Plants need balanced nutrition to thrive, just like people. One of the important nutrients for plant growth and development is Potassium (K), which is a component of most standard lawn fertilizers. To use Potassium fertilizers correctly, it is important to understand how Potassium functions in plants, and how to recognize the signs of Potassium deficiency.

Potassium in Fertilizer

Potassium is one of the “big three” nutrients found in most lawn fertilizers. Most fertilizer analysis gives the N-P-K number, which indicates what percentage of each nutrient is in the fertilizer. The percentage of Potassium is indicated by the last number in the N-P-K analysis.

Potassium Function in Plants

Potassium is integral to many growth processes in plants, including:

• Photosynthesis
• Starch and protein production
• Enzyme reactions
• Water movement
• Protein synthesis
• Cell wall components
• Fruit development

Recognizing Potassium Deficiencies

(See above picture.) Potassium deficiency is a serious problem for all plants, because it is involved in so many different plant processes. Plants experiencing potassium deficiencies will show the following symptoms:

• Yellowing and curling of edges of lower (older) leaves
• Sometimes leaves will turn purple
• More likely to occur in times of drought stress
• Leaf edges looked burned

There are a number of things that can cause potassium deficiency. Sandy soils tend to be more deficient in potassium, because it is leached easily from soils that do not have a high CEC (Cation Exchange Capacity). Adding organic matter to the soil can help in potassium retention. Soils with a low pH (acidic soils) sometimes have enough Potassium, but it is not available to plants. It is important to test the soil pH to see if the potassium is there, but not available.

Correct Application of Fertilizers

Many soils are deficient in Potassium, but it is always a good idea to look at the soil test before adding any fertilizer. Flowers, fruits and vegetables need more potassium fertilizers during flowering and fruiting. General lawn fertilizers will usually have a balanced analysis, and will have enough Potassium for the average lawn, unless the soil is severely depleted or the pH is off. Apply potassium fertilizers that are balanced with Nitrogen and Phosphorous, and your soil will receive its necessary requirements to support plant growth.

The most common form of potassium fertilizer used in Alberta is potassium chloride (KCl), which has the analysis 0-0-60 or 0-0-62 (Table 4). It is mined and refined in Saskatchewan. Potassium chloride can be blended with nitrogen and phosphate fertilizers to produce grades such as 10-30-10, 6-24-24, etc.

Table 4. Potassium fertilizers

Nutrients – % by weight
Name	N	P205	K20	S	Remarks
Potassium chloride	0	0	60	0	Most commonly available K fertilizer and usually cheapest
	0	0	62	0
Potassium sulphate	0	0	50	18	Contains sulfur as well as potassium
Potassium nitrate	13	0	37	0	Used mainly for vegetables and fruit trees
Sul-Po-MagTM	0	0	23	16	Specialty fertilizer, containing magnesium

Although not extensively utilized to date, potassium sulphate (K2SO4) will soon be produced in Saskatchewan and could be an important fertilizer source in areas where both potassium and sulfur are required nutrients. In the past, potassium sulphate produced in the USA has not been competitively priced with potassium chloride from Saskatchewan.

Method of Potassium Fertilizer Application

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.

Determining the Need for Potassium Fertilization

The easiest way to determine the need for potassium fertilization is through a soil test. In Alberta, response to potassium fertilizer has been related to the amount of potassium extracted from the soil with ammonium acetate. Results of potassium fertilizer research with barley in central Alberta are shown in Table 2.

Large increases in barley yield were usually obtained when potassium fertilizer was applied to soils with less than 151 lb/ac of extractable potassium. On soils with 151 to 250 lb/ac of extractable potassium, moderate fertilization (15 to 30 lb/ac of K2O) usually resulted in a profitable response.

Table 2. Yield response of barley to potassium fertilizer at different soil extractable K levels (Lacombe Research Station and ADA date)

Soil Extractable-K (lb/ac in the 0-6 in. depth)	No. of Sites	Average Increase in Yield (bu/ac)
less than 101	17	25.8
101 – 150	21	12.1
151 – 200	18	5.2
201 – 250	8	5.9
greater than 250	34	3.4

Response to potassium fertilization is sometimes obtained on soils not considered deficient in potassium. Research, principally in Oregon, Washington and South Dakota, has shown that the presence of chloride in potassium chloride can result in increased yield through the suppression of plant diseases such as take-all and common root rot. Such responses cannot be predicted at this time. Therefore, the use of potassium chloride on non-potassium deficient soil for the suppression of disease must be on a trial and error basis.

Research in Montana has indicated that potassium deficiency may occur on soil with high soil-test potassium because of slow potassium diffusion in cold, dense soils. These results have been used to promote the need for potassium fertilization for early seeding of cereal crops in central and northern Alberta.

Research in Alberta on potassium deficient soils has shown equal response of barley to potassium with early and late seeding. If soil potassium was less available at lower soil temperatures, greater response to potassium should have been obtained with early than with late seeding. The results do not support a great potassium requirement for early seeding.