Effect of tillage and rice residue return on CH4 and N2O emission from double rice field.

Greenhouse gas intensity (GHGI) (methane and nitrous oxide) of double rice paddy was controlled by various field managements, tillage, and rice straw return to the field. On one hand, the choice of the tillage mode affects the gas permeability of soil during the crop-growing stage. On the other, the incorporation of rice straw can be a critical way to amend the loss of soil carbon. Both of the two practices have their advantages and disadvantages on rice production and environmental effects. In fact, no tillage causes less methane emissions from double rice fields than the field with conventional tillage. Nevertheless, rice straw return to the field increases tremendous methane production and emission of organic carbon. In spite of its promotion on rice productivity and sequestration of soil organic carbon pool, this practice is still under discussion .Therefore, multi-management mode should be considered simultaneously when regional or national policy is made to reduce GHGI from agriculture. To date, the study of the interaction effect of tillage and the rice residue return on GHGI from double rice fields is lacking. Most of the previous studies focused only on one field management and its influence mechanism. Consequently, we conducted a measurement for 4 rice growing seasons on GHGI of a double rice field in Hunan, China to investigate the interaction effect of tillage and rice straw return on both the social-economical and environmental benefits. The improved static chamber-GC (gas chromatography) method was used to monitor the greenhouse gas emissions from the rice paddy. Major improvements made on the chamber include the adjustable sampling tube and the pores in the base. The former was designed to change with the growth of the rice plant and the latter favored the communication of soil water between the inside and outside of the base. Both of them enhanced the accuracy of the field measurement. Four field practices were included in this research, viz. CWS (Conventional tillage, without straw residue return), NWS (No till, without straw residue return), HN (High stubble residue retain, no till), and HC (High stubble residue retain, conventional tillage). Results showed that there is a significant interaction effect of tillage and rice residue return on methane emissions (P<0.05) instead of nitrous oxide emissions from the double rice field. The interaction effect has pronounced seasonal and inter-annual variation. By the seasonal average value, the sequence of methane flux of each treatment is the following: HC>HN>CWS>NWS (HC significantly greater than HN while no significant difference between HN and CWS). Similarly, the amount of rice grain yield of each treatment of the 4 seasons is the following: CWS>HN>HC>NWS (no significant difference between HN and CWS). For the GHGI, the following order is disclosed: HC>CWS>HN>NWS (HN less than HC and CWS significantly, P<0.05). This indicated that compared to CWS, "no-till plus high stubble residue (HN)" offset the stimulations of conventional tillage on methane production and emission while simultaneously promoting the rice grain yield. Thus the multimanagement mode mitigated the GHGI of the double rice field significantly. Under the requirement of organic tillage and the sequestration of agricultural soil carbon pool, HN mode should be considered of great importance. This study can provide scientific support on the measurement choice of greenhouse gases effect reduction from the major rice production region of China. [ABSTRACT FROM AUTHOR]