## 4 Results and Discussion
### Intermittent Evaporation  
The amount of water which was added to the soil columns' macro and nano-biochar during the four cycles of wetting/evaporation was 50.94 mm. At the end of the experiment, the amount of water reserved in the columns (added minus evaporation) varied between 7.70 mm to 14.30 mm (Table 2). Cumulative evaporation was highest in the untreated treatments, found to be between 32.13 mm and 30.11 mm after 4 weeks. The application of macro-biochar reduced cumulative evaporation in comparison to the control by 4%, 24%, and 14% for the macro-biochar particles at soil depths of 0-5 (D1), 5-10 (D2), and 10-15 cm (D3), respectively (Figure 4A). The application of nano-biochar reduced cumulative evaporation in comparison to the control by 8%, 12%, and 4% for the nano-biochar particles at soil depths of 0-5 (D1), 5-10 (D2), and 10-15 cm (D3), respectively (Figure 4B). The results of the evaporation studies could be like previous research, which indicated that soil treated with biochar showed lower evaporation rates, attributed to the biochar particles' ability to minimize bigger soil pores and enhance water retention [30; 31]. Furthermore, Table 2 and Figure 4 illustrate the results of the weekly evaporation of each wetting/dry cycle and total water recovered for the control and biochar at different application depths (D1, D2, and D3). In general, cumulative evaporation at the end of each wet/dry cycle was lower by 8.76, 6.12, 11.51, and 6.88 mm for the 1 st, 2 nd, 3 rd, and 4 th positions, respectively, compared to untreated soils with biochar as well as the total of 33.28 mm for the control treatments. Table 2 and Figure 4A show that the untreated sandy soil had the highest values of total cumulative evaporation and weekly evaporation compared to other macroparticle biochar treatments. Concerning nano-biochar addition, Table 2 and Figure 4B show that  
Figure 3: Transmission Electron Microscope (TEM) images of biochar nanoparticles. treatment at depth D2 has the highest water retained, followed by treatment at D1, D3, and the control. The cumulative evaporation of nano treatment was 34.4, 37,85, 24.67, and 25.81 mm at the end of four wetting/drying cycles for the control, D1, D2, and D3, respectively. The beneficial effect of enhancing the ability of sand soil to maintain water occurs primarily via the use of materials that are highly porous, such as biochar [10; 32; 33]. The improvement in soil water could be related to decreasing the large pores of sandy soil. Several studies indicated that the enhancement of soil moisture retention by adding biochar with smaller particles might be explained by increasing the amounts of small pores in sandy soil [10; 32; 34]. In addition, the large surface area of biochar may be the cause of an increase in the soil water-holding capacity, especially in sandy soils. In another study, using different biochar waste in conjunction with the size of microparticles in the soil was found to increase the soil surface area [13]. In general, adding biochar might alter and enhance water retention of soil by increasing the surface area and porosity and reducing bulk density [32; 33; 35]. Figure 4A,B show the impact of the application depth of macro and nano-biochar on cumulative evaporation and, sequentially, how this increases the water retained in soils. Generally, the addition of macro or nano-biochar at a depth of 5-10 cm (D2) has better results in retaining water compared to other depth treatments. Added the biochar into the 5-10 cm (D1) layer improved the conserved water and reduced the evaporation rates significantly. In general, biochar acted exceptionally well when placed at a depth of D2, where the maximum decrease in cumulative evaporation was noticed.