An Agro-Environmental Phosphorus Model for Potato in the Canadian Maritime Provinces

Phosphorus is essential for potato (Solanum tuberosum L.), an economically important crop for the Canadian Maritime provinces. Nutrient loss, including P, into waterways and estuaries has contributed to reduced water quality such as algae blooms. The objective of this study was to develop an agro-environmental model for potato based on the phosphorus saturation indicator (PSI) expressed as the ratio between Mehlich-III extractable P and Al (P/Al)(M3). A total of 42 field trials (6 conducted from 2000 to 2002 and 36 from 2013 to 2015) were conducted in Prince Edward Island (PEI), New Brunswick (NB), and Nova Scotia (NS) with six increasing P rates. A critical agronomic PSI of 10% was identified, which corresponded to 85% of relative yield. The P recommendation model was subdivided into seven P fertility and environmental risk classes with P rates ranging from 21 to 105 kg P ha(-1), i.e., on average from one to five times the level of P removal by the potato crop, corresponding to the highest ([P/Al](M3) >= 14) and lowest ([P/Al](M3) <= 2.5) PSI levels, respectively. Only one site was in the very low fertility class. Additional trials are needed within this class to build a more robust and representative model. This is the first agro-environmental P model for sustainable potato production that reduces the risk of P loss to watercourses in the region. The new P rates were developed at plot scale and need to be validated at larger scale.