Change in soil oxygen and water contents under alternate wetting and drying in paddy fields

Alternate wetting and drying technique at late growth stage of rice has been widely used in high-yield cultivation techniques to increase water use efficiency, improve soil aeration and enhance root growth in paddy fields. The aim of alternate wetting and drying technique was to coordinate and balance soil water and soil oxygen, making the technique typically different from traditional rice cultivation techniques. To further enhance production under high-yield cultivation techniques like alternate wetting and drying technique, change in soil oxygen and soil water contents were investigated in a paddy field in Sanya, Hainan Province. A field experiment was carried out with alternate wetting and drying treatments at the late growth stage (February to April) of rice in 2013. The aim of the experiment was to develop a novel strategy for further research on physiological mechanism of rice with alternate wetting and drying technique. Soil oxygen content, soil water content and soil temperature at 5 cm soil depth in the studied paddy filed were synchronously monitored from 8:00 to 17:59 every day from heading to maturity stage of rice. While the soil was saturated with water under alternate wetting and drying, soil oxygen was almost impossibly detected by Firesting O2. While soil water content at the 5 cm soil depth decreased gradually as soil slowly dried up, soil oxygen content increased. On the 19th, 24th and 29th day of post-anthesis, soil water content decreased to 25.4%, 25.1% and 24.7% while soil oxygen content increased to 17.5%, 17.4% and 17.4%, respectively. During flowering, grain-filling and maturity stages of rice, daily soil oxygen content initially decreased and then increased later in the day, with the lowest value generally appearing at 14:00 15:00. Soil water content fluctuated but gradually decreased during the day. Soil temperature increased initially and then decreased later in the day, with peak value generally appearing at 15:00 16:00. When soil temperature was the highest during 8:00 17:59, soil water content was lower while soil oxygen content increased. At flowering, grain-filling and maturity stages, a significantly negative correlation was noted between soil oxygen content and soil water content. Although soil water content was negatively influenced by soil temperature, the correlation between soil oxygen content and soil temperature was insignificant. Under alternate wetting and drying cultivation, a reciprocal relationship existed between soil oxygen content and water content in paddy fields during late growth stages of rice. Thus through moderate alternate dry-wet management measure, soil water and soil oxygen balance in root-zone soil layer was adjusted to some extent.