Variation of natural15N abundance of crops and soils in Japan with special reference to the effect of soil conditions and Fertilizer application

Abstract

The natural ¹⁵N abundance (δ¹⁵N) of the crops subjected to long-term fertilizer treatments under paddy and upland conditions in the different experimental stations throughout Japan were analyzed. The δ¹⁵N values of the grains of paddy rice which were +6.3‰ on the average in the fields without application of chemical fertilizers decreased by the treatment with chemical fertilizers. The average δ¹⁵N values of the upland crops were lower than those of paddy rice without application of N fertilizers. The δ¹⁵N values of upland crops decreased with the dose of chemical fertilizer N, but increased with the application of composts containing animal feces. The pot experiments using three soils showed that the δ¹⁵N values of paddy rice were higher than those of upland rice and sorghum and that these values were comparable to the δ¹⁵N values of ammonium and nitrate produced in the incubated soils, respectively. The δ¹⁵N values of fertilizer N absorbed by paddy rice were higher than those of fertilizer N, whereas the δ¹⁵N values of the fertilizer N in upland rice and sorghum were increased in the alluvial soils but decreased in Andosols as compared to those of fertilizer N applied. The δ¹⁵N values of the Andosols in Japan showed small variations, with an average value of +6.5‰, whereas those of alluvial soils in Japan showed large variations with an average value lower than that of Andosols.