Effectiveness of Subsoil Improvement Practices in Bangkok Heavy Clay Soil

Abstract

The Bangkok clay is characterized by compacted subsoil which is one of the causes of poor drainage and restricted agricultural production in the Bangkok plain. Subsoil improvement practices (subsoiling, deep plowing, and a combination of the two) were tested to see whether they improve the soil physical properties and thereby plant growth. The soybean was selected as a reference crop. The results showed that the subsoil improvement practices altered soil structure, enhanced soil permeability, reduced soil hardness, induced subsurface drainage, and improved soil aeration. The soil physical condition was improved mainly due to the loosening of the compacted subsoil and break up of the plow pan. Thus, favorable soil physical conditions for plant growth were achieved. The combination treatment of subsoil improvement had the most significant effects on improving soil physical properties. The plant growth parameters of the soybean, including root length, dry matter production, and yield, were significantly higher in the combination treatment than in other treatments.