Application of digestate from rural anaerobic digesters for degraded soil restoration in Colombia

Anaerobic digestion is a promising technology to improve the living standards of rural communities, reduce environmental pollution and promote sustainable development. Apart from biogas, digestate is the other product of the anaerobic digesters and its reuse in agriculture can be as important as biogas in rural households and small farms of Latin America. According to the UNCCD, there are more than 2 billion hectares of degraded land in the world, of which 14% is in Latin America. In this context, this study reports the results of a rst attempt to use digestate from rural digesters for degraded soil restoration in Colombia. Digestate from anaerobic digester fed with pig slurry and operating under psychrophilic temperature (15°C) was applied daily during 4 months to a degraded soil subjected to intensive cultivation for many years (latitude of 5°51'42.3'N, 72°57'51.6'W Colombia). Digestate produced daily (3 m3) was spread uniformly onto all the experimental site and the soil was subjected to no tillage nor cultivation of crops. After 4 months of daily application, the digestate spreading was stopped. During the following months, the experimental site was not used nor for cultivation, nor for grazing. Soils samples (10-20 cm depth) were collected before the start of the experiment (M1), after 4 months of daily digestate application (M2) and after 4 months from the last digestate application (M3). Following digestate application, soil pH and cation exchange capacity signicantly increased. Soil organic C signicantly increased (+60% from M1 to M2) and its concentration was stable from M2 to M3. Digestate application enhanced the stable, mineral-protected and recalcitrant pools of C in soil, proving that digestate may effectively increase soil organic C content, improving soil fertility and acting in C storage and sequestration in soil (Figure 1) . All plant nutrients analyzed signicantly increased after digestate application (N, available P, Ca, K, Mg, Fe, Mn, Mo). No signicant threats of heavy metals accumulation were identied after digestate application.