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Stable and unstable carbon fraction under different vegetable farming system on Mt. Merbabu’s andisols, Central Java

This study aims to find out the effect of vegetable cultivation systems that are managed organically, semi-organic, and conventionally on the unstable and stable carbon fraction of Andisol soil on the north slope of Merbabu. Field research was carried out using a sampling method in 3 different farming systems, namely organic (O), semi-organic (SO), and conventional (K) and 3 soil depths, namely 0-20 cm, 20-40 cm, and 40-60 cm. The parameters measured include the physical, chemical, and biological properties of the soil. The physicochemical properties of the soil analyzed included texture, volume weight of soil, pH-H2O, pH-NaF, organic matter, cation exchange capacity, total-N, Al/Fe extracted oxalate and pyrophosphate. The carbon fractions analyzed included particulate organic matter carbon, water-soluble carbon, soil organic carbon mineralization, microbial biomass carbon, humic acid, and fulvic acid. Analysis of Variance (ANOVA) was conducted to determine the effect of farming system and soil depth on soil physicochemical properties, while the difference between the two-treatment means was analyzed by DMRT. Regression-correlation analysis was carried out to determine the close relationship between the independent and dependent variables. The results showed that the farming system and soil depth had a significant effect on soil physical and chemical properties. Parameters of soil chemical properties that significantly affect the farming system and soil depth are pH-H2O, pH NaF, organic matter, cation exchange capacity, total-N, and Al/Fe pyrophosphate extracted. Organic farming systems have an unstable and stable organic carbon fraction that is more dominant than semi-organic and conventional farming systems. Parameters of soil chemical properties such as organic matter, total organic carbon, and total-N are closely related to particulate organic matter carbon, water-soluble carbon, microbial biomass carbon, soil organic carbon mineralization, soil humic and fulvic acid. The organic farming system has been proven to improve the physical and chemical properties of the soil and increasing the availability of organic carbon fraction in Andisol soil.