The Role of Potassium Fertilizer in Crop Nutrition, Which Crops It Suits, and the Best Placement for Application

Potassium fertilizer has always been one of the three indispensable elements in crop growth. When crops lack potassium fertilizer, they develop “soft bone disease” and are prone to lodging. So what are the roles of potassium fertilizer? Which crops is it most suitable for?

The roles of potassium fertilizer

First, it improves stress resistance. During plant growth, potassium participates in many physiological activities. It can promote the metabolism of carbohydrates and nitrogen, control and regulate the activity of various mineral nutrients, activate the activity of various enzymes, control the transport of nutrients and water, and maintain the internal pressure of cells, thereby preventing plants from wilting.

Second, it improves quality. Applying potassium fertilizer can improve crop stress resistance and plays a very important role in ensuring high and stable crop yields. For example, in corn, applying potassium fertilizer can improve the quality of corn stalks and prevent lodging.

Third, it increases yield. Because the original soil in some areas has relatively high potassium content, many farmers have not yet realized the important effect of potassium on yield.

Which crops is potassium fertilizer most suitable for?

Types of potassium fertilizer include potassium sulfate, potassium chloride, monopotassium phosphate, potassium nitrate, and plant ash (whose main component is potassium carbonate).

1. Monopotassium phosphate: Monopotassium phosphate is a colorless tetragonal crystal or white crystalline powder. In agriculture it is used as a high-efficiency phosphorus-potassium compound fertilizer; monopotassium phosphate products are widely suitable for almost all types of crops, including various cash crops, grains, melons and fruits, and vegetables.

2. Potassium chloride: The active ingredient content is generally 50-60%. It is a physiologically acidic fertilizer and can be used as a base fertilizer, topdressing, and foliar topdressing. Application should be avoided in coastal areas, and it is prohibited for varieties prone to manganese toxicity (apple rough bark disease), such as Fuji and Red Star.

3. Potassium sulfate: The active ingredient content is generally 50%-52%. It is a good potassium sulfate compound fertilizer suitable for various fruit trees and can be applied as a base fertilizer and topdressing.

4. Plant ash: It contains a variety of ash elements, such as potassium, calcium, magnesium, sulfur, iron, and silicon. Among them, potassium and calcium are the most abundant, followed by phosphorus. Grass-family plant ash contains K2O-8.09%, P2O5-2.3%, and CaO-10.72%. Plant ash can be applied as a base fertilizer and topdressing. Broadcasting it in early spring gives the best effect; it can not only meet the needs of fruit tree growth and development, but also raise soil temperature and benefit root growth. Plant ash is alkaline and must not be mixed with ammonium nitrogen fertilizers, so as to avoid ammonia volatilization.

Should potassium fertilizer be applied?

The application of potassium fertilizer has never received much attention, which is closely related to the potassium content in the soil. The potassium supply capacity of China's soils varies greatly from region to region, generally low in the south and high in the north, and low in the east and high in the west. However, because people have long paid no attention to potassium fertilizer application, soil potassium content in many areas is declining. So, should potassium fertilizer be applied or not?

First, look at the soil. Potassium content in China's soils is gradually decreasing. In addition, potassium fertilizer should be applied in appropriate amounts to northern soils.

Second, look at the crop. Because potassium plays an important role in increasing the protein and sugar content of crops, potassium fertilizer is generally recommended for cash crops, especially legume crops, tuber crops, cotton and hemp, tobacco, and fruit trees.

Third, look at external nutrient inputs. In recent years, returning straw to the field has been promoted, because straw has a relatively high potassium content and releases it easily, supplying a large amount of potassium to the soil.

Where is application most effective?

When potassium-demanding crops are in a rapid growth period, foliar spraying is best. For example, cotton is a potassium-loving crop. During the rapid growth period of cotton bolls, the amount of potassium transported by the root system cannot meet demand, and the potassium contained in the leaves near the cotton bolls is quickly depleted. At this time, spraying potassium fertilizer on the crop leaves can make up for the potassium deficiency and increase cotton lint yield.

When crop roots are developing, deep application is best. The commonly used conservation tillage leaves more crop residues on the soil surface, which also causes a relatively high concentration of potassium to accumulate in the surface soil and prevents it from reaching deeper soil layers.

When soil moisture is good, this potassium can infiltrate downward smoothly, but when the soil is dry, potassium uptake is restricted. Because crops root deeper below the soil layer richest in potassium in order to obtain enough water, this mismatch leads to potassium deficiency in crops. In this case, deep application of potassium fertilizer can significantly improve potassium availability.

The placement of other nutrients also determines how much potassium crop roots can come into contact with. Nitrogen and phosphorus can stimulate crop root branching, and where the concentration of these nutrients is higher, the proportion of roots will be greater. Applying potassium fertilizer in the same furrow as nitrogen and phosphorus fertilizers can increase the opportunities for roots to contact potassium.

What to pay attention to when applying potassium fertilizer?

1. Apply according to the soil

Potassium fertilizer should first be applied to areas with severe soil potassium deficiency. From the perspective of soil texture, sandy soils often have lower available potassium content and should receive more potassium fertilizer; clayey soils often have higher available potassium content and can receive less or none. Soils deficient in both potassium and sulfur can be given potassium sulfate, while potassium chloride must not be applied to saline-alkali land.

2. Apply according to the crop

In rainy areas or areas with irrigation conditions and good drainage, most crops can be given potassium chloride. A small number of cash crops should not be given potassium chloride in order to improve quality.

3. Reasonable combination

For tobacco, sugar crops, and fruit trees, potassium sulfate is the better choice; because potassium sulfate costs relatively more, potassium sulfate can be chosen for high-efficiency cash crop fields, while for ordinary field crops, except for a few chlorine-sensitive crops, the cheaper potassium chloride is preferable.