Do fertilizers have an expiration date? Do they lose their effectiveness if stored for too long? We’ve got the answer!
Release Date:
2020-05-19
Whether it’s an agricultural supply store or a farmer, when fertilizer is left unsold or unused because the growing season has passed, and it’s stored for an extended period, the question arises: Does fertilizer lose its effectiveness over time? And how quickly does this degradation vary among different types of fertilizers?
Whether it’s an agricultural supply store or a farmer, when fertilizer is left unsold or unused because the growing season has passed, and it’s stored for an extended period, the question arises: Does fertilizer lose its effectiveness over time? And how quickly does this degradation vary among different types of fertilizers?
Do fertilizers lose their effectiveness over time?
From the perspective of fertilizer characteristics, as long as chemical fertilizers are stored properly—ensuring that the packaging remains intact, is protected from rain, kept dry, and not stored together with alkaline substances—they can generally be stored for extended periods; therefore, Currently, the state has no regulations regarding the shelf life of fertilizers. . For example Urea, superphosphate, potassium sulfate, and other fertilizers can be stored in a cool, dry warehouse for up to 20 years; apart from the formation of clumps, their nutrient content and other quality parameters remain unchanged.
Do some fertilizers lose their effectiveness over time while others do not? It depends on the specific type of fertilizer. Below is an overview of several major, commonly used varieties:
1. Ammonium bicarbonate does not lose its effectiveness; it only loses weight.
In winter, when temperatures hover around 0°C, the fertilizer’s effectiveness remains virtually unchanged. Farmers can take advantage of the seasonal price drop in ammonium bicarbonate during this season and purchase it in preparation for spring plowing.
When summer temperatures rise above 30°C, ammonium carbonate volatilizes extensively. In dry conditions, the ammonia released causes the material to become damp, leading to a reduction in its weight. Therefore, it is essential to tightly seal the bag to prevent moisture ingress and minimize losses.
However, ammonium bicarbonate does not lose its effectiveness over time; its fertilizing power remains strong, and its efficacy does not decline when calculated on a dry‑weight basis. Farmers should not equate weight loss with loss of efficacy.
2, Urea only loses its potency; it does not become ineffective.
When dry, it can be stored for long periods. At temperatures as high as 122°C, urea decomposes, with the resulting ammonia and carbon dioxide volatilizing and causing a loss of weight. Therefore, even if a warehouse catches fire, the remaining urea retains its properties. However, urea is highly susceptible to moisture; exposure to water can lead to leaching and a corresponding loss of weight.
3, The fertilizer efficiency of superphosphate remains unchanged.
If exposed to rain, the fertilizer’s effectiveness will decline. Moreover, superphosphate produced from phosphate rock with high iron and aluminum content should not be stored for more than one year, as after approximately 170 days, the calcium carbonate it contains can gradually convert into iron phosphate and aluminum phosphate—insoluble compounds—thereby reducing its fertilizing efficacy.
4. Potassium chloride and potassium sulfate are very stable.
Potassium chloride and potassium sulfate are highly stable compounds; they tend to cake when exposed to moisture, but their fertilizer efficacy remains unchanged if the clumps are broken up before application. However, when applying these fertilizers, the dosage should be calculated on a dry‑weight basis.
5. Diammonium phosphate is sensitive to high temperatures.
Diammonium phosphate gradually converts to monoammonium phosphate at elevated temperatures—typically when the ambient temperature exceeds 30°C—and a small amount of ammonia volatilizes. Therefore, when storing diammonium phosphate, be sure to seal the fertilizer bag tightly to prevent ammonia loss.
6, Ferrous sulfate deteriorates upon absorbing moisture.
Ferrous sulfate is a strong oxidizing agent; when exposed to moisture, it readily converts to ferric sulfate, which crops cannot absorb. As a result, its fertilizing efficacy is poor and it is the most prone to losing effectiveness.
7. Expired microbial fertilizers should not be used.
The viability of the microbial strains in biofertilizers is subject to a time limit. According to the biofertilizer standard, the expiration date of the microbial strains must be clearly indicated on the packaging. Under normal storage conditions, the shelf life is up to two years.
Microbial fertilizers must not be used once they have expired. They should be stored in a cool, dark, well‑ventilated environment at an optimal temperature of 4°C to 10°C to prevent loss of efficacy. Some strains require specific temperature ranges; for example, Trichoderma harzianum should be kept in a constant‑temperature incubator at 2°C to 8°C, with a shelf life of one year. Meanwhile, certain Bacillus species can remain viable for up to a year and a half or longer, depending on their spore‑formation quality—higher spore counts yield longer storage stability—while those with poor spore formation may lose potency in less than six months. Therefore, vegetable growers should carefully select microbial fertilizer products.
Do not be tempted by low prices and choose expired products, as they contain very few beneficial microorganisms and have lost their effectiveness. In general, bio‑fertilizers that are more than two years old should be selected with caution.
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