Description
Potash is used primarily as an agricultural fertilizer because it is an excellent source of soluble potassium.
The Key Role of Potassium in Plant Nutrition
Potassium is essential in nearly all processes needed to sustain plant growth and reproduction.
Potassium increases the yield and quality of agricultural produce and enhances the ability of plants to resist diseases, insect attacks, cold and drought stresses, and other adverse conditions. It helps in the development of a strong and healthy root system and increases the efficiency of the uptake and use of nitrogen and other nutrients. In addition, potassium has an important role in animal and human nutrition.
Is potash good for plants?
Potassium not only increases yields but also enhances crop quality. It improves the nutritive value of grains, tubers, and fruits by increasing the contents of protein and oil in seeds, starch in tubers and seeds, and vitamin C and sugar in fruits. With an adequate supply of potassium, cereals produce plump grains and strong stalks. Potassium also improves the flavor and color of fruits and increases the size of tubers and fruits. In addition, it increases the resistance to various injuries during storage and transportation, thus extending shelf life.
Potassium in fruits and agricultural produce is taken away from the farm’s ecosystem at harvest, thus high quantities of potassium are removed from the soil. The higher the yields, the higher the uptake of potassium. The result: the potassium levels tend to decline over time, and soils can become deficient in potassium. Without any replenishment of the potassium natural reserves, yields and sustainability cannot be maintained in the long term.
The potassium in potash fertilizer is vital to the proper functioning of plant physiological processes. Potassium is associated with the movement of water, nutrients, and carbohydrates in plant tissue. It affects protein, starch, and adenosine triphosphate (ATP) production which in turn can regulate the rate of photosynthesis.
The main functions of potassium in crops are as follows:
- Photosynthesis
- Nitrogen fixation
- Translocation of plant starch and sugars
- Increase plant tolerance to disease
- Maintain water balance in plant cells
- Activate over 80 cellular enzymes
Potassium also assists in the control of the opening and closing of the stomata, which in turn controls the exchange of water vapor, oxygen, and carbon dioxide. If potassium is deficient or not supplied in adequate amounts, plant growth and yield is reduced or compromised.
Organic Crop Production
The basic principles of plant nutrition are the same, whatever the production system used. Both organic and conventional production systems have many common objectives and generally work with the same basic global resources. While specific nutrient management techniques and options may vary between the two systems, the fundamental processes supporting soil fertility and plant nutrition do not change. In general, the objectives of organic plant nutrition are to (i) work within natural systems and cycles, (ii) maintain or increase long-term soil fertility, (iii) use renewable resources as much as possible, and (iv) produce food that is safe, wholesome, and nutritious.
Which Organic Standards to Follow?
The use of approved nutrient sources is governed by a variety of regional, national, and international oversight organizations. Each organization maintains somewhat different standards and allows different materials to be used in their organic production systems as they individually interpret the intent of organic agricultural principles. As a result, a grower seeking advice on permissible organic materials should first know where the agricultural produce will be sold in order to meet the requirements of that market. In general, regulations for mined K sources specify that they must not be processed, purified, or altered from their original form. However, there is disagreement between different certifying bodies over what specific materials can be used. Unfortunately, some of these restrictions on certain nutrient materials do not have solid scientific justification and their inclusion or exclusion on various lists should not be viewed as one material being more or less “safe” than another fertilizer material.
Using On-Farm Resources
There are many variations possible for successful K management in organic production systems. The largest differences occur on farms that produce both livestock and crops compared with farms that strictly produce crops for off-farm sale. In the mixed livestock/crop systems, the nutrition of the animals generally takes first priority and the residual manure is returned to surrounding cropland. In these cases, imported K in feed and bedding frequently exceeds the output in milk and meat products, sometimes leading to an accumulation of K in the surrounding fields that receive manure. Large losses of K may occur on these farms during manure storage and composting. Since excreted K mostly goes into urine, if this fraction is not effectively recovered it will not be returned to the field with the solid portion of the manure.
Crop rotations are a central part of organic production systems. While this practice can be helpful for supplying N when legume crops are included and may also reduce K leaching losses, rotations alone do not supply any additional K to the farm. Plant roots have been shown to enhance soil mineral weathering by depleting rhizosphere K and causing a shift in the K equilibrium. This shift can speed natural processes and enhance the rate of clay transformations. Subsoil K reserves may be important for some crop rotation systems where deep rooted plants can extract K which may be subsequently used by shallow-rooted crops. While rotational crops may influence the availability of existing soil K, the removal of any plant material from the field continually depletes the soil nutrient supply and ultimately reduces long-term productivity. Plant-available K is usually measured in the topsoil, but some deep-rooted plant species can take up considerable amounts of K from the subsoil. The contribution of subsoil K to the plant K requirement depends on the amount of plant available K in the top and subsoil, potential root-limiting factors, and the root distribution pattern of the specific crop. Soil testing done near the soil surface will not account for this subsoil contribution to the K supply.
Potassium Balance
Since off-farm sales will always lead to a removal of K and additional loss of K through leaching and runoff is inevitable, the potential of a cropping management system to replenish the K reserve is important. The use of farm budgets is useful for describing the nutrient flow within a farming system and to assist with nutrient planning for long-term rotations and mixed farming systems. Depending on a variety of factors, the on-farm budgets of N, P, and K on organic farms have been shown to range from a surplus to a deficit. The demand for K by various crops has been well established by measuring the K concentration in the harvested portion of the crop. However, much less attention has been paid to the rate at which K must be supplied to growing plants. Both the total amount required (quantity) and the rate of supply (intensity) are equally important. This concept is important for all crop growth, but requires special attention when using low-solubility nutrient sources that may provide an adequate amount of total K, but not at a rate sufficiently rapid to meet peak-demand periods of plant growth.
Potassium Release from Soil Minerals
The most common mineral sources of K in soils are feldspars and micas…soil minerals remaining from the primary parent material. Weathering of these primary minerals produces a range of secondary minerals that may also serve as a source of K in soil. These minerals include micaceous clays such as illite and vermiculite. Crushed rocks and minerals have been evaluated as K sources in many field and greenhouse experiments. In general, plants are able to gain a very limited amount of K from minerals applied as biotite, phlogopite, muscovite, and nepheline. Feldspar K is not plant available without additional treatment or weathering.
The rate of K release from minerals is influenced by factors such as soil pH, temperature, moisture, microbial activity, the reactive surface area, and the type of vegetation. Therefore, a mineral that is somewhat effective as a K source in one condition may be ineffective in another environment. Some soil minerals may act as a sink for removing K from solution. When K is adsorbed in the interlayer sites of illite, vermiculite and other smectite clays, the clay layers collapse and trap the K within the mineral lattice. This fixation process is relatively fast, while the release of this interlayer K is very slow. Non-exchangeable K should not be confused with mineral K, since non-exchangeable K is held between adjacent tetrahedral layers of clay, instead of being covalently bonded in mineral crystal structures.
