Potash fertilizers come in two main categories: simple potassium fertilizers and compound fertilizers that contain potassium. Understanding the differences between them is essential for proper use and identification.
Simple potassium fertilizers include potassium chloride, potassium sulfate, and potassium silicate. Potassium chloride is commonly available in red and white varieties, with a granular or powdered appearance. The potassium oxide (Kâ‚‚O) content varies, with imported products typically containing around 60%, while domestically produced ones range from 57% to 60%. Potassium sulfate, usually white in color, appears as crystalline particles or powder. It may contain minor impurities, resulting in slight discoloration. Domestic potassium sulfate, such as from Lop Nur or Taiwan, generally contains about 50% Kâ‚‚O, while German production tends to be slightly higher at 54%. Potassium silicate, on the other hand, is a dark gray powder, often a by-product of industrial processes. Its potassium content can only be accurately determined through laboratory testing, typically ranging from 10% to 14%, and it has an alkaline nature.
Compound potassium fertilizers are labeled with N-Pâ‚‚Oâ‚…-Kâ‚‚O values on their packaging. A common example is potassium nitrate, which appears as white crystalline particles but is less commonly found in the market.
Identifying potash fertilizers can be quite challenging without professional tools. While some basic methods exist, they are mostly qualitative and not suitable for determining exact potassium levels. One such method is the iron-burning test. When fertilizer particles are placed on a red-hot iron plate, if they don’t melt, don’t emit any odor, and bounce when heated, they may be potassium-based. If the iron is tilted to expose the fertilizer directly to high heat, a colored flame may appear. A golden flame suggests sodium, while a pale yellow flame with a lavender tint indicates potassium. For powdered potassium fertilizers, the color may vary—brick red, light red, or white. When burned, potassium fertilizers do not melt or smell, whereas phosphorus-based fertilizers tend to emit an odor and may not melt.
Another method involves soaking the fertilizer in water to create a saturated solution, then dipping a wire coil into the solution and holding it over a flame. The color of the flame can help identify the type of fertilizer. However, distinguishing between potassium and sodium based on flame color can be tricky. In cases where low-quality or unrefined materials like potassium feldspar are used, laboratory analysis is necessary to determine the actual soluble potassium content. These methods are limited to qualitative assessments, meaning they can confirm authenticity but not the quality or concentration.
For farmers and users, it's crucial to purchase fertilizers from reputable sources to avoid being misled by substandard products. Always check labels, understand the composition, and consider lab testing when in doubt.
Author: Cao Yiping (China Agricultural University)
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