Application Effects of Cotton Mulch Seeding Method On Nutrients Dynamics in Rice Paddy Field.

Rice is a staple crop and cultivated in all over Japan. But in spring, water quality declines due to the contamination of nutrients-rich effluent from the paddy rice fields and it has become a big problem in agroecosystems. In this study, rice seeds were sown in paddy field by spreading the cotton mulch sheet made from cotton waste and including rice seeds. Japanese organic rice farmers have used for weed repression and saving labors. After flooding, the seeds initiated germination and grew from the sheet. Meanwhile, decomposition of the sheet by microorganisms started with accumulation of N, P and other nutrients from the flooded water and upper soil. Because rice plant can not uptake so much amount of nutrients at the early stage, the lower concentration of nutrients in the flooded water did not affect rice growth seriously. It rather retained the excess nutrients in flooded water of the field into the sheet and reduced nutrient losses by effluent and denitrification. By 72 days after seeding, the sheet accumulated 20.7 kg ha^-1 of the excess N from the flooded water, but after then it released N gradually and rice took up the N reserved in the sheet. The timing of N release to the soil was suitable for contributing to increase yield and quality of rice. At harvest almost of sheet was decomposed and the remains would increase the soil fertility as soil organic matter. As described above, the application of cotton mulch sheet for rice cultivation is evaluated as a useful method for conserving water quality in agroecosystems around rice paddy fields and saving nutrients resources. In addition, the cotton mulch sheet has been made from cotton waste recycled which had been disposed by incineration leading to CO₂ emission.