Humic substances and distribution in Mollisols affected by six‐year organic amendments

Abstract

Organic amendments under crop rotation influence soil organic matter (SOM) content, while the distribution and structural changes of humic substances have not been thoroughly examined. Three-dimensional excitation-emission matrix (3DEEM) fluorescence spectroscopy with parallel factor analysis (PARAFAC) and fluorescence regional integration (FRI), and projection procedure regression (PPR) were used to comprehensively evaluate the structural characteristics and distribution of fulvic acids (FA). The fertilization regimes were: CNoF-SNoF (corn and soybean without fertilizer), CCF-SNoF (corn with chemical fertilizer and soybean without fertilizer), CCR-SNoF (corn and soybean stovers with chemical fertilizer and soybean without fertilizer), CCF-SCF (corn and soybean with chemical fertilizer), and CCF-SFM (corn with chemical fertilizer and soybean with dairy manure). Six-year organic amendments mainly increased SOM, FA and humic acids (HA) contents, and the ratio of HA to FA (HA/FA), the ratio of percent fluorescence response in the ultraviolet to visible region (P V,n /P III,n) and projection values in topsoil. Six-year stover return enhanced labile fractions of SOM in 20-30 cm soil depth, while dairy manure application increased labile fractions of SOM in 0-10 cm and 20-30 cm soil depths. The organic amendments had higher Fmax of component C1 (bioavailable aliphatic compounds) and component C2 (high molecular structure

Fifteen years of conservation tillage increases soil aggregate stability by altering the contents and chemical composition of organic carbon fractions in Mollisols

“…It is necessary to analyze the chemical composition of each OC fraction detailedly in order to explore the SOC stabilization mechanisms not only on SOC quantity but also on SOC quality (Zhou, Wang, et al, 2020). Spectroscopic techniques, such as Fourier transform infrared (FTIR) spectroscopy, have been applied over the past few decades to determine the molecular composition or compositional changes of SOC (Fissore et al, 2017).…”

Gas Emissions and Environmental Benefits of Wheat Cultivated under Different Fertilization Managements in Mollisols

“…The replacement of chemical fertilizer with organic fertilizer and phased fertilization in stages are important measures to reduce the amounts of chemical fertilizers applied. Replacing chemical fertilizer with organic fertilizer can effectively avoid soil acidification and improve soil nutrient contents and soil enzyme activity [14,15]. Fertilization in stages can significantly improve the fertilizer utilization rate and increase maize yield in the North China Plain [16].…”