Annual Crops

Since potassium uptake depends primarily on root interception, placement of potassium fertilizers with or near the seed is usually the most effective method of application provided the rate of application is not greater than the seed can tolerate. If too much potassium or other fertilizer is placed with the seed, germination and emergence may be delayed or reduced.

The safe level of potassium that can be applied with the seed depends on the crop. In general, smaller seeded crops such as canola have a lower tolerance than cereal grains. The clay and organic matter content of the soil and the soil moisture content will also have an effect on possible germination problems.

With average soil moisture conditions and for medium textures, the total amount of seed placed fertilizer materials should not exceed 175 lb/ac, and the amount of N plus K2O should not exceed 40 lb/ac. For less tolerant crops such as canola, flax and peas, the application of potassium with the seed should not exceed 15 lb K2O/ac, provided other fertilizers are not seed placed. These recommendations are based on the use of a double-disc or similar drill, which places the seed and fertilizer in a very narrow band. If the opener spreads the seed over a wider band, higher rates of fertilizer can be safely placed with the seed.

Side-band placement is an efficient means of applying potassium. In this placement, the fertilizer is in a band approximately 2.5 cm (1 inch) to the side and 2.5 cm (1 inch) beneath the seed. This separation of fertilizer and seed reduces the possible detrimental effects on germination when high rates are applied. Machinery for placing seed and fertilizer in this configuration is not readily available commercially, and the method is not widely practised.

Banding (also referred as deep-banding of potassium into the soil prior to seeding has, to date, not received a great deal of research attention, but there is no reason to believe that this should not be a good method of applying potassium fertilizer.

The two methods, banding prior to seeding and side-banding, should give similar results.

Broadcasting potassium before seeding is less efficient than applying potassium in a band with or near the seed. The major role for broadcast applications of potassium fertilizer will be in "building up" soils extremely deficient in potassium.

Perennial crops

For perennial forage crops, potassium is best applied by broadcasting and incorporating before seeding. This approach will overcome the problem of limited movement of potassium into the soil when applications are made after stand establishment.

Where established stands require potassium fertilizer, then broadcast applications are the only option, and relatively high rates may be required on severely potassium-deficient soils. Fall or spring applications could be made, but fall applications would likely be preferred in dry areas because of the additional moisture available to leach the potassium to the root zone. For potassium deficient soils, potassium fertilizer will reduce alfalfa winter-kill and help maintain the proportion of alfalfa in mixed stands.