Degree of Phosphorus Saturation as a Predictor of Redox-Induced Phosphorus Release from Flooded Soils to Floodwater

Phosphorus (P) loss from soils is often enhanced under flooded, anaerobic conditions, increasing the risk of freshwater eutrophication. We aimed to develop a predictive tool to identify soils with greater P release potential under summer‐flooded conditions, which would help in developing strategies to mitigate P losses. One in situ mesocosm study was conducted in field plots with three treatments: cattle manure amended, monoammonium phosphate amended, and unamended. Two ex situ field mesocosm studies were conducted, each having 12 surface soils from agricultural fields. Prior to flooding, soils were analyzed for various soil test P (STP, intensity) and P sorption measures (capacity), and degree of P saturation (DPS) indices were calculated using different intensity and capacity combinations. Mesocosms were flooded and redox potential, pore water, and floodwater dissolved reactive P (DRP) concentrations were determined periodically up to 42 (in situ) and 56 d (ex situ) after the onset of flooding. Floodwater DRP increased significantly in most soils with flooding time, and the maximum DRP (DRPmax) was considered as the flooding‐induced P release risk. Relationships between floodwater DRPmax and STP or DPS indices were established separately for low‐P (Olsen P ≤ 30 mg kg−1) and high‐P (>30 mg kg−1) soils. Several STP indices effectively predicted the P release risk from high‐P soils, but not from low‐P soils. However, DPS calculated using Olsen P (intensity) and P sorption capacity or P saturation index (capacity) performed better in predicting summer flooding‐induced P release across all soil categories, with a higher predictive power."This work was supported by the Manitoba Conservation and Water Stewardship Fund, Environment Canada through the Lake Winnipeg Basin Stewardship Fund (EC no. 1300328), and a University of Winnipeg major grant. We also acknowledge the Manitoba Graduate Scholarship program and the University of Winnipeg Graduate Assistantship Program."https://acsess.onlinelibrary.wiley.com/doi/10.2134/jeq2019.04.015

Nitrous Oxide Emissions from a Clay Soil Receiving Granular Urea Formulations and Dairy Manure

Soil N2O emissions vary with N source. A study was undertaken on a clay soil in the Red River Valley, Manitoba, Canada, to determine the effect of granular N fertilizers and dairy manure on N2O emissions from a field cropped to rapeseed (Brassica napus L.) in 2009 and spring wheat (Triticum aestivum L.) in 2010. Treatments included an unamended control, granular urea, controlled-release urea (ESN), stabilized urea (SuperU), and solid dairy manure added at rates to achieve a total of 140 kg available N ha-1 (product plus soil N test). The N fertilizers were broadcast and shallowly incorporated each spring before planting; the manure was broadcast incorporated the previous fall. Nitrous oxide emissions were monitored from planting to freeze in fall and during spring thaw in 2011 using static-vented chambers. In both years, N2O emissions occurred within 4 to 5 wk of planting but not in fall after manure application. Area-scale cumulative N2O emissions (∑N2O, kg N ha-1) from planting to freeze were control < ESN = manure < urea = SuperU. Nitrous oxide emission factors were 0.017 kg N2O-N kg-1 available N added for urea and SuperU and 0.007 kg N2O-N kg-1 available N for ESN. Seventy-eight percent of the variation in ∑N2O could be explained by NO3- intensity, an integration of soil NO3- concentrations during the study periods. Greater ∑N2O were also associated with higher yields. These findings suggest that N release rates, as indicated by NO3- intensity and yield, determined N2O emissions. The results highlight the challenge of meeting crop demand yet reducing N2O emissions by selection of an N source. © 2014 by the American Society of Agronomy, 5585 Guilford Road, Madison, WI 53711. All rights reserved

Determination of phosphorous sorption - desorption characteristics of Manitoba soils

Project: MLMMI 03-01-15Develop a relationship between routinely measured soil properties and sorption maxima and degree of P saturation of Manitoba soilshttp://www.manure.mb.ca/projects/viewproject.php?id=2