The role of organic amendments (Compost, vermicompost, biochar) in improving soil fertility and crop performance: A review

Abstract

Degradation of soil fertility presents an important risk to food security globally especially in developing areas with long term agricultural use of soil that has caused significant depletion of nutrients and organic matter in soil. A synthesis of recent research was completed to evaluate the effectiveness of three primary organic amendments (compost, vermicompost, and biochar) in providing benefits to soil fertility as well as crop productivity. Analysis of over 100 peer reviewed articles evaluated the effectiveness of the different amendments to improve the physical, chemical, and biological properties of soil; promote the recycling of nutrients; produce increased crop yields; and provide potential for climate change mitigation through carbon sequestration. Composting added N and P into tropical soils and improved water retention capacity. However, vermicomposting produced significantly better results than composting, increasing total soil N levels by 157-210% compared to control plots when applied at 10 t ha-1 and produced a 1.5-fold increase in grain yields in wheat and maize production systems. Similarly, biochar provided consistent increases in crop yields due to its unique pore structure and high cation exchange capacity. Furthermore, the synergistic application of combined amendments resulted in greater amounts of soil organic C being stored while decreasing the amount of greenhouse gases emitted from the soil. Ultimately, however, the efficiency of each of the amendments is highly dependent upon the specific characteristics of the amendments themselves, specifically feedstock used to make the amendments, pyrolysis conditions used to produce the amendments, the type of soil amended, the climate in which they are applied, and the plant species grown in the soil. As such, there is a need to complete additional long-term field-based validation studies to determine optimal application rates and timing for different agroecological zones. Overall, this review indicates that sustainable agriculture can be achieved through the integration of organic amendments with reduced chemical fertilizer applications, promoting both sustainable intensification and climate-resilient agriculture.