Total Emissions of CO2, CH4 and N2Ο From a Lysimeter Paddy Field Under Paddy-Upland Rotation.

Paddy-upland rotation is effective for conserving soil fertility and inhibiting continuous cropping hazard. In Japan, 28.4% of paddy area has been converted to upland crop cultivation mainly due to the governmental production adjustment of rice. Paddy-upland rotation changes the physical and chemical properties of soils, and thus will affect the emission and uptake of greenhouse gases (GHGs), such as carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O). In the previous studies using lysimeters, we have revealed the effects of paddy-upland rotation on soil-surface GHG emissions, dissolved GHG emissions through subsurface drainage, and soil carbon budget. However, for evaluating this cropping system, it is necessary to include the whole period of a crop rotation cycle (i.e., converted upland and restored paddy).

We carried out a 4-year field experiment at the lysimeter facility, NIAES, Tsukuba, Japan from April 2006 to March 2010. Each lysimeter contained a 1-m depth of a lowland soil (Fluvisol). Shallow groundwater table was established under upland conditions. We compared the following three cropping systems: continuous single cropping of paddy rice (PR) as a control, double cropping of soybean and wheat (SW), and single cropping of upland rice (UR). In the SW and UR plots, the first half of the 4 years was for the converted upland, and the latter half was for the restored paddy. Soil-surface GHG emissions were monitored by an automated closed chamber system. Soil carbon budget was estimated from soil-surface CO₂ exchange, harvested crop biomass, incorporated crop residue, and other components. Dissolved GHG emissions were estimated from the volume of subsurface drainage and dissolved GHG concentrations in the drainage.

In the poster presentation, we will evaluate the paddy-upland rotation from the results of 4-year net Global Warming Potential. Moreover, we will verify the results of soil carbon budget with the results of soil carbon content.