Impact of Biochar on Red Paddy Soil Physical and Hydraulic Properties and Rice Yield over 3 Years

Purpose Biochar is a promising soil amendment to improve soil quality. This study was conducted to understand the effect of biochar on soil physical and hydraulic properties and rice yield in a 3-year field experiment in Hunan Province of southern China. Materials and methods We carried out a field experiment at the red paddy soils for 3 years to study the impact of biochar with different adding rates (at 0, 10, 20, 30, and 40 t/ha) on soil physical and hydraulic properties and rice yield. The clay content, soil bulk density, soil pH, soil organic matter, soil total nitrogen, soil total phosphorus, soil aggregates, the field capacity, the wilting point, the soil available water, and the rice yield were determined to explore long-term improved effects of biochar on soil properties and rice yield. Results and discussion The results indicated that soil bulk density decreased significantly, but total porosity increased with biochar amendment. Biochar addition also caused macro-aggregates (> 2 mm) to increase and micro-aggregates (< 0.25 mm) decrease significantly, hence improving mean weight diameter of soil aggregates. Biochar addition had positive impact on soil field capacity and soil available water but no effect on soil wilting point. Soil saturated hydraulic conductivity was increased after biochar addition. Consequently, rice yield was increased due to the improvement of soil physical and hydraulic properties. Conclusions The results showed there were significant differences in soil properties between biochar treatments and the control treatments over the 3-year field experiment, suggesting biochar addition had long-term effect on soil physical and hydraulic properties, as well as increasing rice yield.