The Effect of Two Types of Agricultural Waste Biochar on Some Physical Properties and Water Repellency of Soil

In recent decade, biochar application as a soil amendment has received attention from many researchers around the world. With respect to report of different impacts of biochars on soil properties and crop type the use of biochar in soil as an amendment must be scientifically and practically studied in relation to the type of soil, type of biochar and type of plant to investigate and determine its positive or negative effects. The aim of this study was to investigate the effect of biochar derived from pistachio waste and date palm leaves on some physical properties and water repellency of soil.

For this purpose, two types of soil (i.e. sand and sandy loam) were combined with two types of biochar, date palm leaf biochar (DPLB) and pistachio harvesting waste biochar (PHWB), at 4 application levels (1, 2, 3, and 5% by weight), also the treatment without biochar application was considered as a control. These biochars were mixed with soil and after a two-month incubation period, then physical properties of soil such as bulk density, specific surface area, hygroscopic moisture, water repellency, and dispersible clay were measured and the obtained results were statistically analyzed.

The results showed that the application of biochars generally decreased the bulk density (BD) and increased the specific surface area (SSA) and hygroscopic moisture content (HMC) in the both soils. Although the application of DPLB caused decrease in dispersible clay (DC) of the soils but PHWB increased this parameter compared to the control. Application of 5% DPLB in both soils reduced DC by 60% but on the other hand, PHWB increased DC by 43% and 114% in sandy soil and sandy loam soil, respectively. In general, the low levels of biochar application (1% level) caused a significant decrease in the water repellency of sandy loam soil compared to the control, and increasing the levels of biochar application, resulted in an increase in soil hydrophobicity. The effect of DPLB application in sandy loam soil on water repellency was not significant, and the application of PHWB had a different effect on water repellency of sandy soil. Increasing levels of PHWB caused a significant decrease in water repellency of sandy soil, so that the application of 5% of PHWB reduced this index by 31% in this soil. It seems that PHWB has increased the SSA of sandy soil and on the other hand, the greater tendency of this biochar to absorb water on the surface (increased HWC), has increased the tendency of sandy soil to suck the water, so decreased the water repellency of this soil.

In general, the effects of the studied biochars on the physical properties of the both soils were positive, and the reduction of the BD and DC also the increasing of the SSA and HWC could be considered as an increasing in the soil quality, but this doesn't mean that the application of biochars can have positive effects on plant growth in the soil, because the aspects of the impact of these amendments on other soil properties (i.e. chemical properties) should also be considered. So, considering that the effect of biochar can be greatly influenced by the combination of biochar properties and soil conditions, effective use of biochar in agricultural soils requires prior evaluation of the biochar effect based on soil and plant conditions.