How Long Is the Shelf Life of Common Fertilizers? Detailed Explanation of Losing Effectiveness After Long Storage and Storage Methods

I believe many farmer friends are very concerned about this question: Do fertilizers have a shelf life? Whether at agricultural supply stores or for farmers, fertilizer often cannot be sold out or used up after the application season, and is left piled up for a long time. So the question arises: will fertilizer lose its effectiveness after being stored for a long time? How quickly do different fertilizers lose effectiveness?

Will fertilizer lose its effectiveness after being stored for a long time?

Judging from the characteristics of fertilizers, as long as chemical fertilizers are stored properly, with packaging bags not damaged, not exposed to rain, not affected by moisture, and not mixed with alkaline substances, they can generally be stored for a long time. Therefore, there is currently no regulation on the shelf life of chemical fertilizers. For example, fertilizers such as urea, superphosphate, and potassium sulfate can be piled up in a cool, dry warehouse for 20 years, and aside from the fertilizer caking, indicators such as nutrient content do not change.

Will some fertilizers lose effectiveness after long storage while others will not? It depends on the specific type of fertilizer. Several main common types are introduced below:

1. Ammonium bicarbonate will not lose effectiveness, only lose weight

In winter, when the temperature is around 0°C, the fertilizer effect hardly changes. Farmer friends can take advantage of the seasonal price reduction of ammonium bicarbonate in winter, and it is appropriate to buy ammonium bicarbonate in preparation for spring plowing.

In summer, when the temperature is above 30°C, ammonium bicarbonate will volatilize in large amounts. Very dry ammonium bicarbonate becomes moist due to ammonia volatilization, causing the weight of ammonium bicarbonate to decrease. Therefore, the bag opening must be tied tightly to strictly prevent moisture and reduce losses.

However, ammonium bicarbonate will not lose effectiveness due to long storage, and the fertilizer effect is still very good. Calculated by dry weight, the fertilizer effect does not decline. Farmer friends must not regard weight loss as loss of effectiveness.

2. Urea will only lose weight, not lose effectiveness

When dry, it can be stored for a long time. When the temperature reaches as high as 122°C, urea decomposes, and the decomposed ammonia and carbon dioxide volatilize simultaneously, causing weight loss. So even if the warehouse catches fire, the properties of the remaining urea do not change. But urea is afraid of moisture, and is prone to weight loss through leaching when exposed to water.

3. Superphosphate fertilizer effect does not change

If exposed to rain, the fertilizer effect will become worse due to loss. If superphosphate is produced from phosphate rock powder with high iron and aluminum content, it is not suitable to store for more than one year. This is because after about 170 days of storage, the calcium carbonate contained within can slowly convert into iron phosphate and aluminum phosphate, becoming poorly soluble substances, and the fertilizer effect becomes worse.

4. Potassium chloride and potassium sulfate are very stable

Potassium chloride and potassium sulfate are very stable compounds. They cake when exposed to water, but after being crushed and applied, the fertilizer effect does not change. However, when applying, the amount used must be calculated by dry weight.

5. Diammonium phosphate is afraid of high temperatures

At relatively high temperatures, such as above 30°C, diammonium phosphate will slowly convert into monoammonium phosphate, with a small amount of ammonia volatilizing. Therefore, when storing diammonium phosphate, the fertilizer bag opening must be tied tightly to prevent ammonia volatilization.

6. Ferrous sulfate deteriorates when it absorbs moisture

Ferrous sulfate is a strong oxidant. If it encounters moisture, it easily converts into ferric sulfate, which crops cannot absorb. The fertilizer effect is poor, and it easily loses effectiveness.

7. Microbial fertilizers past their expiration date cannot be used

The activity of the microbial strains in biological fertilizers is time-limited. Microbial fertilizer standards stipulate that the expiration date of the microbial strains should be marked on the packaging bag. Under normal storage conditions, the expiration date is generally two years.

Microbial fertilizer past its expiration date cannot be used. Microbial fertilizer must be stored in a low-temperature (suitable temperature 4°C-10°C), cool, ventilated, and light-protected place to avoid losing effectiveness.

Some microbial strains require a specific temperature range. For example, Trichoderma harzianum needs to be stored in a constant-temperature chamber at 2°C-8°C, with an expiration date of one year. Some Bacillus species, depending on production quality, mainly depending on the level of sporulation, those with high sporulation can be stored for one and a half years or even longer, while those with poor sporulation lose effectiveness in less than half a year. Therefore, vegetable growers should carefully choose microbial fertilizer products.

Do not choose expired products just to save money. Such biological bacteria content is very low and loses its effect. Generally, biological microbial fertilizers over two years old should be chosen with caution.

How to store fertilizers scientifically?

In hot and rainy seasons, chemical fertilizers should mainly be stored in warehouses. The warehouse must be ventilated and cooled, while also being protected from rain and moisture. There are two storage methods for fertilizers in warehouses: bulk storage and bagged storage.

For nitrogen fertilizer types with relatively strong hygroscopicity, such as ammonium, whether stored in bulk piles or in bags, in order to avoid caking, the height of bulk piles and bag piles should be controlled. For example, for 25-40 kg large bags, 20 bags per pile is a moderate height.

If choosing a goods shed for storage, the stacking location should be chosen in a place with relatively high terrain, level ground, and no water accumulation, with reed mats or plastic film laid underneath. After the fertilizer is stacked neatly, plastic film should be used to cover it on top, while measures such as erecting a shed roof and adding tarpaulins should be taken to prevent rain.

Fertilizer storage must achieve the “six preventions”:

First, prevent volatilization. Ammonia water and ammonium bicarbonate volatilize very easily, so they must be sealed during storage. Also, nitrogen fertilizers and superphosphate must strictly not be mixed and piled with alkaline substances such as lime and plant ash, to prevent chemical reactions that cause nitrogen fertilizer volatilization and reduce the fertilizer effect of phosphate fertilizer.

Second, prevent moisture. Ammonium, lime nitrogen, and superphosphate easily cake after absorbing moisture, affecting the application effect. Also, after ammonium bicarbonate absorbs moisture, nitrogen easily volatilizes, so it must be sealed tightly to avoid contact with air. Therefore, these fertilizers should be stored in a dry, cool place.

Third, prevent corrosion. Superphosphate is corrosive and should be prevented from contacting skin and metal utensils; ammonia water is strongly corrosive to copper and iron, and should be stored in ceramic, plastic, or wooden containers. In addition, fertilizers cannot be piled together with seeds, and fertilizer bags should not be used to hold seeds, so as not to affect seed germination.

Fourth, prevent high temperatures. When nitrogen fertilizers are exposed to sunlight, nitrogen volatilization loss accelerates; ammonium decomposes oxygen when exposed to high temperatures. These will cause fertilizers to lose effectiveness.

Fifth, prevent fire. Ammonium, potassium, and others have combustion-supporting properties, and must not be piled together with flammable materials such as kerosene, gasoline, crop stalks, and wood shavings during storage, to avoid causing fires.

Sixth, prevent metal. If ammonium, potassium, and others are mixed with metal powders such as copper and iron, once friction or impact occurs, accidents will be caused. Therefore, after these fertilizers cake and harden, do not strike them hard with metal objects; use heavy objects to crush them.