Isotope and molecular evidence for direct input of maize leaf wax n-alkanes into crop soils

The contribution of plant carbon to crop soils can be followed by isotope labelling at natural abundance, such as growing a C₄ plant on a soil which was previously under C₃ vegetation. For this purpose, carbon isotope compositions and relative abundances of n-alkanes of maize leaf waxes and maize crop soils were compared. Isotope values of soil n-alkanes increased with time of maize cultivation as the result of maize carbon integration into soil organic matter. With increasing time of cultivation, the increase in isotopic difference between n-heptacosane (C₂₇) and n-nonacosane (C₂₉) is explained, at least partly, by a direct input of maize leaf n-alkanes. The amount of maize-derived carbon within each n-alkane has been calculated by isotopic means.