1. Protecting fertilizer effect and application significance of nitrification inhibitor

Fertilizer application has been a key measure for farmers to increase vegetable crop yield and nitrogen fertilizer is the most effective fertilizer. According to the increasing rate of nitrogen fertilizer usage in recent years, global nitrogen use for agriculture will be 300 million tons in 2050, which is about six times the amount of nitrogen currently used.

Excessive use of fertilizer results in low fertilizer utilization. Nitrogen fertilizer utilization rate is about 30%, and the remaining 70% of nitrogen loss in the environment, will cause adverse consequences such as non-point source pollution of farmland and water eutrophication. Much nitrogen is lost through nitrification and denitrification. Take the most common nitrogen fertilizer - urea as example, when urea enters the soil, it is broken down into ammonium carbonate. One reduced ammonium nitrogen(most other nitrogen fertilizers are supplementary to the ammonium nitrogen content in the soil), is easily fixed in the soil and absorbed by plants. Ammonium nitrogen in soil can be converted into oxidized nitrate nitrogen through nitrification process, which has strong fluidity and is easy to be lost. In addition, oxidized nitrate nitrogen can be denitrified into nitrogen, an important component of air. But the process produces harmful nitrogen-containing greenhouse gases that escape into the atmosphere, contributing to the decline in acidity. Faced with such severe environmental problems, in the process of vegetable planting and fertilization, nitrification inhibitors can be added into the fertilizer to maintain the stability of ammonium nitrogen in the soil. It effectively reduce the nitrification process of nitrogen fertilizer, so as to reduce the loss and improve the efficiency of nitrogen fertilizer.

2. Application status and prospect of nitrification inhibitor

At present, the common nitrification inhibitors on the market are synthetic nitrification inhibitors such as trichloromethyl pyridine (CP), dicyandiamide (DCD) and dimethylpyrazole phosphate (DMPP). These substances can inhibit the activity of a specific key enzyme in the nitrification process to inhibit the whole nitrification process. At present, a large number of studies have been carried out on the application of nitrification inhibitors in vegetable fields. These synthetic nitrification inhibitors significantly reduced the greenhouse gas emissions during the denitrification process of vegetable soil and improved the nitrogen utilization rate of plants. But the increase in vegetable yield was not significant. In addition, there are other disadvantages such as high cost, weak applicability to different soil environments and pungent smell, so the synthetic nitrification inhibitors are not widely used. However, it can be used together with urease inhibitors to increase the utilization rate of soil fertilizer and prolong the effect of fertilizer. 

In addition to synthetic nitrification inhibitors, related studies have found that some secondary metabolites secreted by plant roots have also been proved have the process of inhibit nitrification. These substances are known as biological nitrification inhibitors. It is the substance  of inhibiting nitrification that secrets from the plant through plant root system's perception of the concentration of ammonium nitrogen in soil. Biological nitrification inhibitors are highly targeted and show high nitrification inhibitory activity. Further studies on the extraction, mass production and actual production of such substances are needed. Compared with synthetic inhibitors, biological nitrification inhibitors have another level of advantage. They can study the expression process of related synthetic genes, have mass production or improve existing vegetable varieties through genetic engineering. This is also a feasible method for the research of nitrification inhibition. Studies on biological nitrification inhibitors secreted by herbage roots have been carried out extensively. At present, new biological nitrification inhibitors have also been found in root secretions of sorghum and wild rice, which provides a new idea for the research on the inhibition mechanism of nitrification process. Progress in mechanism research can in turn guide practical activities, providing a new way to improve the utilization rate of nitrogen fertilizer in vegetable soil, increase vegetable yield, and reduce the pressure on the environment caused by excessive use of fertilizers.