シグモイド型被覆尿素側条施肥によるダイズの増収効果
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概要
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1)ダイズ根粒の窒素固定依存率は最繁期(R3)を頂点とする放物線型をなした。根粒活性の硝酸に対する感受性は最繁期まで明確に認められるが,最繁期以降は植物体としては硝酸吸収による窒素固定の阻害は認められない。したがって,最繁期以降の肥料窒素供給はダイズの窒素固定と調和する。2)ダイズの最繁期以降に溶出が開始される窒素肥料として,施用後一定期間溶出が抑制されるシグモイド型被覆尿素を選定した.溶出タイプは基肥施用の場合はCUS120,培土期追肥ではCUS60が適当であった。3)慣行区に対して基肥CUS120,追肥CUS60両区とも窒素固定依存率に差は認められず,施肥による根粒の活性阻害はなかった.CUS施用両区では生育後半で葉色の退色が抑制された。慣行区収量439gm^<-2>に比べて,CUS120区は10%増収,CUS60区は19%増収し,品質も低下しなかった。4)現地農家の実証試験でも慣行区370gm^<-2>に対し,CUS60の追肥は21%増の449gm^<-2>を得ることができ,子実の粗タンパク質含有量は増加した。We analyzed the characteristics of nitrogen fixation by the root nodules of soybean plant by the relative ureide method in a field experiment from 1990 to 1994. Based on the results, we used the sigmoidal types of coated urea slow release N fertilizer in which nitrogen release starts at a one- or two-month period after application, in upland field converted from paddy field in 2001. Basal or top dressing of selected coated urea fertilizers of two types were effective in increasing soybean yields. Two kinds of the coated urea started to release N after the R3 stage, and they did not inhibit nitrogen fixation by the root nodules. 1) It was confirmed that the relative dependence on nitrogen fixation by soybean root nodules follows a hyperbolic curve with the maximum at the R3 stage. The sensitivity of the root nodules to the NO_3^- seemed to be obvious until the R3 stage, but after the R3 stage, nitrate absorption appeared to be beneficial to maintain nitrogen fixation activity through promoting photosynthetic activity. Therefore, the fertilizer nitrogen supply after the R3 stage harmonizes with the nitrogen fixation of root nodules. 2) Sigmoidal releasing-type coated urea (CUS), which starts to release fertilizer nitrogen after R3 stage, was adopted. CUS120 was suitable for basal application and CUS60 for top-dressing. To select a type, we simulated the soil temperature at fertilization depth. 3) Neither the CUS120 basal application nor the CUS60 top-dressing depressed the nitrogen fixation. In both CUS treatments, degradation of the leaf chlorophyll was restrained in the maturing stage. The seed yield in the CUS120 treatment increased by more than 10% above the control, and in the CUS60 treatment, indreased by 19% mofe than the control (439 g m^<-2>). Moreover, no decline in the seed quality was observed in either CUS treatment. 4) The top dressing of CUS60 fertilizer was applied in a farmer's field. The seed yield of CUS60 top-dressing achieved 449 g m^<-2>, or 21% over the conventional field (370 g m^<-2>). Still more promisingly, crude protein of seeds in the CUS60 treatment increased, compared with that for the conventional field.
- 日本土壌肥料学会の論文
- 2003-02-00
日本土壌肥料学会 | 論文
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