Biochar application impacts on water infiltration rate into soil and field saturation hydraulic conductivity of sandy loam soil

Adding organic residues as biochar to the soil to improve its physical, chemical and biological properties is a new approach in the management of plant residues and organic wastes. Biochar is a carbon-rich porous material that has recently been added to soil as a modifier. Adding biochar to the soil, besides carbon sequestration in the soil, has many positive agronomic and environmental effects. In the studies, the researchers paid the most attention to the amount of biochar added to the soil. The aim of this study was to investigate the impact of wheat straw, vermicompost and apricot wood in different amounts and particle sizes on the average water infiltration rate and field saturated hydraulic conductivity.

Wheat straw, vermicompost and apricot wood were prepared at 330 °C. The effect of the mentioned biochars in the amounts of 0.5%, 1.5% and 3% and particle sizes of 0-0.5, 0.5-1 and 1-2 mm were evaluated in a factorial experiment with a randomized complete block design with three replicate. A control plot was also considered in each block.

The results showed that the effect of the studied treatments on iave and Kfs was significant. The iave had a significant increase in biochar treatments with medium and high amounts and large particle size compared to the control. Changes in biochar type, biochar amount and biochar particle size had a significant effect on iave and Kfs. The interaction effects of biochar type and biochar particle size, biochar type and biochar amount and biochar particle size and also biochar type and biochar amount in iave change contributed to 25.75%, 16.73% and 15.96%, respectively. In Kfs changes, the main effect of biochar amount and the interaction effects of the type of biochar and the amount of biochar and the size of biochar particles and also the amount of biochar and the size of biochar particles contributed 31.93%, 21.93% and 10.78%, respectively. In the studied biochars, depending on the type of biochar, the interaction effect of the amount of biochar and the size of biochar particles on the average infiltration rate was not the same. Among the treatments of wheat straw biochar, the amount of 3% and particle size of 1-2 mm, has the highest iave, which was not significantly different from the treatment of wheat straw at 3% and particle size of 0.5-1-1 mm. In vermicompost treatments in the amount of 1.5% and particle size of 1-2 mm particle size, the highest iave was observed, which was significantly different from the other values and particle size in that biochar. Among all treatments, the highest iave was in vermicompost biochar with an amount of 1.5% and a particle size of 1-2 mm. However, in apricot wood biochar, the highest average water infiltration rate was observed in the amount of 0.5% and particle size of 0.5-1. There was no significant difference with the average water infiltration rate in the amount of ٪ 1.5 and particle size of 0.5-1 mm of this type of biochar In all treatments, the highest iave (0.2615 m hr-1) was in vermicompost biochar with an amount of 1.5% and particle size of 1-2 mm. Comparison of the Kfs means in each biochar showed that in the wheat straw biochar treatments the highest Kfs is in the amount of 0.5% and particle size is 0.5-1 mm. At amounts of 1.5% and 3% of wheat straw biochar, the field saturated hydraulic conductivity of soil decreased with increasing biochar particle size. In vermicompost biochar, the highest Kfs was observed in the amount of 0.5% and particle size of 0.5-1 mm. In apricot wood biochar, the highest Kfs was in the amount of 0.5% and the particle size was 0-0.5 mm, which was not significantly different from Kfs in the amount of 1.5% and the particle size of 0.5-1 mm. In this type of biochar the lowest Kfs observed in the amount of 3% and particle size 0.5-0 mm. between all treatments, the highest Kfs (0.00256 cm sec-1) was observed in wheat straw biochar with an amount of 0.5% and a particle size of 0-0.5 mm. To obtain the desired result from the addition of biochar on the hydraulic properties of the soil, biochar should be designed with the appropriate amount and size of biochar particles.