Features of application of potassium fertilizers

Potassium is still regarded as a third-rate element, the reserves of which in the soil are considered inexhaustible, especially on chernozems. Although back in 1968. A.V. Sokolov, in his work "Geographical patterns of fertilizer efficiency" based on the results of experiments at the Mironovskaya research station (Kiev region) On typical chernozem, gave a convincing example of the appearance of potassium deficiency after many years of traditional farming. 

The experience of world agriculture has shown that potassium is an element of a high yield. However, the use of potash fertilizers in Ukraine has not yet received due attention. This is due to the high natural content of potassium in most soils and a much better supply of it with mobile compounds. Areas with medium and low content of mobile potassium compounds are 30%. Mostly these are soils of sandy and sandy loam granulometric composition. First of all, the sod-podzolic soils of Polissya and the podzolized soils of the Forest-steppe need potash fertilizers. The soils of the Southern Forest-Steppe and almost all the soils of the Steppe are characterized by an increased and high content of mobile potassium compounds. 

Potash fertilizers are most effective on light sod-podzolic soils of Polesie, on drained peatlands, gray forest soils and matured chernozems of the Forest-steppe. 

In the Steppe, where the natural content of potassium is high, it is advisable to apply potash fertilizers primarily to non-saline chernozems, primarily in irrigated fields. Potash fertilizers are not applied to solonetzic and saline soils.

In sandy soils requiring liming, the application of potassium fertilizers increases the need to neutralize soil acidity, since potassium displaces H +, Al3 +, Mn2 + ions into the solution, which reduce the pH. Potash fertilizers become even more important after liming of acidic soils. Yield gains from the application of potassium on soils after liming increase both in absolute and in relative terms. The action of lime on acidic soils, in addition to improving the physicochemical properties of the soil, is also manifested in an increase in the nitrogen-phosphorus nutrition of plants and in a slight decrease in the supply of plants with potassium as a result of the activation of the processes of fixing it with soil colloids. In addition, with an increase in yields from liming, the removal of potassium from the soil increases, and its transition into accessible forms in the soil is slower than in acidic soils. 

As a result of the antagonism of potassium and calcium, there is a need to increase the doses of potassium fertilizers during liming and on soils with a reaction close to neutral. Simultaneously with the improvement of the potash regime of the soil, the efficiency of liming also increases. 

Chernozem soils of the Forest-steppe i Steppe contain a significant amount of potassium available for plants. They are also rich in non-exchangeable potassium, which actively transforms into mobile forms, so the effectiveness of potash fertilizers on these soils is negligible. Even crops that assimilate a large amount of potassium (millet and technical), react poorly to the introduction of potash fertilizers. This can be seen especially clearly on soils with a heavy granulometric composition. However, over time, in particular, for the systematic cultivation of potassium crops and for the introduction of high doses of nitrogen and phosphorus fertilizers, the effectiveness of potash fertilizers increases. This is explained by the depletion of unfertilized soils in potassium as a result of its removal by crops.

Experience shows that at the land-use level, it is sufficient to know the answers to three basic questions to assess the potassium state of the soil in a given field: 

  • What is the optimal amount of potassium available to plants in the soil? 
  • What are the potential potassium reserves in the soil and how mobile are they? 
  • How much potassium is available to plants in the soil and how resistant is it to external influences?

On the same soil, some crops may be sufficiently supplied with potassium, while others may feel a clear lack of it. So, K.P. Magnitsky (1972) drew attention to the fact that crops that assimilate more silicium (cereals) feel less need for potassium due to the increased ability of their root systems to act on potassium-containing aluminosilicates of the soil. The large difference in the assimilation of potassium by individual crops from different layers of the soil profile is associated with the peculiarities of the development of their root systems. 

This whole system functions “smoothly” when the needs of plants correspond to the capabilities of the soil at all stages of their growth and development. Especially when the opposite process acts as a competing factor, for example, in a dry season - fixation of labile potassium in a hard-to-reach state. 

The first two indicators depend on the genetic characteristics of the soil, therefore they change rather slowly over time. The need for their clarification arises no earlier than 5-10 years on soils of light and 10-20 years - of heavy texture. The answer to the third question should be clarified annually (V. Prokoshev, I.P. Deryugin, 2000).

The systematic application of fertilizers, even taking into account the removal by crops, does not significantly increase the content of mobile forms of potassium in chernozems, which is associated with the high saturation of GWC with bivalent bases, which prevent the absorption of potassium. The non-exchangeable uptake of potassium in the upper layers of chernozems is facilitated by the following factors: mineralogical composition – hydromica and highly dispersed minerals of the montmorillonite group, capable of actively fixing monovalent cations, high saturation of HVA with bases, a significant amount of organic substances, almost complete absence of the main competitor of potassium - absorbed ammonium, irreversible coagulation of colloids in case of periodic drying of the top layer. In this regard, potassium, unlike phosphorus, can be applied for the future only for 2-3 years, but this method of applying potash fertilizers for onions and pastures is not recommended. 

An important component of potash fertilizers is sodium, the positive value of which is underestimated. In the production of potash fertilizers, it is completely removed as a ballast element. However, in plants, sodium, along with potassium, performs important physiological functions. As the effect of potassium is less noticeable on soils enriched with sodium, so the effectiveness of sodium decreases with increasing availability of potassium from the soil. 

High doses of potassium fertilizers can cause undesirable effects. In addition to an increase in the potassium content in feed to a toxic level (> 2.5-30%), the content of Mg, Ca and Na in grasses decreases.The use of potash fertilizers containing sodium has a positive effect on both the yield of grasses and their quality (eating), especially the cereal component. 

Intensive combined use of nitrogen and potassium fertilizers on soils of light particle size distribution can contribute to the loss of magnesium and calcium due to the leaching and decrease of their input into plants. To maintain the ratio of cations (K + Na) :( Ca + Mg) in feed close to 2.2 and magnesium content in hay> 0.2% and to prevent cattle from grazing titanium and hypomagnesium, the most reliable method is soil liming with magnesium-containing lime materials.

For most agricultural crops, the average doses of potash fertilizers are 45-60 kg / ha K2O. In crops that carry a lot of potassium with the harvest (beets, potatoes, tobacco, sunflowers, fruit and some vegetables), the dose of fertilizers is increased to 

90-120 kg / ha K2O. The optimal content of exchangeable potassium in the soil for potassium-philic crops is higher in comparison with cereals, legumes, annual and perennial grasses. Naturally, the effect of potash fertilizers is when the content of mobile potassium compounds is 60-100 mg / kg, that is, for most arable lands, the effectiveness of potash fertilizers is variable. 

Usually the dose of potassium fertilizers in conditions of intensive farming should correspond to the withdrawal of potassium from the field by agricultural products (main i non-marketable) with the value of exchangeable potassium in the soil close to optimal. This can be seen in the example of the developed countries of Europe, where on fertile soils the doses of potash fertilizers are maintenance and hardly change. 

Now more and more examples of effective use of potash fertilizers appear on soils where they were not previously used, which indicates not only limiting the potential reserves of potassium in the soil, but also decreasing from year to year the rate of its release into forms accessible to plants. In long-term experiments with fertilizers, a significant decrease in the amount of available forms of potassium in the soil is usually not observed.So, the main reason for the deterioration in the supply of potassium to plants is not an absolute decrease in its amount, but a weakening of the soil's ability to maintain its initial state, to restore the required potassium content in an accessible form (V. Prokoshev, I.P. Deryugin, 2000). It is believed (A.E. Johnston et al., 1998) that in order to obtain high and stable yields from the soil, the following should be assimilated, kg / ha per day: N - 5.0, P2O5 - 0.5 and К2О - 5.0. The potassium content in the soil solution was experimentally established, which provides such a value for the daily assimilation of this element. It depends on several factors and, above all, on the characteristics of the root system of different crops. The power of the root system in different crops is quite different. And the smaller its volume, the higher the reaction of plants to potassium.

Despite the fact that the optimal levels of the content of mobile potassium compounds in the soil have been established, they need to be clarified and differentiated. The value of the indicator of the content of mobile potassium compounds for the corresponding conditions should not be underestimated. It is necessary to know it not only in order to strive to achieve the optimum, but even more in order to avoid excessive application of potassium in areas with high potassium content and unjustified losses of potassium. 

Based on many years of research, a soil model with optimal by a combination of absorbed exchangeable cations in the CEC,%: Ca2 + - 65, Mg2 +, K + - 5, H + - 20 (Bayer, 1945). 

In many European countries, the value of the optimal potassium content has been established depending on the cation exchange capacity (CEC) as an indicator, which guarantees high and stable yields. For practice, the calculation of the optimal content of exchangeable potassium is proposed to be carried out according to the following equation (E.O. McLean et al., 1982):

Opt Ke, mg/kg = 110 + 2.5 CEC. 

In this case, for example, for sandy soils with a CEC of 5 cmol / kg, the value of opt Ke will be 122 mg / kg, and for soils with a heavy granulometric composition with an CEC of 20 cmol / kg – 160 mg / kg of soil. 

In the practice of farming, it is usually difficult to achieve the calculated level of the optimal potassium content in the soil, especially since the concept of calculating fertilizer doses adopted in Ukraine is based on the economically expedient principle - "fertilize plants, not the soil", but for orientation an agronomist must own the following data. For example, on podzolized chernozem, sugar beets did not respond to the application of potassium fertilizers in terms of the content of mobile potassium compounds >160 mg / kg (G.M. Gospodarenko et al., 1998). That is, this is the upper limit of its optimal content for crops of field seeding on this soil subtype. 

The content of mobile potassium compounds in the soil depends on many reasons and conditions.

  1. The balance of potassium in the soils of Ukraine is sharply deficient, but agricultural crops respond little or no response to the use of potash fertilizers. This is apparently due to the imperfection of methods for diagnosing potash regimes of the soil. 
  2. Potassium fertilization helps replenish all forms of potassium in the soil. Each soil feature has its own, only for it, a characteristic capacity for assimilable forms of potassium. In soils of the sod-podzolic type, exchangeable forms of potassium accumulate more, in chernozems - non-exchangeable ones, which can reach 60% of the introduced potassium. In all cases, the available forms of potassium, as they are used, are replenished from its non-exchangeable forms. Therefore, they need to be considered as potentially available forms. 
  3. In terms of movement in the soil, potassium occupies an intermediate position between nitrogen and phosphorus, therefore, for attempts to create an optimal potassium level with a single application of high doses of potassium fertilizers in soils with a heavy granulometric composition, potassium passes into a non-changeable, less accessible form for plants, but in soils of a light granulometric composition. composition, it migrates in significant numbers along its profile. 
  4. Due to the antagonism of calcium and potassium during liming of acidic soils, the content of mobile potassium compounds should be higher. For this, the dose of potash fertilizers is increased by 30-50%.
  5. Cultivated plants react differently to the level of potassium nutrition, therefore, a differentiated approach to its optimization is required during the seeding shift. Potash inaccessibility exists on different types of soils and is most of all tied to individual crops. First of all, potassium-philic crops are fertilized - beets, potatoes, sunflowers, etc. With optimal fertilization systems in the seeding shift, there is usually no need for potash fertilizers for cereals and leguminous crops. 
  6. Chlorine-containing potash fertilizers are usually supplied to agriculture. The negative effect of chlorine is eliminated by optimizing the doses, timing of i methods of fertilization. 

The effectiveness of some forms of potash fertilizers depends on soil and climatic conditions and biological characteristics of crops. In addition to potassium, other elements contained in potash fertilizers - sodium, magnesium, sulfur, chlorine, and the like - also affect the formation of agricultural crops and its quality. On light-textured soils, potassium-magnesia fertilizers (potassium magnesium, kalimag, etc.), which, in addition to potassium, also contain magnesium, are important. On chernozem soils, all forms of potash fertilizers are almost equivalent in efficiency. Almost all of them acidify the soil, therefore, on acidic soils, their use must be combined with liming.

On soils of medium and heavy granulometric composition, potash fertilizers are applied during autumn tillage. At the same time, fertilizers fall into the moist soil layer, where the bulk of plant roots is localized, and are better absorbed by plants. Due to adsorption, potassium is contained in the arable layer of the soil, and chlorine, under the influence of atmospheric precipitation, moves (is washed out) down the soil profile. On light-textured soils in conditions of sufficient moisture, potash fertilizers are best used in spring during pre-sowing soil cultivation. For top dressing, potash fertilizers are less effective than with a single application of the entire dose before sowing, since the root system of plants develops in search of moisture in deep soil layers. Only under irrigation conditions on soils of light granulometric composition, it is sometimes advisable to use a part of the potassium dose for feeding tilled crops. 

Small doses of potash fertilizers (10-15 kg / ha K2O) are applied during sowing of agricultural crops. The line application of potash fertilizers simultaneously with phosphorus fertilizers during sowing of winter crops is especially effective, and contributes to an increase in their winter hardiness. However, an increase in the dose of ordinary application of potash fertilizers reduces the germination of seeds.

Source:

Господаренко Г. М. Система застосування добрив / Григорій Миколайович Господаренко. – Київ: ТОВ "СІК ГРУП УКРАЇНА, 2018. – 376 с.

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