Opportunity costs seriously limit the large-scale production of bio-organic fertilizers (BOFs) both in China and internationally. This study addresses the utilization of amino acids resulting from the acidic hydrolysis of pig corpses as organic nitrogen sources to increase the density of TrichodermaharzianumT-E5 (a typical plant growth-promoting fungi, PGPF). This results in a novel, economical, highly efficient and environmentally friendly BOF product. Fluorescence excitation-emission matrix (EEM) spectroscopy combined with fluorescence regional integration (FRI) was employed to monitor compost maturity levels, while pot experiments were utilized to test the effects of this novel BOF on plant growth. An optimization experiment, based on response surface methodologies (RSMs), showed that a maximum T-E5 population (3.72 × 108 ITS copies g−1) was obtained from a mixture of 65.17% cattle manure compost (W/W), 19.33% maggot manure (W/W), 15.50% (V/W)hydrolytic amino acid solution and 4.69% (V/W) inoculum at 28.7°C after a 14 day secondary solid fermentation. Spectroscopy analysis revealed that the compost transformation process involved the degradation of protein-like substances and the formation of fulvic-like and humic-like substances. FRI parameters (PI, n, PII, n, PIII, n and PV, n) were used to characterize the degree of compost maturity. The BOF resulted in significantly higher increased chlorophyll content, shoot length, and shoot and root dry weights of three vegetables (cucumber, tomato and pepper) by 9.9%~22.4%, 22.9%~58.5%, 31.0%~84.9%, and 24.2%~34.1%, respectively. In summary, this study presents an operational means of increasing PGPF T-E5 populations in BOF to promote plant growth with a concomitant reduction in production cost. In addition, a BOF compost maturity assessment using fluorescence EEM spectroscopy and FRI ensured its safe field application.

Abbreviations: CK, control with no fertilizer; CMR, C mineralization rate; CMR, Fed, diothionate extractable iron oxides; Feo, oxalate-extractable iron oxides; MBC, microbial biomass C; NPK, Chemical fertilizer; NPKM, 50% chmical fertilizer plus manure; NPKS, 100% chemical fertilizer plus straw; NPKMOI, 20% chemical fertilizer plus manure organic-inorganic compound fertilizer; SCMR, specific C mineralization rate; SOC, soil organic C; SRO, short-ranged order. S oil organic carbon constitutes the largest terrestrial C reservoir in the global C cycle (Heimann and Reichstein, 2008). The long-term storage and stability of SOC have a profound influence on soil fertility enhancement, food security improvement, and global warming mitigation (Lal, 2004). Furthermore, SOC is closely associated with a wide range of soil biogeochemistries and thus plays an important role in improving soil quality and agro-ecosystem productivity (Reeves, 1997). Therefore, C sequestration in agricultural soils by increasing organic amendment inputs has long been considered an important issue in increasing the SOC content and the mechanisms underlying the accumulation of SOC have drawn increasing attention Wen et al., 2014 • Oxalate extractable iron oxides contributed to soil organic carbon sequestration.• Soil organic carbon from 20 to 40 cm was more labile than that from 0 to 20 cm.• Oxalate extractable iron oxides preferentially preserved aromatic compounds.