Application of Potassium Fertilizers

Last updated: June 21, 2025

Timing, Methods, and Forms of Applying Potassium Fertilizers

On medium- and heavy-textured soils, chlorine-containing potassium fertilizers at the full rate, except for row application in small rates for some crops, should be applied for autumn tillage. This allows fertilizers to be placed in a wetter soil layer where the bulk of roots develop; during autumn-spring, chlorine is leached from the arable layer. Only on light, peat-bog, and floodplain soils are potassium fertilizers applied in spring. For row and vegetable crops, part of the total potassium rate should be applied as top dressing.

In crop rotation, potassium fertilizers are applied first of all for potassium-demanding crops, which produce significant yield increases.

Flax and hemp consume relatively little potassium, but because of their weak root system, which under normal conditions cannot provide plants with sufficient potassium, increased rates of potassium fertilizers are applied to these crops.

For chlorine-sensitive crops, it is advisable to apply potassium fertilizers with a minimum chlorine content. When chlorine-containing potassium fertilizers are used for potato, starch content decreases by 7-15% compared with chlorine-free fertilizers.

Application of Potassium Fertilizers on Various Soils

In Russia, over 1/3 of arable land is characterized by low and medium levels of exchangeable potassium and requires potassium fertilizers. Their use is most effective on sandy, sandy loam sod-podzolic, peat-bog, floodplain soils, and red soils. They also have a positive effect in the zone of sufficient moisture on loamy sod-podzolic, gray forest soils, podzolized and leached chernozems with low and medium potassium supply.

Sod-Podzolic Soils

Sod-podzolic soils have relatively small reserves of available potassium. Nonexchangeable potassium is part of the secondary clay minerals predominant in these soils—kaolinite and montmorillonite—which cannot restore exchangeable potassium reserves. This explains the positive effect of potassium fertilizers on sod-podzolic soils.

According to long-term experiments, annual application of potassium fertilizers at 30-90 kg K₂O per 1 ha increases yields of root and tuber crops, primarily potato, and cereal crops. The greatest yield increases, up to 30-50%, are obtained on light loamy and sandy soils, where potassium reserves are extremely small. In shorter experiments on a nitrogen-phosphorus background, potassium fertilizers also give yield increases of all crops already in the first crop rotation: increases in cereal crops averaged 10-20%, root and tuber crops—more than 30%.

As soil potassium reserves are depleted and nitrogen-phosphorus plant nutrition improves, the need for potassium fertilizers increases, and their effectiveness rises, especially on soils heavy in granulometric composition. Because of the small reserves of mobile potassium in sod-podzolic soils, application of moderate rates up to 90 kg/ha K₂O does not ensure a positive balance. However, the content of exchangeable potassium in the soil, owing to dynamic equilibrium between potassium forms in the control, remains at the initial level. This is associated with mobilization of natural soil potassium caused by the physiological acidity of fertilizers, biological accumulation by plants as a result of their better development in fertilized variants, and also with inclusion of potassium from the subarable and underlying soil layers. Mobilization of nonexchangeable potassium under the influence of fertilizers ensures an increase in mobile potassium forms and is accompanied by a decrease in its reserves.

Gray Forest Soils

Gray forest soils are characterized by a low content of exchangeable potassium in the arable layer. However, compared with sod-podzolic soils, the effect of potassium fertilizers on the yield of various crops is weaker. This is because nonexchangeable potassium of the silt fraction is part of hydromicas of loess-like loams—the main soil-forming rock of gray forest soils. Hydromicas have a high fixing capacity for monovalent cations and can easily release nonexchangeably absorbed potassium, which either passes into exchangeable state or is used directly by plants.

Study of the potassium regime of gray forest soils in long-term experiments showed that during one crop rotation, with application of low fertilizer rates, a negative potassium balance develops. But despite this, an increase in the content of available potassium forms (exchangeable and easily hydrolyzable) is noted while the level of the nonexchangeable form is maintained in fertilized variants. Under the influence of plants and fertilizers, all reserve potassium forms are mobilized and pass into exchangeable state.

With long-term use of nitrogen-phosphorus fertilizers in crop rotation on gray forest soils, the effect of potassium increases from rotation to rotation.

Chernozem Soils of the Forest-Steppe and Steppe Zones

Chernozem soils of the forest-steppe and steppe zones contain sufficient reserves of plant-available potassium. The soil-forming rocks and clay minerals of chernozems are rich in nonexchangeable potassium, which actively passes into mobile forms; therefore, the effectiveness of potassium fertilizers on these soils is small. Even potassium-demanding crops (row and industrial crops) respond little to potassium fertilizers. This is especially noted on soils of heavy granulometric composition.

Over time, the effectiveness of potassium fertilizers increases, which is especially noticeable in sugar beet cultivation and other potassium-demanding crops, as well as when potassium is applied against a background of nitrogen-phosphorus fertilizers. This is explained by depletion of soils not fertilized with potassium due to removal by crop harvests.

Systematic fertilizer application does not lead to a significant increase in the content of mobile forms in chernozems even with a positive balance. This is due to the high saturation of the absorption complex of chernozems with divalent bases, which prevents potassium absorption. Favorable conditions for potassium fixation in chernozems include: mineralogical composition of the silt fraction—hydromicas and highly dispersed minerals of the montmorillonite group, which are characterized by a high ability to fix monovalent cations; high saturation of the SAC with bases; increased soil acidity; high organic matter content; absence of a potassium competitor—absorbed ammonium; and irreversible coagulation of colloids during periodic drying of the upper layer. These conditions promote nonexchangeable potassium absorption in the arable and subarable layers. With a negative balance in fertilized variants, the increase in nonexchangeable potassium is explained by mobilization of less mobile forms under the influence of plants and fertilizers, as well as by release of potassium from secondary minerals—hydromicas.

Potassium has a positive effect under unfavorable weather conditions. With abundant atmospheric precipitation, it reduces lodging of cereal crops; in dry years it helps combat scorching caused by dry winds. Correct use of potassium fertilizers on chernozems, that is, against a background of nitrogen-phosphorus fertilizers in wet and dry years, increases yields of the main crops, especially potassium-demanding ones.

Chestnut Soils and Serozems

The content of mobile potassium in chestnut soils of the dry steppe and serozems of Central Asia is high, reaching 40-60 mg K₂O/100 g soil. Potassium reserves are huge, since it is part of hydromicas and is easily released; therefore, the effectiveness of potassium fertilizers is insignificant.

On old-arable, long-used irrigated serozems, with systematic application of nitrogen and phosphorus fertilizers, the content of mobile forms is low; therefore, yield and quality of crops, primarily cotton, increase.

Soils of Steppe and Dry-Steppe Regions

Soils of steppe and dry-steppe regions are most often well supplied with potassium. Due to variability in moisture supply conditions, on typical, ordinary, southern chernozems, chestnut soils, and serozems, the effect of potassium fertilizers is small or does not appear at all. Application of potassium fertilizers is justified only for potassium-demanding crops—sugar beet, sunflower, vegetables—on chestnut soils and serozems under irrigation.

The process of potassium depletion of soils in the dry-steppe and desert zones, owing to large reserves of nonexchangeable potassium, mineralogical soil composition, and soil-forming rocks, proceeds slowly. Periodic replenishment of potassium reserves through its input with irrigation water is important. A decrease in soil potassium content during long-term use and systematic application of nitrogen and phosphorus manifests itself as signs of potassium starvation in plants and an increase in the effectiveness of potassium fertilizers.

On solonetzes, as a rule rich in potassium, potassium fertilizers are not applied, since they increase solonetzicity and do not produce the expected effect.

Application of Potassium Fertilizers and Liming

Application of potassium fertilizers on sandy soils that need liming increases the need for neutralizing soil acidity, since potassium displaces hydrogen, aluminum, and manganese ions, which reduce pH, from the soil absorbing complex. When acidic soils are limed, the need for potassium fertilizers increases. Increases from potassium against the background of lime increase in absolute and relative terms. The effect of lime, in addition to improving the physicochemical properties of soils, is manifested in improving nitrogen-phosphorus plant nutrition and some reduction in potassium availability to plants due to increased fixation by soil colloids. With yield growth under liming, potassium removal from soil also increases, while transition into available forms proceeds less intensively than in acidic soils.

Because of the antagonism of potassium and calcium, it becomes necessary to increase rates of potassium fertilizers during liming and on soils with a neutral reaction. Liming soils in such cases significantly increases the effectiveness of potassium fertilizers.

On the other hand, improvement of the potassium regime increases the return from liming. Application of manure reduces the effect of potassium fertilizers, since it influences the nutrient regime of soils while also being a good source of potassium.

Increasing the Effectiveness of Potassium Fertilizers

Main ways to increase the effectiveness of potassium fertilizers:

Application taking into account natural-economic conditions and soil supply with mobile potassium forms.
Improving farming culture, soil cultivation, optimal provision of crop rotation crops with other fertilizers, that is, balanced nutrition of agricultural crops.
Liming acidic soils.
Applying potassium in crop rotation first of all for crops with high response to potassium.
Selecting forms of potassium fertilizers taking into account biological characteristics of crops. For example, potassium sulfate and potassium chloride affect the yield of most crops equally. Chlorine-free forms help increase yields of buckwheat, millet, and some varieties of tobacco, increase sugar content in berries of certain grape varieties, starch content in tubers of late potato varieties, and improve flax fiber quality.
Correct selection of timing and methods of application. In most regions of the country, potassium fertilizers are applied in autumn for autumn plowing, except for sandy soils and flooded floodplains. This promotes uniform distribution of potassium in the arable layer and leaching of chlorine into underlying horizons during autumn-winter and spring periods.
Optimization of potassium fertilizer rates taking into account meteorological conditions. Thus, application of 80 kg/ha K₂O against N60P60 increased the yield of winter wheat compared with the background at an average temperature for May-July of 16.5 °C by 2.4 c/ha, at 15.2 °C by 6.6 c/ha, and at 13 °C by 11.9 c/ha. This is due to difficulty of potassium uptake by plants at low temperature. Potassium fertilizers improve the physical properties of grain, especially with excess precipitation in July of more than 80 mm, during filling and ripening. For example, in the Non-Chernozem zone during this period, potassium deficiency produces small and shriveled grain.
Full provision with optimal rates of potassium fertilizers in combination with other nutrients for peat (newly developed and old-arable), peat-bog soils, which are poor in this element (0.02-0.3 of total content). In these soils potassium is mobile, does not accumulate in the arable horizon, and is almost completely used by plants in the first year of application. The effect of fertilizers increases with dual regulation (irrigation and drainage) of these soils. The greatest effect is achieved for vegetables and fodder root crops, which repay potassium application with yield increases.

According to soil supply with exchangeable potassium, several soil groups are distinguished.

Table. Gradations of soil supply with mobile (exchangeable) potassium, mg/kg soil (Methodological guidelines for integrated monitoring of soil fertility of agricultural lands, 2003).

Supply level	Kirsanov method	Chirikov method	Machigin method	Maslova method	Egner-Riehm method
Very low	< 40	< 20	< 100	< 50	*
Low	41-80	21-40	101-200	51-100	< 70
Medium	81-120	41-80	201-300	101-150	71-140
Increased	121-170	81-120	301-400	151-200	> 140
High	171-250	121-180	401-600	201-300	*
Very high	> 250	> 180	> 600	> 300	*

Generalization of long-term stationary experiment data from the geographic network showed that a content of 10-15 mg K₂O/100 g soil and application of 60-90 kg K₂O/ha on sod-podzolic, gray forest soils, and leached chernozems ensures crop rotation productivity of 3-5 t/ha of grain units. However, substantial potassium reserves and dynamic equilibrium between its forms make the indicator of exchangeable potassium content, as characterizing the soil's ability to provide potassium nutrition to plants, less reliable. All forms of soil potassium participate in plant nutrition; therefore, mobile forms (soil solution and exchangeable) and nonexchangeable potassium of primary and clay minerals should be taken into account, as well as mobility, ability, and rate of restoration of exchangeable potassium from reserve forms.

Soil supply with nonexchangeable potassium depends on the type of clay minerals, genetic characteristics, and granulometric composition of soils. The greatest amount is bound by micaceous minerals (hydromicas, illite, vermiculite), less by montmorillonite, and the least nonexchangeable absorption is by kaolinite.

According to the degree of supply with nonexchangeable potassium, soils are divided into groups:

low 10-20 mg K₂O/100 g soil,
medium 20-50 mg K₂O/100 g soil,
increased 50-100 mg K₂O/100 g soil,
high 100-150 mg K₂O/100 g soil.

With long-term application of potassium fertilizers, the amount of exchangeable potassium increases, its mobility and share in the easily hydrolyzable and nonexchangeable fractions grow. As these indicators increase, the effectiveness of "freshly applied" potassium decreases and the aftereffect of "residual" potassium accumulated as a result of fertilizer application increases. However, these data do not allow establishing criteria of potassium supply common to all soils.

There are different methodological approaches for determining the degree of supply with mobile potassium. For example, this indicator can be determined by saturation of the absorbing complex with exchangeable potassium, taking 1.8-3.0% as the active level. However, the value of saturation of the soil absorbing complex with exchangeable potassium should be established for each soil type depending on the mineralogical composition of the silt fraction of the soil and underlying soil-forming rock, biological characteristics of crops, conditions of nitrogen-phosphorus nutrition, and moisture supply. In each specific case, the lower the saturation of the absorbing complex with potassium, the higher the effectiveness of applied fertilizers.

Optimal potassium concentrations in soil have been established, although they require refinement.

1. Potassium in soil is in various interconnected forms. When potassium fertilizers are applied, its reserves are replenished, but due to differences in the composition of clay minerals, the content of the exchangeable form increases more in sod-podzolic soils, while in chernozems the nonexchangeable form increases more. In all cases, during plant nutrition, available potassium forms are replenished from nonexchangeable forms. Therefore, this is taken into account when determining potential reserves of available potassium.

2. Potassium in soil is less mobile than nitrogen but more mobile than phosphorus. Therefore, when attempting to create an optimal potassium level by periodic application of high rates on heavy clay soils, potassium is fixed by minerals, while on light sandy and sandy loam soils it migrates through the soil profile beyond the root-inhabited layer.

3. Application of increased rates of fertilizers and chemical ameliorants changes potassium availability to plants. For example, when acidic soils are limed, even with a high potassium content, its availability decreases due to calcium-potassium antagonism. Therefore, on limed soils, optimal rates of potassium fertilizers are increased by 1.5-2 times. Antagonism and synergism exist between potassium and other cations and anions.

4. Cultivated plants respond differently to potassium nutrition. A group of potassium-demanding crops has been identified, for which the optimal level of exchangeable potassium should be higher than, for example, for cereal grains, grain legumes, annual and perennial grasses.

5. Chlorine-sensitive crops respond negatively to excess chlorine in soil. Elimination of this negative phenomenon is achieved by regulating rates, timing, and methods of application. For example, early application of chlorine-containing potassium fertilizers in autumn for autumn plowing.

Rates of Potassium Fertilizers

Optimal rates of potassium fertilizers in crop rotations depend on the place, frequency, and sequence of applying lime and manure. When sod-podzolic soils are limed and yields increase accordingly, the need for potassium fertilizers increases especially strongly.

According to long-term field experiments on sod-podzolic soils with an initial pH of 4.2, when potassium fertilizers were applied in parallel against a lime background and without it, it was shown that after the first rotation (6-8 years) the amount of exchangeable potassium in limed soils with pH 5.0-5.6 decreased by 2 times compared with unlimed soils with pH 4.0-4.3 and was associated with increasing potassium fixation. With application of 35-50 kg K₂O/ha, this ratio was preserved, although the content of exchangeable potassium in both backgrounds increased by 10%. When the potassium rate was increased to 70-100 kg/ha, the difference between backgrounds was 20% and disappeared at rates above 100 kg K₂O/ha. This explains the fact that against a limed background higher rates of potassium fertilizers were effective, since the same level of exchangeable potassium content (11 mg K₂O/100 g) was achieved without liming with a rate of 60 kg K₂O/ha, and with liming with 100 kg/ha potassium.

Thus, the effectiveness of potassium fertilizers on sod-podzolic soils is related to acidity: the lower it is, the higher the effect from K₂O application. On acidic sod-podzolic soils, increasing potassium rates above 60 kg/ha on average per crop rotation does not increase productivity while reducing return. On limed soils, when nitrogen and phosphorus are applied at rates of 100-120 kg/ha, the effectiveness of potassium fertilizers is substantial, does not decrease with increasing potassium rates up to 140 kg/ha, and averages 20-25%. The return on increased potassium rates is at least 5 grain units/kg.

Application of organic fertilizer without liming reduces the effectiveness of potassium fertilizers the more, the higher the manure rates.

On chernozems, primarily in steppe regions, the effect of potassium fertilizers is weaker, which is explained by the high content of mobile potassium forms. However, with systematic application of high rates of nitrogen-phosphorus fertilizers, the role of potassium increases. Therefore, when determining the effectiveness of potassium fertilizers, the intensity of crop rotation, saturation with potassium-demanding crops, and optimization of plant nutrition with macro- and microelements are taken into account.

Response of Crops to Potassium Nutrition

Potassium fertilizers often contain large amounts of ballast elements; therefore, application of chlorine-containing fertilizers to a crop that responds negatively to chlorine leads to reduced yield and worsened product quality. If chlorine-containing potassium fertilizers must be applied, they are applied in autumn for autumn plowing. In this case, chlorine, which is poorly adsorbed by soil, is leached into underlying layers and does not have a negative effect on yield. Application of chlorine-containing potassium fertilizers to chlorine-sensitive crops during the growing season is especially unacceptable.

References

1. Yagodin B. A., Zhukov Yu. P., Kobzarenko V. I. (2002). Agrochemistry. Ed. B. A. Yagodin. Moscow: Kolos.

2. Evtefeev Yu. V., Kazantsev G. M. (2013). Fundamentals of Agronomy: textbook. Moscow: FORUM.

3. Mineev V. G., Sychev V. G., Gamzikov G. P. et al. (2017). Agrochemistry. Textbook. Ed. Mineev V. G. Moscow: Publishing House of VNIIA named after D. N. Pryanishnikov.