How does fertilizer solubility affect fertilizer use efficiency?
As a farmer (a real farmer who actually works the land), whether you grow grain, vegetables or fruit trees, you can't avoid dealing with fertilizer every year. And for most farmers, whether the water solubility of fertilizer affects fertilizer use efficiency, and by how much, is unknown. Normally, when farmers choose fertilizer they pay more attention to price and less to solubility. Below I'll talk about how fertilizer solubility (water solubility) affects fertilizer efficacy, as a reference for everyone when buying fertilizer in the future.
First, nitrogen. Nitrate nitrogen has the best water solubility, and nitrate nitrogen also has the highest use efficiency. Next comes amide nitrogen, ammonium nitrogen, etc.
Second, phosphorus. Phosphorus has poor water solubility, especially single superphosphate, calcium magnesium phosphate fertilizer and the like, whose water solubility is poor, so their use efficiency is not as good as relatively water-soluble phosphorus-containing compound fertilizers such as monoammonium phosphate, diammonium phosphate, and nitrophosphate. This is also why the use efficiency of agricultural monoammonium phosphate is lower than that of industrial monoammonium phosphate.
Third, potassium. Potassium also has poor water solubility, especially domestically produced granular potassium sulfate, whose water solubility is extremely poor and whose use efficiency is relatively low. Potassium nitrate, however, has high water solubility and also high use efficiency.
Plants mainly absorb nutrients through their roots. How does the fertilizer we apply to the soil reach the area around the plant roots? There are usually two processes. One is called diffusion. After fertilizer dissolves it enters the soil solution; the nutrients near the root surface are absorbed and their concentration drops, while the soil solution farther from the root surface has a relatively higher concentration, resulting in diffusion, with nutrients moving toward the low-concentration root surface and finally being absorbed. The other is through mass flow, that is, under light the plant's leaf stomata open and transpiration occurs, causing water loss. The roots must continuously absorb water to supply the transpiration loss from the leaves. When the water near the roots is absorbed, water from farther away flows toward the root surface, and the nutrients dissolved in the water arrive at the root surface along with it, where they are absorbed by the roots. Therefore, fertilizer must dissolve to be absorbed; undissolved fertilizer cannot be absorbed by plant roots and is ineffective. So the higher the water solubility of the fertilizer, the higher the chance the plant roots will absorb it, which is why fully water-soluble fertilizer has high use efficiency.
The above are my personal views, and everyone is welcome to discuss them together!
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