Objectives Carbon acts as the main nutrient and energy source in microbial metabolic activities, driving the microbial turnover in soil and consequently affecting the nutrient uptake and utilization by crops. We studied the effect of carbon from different organic sources on the P efficient utilization in P-rich soil.
Methods Two field experiments were carried out in greenhouse of Dongying City (fluvo-aquic soil) and Linzi City (cinnamon soil), Shandong Province. The test materials were tomato and zucchini, respectively. Five treatments included no fertilization control (CK), optimized fertilization (OPT), optimized fertilization plus humic acid (OPT+HA), earthworm castings (OPT+EC), and mushroom residues (OPT+MR). The tomato and zucchini fruit yields were investigated. The soil was sampled after the vines removed for the determination of soil carbon and P contents, extracellular enzyme activities, and bacterial community structures and relative abundances of main microorganisms.
Results 1) Compared with OPT, all the organic materials increased the yield and P uptake of tomato and zucchini, increased the soil fertilities and enzyme activities, especially MR treatment. 2) In Dongying experiment, MR application increased soil microbial biomass carbon (MBC) and dissolved organic carbon (DOC) content by 17.46% and 17.03%, enhanced soil β-glucosidase (β-GC) and acid phosphatase (ACP) activities by 19.75% and 13.12%, decreased soil Olsen-P content by 28.50%. In Linzi experiment, MR application increased all the test carbon component contents in soil, with the increase range of 16.19%–54.30%, and increased soil β-GC activity by 24.55%. 3) Compared to OPT, EC and MR application significantly increased the Chao1 and Shannon indices of soil bacterial community; MR treatment enhanced the relative abundances of Prosthecobacter and Sorangium; HA input increased the relative abundance of Vermiphilaceae, MWH_CFBk5, and Pedobacter, respectively. EC treatment enriched Fodinicola and Phaselicystis in soil, and changed the soil microbial community structure.
Conclusions The input of organic materials, especially mushroom residues, can effectively increase the proportion of soil soluble organic carbon and the soil β-glucosidase activity, and significantly improve the soil microbial community structure and the relative abundance of beneficial bacteria, consequently enhance the mobilization of soil P and improve the P uptake and utilization by vegetables, decrease the Olsen-P content after vegetable harvest. Therefore, the application of mushroom residues under the optimum fertilization is a feasible measure to improve soil microbial activity and vegetable P nutrition in P-rich vegetable fields.
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