Key Technical Points of Nitrogen Fertilizer Application and Scientific Fertilization Methods

China ranks first in the world in both the production and consumption of nitrogen fertilizer, but the utilization rate after application is not high and losses are substantial. According to the comprehensive results of 528 rice trials nationwide by the Nanjing Institute of Soil Science, Chinese Academy of Sciences, the average utilization rate of nitrogen fertilizer is 33%-38%; the results of 254 trials on wheat crops (wheat, barley, naked barley) showed an average nitrogen fertilizer utilization rate of 28%-41%; and it was estimated that the loss rate of nitrogen fertilizer exceeds 50% in paddy fields and is around 45% in dryland fields. The crop's utilization rate of nitrogen fertilizer refers to the proportion of the nitrogen fertilizer applied to farmland that is absorbed into the plant body by the crop in the current season:

The nitrogen fertilizer utilization rate is usually measured by two methods: one is the difference method, and the other is the isotope 15N dilution method. The former is commonly used for calculating nitrogen fertilizer application rates, while the latter is commonly used for studying the fate of nitrogen fertilizer applied to soil.

The level of nitrogen fertilizer utilization rate is generally consistent with the level of fertilizer efficiency (the yield increase per unit of nutrient applied). However, under certain special circumstances, such as excessive nitrogen application causing crops to remain green and lodge, they may also be inconsistent. Therefore, rational application of nitrogen fertilizer means improving both the utilization rate and fertilizer efficiency of nitrogen fertilizer. Based on many years of experience in China, the following main techniques should be mastered.

1. Apply nitrogen fertilizer in combination with phosphorus and potassium fertilizers to achieve balanced fertilization. Around the 1950s, applying nitrogen fertilizer alone produced very high fertilizer efficiency. Afterwards, due to the depletion of soil phosphorus and potassium, it could no longer meet the needs of high crop yields and became a nutrient-limiting factor for increasing crop yields. Under such circumstances, applying nitrogen fertilizer alone was often ineffective, and it had to be applied together with phosphorus and potassium fertilizers. For example, in 1981-1982, the Institute of Soil and Fertilizer, Chinese Academy of Agricultural Sciences, conducted a nitrogen fertilizer (urea) rate experiment on wheat on a relatively barren fluvo-aquic soil in Jingxian County, Hebei Province. Because the soil of that plot was severely deficient in phosphorus, applying nitrogen fertilizer alone hardly increased yield, but when applied per mu7.5 kgP2O5 (superphosphate) as a base, then applying nitrogen fertilizer achieved a significant yield increase. There was also a positive interaction between nitrogen fertilizer and phosphorus fertilizer. At a plot with low available phosphorus and potassium content, the Institute of Agricultural Sciences of Shangrao Prefecture, Jiangxi Province, applied nitrogen fertilizer alone (per mu N10 kg) for three consecutive rice seasons, with an average yield per mu of275 kg; nitrogen fertilizer combined with phosphorus fertilizer (per mu P2O53 kg), with an average yield per mu of324 kg; nitrogen fertilizer combined with potassium fertilizer (per mu K2O6 kg), with an average yield per mu of317 kg; and nitrogen, phosphorus, and potassium fertilizers combined, with a yield per mu of344 kg. The combined application of nitrogen fertilizer with phosphorus and potassium fertilizers not only increased rice grain yield, but also increased the milled rice rate and the protein content in brown rice.

When phosphorus and potassium fertilizers are insufficient, the combined application of nitrogen fertilizer with organic fertilizer also has a very good yield-increasing effect. This is because organic fertilizer is a complete fertilizer and often contains abundant phosphorus, potassium, and medium and trace elements.

2. Master the appropriate application rate of nitrogen fertilizer. Generally speaking, as the nitrogen fertilizer application rate increases, the yield per unit area increases, but both the nitrogen fertilizer utilization rate and fertilizer efficiency show a clear downward trend. In 1985, the Institute of Soil and Fertilizer, Jilin Academy of Agricultural Sciences, conducted an experiment on corn with different urea application rates and utilization rates:

Nitrogen fertilizer application rate (kg/mu)

0

8.5

11.9

15.3

18.7

Corn yield (kg/mu)

253

444

447

437

435

Nitrogen fertilizer utilization rate (%)

-

45.2

41.1

35.4

26.4