In accordance with long-standing convention, fertilizer potash analyses and crop potash requirements are expressed in this publication on the oxide basis (chemical formula K₂O), rather than as elemental potassium (chemical symbol K). ]

There are several general principles governing the management of soil fertility for crop production (with reference to the soil potash cycle presented in Section 2.).

1. Take advantage of existing soil potash stocks.
2. Use harvest residues in the form of crop residues & livestock manure
3. Minimize losses from soil.
4. Supplemental with fertilizers, if necessary.

Managing existing soil potash stocks.

Natural soil potash stocks in the Atlantic region are usually too low for sustained high crop yields, however, use of livestock manure and / or fertilizer phosphorus may build up the soil phosphorus content to the point that a significant portion of the crops requirements can be met by the soil stocks. The best way to determine the levels of available potash in your soil is by a soil test*. (Analytical labs maintained by the provincial Departments of Agriculture in the Atlantic Region will analyse your soil for a small fee). The soil test lab will deduct a "credit" for available soil potash from the total crop potash requirements. The net potash requirements (total potash requirements minus available soil and manure potash) are reported on the soil test report as a guide for supplemental potash applications.
 

Use and Management of harvest residues and livestock manure.

Plants do not concentrate potash in the seed, as they do for nitrogen and phosphorus. A high proportion of plant potash uptake may remain in the crop residues. Leaving these residues on the soil and incorporating them by tillage helps maintain the available soil potash supply for future crops.

Livestock manure is rich in potash. Most of the potash in livestock feed ends up in the manure. Manure potash is highly soluble and available for plant uptake. Livestock manure may supply most or all of the potash requirements of many crops. Long term, heavy applications of manure can build up soil potash to excessive levels which produce high potash feed that can cause unhealthy nutrient imbalances in livestock.

Management of Livestock Manure

Since nearly all of the potash in manure is soluble K⁺ (the same form that is released by commercial fertilizers) it does not require decomposition of the manure to become available for plant uptake.

Potash credits for manure application should be equal to fertilizer potash credit - in other words, fertilizer applications can be reduced by 1 kg of K₂O for every kg of manure K₂O applied.

Losses of soil, fertilizer and manure potash occur by crop harvest, leaching and erosion. Harvest usually causes the greatest loss. Returning residues in the form of plant residues or livestock manure helps reduce the loss.

Leaching can be a significant loss from sandy soils. Heavy potash applications (more than about 100 kg K₂O / ha) should be split into 2 applications to avoid leaching losses.

Soil conservation measures will ensure that erosion losses of potash are minimized. Avoid over-application of manure and fertilizer potash. Soil tests will indicate the optimum amount of K₂O to use. Incorporation of added potash into soil helps to reduce loss and pollution, while reducing the time it takes the nutrient to reach the crop root zone.

Waterlogged soils produce potash-deficient crops, even when soil potash levels seem sufficient for high crop yield. Uptake of potash by plant roots is dependent soil oxygen supply, which is restricted by excess soil water. Drainage improvement will increase crop potash recovery in poorly drained soils. (see "Farm Drainage in the Atlantic Provinces", ACAE Publ.No.3, Agdex 752, by Advisory Cmte. on Soil & Water, Atlantic Prov. Agr. Serv. Coord. Cmte., 1986.)

Most cropping systems in this region require supplementation of soil potash fertility for sustained crop yield. Supplemental off-farm sources of potash fertility include commercial fertilizers and manure from feedlots and poultry producers. Potash fertilizers used in the Atlantic Provinces are listed in the following table.

Commercial fertilizers are the most common form of off-farm potash supplies for crop production. Muriate of potash (KCl), accounts for more than 90% of the potash fertilizer used in the Atlantic Provinces. Muriate of potash is the highest analysis (0-0-60) and most economical potash fertilizer available.

Timing and placement of potash fertilizer are less critical than for nitrogen or phosphorus fertilizers. Potash can be mixed with N and/or P₂O₅ fertilizers and spread according to the schedule for nitrogen or phosphorus. Potash fertilizer has high salt index, so if you include it in a banded application, the additional fertilizer increases the risk of fertilizer burn to the seed or seedling.