Effect of long term application of corn stalks and inorganic fertilizers on fluorescence characteristics of water extractable organic matter in a meadow black soil of northeast China
ABSTRACT Returning crop residues into fields, either alone or in combination with inorganic fertilizer, is considered as a practical way to enhance soil fertility. However, information concerning the effects of crop residues and inorganic fertilizer application on water extractable organic matter (WEOM) in soil is scarce. The aim of this study was to examine the 10 year effect of corn residue (CR) return with or without the application of nitrogen, phosphorus, and potassium (NPK) fertilizer on the quantity and quality of WEOM in a black soil of northeast China by means of ultraviolet absorbance, fluorescence excitation emission matrix, and derived spectroscopic indices. The application of NPK fertilizers and CR, alone or together, increased the content of total soil organic carbon (SOC) water extractable organic carbon (WEOC) and ratio of WEOC/SOC, with the sequence being NPK CR CR NPK CK. Compared with control treatment, the individual application of NPK fertilizer decreased the aromaticity of WEOM. In contrast, elevated proportion of tryptophan like fluorophore and microbially derived fulvic acid like components with low molecular weight was detected in the WEOM. The amendment with CR alone resulted in increase in aromaticity of WEOM and proportion of plant derived humic acid like component with large molecular weight, accompanied by reduced proportion of tyrosine like compounds. For the soil with CR restoration, the application of NPK fertilizer increased aromaticity of WEOM, and large molecular weight fulvic acid like and humic acid like compounds were found. However, the proportions of tyrosine like and tryptophan like compounds were diminished. The quantitative and qualitative analysis of WEOM using fluorescence spectroscopy describes responses to be observed in long term different fertilization strategies.