Traditionally rice paddies are irrigated with cycles of flooding followed by dry periods. The dominant greenhouse gas emitted from flooded rice fields is methane produced by bacteria in the waterlogged soil in large quantities. However, there is another gas, Nitrous oxide, which is also produced by soil microbes in rice fields.
Methane gas is produced by the decomposition of organic matter under anaerobic conditions or flooded rice fields and released to the atmosphere whereas in aerobic conditions it is absorbed in the soil.
Figure 1: Gas Emission process
We measured CH4 emission at the 10th minute point in a closed chamber.
Figure 2: CH4 emission test results
Our study revealed that emission of CH4 is more in paddy rice , i.e 55 ppm compared to 5 ppm in drip irrigated rice.
Figure 3: Greenhouse gas emission impact
According to US-based advocacy group Environmental Defense Fund (EDF), methane and nitrous oxide emissions from rice farms could have the same short-term warming impact as about 600 coal plants (1,900 MMT per year CO2e100).
With the looming global warming crisis, can we afford to have more greenhouse gas emissions? The question lies in how we can effectively mitigate greenhouse emissions from rice paddy fields without compromising yield.
The answer lies in adopting a more integrated approach to rice paddy irrigation and fertilizer application to significantly reduce greenhouse emissions. Many studies have shown that some rice varieties can be successfully grown under much drier conditions than traditional methods, with reduced methane emissions and without any loss in yield.
Studies done by Netafim showed that rice paddies irrigated by flooding, in the southern state of Tamil Nadu in India, produced about 2.9 milligrams of nitrous oxides per square meter each day. Whereas, those same paddies irrigated by drip irrigation only produce about 0.5 milligrams of nitrous oxides per square meter daily. Drip irrigation is not only important to water the rice plants, but it is also critical to use it for fertilization, he stressed.
With drip irrigation, plants can absorb water and nutrients without any risk of downward seepage of nitrates from fertilizers into the groundwater and surrounding environments – thus reducing the emission of greenhouse gases.
Drip irrigated rice not only curbs greenhouse gas production and conserve water, it can also lead to higher yields. In trials done by Netafim on drip irrigated rice in India, farmers reported almost 20 - 25% higher yield compared to traditional methods.