While in the past six decades, fertilizers were able to contribute half of the crops produced and caused a cooling effect as they increased carbon sinks, the situation now has reversed as they increase warming in China. Reduction of fertilizer use would decrease this warming effect without affecting crop and carbon sinks production.
This is according to a study recently published in Environmental Research Letters that calls for a 60% reduction in fertilizer usage to reduce greenhouse gas emissions, specifically nitrous oxide (N2O), in some areas of China which are using much more fertilizers than they actually need.
Nitrogen-based fertilizers, aside from boosting food production, also decrease CO2 levels from the surroundings. They provide nutrients to plants which act as carbon sinks, improving plant growth and so is absorption of CO2. However, these fertilizers also react with the bacteria in soil that convert them to N2O, which is known as the most potent greenhouse gas.
From 1949 to 1990, nitrogen fertilizers caused increase in crop production and a substantial cooling effect in China. From 1990 onwards, the usage has been increased, but the effect on crop production has been stagnant. According to the researchers, this implicates that the fertilizers have become less efficient, causing no further increase in production of crops and carbon sinks, but causing more N2O emissions and consequently, increase in warming effect.
The soils in China can be thought of as if they have already reached a saturated level during the 1990’s, rendering the succeeding amount of fertilizers being used as excessive, resulting to more N2O production than CO2 reduction.
As stated by co-author of the study, Dr Hanqin Tian, “Nitrogen fertilizer has become less efficient in recent years as the nitrogen input has surpassed nitrogen demands of plants and microbes. Excess nitrogen is not stimulating plant growth but leaving the system through leaching and nitrous gas emissions.
“We need to advance education programs to inform Chinese farmers of both the economic and environmental costs of excessive nitrogen fertilizer use. Effective management practices such as compound fertilizer use and optimized irrigation and tillage should be advanced to increase nitrogen use efficiency.”