Research by Hiroshima University, Kyoto University, and Research Institute for Humanity and Nature, that a farming method called "winter water tank" that stores water in paddy fields in winter reduces the outflow of phosphorus, which leads to eutrophication of rivers and lakes, by 26%. The team found out.Although it has been reported in the past that winter water tanks restore biodiversity, they have also been found to be effective for water quality conservation in watersheds.
According to Hiroshima University and others, the researchers were Assistant Professor Takuya Ishida of the Graduate School of Advanced Science and Technology, Hiroshima University, Associate Professor Noboru Okuda of the Ecological Research Center of Kyoto University, and Toru Ikeya, an outpatient researcher of the Research Institute for Humanity and Nature.
Assistant Professor Ishida and his colleagues collected soil from a total of 10 paddy fields where winter water tanks were carried out and those where winter water tanks were not carried out in Koka City, Shiga Prefecture. Chlorophyll concentrations were measured to determine the amount of algae that were supposed to absorb the phosphorus contained.
As a result, the winter water tank suppressed the outflow of phosphorus derived from fertilizer by an average of 26%.Regarding the concentration of phosphorus contained in the surface water, there were some where the effect of winter water tanks appeared and some where it did not, but it was considered that phosphorus was adsorbed by iron and taken into the soil where the effect was obtained.
However, there was no big difference in the chlorophyll concentration between the implementation and the non-implementation, and the research team thinks that it became difficult to measure because the soil was agitated at the time of raising the rice field.
Excessive outflow of phosphorus from paddy fields into the basin causes eutrophication with excess nutrients.In stagnant waters such as ponds and swamps, oxygen consumption increases at night when photosynthesis stops, causing oxygen deficiency in the water, causing red tides and foul odors.
Paper information:[Limnology] Effects of winter flooding on phosphorus dynamics in rice fields
