Structural Stability of Humid Tropical Soils as Influenced by Manure Incorporation and Incubation Duration

Soil erosion due to the impact of high-intensity tropical rainfall is one of the important environmental problems in the Republic of Trinidad and Tobago. Organic matter and incubation can increase soil cohesion after soil structure disruption and therefore influence aggregate stability and saturated hydraulic conductivity (K-sat), which are key properties in improving soil and water management. We examined the influence of manure incorporation and incubation duration on the structural stability of three tropical soils with different clay contents and mineralogies. Samples were treated with farmyard manure (FYM) at the rates of 0, 6, and 12% per dry mass of soil, brought to field capacity (FC), and incubated for 56 and at an average temperature and humidity of 26 C and 67.5%, respectively. Subsamples were. taken at 14, 28, and 56 d for the determination of water-stable aggregation (WSA) and K-sat We found an increase in WSA of 23 to 27% for the three soils studied when we compared the natural sample with no treatment to the largest treatment combination (12% FYM and 56-d incubation). The higher the load of FYM incorporation, the more stable the soil became with incubation. Greater improvement was found in K-sat, whose values increased between 50 and 700%. Also, both WSA and K-sat increased with incubation duration regardless of FYM level or clay content and mineralogy. This suggests that, by itself, soil incubation at FC after structural disturbance, with or without FYM incorporation, is a desirable practice that encourages particle bonding and structural improvement.