Researchers contend that draining water is an ecofriendly and cost-effective way to decrease methane emissions, even though certain chemical fertilisers produce better results purely in terms of reducing methane emissions. "The yield is also not affected due to the draining," says S N Singh, lead author of the nbri study. However, the method means more pressure on water resources.
Interestingly, China has a different story to tell. According to the study by unh, new management techniques have saved water along with reducing emissions of rice fields. The researchers evaluated farming practices of Chinese farmers. During the last two decades, water shortage has forced Chinese farmers to allow their rice fields to be drained two to five times when the crop is being grown. The catch is that fields are not literally drained and flooded again as was done during the nbri study. "The Chinese farmers just let the fields dry naturally due to evaporation and/or leakage. Unlike in other parts of the world, they don't flood the soil again until it is dry. In the process, they save a lot of water," explains Changsheng Li, the lead author of the unh research.
A significant, though unintended, consequence of this shift in farming practice was an annual decrease of about five million tonnes of methane emissions during 1980-2000. The practice actually resulted in higher yields, as draining stimulates the development of plant roots and also accelerates decomposition of organic matter in the soil. This in turn, produces more inorganic nitrogen -- an important fertiliser.
Changsheng and his colleagues observed that reduction in methane emissions varied greatly with time and location. A biogeochemical model was developed to take into account the main factors related to methane emissions such as weather conditions, soil properties, crop types, tillage, fertiliser use and water management. The researchers found that irrespective of any of these factors, on an average, methane emissions decreased by about 40 per cent if the fields were drained thrice during a growing season.
"The decline in methane emissions of China is consistent with the reduction in atmospheric methane witnessed during 1980-2000," says Changsheng.