Slow-release nitrogen fertilizer refers to nitrogenous fertilizers containing release retardants, which can slowly release nitrogen for plant absorption. When nitrogen in the soil is absorbed by plants, the remaining nitrogen combines with soil organic matter to form ammonia, which volatilizes into the atmosphere, leading to soil acidification.

Firstly, slow-release nitrogen fertilizers contain release agents that slow down nitrogen release. As these agents decompose or degrade, they release nitrogen, but this process requires time. Consequently, during the initial application phase, soil nitrogen levels are relatively high. as time progresses, nitrogen is gradually absorbed by plants, reducing the residual nitrogen content.

Secondly, these fertilizers have high organic matter content. Organic matter consists of complex organic compounds primarily made up of carbon, hydrogen, and oxygen. In soil, organic matter reacts with nitrogen to produce ammonia, the main cause of soil acidification.

When organic matter in slow-release fertilizers decomposes, it releases ammonia. Ammonia is an alkaline gas with strong corrosive properties. It undergoes acid-base neutralization reactions with soil acidity components, reducing soil pH. Additionally, ammonia can chemically react with other ions in the soil, further affecting its pH level.

Besides organic matter, other components in slow-release nitrogen fertilizers may also impact soil acidification. For example, some contain nutrients like phosphorus and potassium, whose forms in the soil influence its acidity. If these elements react with soil acidity components, they may intensify soil acidification.

microbial activity in the soil affects its pH. Soil microorganisms decompose organic material, producing metabolic byproducts that can alter soil acidity. For instance, some microbes break down organic matter into ammonia and carbon dioxide, potentially lowering soil acidity.

organic matter and nitrogen in slow-release fertilizers are primary factors causing soil acidification. Due to their high organic matter content, careful control of application rates and methods is necessary when using these fertilizers to prevent excessive soil acidification. Concurrently, enhanced soil management practices such as crop rotation and organic fertilizer supplementation should be employed to improve soil conditions and fertility.