Quantifying impacts of water management on crop yield, net greenhouse gas emissions and water use efficiency for rice production in Asia with remote sensing and biogeochemical modeling approaches
Changsheng
Li, Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, changsheng.li@unh.edu
(Presenting)
Xiangming
Xiao, Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, xiangming.xiao@unh.edu
Steve
Frolking, Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, steve.frolking@unh.edu
Berrien
Moore, Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, berrien.moore@unh.edu
William
Salas, Applied Geosolution, wsalas@agsemail.com
Driven by increasing demand for water resources due to urbanization and climate change, most of the rice-producing countries in Asia are developing alternative management practices to increase water use efficiency for rice production, a traditionally water-consuming industry, meanwhile to maintain optimum yields. Since rice paddies is an important source of atmospheric methane, predicting impacts of the changes in water management on methane emissions at large scale could be helpful to answer the question, i.e., in what degree human’s activity in agriculture could alter atmospheric chemistry. An integrated approach constructed by combining remote sensing analysis with a biogeochemical model, DNDC, was applied for the 120 million hectare of rice fields in 18 major rice-producing countries in Asia to quantify methane emissions under three alternative water management conditions. The results indicated that converting the conventional management practice (i.e., continuous flooding or CF) to midseason drainage (MD), which is currently being spread in Asia, would reduce the total methane emission from the Asian rice fields by 40% (from 28 to 17 Tg CH4-C); and applying a new practice (i.e., shallow flooding or SF) reduced the emission by 75% (7 Tg CH4-C). The magnitude of the reductions is so large that could affect the trend of methane accumulation in the atmosphere. By the conversion of CF to MD or SF, nitrous oxide (N2O) emissions from the rice fields increased from 1.0 to 1.2 or 1.5 Tg N, respectively. The entire Asian rice land is a weak source of atmospheric carbon dioxide (CO2) with 140 Tg C annually released into the atmosphere. The changes in water management only slightly decreased the CO2 emissions. Converting CF to MD or SF elevated the total rice production of the 18 countries from 0.56 to 0.63 or 0.65 trillion tons, respectively, meanwhile reduced water use from 1.45 to 1.34 or 1.10 trillion cubic meters, respectively. It is the increase in yield and the decrease in water use that motivate the farmers to adopt the new water management practices, which unintentionally reduced net greenhouse gas emissions by 180- 360 Tg CO2 equivalent each year for the rice agriculture in Asia.