Animal abundance and soil properties affected by long-term organic farming in rice paddies in a typical Japanese yatsuda landscape

Organic farming was developed to reduce agriculture’s negative impacts on the environment and enhance biodiversity for sustainable productivity in agricultural ecosystems, but the long-term effectiveness of its application in Japanese rice paddies is unclear. We sought to understand how long-term organic farming affects the abundance of animals in both the rice growth and fallow seasons, and how soil properties change. We investigated the abundance of fishes, frogs, beetles, and shellfish in the floodwater in summer, and the abundance of earthworms (mainly Enchytraeidae), arthropods (spiders and springtails), and soil properties in aerobic soils in autumn. We examined fields which had been farmed organically for 10 and 18 years in Tochigi, Japan. Fields farmed with conventional management, located close to the selected organic fields, were used as a control. All selected fields were located in a valley, which is the typical landscape of a traditional Japanese farming village, called a yatsuda in Japanese. The results showed an increase in soil organic carbon, total nitrogen, and available phosphorus in plowed soils that had been converted from conventional to organic farming both 10 and 18 years earlier. However, the abundance of various animals were not affected significantly by long-term organic rice farming, other than arthropods in the aerobic soils that had been farmed organically for 18 years. The quantity of most animals in floodwater and fallow season soil was unaffected by long-term organic rice farming in the yatsuda paddy fields, probably due to the circumstances and similar irrigation systems for both conventional and organic rice farming, as well as lighter doses of agrochemical application for conventional rice cultivation.