Nitrogen fertilizer is used skillfully, economically and efficiently.

When alkaline soil is applied according to soil characteristics, acidic or physiologically acidic nitrogen fertilizer can be applied, such as ammonium sulfate, ammonium chloride, etc., which can not only neutralize the alkalinity in the soil, but also form ammonium nitrogen that can be easily absorbed by crops, while in acidic soil, alkaline or physiological basic nitrogen fertilizer can be selected, such as urea, sodium nitrate, calcium nitrate, ammonium calcium nitrate or lime nitrogen. On the one hand, they can reduce the acidity of soil, on the other hand, they can form nitrate nitrogen which can be easily absorbed by crops under acidic conditions. Ammonium chloride containing chlorine should not be applied in saline-alkali soil so as not to increase salinity and affect crop growth. The amount of nitrogen application in fertile soil is less, and the number of fertilization in soil with strong fertilizer conservation capacity can be less; on the contrary, the amount of nitrogen application should be increased appropriately, and should be applied in stages. According to crop types and growth conditions, the nitrogen demand of various crops is different, such as sugarcane, leafy vegetables and other crops need more nitrogen, rice, corn, wheat and other crops need medium nitrogen, while legume crops have rhizobium to fix nitrogen in the air, so they need less nitrogen. Different crops have different responses to nitrogen fertilizer varieties, such as the application of ammonium nitrogen fertilizer to rice, especially ammonium chloride, ammonium bicarbonate and urea. The effect of applying ammonium sulfate to potato is good. Avoid chlorine crops such as tobacco, starch crops, grapes and so on should apply little or no ammonium chloride. The effect of applying nitrate fertilizer to most vegetables is good. The effect of applying nitrogen fertilizer in different growth stages of crops is also different. In the critical period when crops need fertilizer, such as the critical period of nutrition or the period of maximum efficiency, the effect of increasing yield is significant. For example, maize needs the most nutrients before and after heading and flowering, and heavy application of ear fertilizer can significantly increase yield. Therefore, according to the nutrient requirements of crops, mastering the appropriate fertilization period and quantity is the key to the effective application of nitrogen fertilizer. According to the nature of nitrogen fertilizer, ammonium bicarbonate and ammonia should be applied deeply to cover the soil to prevent volatilization. Because they are all quick-acting fertilizers and are not easy to lose in the soil, they can be used as base fertilizer and topdressing fertilizer and are suitable for application in paddy field and dry land. Nitrate nitrogen fertilizer has great mobility in soil and fast fertilizer effect, so it is suitable to be used as topdressing in dry land. The nitrogen in urea exists in amino state, which generally needs to be transformed in soil before crops can absorb a large amount of nitrogen. Before transformation, its fertilizer effect is not as fast as ammonium nitrogen fertilizer and nitrate nitrogen fertilizer, so it should be used as topdressing 3-5 days earlier than general fertilizer, but urea as extra-root topdressing is the most ideal and suitable for all kinds of soil and crops. In short, the application method of nitrogen fertilizer should be considered according to the characteristics of nitrogen fertilizer. When combined with appropriate amount of phosphorus and potassium fertilizer in the soil lacking available phosphorus and potassium, the effect of single application of nitrogen fertilizer is very poor, and the yield may be reduced by increasing the application of nitrogen fertilizer. Because in the case of lack of phosphorus and potassium, protein and many important nitrogen compounds are difficult to form, seriously affecting crop growth. Experiments in various places have proved that the combined application of nitrogen fertilizer and appropriate amount of phosphorus and potassium fertilizer can significantly increase the yield.