Despite the vital role of sulfur in crop productivity, this element has not always received due attention. For many years, sulfur deficiency did not bother most potato growers.
In the past, mineralized organic matter and high-sulphur emissions supplied the needs of crops. Over the past 30 years, with the passing of the Clean Air Act, sulfur emissions have significantly reduced its availability. The fact is that, along with nitrogen, phosphorus and potassium, sulfur is an important nutrient and a limiting factor in the yield and quality of agricultural products.
Sulfur can have a significant impact on both the quality and quantity of potato tubers. It is an essential chemical for building amino acids, and therefore proteins, and can influence tuber development, carbohydrate formation, disease resistance, and chlorophyll production. Research shows that this element has a significant impact on specific gravity, dry matter, sugar and starch content, and tuber size.
Since sulfur deficiency at any stage of plant development can lead to a decrease in yield, a constant supply of sulfur is required - from the emergence of seedlings to the end of the growing season. It is important for crops to have access to sulfur when they need it most.
With sulfur starvation, the tops begin to turn yellow from the tops. Sulfur moves very slowly through the vessels of the plant, so young potato leaves do not pull it away from old ones and turn yellow prematurely.
Sulfur is involved in the synthesis of the amino acids methionine and cysteine, vitamins B1 (thiamine) and B7 (biotin). If the tubers lack sulfur, the nitrogen absorbed by them from the soil does not turn into a protein form.
In potatoes grown under conditions of sulfur starvation, the content of nitrates increases by an average of 22%. The starch content of tubers also decreases, their taste qualities deteriorate, and they ripen longer.
Plants absorb part of the sulfur from the air: the microelement is part of the sulfur dioxide, which is emitted into the atmosphere by industrial enterprises. Rain and melt water also enrich the soil for potatoes with sulfur. In a ton of organic fertilizers (compost or humus) - approximately 0,5 kg of a trace element.
But practice shows that when growing 1 ton of potatoes, 2–4 kg of a microelement is needed. Plants absorb only half of this dose from the air, rain and melt water, and compost.
Polysulfate (0-0-14-19.2S-12.2Ca-3.6Mg) is obtained from polyhalite (natural mineral). This multi-ingredient fertilizer is a sulfate-based source of soluble potassium, magnesium and calcium with a low chlorine content.
The polysulfate extended release characteristic means that the four key nutrients (S 19.2%, K 14%, Mg 3.6%, Ca 12.2%) contained in each granule will be available to the potato during periods of peak demand, from the beginning of leaf growth to tuber maturity.
Calcium in the fertilizer affects the chemical composition of the soil, as well as the quality characteristics of potato tubers. In soils or irrigated cropping systems where water quality can be an issue, adding calcium to the soil can help restore stored salts. Polysulfate is applied before planting, at planting or during ridge formation.
There are three main types of sulfur fertilizers.
- Sulfate-sulfur Fertilizers contain sulfur combined with other nutrients such as nitrogen or potassium. Fertilizer is readily available to growing crops, and sulphate-sulfur fertilizers dissolve quickly. The most common sulfate-sulfur fertilizer is granular ammonium sulfate (20-0-0-24, 21-0-0-24, 19-2-0-22).
- Ammonium sulfate can be mixed with other granular fertilizers, but care should be taken that its physical nature allows the mixture to remain homogeneous.
- Potassium sulphate (0-0-50-18 and other formulations) is also available and works well for legumes such as alfalfa.
There are other fertilizers that contain some amount of sulfur sulfate, either in a mixture or in a commercial product.
- elemental sulfur. Granular fertilizers (from 0-0-0-90 to 99), with a sulfur content of 90 to 99% in elemental form. It cannot be directly used by plants. First, it must be converted by soil microorganisms.
Fertilizers containing sulfur in the form of thiosulfate, such as liquid ammonium thiosulfate (12-0-0-26) and 15-0-0-20 must also be oxidized by microbes in the soil to the sulfate form. Fertilizer can be applied before, during or after planting. However, when applied to the leaves, it can cause burns.
animal dung can provide plants with sulfur along with other nutrients, but the content of the element and the balance with other nutrients must be determined using special analyzes. For example, some pig slurries are low in available sulfur compared to nitrogen.