The Effect Of Rice-derived Bichoar On Red Soil Biophysical Properties And Its Physicochemical Characteristics

Applying biochar to soils may cause a win-win situation resulting in C sequestration and soil fertility improvement. The effect may be more evident in highly weathered and infertile tropical soils, but will be dependent on biochar quality and amount. An Ultisol, typical to southern China, was used to evaluate amendment with biochars produced by a range of temperatures and durations, to investigate its effect on soil properties and plant growth. Rice straw-derived biochars were charred at temperatures from 250 to 450℃for between 2,4 and 8 hrs. Major conclusions were made below:(1) Characteristics of biocharsThe physical and chemical properties of biochars depend strongly on charring temperature and duration. The increase of charring temperature from 250 to 450℃and duration from 2 to 8 hrs decreased the yield of biochars from 63.2%to 26%, but increased C, K, P and ash content. The higher charring temperature further caused smaller less structured fragments as viewed by SEM, and form with less O, H and aliphatic C functional groups, but more aromatic C as indicated by infrared spectroscopy.(2) Effect of biochar amendment on soil biophysical propertiesDuring the 11-day incubation, the biochar amendment increased CO2 respiration as compared to control without biochar addition (P<0.05) but this effect disapeared with increasing incubation up to 55 days. The mean residence time (MRT) of biochars under controlled conditions (25℃,40% field capacity) was estimated from 200 to 1700 years, generally increasing with charring temperature and duration. But rice straw MRT was only 7 years. Amendment of 1%biochar increased pH by 0.1-0.46 (P< 0.01) and CEC by 3.9-17.3%(P< 0.05), but had no effect on microbial C and N (P< 0.05), aggregate stability (P> 0.05) and soil tensile strength (P> 0.05), disliking other organic materials (straw in this study).(3) Effect of biochar amendment on maize growthDuring the 40-day pot trials the biochar amendment did not significantly increase maize biomass (P> 0.05), but biochar plus NPK fertilizer increased biomass by 157% (P< 0.001). However, the biochar quality (as indicated by different charring temperatures) and amount (1% and 2%) did not have an effect on maize growth. This study further proved that the biochar as a fertilizer function only contributed to 7% of biomass, but as a conditioner accounted for 54% of biomass. The study emphasizes that amendment with biochar can improve soil fertility at least in the short term.