Colloidal dynamics of soil clay under the effect of fine-sized biochars: Implication for biochar amendment towards preventing clay loss and soil erosion

<p>In soils clay loss by leaching and surface runoff is one of the initial steps increasing the risk of erosion. Here we set out to determine the effect of fine-sized biochar amendment on colloidal dynamics of soil clay, with the aim of answering whether biochar addition enhances or curbs soil erosion. Fine-sized biochar samples were prepared from fern Dicranopteris linearis’s biomass under non-biochar-oriented pyrolysis (open heating) and biochar-oriented pyrolysis (N<sub>2</sub>-supported heating) over a temperature range from 400 to 900°C. The clay fraction (< 2 µm) separated from a clay-rich soil in a hilly area of the Red River basin containing relatively high amounts of kaolinite was tested for its dispersion properties under the presence of the prepared biochars. Surface charge of biochar-soil clay mixtures was determined by polyelectrolyte titration using a particle charge detector, while corresponding colloidal properties of the mixtures were examined by the test tube method. Both, the soil clay fraction and biochar samples showed strongly negative surface charge and their surface charge was variable depending on pH. In a pH range from 3 to 10 and at an electrolyte background of 0.01 M NaCl, surface charge of the clay fraction decreased from -1.68 to -44.75 mmol<sub>c</sub> Kg<sup>-1</sup>, while the biochars surface charge varied from -0.6 to -48.8 mmol<sub>c</sub> Kg<sup>-1</sup>. Soil clays were more strongly dispersed in the presence of biochars by increasing electrostatic repulsive forces. The biochar preparation method had a crucial role for surface charge properties of biochars and in consequence colloidal dynamics of biochar-clay mixtures. The N<sub>2</sub>-supported pyrolysis at lower temperatures does not increase charge density but creates a more porous structure, thereby increasing the total negative net charges. As a result, the N<sub>2</sub>-supported biochars favor clay dispersion more effectively, while the open-pyrolysis biochars showed lesser effects. Our results indicate that fine-sized biochar amendments generally enhance the risk of clay loss, however, such techniques for creating low-charged biochars can help to decrease clay dispersibility when applying biochar for soil.</p>

Pengaruh Waktu Pemeraman Dengan Penambahan Kapur Sebagai Bahan Additve Pada Tanah Lempung Ekspansif Terhadap Nilai CBR Tanah

<p><em>The soil is an essential element of a structure under construction so that the soil should have a good carrying capacity. But the fact the field is found soil that has the low bearing capacity, so it is necessary to conduct soil stabilisation with lime. The study aims to determine the percentage that is effective in adding lime and the effect of adding lime to the soil physical properties change in terms of the value of CBR (California Bearing Ratio) to the long curing time. This research was conducted in the laboratory, by testing the physical properties of soil and the strong support of land (CBR) with the addition of lime variation of 1%, 3%, and 5% by long curing 0, 4, 7 and 14 days. Tests were conducted with two treatments, soil samples were cured first and then compacted and samples were pressed first and brooded. The result is the value of CBR.</em><em> %. From the results of the value of the California Bearing Ratio can be seen that the addition of sand quarsa on soil clays showed an increase in the value of the California Bearing Ratio in soil clays.</em></p>