Impact of Compost Application during 5 Years on Crop Production, Soil Microbial Activity, Carbon Fraction, and Humification Process

Compost amendment is considered as a practical tool to increase the soil organic matter (SOM), which contributes to agricultural sustainability. The objective of the present work was to evaluate the impacts of organic soil management over 5years on orchard prune production (Prunus salicina), microbial activity, soil carbon (C) fraction, and stabilization degrees of soil humification. Plot experiment was designed with two different soil managements: i) for minimizing anthropogenic disturbances, only mulching of orchard residues derived from prune tree plot area was applied to soil surface (S+V); and ii) the amendment of composted manure was annually practiced in addition to the utilization of orchard residues inside the plot area (S+V+C). After 5years, the soil with the continuous compost application (S+V+C) showed higher productivity of Prunus salicina (21.4%), greater fruit diameter (7.8%), and heavier fruit weight (22.4%) than the soil without compost application (S+V). Nutrient content in foliar analysis showed no difference between the two treatments (S+V and S+V+C). By contrast, the amended soil by compost (S+V+C) increased the SOM and water-soluble C fraction in parallel with the increase of microbial parameters (microbial biomass C, adenosine triphosphate (ATP), basal respiration, and dehydrogenase). Analyzing soil humic acid character by chemical spectra techniques of Fourier-transform infrared (FT-IR) spectra and C-13 nuclear magnetic resonance (C-13-NMR), gradual reformation of a more stabilized structure was shown in both soils (S+V and S+V+C), due to the selective biodegradation and humification process after the amendments over 5years. Especially, in the soil treated with compost application (S+V+C), the increase of functional C groups (aromatic and carboxylic groups), which reinforce the recalcitrant character of soil humified fraction, was clearly observed. The continuous application of composted manure for the duration of 5years improved the orchard soil fertility as well as productivity.Abbreviations: ATP, adenosine triphosphate; CPMAS, cross-polarization magic angle spinning; EC, electrical conductivity; FT-IR, Fourier-transform infrared; HA, humic acid; HS, humic substance; INTF, iodonitrotetrazolium formazan; K, Potassium; LSD, least significant differences, N, nitrogen; NMR, nuclear magnetic resonance; O, oxygen; OM, organic matter; MBC, microbial biomass C; P, phosphorous; SD, standard deviation; SE, standard error; SOM, soil organic matter; TOC, total organic carbon; WSC, water-soluble C; WS-Ch, water-soluble carbohydrate