Quantity and Nature of Water-Extractable Organic Matter from Sandy Loam Soils with Potato Cropping Management

This work evaluated the level and nature of water-extractable soil organic matter (WEOM) from a 6-yr potato ( L.) crop rotation field experiment. The content of WEOM was higher in continuous potato soils than in the 2-yr and 3-yr crop rotation soils except for those crop rotation soils with soil improvement management by composted manure. Irrigation increased the level of WEOM in crop rotation soils. Ultraviolet–visible and fluorescence parameters indicated that WEOM in continuous potato soil possessed a high degree of humification and that crop rotation increased the aromatic and low molecular mass portions. In most irrigated soils, WEOM contained less aromatic but higher humified components. Characterization of the WEOM samples with crop rotation and irrigation suggests that these management practices stimulate the decomposition of the humic fraction in soil organic matter pools, implying healthier soil conditions with these management practices than with continuous potato growth.