Effects of application methods of organic manure at transplanting time on riceyield and suppression of paddy weeds in organic rice cultivation

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Organic manure, such as rice bran, is often applied for the purpose of weed control in rice cultivation withoutherbicide. However, its effect is unstable probably due to inappropriate organic manure application managements.Accordingly, field experiments were conducted to determine the appropriate combination of application rates,placement method and C/N ratio of the organic manure applied at transplanting time to increase rice yield andsuppress paddy weed in organic rice cultivation. The treatment at the application rate of 10 g N m-2 resulted insignifi cantly higher rice yield by 25% than the treatment at the application rate of 5 g N m-2. In addition, theapplication of the organic manure to soil surface at the rate of 10 g N m-2 increased rice yield by 31-45 %compared with the other treatments. The incorporation of the organic manure into soil at a depth of 0 to 5 cmcaused organic acids production that might damage rice roots, whereas they were little generated in the treatmentapplying the organic manure to soil surface. Furthermore, the application of the organic manure of C/N = 8produced signifi cantly higher (+83 %) weed dry weight at the harvest time than that of the organic manure ofC/N=16. Consequently, the application of the organic manure of C/N=16 at the rate of 10 g N m-2 to soil surfaceincreased rice yield by 35% and reduced weed dry weight by 93% as compared with the incorporation of theorganic manure of C/N=8 into soil at the rate of 5 g N m-2. Our study showed that appropriate managements ofthe organic manure may play an important role to increase rice yield and suppress paddy weed in organic ricecultivation.除草剤を使わない水稲栽培では,米糠のような有機質肥料が雑草制御にしばしば利用される.しかし,その効果は不安定であり,その一因として有機物施用の不適切さが考えられる.そこで,移植時に施用される有機質肥料の施用量,位置およびC/N比の組合せが,有機水稲栽培の水稲収量および雑草抑制に及ぼす影響を明らかにすることを目的とした圃場試験を実施した.有機質肥料を10gNm-2施用した処理は,それを5gNm-2施用した処理に比べ収量が25%高まった.さらに,10gNm-2の有機質肥料を田表面に施用した処理は,他の施用量と施用位置を組み合わせた処理と較べ収量がもっとも高まった(743gm-2).有機質肥料を深さ0から5cmの土壌にすき込んだ処理では,水稲根の生長を阻害する可能性のある有機酸が,水稲根が存在する深さ2-4cmに生成したが,有機質肥料を田表面に施用した処理ではほとんど生成しなかった.また,C/N比が8の有機質肥料を施用した処理は,C/N比16のものを施用した処理に比べて,収穫時の雑草乾物重が83%高まった.以上のことから,C/N比が16で10gNm-2の有機質肥料を田表面に施用した処理は,C/N比が8で5gNm-2のものを深さ0から5cmにすき込んだ処理に比べて,水稲収量は35%増加し,雑草乾物重は93%減少した.以上より,本研究では,有機質肥料の施用方法を適切に組み合わせることが,有機水稲栽培での収量増加および雑草抑制に重要であることを示せた.
2010-03-31

Effects of application methods of organic manure at transplanting time on riceyield and suppression of paddy weeds in organic rice cultivation

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