Effects of Combined Peat Powder and Fermented Manure on Oat Yield, Soil Enzyme Activities and Microbial Community Composition in Horqin Sandy Land

Low soil fertility caused by organic matter deficit severely restricts crop productivity in sandy lands. To investigate the effects of organic matter addition on plant yield and soil productivity in sandy areas, a two-factor randomized block field experiment was conducted using oat (Avena sativa) with five ratios (7:3, 3:2, 1:1, 2:3, 3:7; w:w) and five application rates (0, 5, 10, 15, and 20, t·ha−1) of peat powder and fermented manure in the Horqin Sandy Land, which is a typical agro-pastoral ecotone in northern China. Application of combined peat powder and fermented manure significantly increased oat yield, and the fertilization rate exerted a stronger effect on oat yield than the mixing ratio of the two organic materials. Furthermore, organic fertilization significantly increased the relative abundances of microorganisms, improved soil C, N and P contents, and enhanced the activities of urease, invertase, and catalase. The combination of an application rate of 20 t·ha−1 and a 3:2 peat-powder-to-fermented-manure ratio represents a promising fertilization regime among treatments tested for oat cultivation in this region, given its highest aboveground dry-matter yield. Collectively, these findings show that rational combined application of fermented manure and peat powder in sandy land can significantly increase soil enzyme activities and optimize soil nutrient stoichiometry, and is positively correlated with rhizosphere microbial community composition and oat yield.