有機物の多量施用時における有機態窒素溶脱の可能性 : 土壌充填カラムによるモデル実験 Possibility of Leaching of Organic Nitrogen in a Field under Heavy Application of Organic Matter : Model Experiment Using Soil Columns
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有機物多施用によるタンパク様窒素の溶脱を明らかにすることを目的として、有機物施用来歴の異なる3種類の土壌を充填した深さ20および60cmのカラムの表層に、発酵鶏糞100mgha(-1)および菜種油粕2.0mgha(-1)を添加し、その後5日ごとに3回散水し、浸透水中の窒素およびカラム土壌中の窒素形態の変化について検討した。1)茶園土壌の20および60cmカラム、堆肥2年および化成土壌の20cmカラムの浸透水中に、有機物無添加カラムの浸透水より多くの有機態窒素が認められ、その中にはタンパク様窒素が含まれていた。これにより、有機物多施用によるタンパク様窒素の溶脱が確認できた。2)化成土壌の20cmカラムの浸透水中にタンパク様窒素が認められたのは、2回目の散水処理以降であり、有機物施用来歴のあるタンパク様窒素の多い土壌より遅かった。また、散水処理後の堆肥2年および化成土壌のカラム充填土壌の上部では、供試土壌に比べてタンパク様窒素が増加した。これらのことから、有機物を多量に施用すると、タンパク様窒素が増加して土壌中に吸着するが、その容量を超えると、水溶性になり溶脱すると考える。
Leaching of organic nitrogen by heavy application of organic matter was examined using 2 types of columns (same diameter of 5.1, 20 and 60cm long) which were filled with three different Andosols (A: soil from a tea plantation field of heavy application of organic matter, B: soil from a field receiving organic matter for only two years at 40Mg ha^<-1> year^<-1>, C: soil from a field receiving no organic matter before). A mixture of 100Mg ha^<-1> of chicken dung and 2.0Mg ha^<-1> of rapeseed cake was added to the surface soil layer of each column. These soil columns were watered three times for every 5 days. Our findings were as follows: In the percolating water from the 20 and 60cm columns filled with soil A, the 20cm column filled with soil B and 20cm column filled with soil C, water soluble organic nitrogen was found. This organic nitrogen in the percolated water had the same molecular weight as PEON (Phosphate buffer Extractable Organic Nitrogen), and it was confirmed by HPSEC. These peaks by HPSEC corresponding to PEON were correlated with the protein concentration detected by the protein assay method. This implies that leaching of PEON increased in the field receiving the high amount of organic matter. It was after the 2nd watering processing that the PEON was found in the percolating water of the 20cm column filled with soil C, and leaching of the PEON was slower than that of the two soil columns filled with soils A and B from fields receiving organic matter. But, in percolated water from 60cm columns filled with soils B and C from common fields, organic nitrogen was not found. This result suggests that the PEON was increased at the surface soil layer in the case of heavy application of organic matter in a field and some portion of the PEON was leached under rainfall to the deep soil layer. Although PEON exists as fixed forms with iron and/or aluminum in a soil, when a high amount of organic matter was fertilized to a soil, excess free PEONs which are not fixed with iron and/or aluminum in a soil can become water-soluble and leached out.
収録刊行物
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- 日本土壌肥料學雜誌 = Journal of the science of soil and manure, Japan
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日本土壌肥料學雜誌 = Journal of the science of soil and manure, Japan 76(6), 843-848, 2005-12-05
日本土壌肥料學會