Do Compost and Vermicompost Improve Macronutrient Retention and Plant Growth in Degraded Tropical Soils?

Soil degradation and water pollution are widespread land degradation problems in Southeast Asia. Policy makers are currently faced with the challenge of designing and implementing strategies to maintain soil fertility and avoid off-site effects. The aim of this study was to determine the effect of organic substrate amendments on soil properties, nutrient leaching and the growth of Ipomea aquatica in an acidic degraded soil from northern Vietnam. Plants were grown in an Acrisol in buckets under natural weather conditions for two months. The same amount of nutrients was applied either in a purely synthetic form (mineral fertilizers) or as two alternative organic substrates (three month old compost or vermicompost from buffalo dung) plus additional amounts of synthetic mineral nutrients to ensure the same quantity of NPK. The influence of these respective substrates on the soil's physical and chemical properties as well as plant growth was examined. Both compost and vermicompost led to an improvement in soil properties with an increase in the pH, soil organic matter and nutrient content, compared to soil fertilized with synthetic mineral products. The highest plant productivity was obtained with vermicompost and synthetic fertilizers, with no significant difference between these two treatments. Chemical fertilization, however, is the least effective practice based on the amount of nutrients leached from the soil (about 38% of N and 22% of K, compared to less than 10 and 5% of N and K with organic amendments). P leaching was not influenced by the fertilizer treatments. In conclusion, vermicompost does appear to be a relevant alternative to chemical fertilizers because it leads to similar enhancements in plant growth, at the same time as increasing soil quality and decreasing nutrient leaching.