Long-term stationary fertilization decreased soil health in field-grown sweetpotato by increasing soil-borne diseases or allelochemicals

Abstract

Fertilization are commonly used strategies to alleviate continuous cropping obstacles, but long-term stationary fertilization also causes varying degrees of soil barriers that hinder the growth of crop with the extension of planting years. However, there was currently a lack of systematic research on which soil properties change caused by long-term stationary fertilization were the reasons for the production obstacles in sweetpotato-planting fields. Here, soil samples from a 21-year-old continuously sweetpotato-planting field covering four fertilizations (CK: no fertilizer; M: organic manure only; NPK: chemical fertilizer only; MNPK: chemical fertilizer plus organic manure) were collected and analyzed. Compared with CK, fertilization significantly increased soil microbial biomass carbon content, the activities of urease, invertase and alkaline phosphatase, and the increase amplitudes in these indicators was the largest in MNPK. Moreover, fertilization significantly decreased the relative abundance of harmful fungi (i.e., Gibberella_avenacea, Alternaria_alternata, Mortierella_alpina, etc.) compared with CK. Especially, the relative abundance of fungal pathogens, Fusarium_oxysporum and Fusarium_proliferatum, showed a trend of MNPK<M < NPK. The abundance of plant-parasites nematodes in M and NPK were higher than that of CK, while long-term application of MNPK decreased the abundance of plant-parasites nematodes compared with CK. Suggesting that fertilization, especially applied MNPK, resulted in a faster cycling of soil nutrients and, to some extent, reduced soil fungal diseases and plant-parasites nematodes abundance, which was positively related to sweetpotato yield based on RDA analysis. However, high concentration of phenolic acids (i.e., syringic acid, syringaldehyde, vanillic acid, vanillin, ferulic acid and p-coumaric acid, etc.) were still observed in MNPK. Our results demonstrated that long-term fertilization, especially MNPK, can improve soil nutrient cycling and decrease the abundance of some harmful fungi and plant-parasites nematodes, while lead to the accumulation of phenolic acids. Therefore, the potential hazards of phenolic acids derived from long-term application of MNPK in sweetpotato-planting fields were deserved further attention.