Biochar and N2O Emission in Agriculture

Urea Plant

The world's production of urea fertilizer in 2020 will reach around 181 million tons and this type of urea fertilizer is the most widely used. In practice, the use of urea fertilizer is mostly inefficient, so it is wasted and pollutes the environment. It is estimated that the level of loss of urea and pollution to the environment, in use reaches around 40% or 72.4 million tonnes globally. Efforts to improve fertilization efficiency can be done by modifying it to become a slow release fertilizer (SRF), one of which is highly recommended, namely biochar, as a slow release agent, read more details here. In addition, the use of urea causes N2O emissions. N2O (nitrogen monoxide) is a greenhouse gas and air pollutant, N2O is a dangerous gas because it has a stronger effect about 300 times per unit weight than CO2 in a span of 100 years. In air, N2O reacts with oxygen atoms to form NO, and NO then breaks down ozone.

Urea is one of the conventional fertilizers commonly used in agriculture. Urea has a main content in the form of nitrogen which is absorbed by plants in the form of ammonium (NH4+) and nitrate (NO3−). Loss of nitrogen in the fertilizer occurs due to evaporation as ammonia (NH3), immobilization in the pores of the soil or washed by water, both rainwater and irrigation water. In addition to economic losses, environmental pollution due to excess nitrogen also causes a number of negative effects. Nitrogen from urea can also be lost due to complete denitrification of nitrates to produce nitrogen gas (N2) or through incomplete nitrate denitrification to produce nitrogen monoxide (NO) and nitrous oxide (N2O) gases, which evaporate from the soil. Nitrate, nitrogen monoxide (NO) and nitrous oxide (N2O) gases contribute to environmental problems. Nitrates are harmful substances that cause water pollution. Excess concentration of nitrate in drinking water is harmful to health, especially in infants and pregnant women.

Meanwhile, nitrous oxide (N2O) has now become the largest ozone depleting substance emitted in the 21st century. The main source of global nitrous oxide (N2O) emissions is nitrogen-based fertilizers, especially urea fertilizer. The presence of N2O in the lowest region of the atmosphere (troposphere) can cause a greenhouse effect or global warming because N2O traps infrared radiation emitted from the earth's surface and then warms the atmosphere. In addition, N2O can migrate up into the stratosphere where it reacts with oxygen atoms to produce some nitric oxide (NO). Then, the depletion of the ozone layer occurs because NO reacts with stratospheric ozone (O3) to form NO2 and O2. Furthermore, NO2 reacts with O to form NO again. The depletion of the ozone layer increases the amount of UV rays from the sun that reach the earth's surface.

Biochar application has been suggested as a strategy to reduce nitrous oxide (N2O) emissions from agricultural soils while increasing soil carbon (C) stocks, especially in tropical areas. Climate change, especially temperature increase, will affect soil environmental conditions and thereby directly affect soil N2O volume. Related to climate issues, there are two aspects of the role of biochar, namely as a carbon sequestration / carbon sink and reducing nitrous oxide (N2O) emissions, while related to agriculture, namely increasing soil fertility and increasing the productivity of agricultural products. The multi-benefit application of biochar is predicted to become a trend in the bioeconomy era, when the aspects of sustainability, food adequacy and as a climate solution become a complete package in one action.

The effort to minimize the use of urea fertilizer is by modifying it to become a slow release fertilizer with biochar as the slow release agent. The use of excess doses of urea apart from damaging the environment is also a waste. The use of urea can still be used to a certain extent, namely that all of the urea can be absorbed by plants with minimal loss or environmental pollution. When all the nutrients/fertilizer nutrients can be completely absorbed by the plants, it means that there is no residue in the soil, so that damage or environmental pollution can be minimized even avoided. The residue, especially in the long term, will cause severe soil damage. Slow release with close to the rate of absorption of nutrients by plants is a condition that is pursued or NUE (nutrient use efficiency) as much as possible. The technique of modifying urea fertilizer into SRF is the key.