Effects of Different Organic Fertilizers on Sweet Potato Growth and Rhizosphere Soil Properties in Newly Reclaimed Land

It is well known that soil fertility is poor in most newly reclaimed land, which has been developed as an effective way to compensate farmland occupation. In order to ameliorate the soil quality of the newly reclaimed land, this study investigated the effect of commercial organic fertilizer (COF) (0.45, 0.90, 1.35 and 1.80 kg/m²), sheep manure (SM) (0.45, 0.75, 1.05 and 1.35 kg/m²), mushroom residue (MR) (1.50, 2.25, 3.00 and 3.75 kg/m²), and chemical compound fertilizer (CCF) (0.075 kg/m²) on the growth of sweet potato, soil pH, organic matter content (OMC), available phosphate, total nitrogen, available potassium, exchangeable Ca and Mg, as well as bacterial and fungal microbial composition during 2019–2021. The results from this study indicated that the COF, SM, MR, and CCF did not significantly change the soil pH, but significantly increased the OMC, which has been regarded as the most significant soil quality parameter. This suggests that the soil amendments used in this study have great potential to improve the soil quality in newly reclaimed land. However, these soil amendments exhibited a differential effect on sweet potato biomass, nutrient elements and the microbial community of the newly reclaimed soil, which depend on the kind and concentration of organic/chemical fertilizer, the application time, as well as the plant and soil parameters. The change was also observed on the bacterial and fungal soil microbial community, which provides us with a microbial basis to understand why organic fertilizer has a great effect on soil improvement. Overall, our results suggest that soil amended with organic fertilizers has great potential for the production of sweet potato in immature soil from the new reclamation land.