Rice yield and soil fertility of an organic paddy system with winter flooding

Organic farming is promoted as a way to produce food while minimizing harm to ecosystems. We examined the feasibility of organic farming using applications of common organic materials to produce standard yields of rice (Oryza sativa L.). From 2012 to 2016, we investigated the effects of rice bran, leftover grains, and soybean (Glycine max (L.) Merr.) curd residue in place of inorganic fertilizer and the effects of winter flooding on brown rice yield and on the availability of nitrogen (N) and phosphorus (P) under rice-rice-soybean rotation in Ibaraki Prefecture, Japan. The yield was greatest at 581 g m(-2) with winter flooding in 2013 and smallest at 347 g m(-2) without winter flooding in 2016. The organic materials applied 7.3-7.5 g N m(-2) and 3.2-4.7 g P m(-2), which supplied 142% +/- 37% of the N and 429% +/- 125% of the P present in the ear of rice at harvest in plots without winter flooding. The rates of organic materials applied would maintain soil N and P content. Winter flooding increased the ammonium concentration in the soil solution, straw dry matter at harvest, and available N in the plow layer during winter. Our practice, which improved N supply in later growth stages and P availability, supported an adequate rice yield and a conserved available N.