Influence of pool substitution on the interpretation of fertilizer experiments with 15N

摘要: SUMMARY The uptake of labelled and unlabelled N by wheat was measured in pot field experiments with 15N-labelled fertilizer. Soils from two sites on the same series were used experiment; one had been bare-fallowed for 22 years contained 1.6% organic C, other under grass many 3.8% C. Fertilizer increased soil both soils, i.e. there a positive ‘added nitrogen interaction’ (ANI). There no ANI experiment. A simulation model is to show how ANIs can arise as result ‘pool substitution’—labelled inorganic fertilizer standing proxy that would otherwise have immobilized. In low-organic fallow soil, pool substitution accounted whole observed did not enhance either gross or net mineralization N. Pool also operated high grassland but here increasing additions fertilizer, giving rise ‘real’ addition larger ‘apparent’ caused substitution. This increase probably decrease immobilization increase, an For operate, must occupy pool. occurred experiment experiment, where remained separate ANI. When occurs, use efficiency predictably lower isotopic method than conventional non-isotopic procedure.