Identifying environmental phosphorus risk classes at the scale of prince edward Island, Canada

Citation

Benjannet, R., Khiari, L., Nyiraneza, J., Thompson, B., He, J., Geng, X., Stiles, K., Jiang, Y., Fillmore, S. (2018). Identifying environmental phosphorus risk classes at the scale of prince edward Island, Canada. Canadian Journal of Soil Science, [online] 98(2), 317-329. http://dx.doi.org/10.1139/cjss-2017-0076

Plain language summary

Within the pH range of soils grown to potatoes in Prince Edward Island, phosphorus (P) is bound to aluminum (Al) decreasing P availability to the crops. This study used 141 soils sampled across PEI to identify an environmental critical phosphorus index (PSI) that takes into account aluminum (Al) levels and reflects a soil’s susceptibility to release P into runoff water. The identified critical value (P/Al) was used to delineate environmental phosphorus risk classes, which in turn were mapped at the scale of Prince Edward Island using data collected between 2003 and 2015. The environmental phosphorus index was greatly influenced by the soil acidity with soils above pH 5.5 releasing more P than those with pH > 5.5. Six environmental P risk classes from very low to extremely high were identified. The moderate risk class was the predominant class across the Island and corresponded to soils whose P level is sufficient to meet crop P requirements and does not pose a risk to the environment. Hot spots within the risk class categorized as very high or extremely high were concentrated mainly in the western part of PEI, with a few patches in the rest of the province. The results are important to support environmental assessment at the provincial scale for identifying risks for P build-up and release in high-P fields.

Abstract

Phosphorus (P) loss from agricultural land poses a major risk to the environment. The main objectives of this study were (i) to adapt a simple P saturation indicator using 141 soils that had contrasting P levels and to deduct critical environmental P values, and (ii) to identify environmental risk classes and their spatial and temporal distribution at the scale of Prince Edward Island, Canada. The P saturation index (PSI) was greatly influenced by the soil acidity, and two critical P saturation indices were identified (i) a PSI (P/Al)M-III of 19.2% for very to extremely acidic soils (pH < 5.5), and (ii) a PSI of 14.2% (corresponding to 200 mg PM-III kg−1) for slightly to moderately acidic soils (pH > 5.5). Above these critical values, P fertilization should be limited to crop requirements. Six environmental P risk classes from very low to extremely high were identified. Spatial distribution of the identified classes was performed using georeferenced soil data collected between 2003 and 2015. The moderate risk class (P/Al ratio from 7% to 14% for soil pH above 5.5) was the predominant class, covering approximately 70% of the total area. Hot spots in the very high to extremely high range were found in about 10% of the total area, and mitigation strategies are needed to reduce P inputs to control P-related eutrophication risks in surrounding waters.