Effect of the amount and particles size of Conocarpus biochar on physical and hydraulic properties and evaporation from loam sandy soil surface

In arid and semi-arid areas, due to the lack of sufficient vegetation and the return of a small amount of plant residues to the soil, the amount of organic matter in the soil is very low, so the use of organic fertilizers can be a suitable solution to improve the physical and chemical conditions of the soil in these areas. In recent years, biochar has been used as a soil modifier (source of organic carbon) and as a method for carbon sequestration in the soils of dry and desert areas. this research aims to maintain and increase the water retention capacity in the soil and improve the physical characteristics of the loam sandy of the Sistan region by using different compositions and sizes.

In this research, the effect of three biochar diameter ranges (<0.25, 0.25-1 and 1-2 mm) and three amounts of Cenocarpus biochar (2, 4, and 8% by weight) on the properties Hydraulic and physical soil and evaporation from the soil surface with loam sandy texture of Sistan region were studied. Experiments were conducted in 3 replications in a completely randomized design. To carry out the work, polyethylene columns with a diameter of 10 cm and a height of 35 cm were prepared. The columns were covered with cloth from the floor. The soil with different treatments of size and amount of biochar was manually added to the columns and filled with gentle blows to the column body until reaching a height of 30 cm. To measure evaporation, 100 mm of water was added to the soil in 5 weeks (20 mm per week). Evaporation from the soil surface was measured by weight method every day. Hydraulic conductivity of saturated soil was measured by constant load method. Also, soil salinity and moisture were calculated at three depths of 0-10, 10-20 and 20-30 cm. The bulk density and water holding capacity of the soil were also measured.

The results showed that with the increase in the amount of biochar used, the bulk density and saturated hydraulic conductivity of the soil decreased by 29.32% and 48.1%, respectively, compared to the control treatment (treatment without biochar). By increasing the amount of biochar and decreasing its particle size, the water holding capacity in the soil increased. The treatment with 8% by weight of biochar and the particle size <0.25 mm had the greatest (43.54%) increase in the water holding capacity in the soil. By increasing the amount of biochar and decreasing its particle size, soil salinity increased compared to the control treatment. But the evaporation from the soil surface decreased with the increase in the amount of biochar and the decrease in its particle size.

According to the obtained results, it can be said that biochar has positive effects on improving the physical and hydraulic properties of soils with a relatively light texture. But these changes depend on the amount and size of biochar particles. Using biochar as a soil modifier in light textured soils that have low water holding capacity and high evaporation, especially in arid and semi-arid areas that are facing the problem of lack of water resources, is a very suitable solution. But it should be noted that increasing biochar levels in soil can increase soil salinity. Therefore, according to the obtained results and the positive effect of biochar on the physical and chemical parameters of the soil, the optimal selection of the biochar surface should be such that its use is economically viable, and this requires more research, especially It is in farm conditions.