal in depressional areas of the landscape accompanied with reduced P fertilizer rates and erosion control are strategies that may be employed to reduce labile P levels and runoff risk in these landscapes.

https://hdl.handle.net/10388/16746