Natural 15N abundances of maize and soil amended with urea and composted pig manure

Abstract

To investigate the effect of inorganic fertilizer and composted manure amendments on the N isotope composition (delta15N) of crop and soil, maize (Zea mays L.) was cultivated under greenhouse conditions for 30, 40, 50, 60, and 70 days. Composted pig manure (delta15N= +13.9‰) and urea (-2.3‰) were applied at 0 and 0 kg N ha−1 (C0U0), 0 and 150 kg N ha−1 (C0U2), 150 and 0 kg N ha−1 (C2U0), and 75 and 75 kg N ha−1 (C1U1), respectively. The delta15N of total soil-N was not affected by both amendments, but delta15N of NH+4 and NO−3 provided some information on the N isotope fractionation in soil. During the early growth stage, significant differences (P < 0.05) in delta15N among maize subjected to different treatments were observed. After 30 days of growth, the delta15N values of maize were +6.6‰ for C0U0, +1.1‰ for C0U2, +7.7‰ for C2U0, and +4.5‰ for C1U1. However, effects of urea and composted manure application on maize delta15N progressively decreased with increasing growth period, probably due to isotope fractionation accompanying N losses and increased uptake of soil-derived N by maize. After 70 days of growth, delta15N of leaves and grains of maize amended with composted pig manure were significantly (P < 0.05) higher than those with urea. The temporal variations in delta15N of maize amended with urea and composted manure indicate that plant delta15N is generally not a good tracer for N sources applied to field. Our data can be used in validation of delta15N fractionation models in relation to N source inputs.