Water management is one of the most effective options in decreasing methane (CH4) emission from a paddy field. We have proposed the water management based on soil redox potential (Eh) named 'Eh control', and demonstrated the effectiveness of Eh control in decreasing CH4 emission in pot experiments. The objective of the present study was to consider the practicability of Eh control under field conditions.
Two-year experiments were carried out in a paddy field at the Agricultural and Forestry Research Center, University of Tsukuba, Japan in 2003 and 2004. Experimental factors were water management and rice (Oryza sativa L., cultivar: Koshihikari) straw treatment. Two methods of water management during rice growing period were continuous flooding and Eh control. For Eh control, drainage was carried out whenever the soil Eh decreased to -150 mV, and flooding was carried out whenever the soil Eh increased to 0 mV in 2003 and 100 mV in 2004. Two methods of rice straw treatment were application and removal in the preceding winters of all straw harvested. The CH4 flux was measured by a closed chamber method and the total emission during the growing period was estimated. Rice grain and straw yields were examined by a quadrat sampling method. The yield component was analyzed only in 2004.
The total CH4 emission was decreased by Eh control to 36% of continuous flooding on the 2-year average. Although straw application hastened the decrease in soil Eh when compared with straw removal, it did not affect the total CH4 emission. Rice grain and straw yields were not affected by the experimental factors. However, yield component analysis showed that Eh control increased the number of particles per hill and resulted in increased brown rice yield. Straw application also increased the number of particles per hill, but did not affect brown rice yield.
Consequently, the present study demonstrates the practicability of Eh control under the field conditions on an experimental level. Two important suggestions were obtained from the above results. One is that Eh control decreases CH4 emission to a minimum level according to the range of soil Eh determined. Another is that it may be possible to change the range of soil Eh to a more positive value that will decrease CH4 emission more and increase rice grain yield. (c) 2006 Elsevier B.V. All rights reserved.