The effect of acidic and neutral biochar on moisture properties of calcareous soils

The purpose of incorporating organic modifiers such as biochar with soil is stabilizing carbon, improving fertility, absorbing pollutants, and consequently increasing crop production. Biochar is a biofuel and the resultant of organic matters thermocouples. Biochars are produced in high temperature ovens and are commonly alkaline and so suitable for the acidic soils. However, if the raw materials are heated at low temperatures, the resulting biochar can be acidic and useful for modifying calcareous soils. The aim of this study was to investigate the effect of two types of acidic biochars of rice husk and pine cone for modifying the physical properties of two calcareous soils of Isfahan province.

Based on a preliminary experiment, rice husk biochar (pH=5.64) and pine cone biochar (pH=6.56) produced at 300°C were selected for this study. The experiment was performed in a completely randomized factorial design with three replications. Treatments included two types of biochar (pine cone and rice husk) mixed with soil at one, three and six percent (g/g), two types of soil (a sandy loam, Tiran and a clay loam, Lavark), and two incubation periods of one and six months, with 4 controls and a total of 28 pots. The treated soils were kept in an incubator at 25°C and 60% of field (pot) capacity. At the end of the incubation periods, the soil moisture contents at field capacity and the permanent wilting point were measured respectively using sand-kaolin box and pressure plate devices and then soil available water contents was calculated.

The results showed that the addition of biochars improved some physical properties of soils. The treatment of the soils with 3% and 6% of biochars caused significant increases in the available water (AW) in the sandy loam soils compared to the control. The physical quality index of Dexter (SDexter) fitted by van Genuchten–Mualem was significantly increased in the sandy loam soil amended with 6% of the biochars and in the clay loam soil amended with 3% and 6% of the biochars. The use of biochars also improved the physical quality of the soil, described by the Dexter index, from poor to very good.

The results of this study showed that addition of 6% rice husk biochar to the clay loam soil and at the 30 days incubation period, could improve soil properties. Therefore, according to these findings, the biochars produced from pine cones and rice husk can be suggested as a suitable conditioner for improving physical properties of the regional calcareous soils.