The anti-flocculation ability of humic acid in liquid fertilizer (especially foliar fertilizer) is more important than the stability of the humic acid raw liquid. Even if the solid particles of the humic acid raw liquid are coarse, and there are some reversible aggregates, it can be quickly dispersed and dissolved after being diluted hundreds to thousands of times during use, and it is still a good liquid fertilizer.
On the contrary, no matter how well the humic acid raw liquid is dispersed, it will flocculate and precipitate when encountering a large amount of hard water. Which will clog the nozzle or drip irrigation hole and cause trouble for fertilization operation. Secondly, spraying the flocculated humic acid on the leaves of plants will not only affect the absorption of nutrients and humic acid by the crop leaves, but also may block the stomata of the leaves and affect the respiration of plants.
There are three reasons why humic acid liquid fertilizer has poor flocculation stability:
1) If there are more high-valent cations in the liquid fertilizer,humic acid itself may become insoluble humate or chelate,and will precipitate immediately even if diluted with soft water.
2) There are only monovalent salts in the liquid fertilizer. Even if most of the humic acid is condensed into insoluble aggregates, it can temporarily form a diffuse double layer after dilution with hard water, making the aggregates evenly dispersed. However, after a few minutes to a few hours, the humic acid anions gradually combine with Ca2+, Mg2+ and a small amount of Fe3+, Al3+ in the water to form insoluble salts or chelates and flocculate.
3) If the liquid fertilizer is diluted with high-hardness water from saline-alkali land. Due to the effect of high concentration of electrolyte ions (Na+, CO3 2-, SO4 2-, etc.) in the water, the double electric layer around the humic acid colloid particles is extremely thin and the electric potential is very low. so the product quickly flocculates and precipitates. Some people call this phenomenon “salting out”.
In view of the above flocculation mechanism, we provide several methods to overcome flocculation for your reference in experiments:
1) Use lignite or peat to selectively oxidize and degrade humic acid as the matrix of liquid fertilizer. This kind of highly active humic acid (or humic acid) is not only a colloid protective agent and dispersant for the original solution, but also an effective anti-flocculating agent for the diluent. After being adsorbed by fertilizer particles, this type of humic acid can make the negative charge of the system absolutely dominant, thickening the double electric layer of the dilute colloidal system. Or humic acid forms water-soluble chelates with high-valent metal ions such as Ca2+ and Mg2+, thereby preventing or delaying the flocculation process.
2) Add chelating agents to liquid fertilizer. One type is high-efficiency organic chelating agents. Such as EDTA, which can form stable water-soluble chelated ions with a variety of metal ions. However, EDTA is expensive, and the amount added cannot be too little, which will significantly increase the cost of liquid fertilizer. There are also many cheaper organic chelating agents, such as tartaric acid, citric acid, salicylic acid, etc. [Chuan, which can be determined through experiments. The other type is inorganic chelating agents, mainly polyphosphates (ammonium salts or potassium salts).
3) Whether adding active humic acid or various organic and inorganic chelating agents, we must explore the rules and avoid blindness. First, we must ensure that the humic acid liquid fertilizer is a stable, homogeneous, and flowable colloidal system to prevent the formation of irreversible insoluble aggregates. This requires more experiments on technical conditions such as addition method, addition order, system pH value, and treatment temperature. Secondly, the amount of humic acid and chelating agent added must be basically calculated.
In addition, to meeting the chelation of metal ions in the liquid fertilizer and the colloid protection of dispersed particles, sufficient margin should be left to ensure the need to chelate cations in hard water after dilution by hundreds to thousands of times. Assuming that the solution is diluted 500 times with water of hardness 10mmol/L, the residual amount of chelating agent in 1ml of the original solution should be at least 5mmol.