Organic matter application on subsoil improves soil organic matter, soil aggregate stability and porosity in coffee plantations

Abstract The cultivation of coffee in dry land, especially in Sumbermanjing Wetan, faces the challenge of low soil organic matter, which affects water availability. Water stress is observed during dry season, marked by yellowing and shedding leaves, as roots are only active in the topsoil. Therefore, optimizing root function to reach the subsoil is essential, one approach being the implementation of biopore infiltration technology. The objectives of this research were to study the impact of apllying organic matters in subsoil on i) soil organic matter content, ii) soil aggregate quality, and iii) soil porosity. This study was conducted in a smallholder coffee plantation in Argotirto Village, Sumbermanjing Wetan District. The research design was Randomized Complete Block Design with five treatments: i) P1 (control/no organic matter addition); ii) P2 (biopore infiltration hole with 40 cm filled with goat manure); iii) P3 (biopore infiltration hole with 40 cm filled with compost); iv) P4 (compost spread on soil surface); v) P5 (goat manure spread on soil surface). The observed variables included organic matter content, soil aggregate stability, and soil porosity. Organic matter application was carried out in 2023 and 2024. Results indicated that the use of biopore infiltration holes filled with goat manure (P2) increased soil organic matter on topsoil (0-20 cm) by 78.11% and in the subsoil (20-60 cm) by 81.89% in the second year of organic matter application. The addition of organic matter, whether manure or compost (P2 and P5), improved soil aggregate stability in both topsoil and subsoil (the average of MWD in topsoil was 4.48 mm, and in subsoil was 1.94 mm). Moreover, P2 had the highest porosity values of 64.7% on the soil surface and 61.5% in the subsoil. These findings indicate that organic matter addition to the subsoil is effective in increasing soil organic matter and soil aggregation.