^<33>Pアイソトープ希釈法によるイタリアンライグラス作付圃場のリン酸肥沃度の評価

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Plant-available P in two Humic Andosols with different P level (total soil P : 1.53 or 8.64 g P kg^<-1>) was evaluated by an A-value technique based on a ^<33>P isotopic dilution method. Before the field study, a P leaching experiment using ^<32>P-labelled fertilizer was carried out in a laboratory for safety assessment and it was predicted that the risk of radioactive contamination into groundwater was negligible. ^<33>P, having longer half-life and lower maximum β-ray energy than ^<32>P, was used for the field study to reduce the amount of radioisotope intended to be applied to the soils and to decrease radiation exposure during the field experiment. Not only calcium phosphate solution labelled with ^<33>P (^<33>P carrier solution) but also ^<33>P carrier-free solution was used to examine the effect of P fixation by the soils on plant-available P measurement by an isotopic dilution method (A-value). The ^<33>P-labelled solutions were incorporated in the soils cropped with Italian ryegrass (Lolium multiflorum LAMARCK) at 6 cm in depth, and the ryegrass was harvested at 36d after ^<33>P application. The A-values of the soils obtained with ^<33>P carrier solution were 300kg P ha^<-1> and 1420kg P ha^<-1> for a low P level soil and for a high P level soil, respectively, indicating that a large amount of plant-available P was accumulated in the soils. In the case of the low P level soil using ^<33>P carrier-free solution, more than 74.4% of applied P was fixed by the soil during the experiment and plant-available P was overestimated, whereas the effect of P-fixing on the A-value was negligible in the high P level soil. Air radiation dose rate in the field was level with background throughout the experiment. Radioactive contamination in soils and plants nearby the test field was not observed. It was concluded that ^<33>P was superior to ^<32>P for field studies from an environmental point of view.
社団法人日本土壌肥料学会の論文
1995-08-05

^<33>Pアイソトープ希釈法によるイタリアンライグラス作付圃場のリン酸肥沃度の評価

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