Crop Nutrient Balance - Atlantic Canada - Phosphorus

The phosphorus (P) balance shows a substantial surplus in Atlantic Canada, largely owing to the prevalence of potato production. The surplus has shrunk over time, though it continues to vary in size from year to year. The surplus has contributed to high soil test levels for P. Phosphorus reacts with common soil substances to form minerals. Whether applied as fertilizer or manure, a fraction is always kept away from plants by reactions with calcium, aluminum and iron. A deficient soil must usually be fertilized with considerably more than the plants remove. Over the years, the fractions that remain in the soil gradually build up, and begin to contribute a greater proportion of the plant’s needs. Eventually, phosphorus no longer needs to be added in amounts greater than plant removal. Building up the soil test is a necessary condition for efficient fertilizer use, where the amount applied doesn’t have to exceed the amount removed. Potatoes grown in Prince Edward Island and New Brunswick are generally fertilized with considerable more P than they remove, owing to their high requirement for optimum growth. Thus, Atlantic Canada has a larger P surplus on a cropland area basis than many other regions (Figure 1). Hay and potatoes have the highest crop removal of P (Figure 2). The P in manure is less susceptible to loss, and thus a greater fraction is recoverable, compared to N (Figure 3). The last two years show decreases in all sources of manure P owing to reductions in livestock and poultry. The actual decreases may be even larger owing to increasing use of diets with reduced P supplementation, and in the case of hogs, phytase. The fate of the non-recoverable fraction is mostly on pastures which are not included in the crop removal figures.

Note: amounts of phosphorus are expressed as P₂O₅ - to convert a figure expressed as P₂O₅ to P, multiply by 0.43.



Figure 1. Phosphorus inputs to cropland include recoverable manure and fertilizer. Removal by harvested crops is shown by the vertical bars. The units are pounds of P₂O₅ per acre of total cropland. Non-recoverable manure is mainly left on pasture, and is not part of the cropland nutrient balance.



Figure 2. Phosphorus removed by harvest of major crops. Stacked areas sum to removal by the listed crops.



Figure 3. Phosphorus in manure, as-excreted and recoverable, from cattle, hogs and poultry.