The production of chemical fertilizers is carried out continuously throughout the year, while the use of chemical fertilizers is seasonal. Therefore, storage before chemical fertilizer application is an indispensable link. Fertilizers may be stored in the hands of factories, wholesalers or distributors. In agricultural production, the seasons that require fertilization are mostly distributed in Spring sowing, summer forced and autumn sowing seasons, which form the peak season of fertilization and off season. The storage of chemical fertilizers is very prone to problems during the hot and rainy seasons, especially the storage of nitrogen fertilizer. In the rainy season, the storage of chemical fertilizers is mainly the problem of moisture absorption and agglomeration of chemical fertilizers. After agglomeration, the commercial properties of the fertilizer deteriorated, making it difficult to achieve mechanical application. Farmers are reluctant to buy, even if the price is reduced, the farmers take it back, increasing the labor of broken and agglomerated, and manpower fertilization is difficult, and uneven application will burn the seedlings.

　　

The precursor to fertilizer agglomeration is to absorb the moisture in the air, which is the hygroscopicity of the fertilizer. It can be said that the hygroscopicity of chemical fertilizers ( especially nitrogen fertilizer ) is the bane of agglomeration, and the quantitative indicator for measuring the hygroscopicity of nitrogen fertilizer is the critical relative humidity.

　　

The so-called "critical relative humidity of fertilizer" refers to the relative humidity of the atmosphere when the fertilizer is exposed to the air at a certain temperature (30" C) . The moisture absorption is proportional to the agglomeration.

　　

Chemical nitrogen hygroscopicity varies by species, i.e. common nitrogen fertilizers hygroscopic critical relative humidity as follows: Ammonium nitrate (59 4) <urea (725.) <Ammonium sulfate (792.). It can be seen that ammonium nitrate is the most hygroscopic in these nitrogen fertilizers, and urea has a strong hygroscopicity.

　　

In addition to the internal factors of fertilizer varieties, the external factors that affect moisture absorption and agglomeration are humidity and temperature. Summer is both hot and rainy, and storage is very difficult.