Electrical conductivity
Under irrigation with saline water, the applications of 3%WCB, 5%WCB, 3%BLB, 5%BLB, 3%SSB, 5%SSB, 3%RSB, and 5%RSB in saline soil led to a significant increase (p ≤ 0.01) in the electrical conductivity (EC) values compared to the control treatment after harvesting arugula plant (Fig. 1). Compared with the control treatment, the EC increased by 1%, 40%, 49%, 17%, 71%, 91%, 20%, 59%, 80%, 10%, 83%, and 107% for 1%WCB, 3%WCB, 5%WCB, 1%BLB, 3%BLB, 5%BLB, 1%SSB, 3%SSB, 5%SSB, 1%RSB, 3%RSB, and 5%RSB treatments, respectively. The lowest value of EC was observed at the control treatment. However, the highest value was noticed in the 5%RSB treatment. The values of EC in saline soil increased with increasing biochar doses (Fig. 1).
Soluble cations and anions
After the arugula plant was harvested, the addition of 3%WCB, 5%WCB, 1%BLB, 3%BLB, 1%SSB, 3%SSB, 5%SSB, 3%RSB, and 5%RSB treatments significantly increased soluble calcium in the soil under study compared with the control treatment (Table 3). Meanwhile, adding 1%WCB, 5%BLB, and 1%RSB showed non-significant increases in soluble calcium. The lowest concentration of soluble calcium was observed at the control treatment, while the highest concentration was observed when applying 3%RSB treatments. Compared with the control treatment, adding 3%BLB, 5%BLB, 3%SSB, and 5%SSB treatments to saline soil significantly increased soluble magnesium, while applying 1%WCB, 3%WCB, 5%WCB, 1%RSB, 3%RSB, and 5%RSB treatments showed non-significant increases in soluble magnesium. Applying 1%BLB and 1%SSB treatments to saline soil showed non-significant decreases in soluble magnesium (Table 3). The lowest concentration of soluble magnesium was observed at 1%BLB treatment, while the highest concentration was observed in the 5%BLB application. The application of 3%WCB, 5%WCB, 1%BLB, 3%BLB, 5%BLB, 1%SSB, 3%SSB, 5%SSB, 3%RSB, and 5%RSB treatments to sandy soil increased significantly soluble sodium compared to the control treatment after harvesting arugula plant (Table 3). However, adding 1%WCB and 1%RSB resulted in a non-significant increase in the soluble sodium. Soluble sodium increased relative to the control treatment by 19%, 254%, 230%, 64%, 250%, 253%, 118%, 271%, 285%, 36%, 327%, and 364% for 1%WCB, 3%WCB, 5%WCB, 1%BLB, 3%BLB, 5%BLB, 1%SSB, 3%SSB, 5%SSB, 1%RSB, 3%RSB, and 5%RSB, respectively. The lowest content of soluble sodium was observed in the control treatment. However, the highest content of soluble sodium was observed when adding 5%RSB. Applying 3%BLB, 5%BLB, 1%SSB, 3%SSB, 5%SSB, 1%RSB, 3%RSB, and 5%RSB to saline soil increased significantly soluble potassium in comparison with the control treatment (Table 3). Meanwhile, adding 1%WCB, 3%WCB, 5%WCB, and 1%BLB showed non-significant increases in soluble potassium. Soluble potassium increased relative to the control treatment by 1.1-fold, 1.3, 1.4, 2.3, 7.8, 11.7, 2.6, 7.2, 11.3, 2.6, 9.8, and 19.4-fold for 1%WCB, 3%WCB, 5%WCB, 1%BLB, 3%BLB, 5%BLB, 1%SSB, 3%SSB, 5%SSB, 1%RSB, 3%RSB, and 5%RSB, respectively. The concentrations of soluble potassium in saline soil increased with increasing biochar doses. The lowest value of soluble potassium was present at the control treatment, while the highest value was observed at the 5%RSB treatment.
Adding 5%WCB, 3%BLB, 5%BLB, 3%SSB, 5%SSB, 3%RSB, and 5%RSB to saline soil showed an increase significant in soluble bicarbonate compared to the control treatment (Table 3). Meanwhile, applying 1%WCB, 3%WCB, 1%BLB, 1%SSB, and 1%RSB showed non-significant increases in soluble bicarbonate. The lowest concentration of soluble bicarbonate was observed in the control treatment. However, the highest concentration of soluble bicarbonate was observed at 5%BLB treatment. The addition of 3%WCB, 5%WCB, 1%BLB, 3%BLB, 5%BLB, 1%SSB, 3%SSB, 5%SSB, 3%RSB, and 5%RSB treatments significantly increased soluble chloride in the soil under study compared with the control treatment (Table 3). Meanwhile, adding 1%WCB and 1%RSB showed non-significant increases in soluble chloride. The lowest concentration of soluble chloride was observed in the control treatment. However, the highest concentration of soluble chloride was observed when applying 5%RSB treatment. Applying 3%BLB, 5%BLB, 3%SSB, 5%SSB, and 5%RSB treatments to saline soil significantly increased soluble sulfate compared to the control treatment after harvesting the arugula plant (Table 3). However, applying 1%WCB, 5%WCB, 1%BLB, 1%SSB, 1%RSB, and 3%RSB to saline soil led to non-significant increases in soluble sulfate. Addition of 3%WCB to saline soil led to a non-significant decrease in soluble sulfate. The lowest concentration of soluble sulfate was observed when adding 3%WCB treatment, whilst the highest concentration of soluble sulfate was observed when applying 5%BLB treatment (Table 3).
Soil organic matter and cation exchange capacity
Compared to the control treatment, all biochar treatments applied to saline soil resulted in significant increases in the soil organic matter (SOM) after harvesting arugula, except for the 1%WCB treatment which showed a non-significant increase (Table 4). The contents of SOM in saline soil increased with increasing biochar doses. Adding biochar to the saline soil contributed to increasing the organic matter by 7.0, 16.0, 30.0, 14.0, 33.9, 51.8, 13.6, 35.7, 50.2, 12.3, 32.7, and 66.2-fold higher than the control treatment for 1%WCB, 3%WCB, 5%WCB, 1%BLB, 3%BLB, 5%BLB, 1%SSB, 3%SSB, 5%SSB, 1%RSB, 3%RSB, and 5%RSB treatments, respectively. The effectiveness of the treatments in this study on the SOM increase was in the order of 5%RSB > 5%BLB > 5%SSB > 3%SSB > 3%BLB > 3%RSB > 5%WCB > 3%WCB > 1%BLB > 1%SSB > 1%RSB > 1%WCB > control. The control treatment had the lowest SOM content. However, the 5%RSB treatments had the highest content (Table 4). Significantly increased the cation exchange capacity (CEC) resulting in the applications of 3%WCB, 5%WCB, 3%BLB, 5%BLB, 3%SSB, 5%SSB, 3%RSB, and 5%RSB treatments to saline soil compared to the control treatment (Table 4). Adding all different types of biochar at levels of 3 and 5% led to a significant increase in the exchange capacity compared to the control treatment. However, applying 1%WCB, 1%BLB, 1%SSB, and 1%RSB treatments had a non-significant increase in CEC. The values of CEC in saline soil increased with increasing biochar doses. Relative to the control treatment, the CEC values increased by 7%, 26%, 22%, 3%, 30%, 58%, 6%, 31%, 54%, 7%, 28%, and 48% for 1%WCB, 3%WCB, 5%WCB, 1%BLB, 3%BLB, 5%BLB, 1%SSB, 3%SSB, 5%SSB, 1%RSB, 3%RSB, and 5%RSB, respectively. The CEC values in saline soil increased with increasing biochar doses. The lowest value of CEC was observed at the control treatment. However, the highest values were shown in the 5%BLB and 5%SSB treatments (Table 4).
Nutrient availability in saline soil
Applying 1%WCB, 3%WCB, 5%WCB, 1%BLB, 3%BLB, 5%BLB, 5%SSB, 1%RSB, and 5%RSB treatments increased significantly available nitrate nitrogen in the soil under study compared with the control treatment after harvesting arugula. Meanwhile, adding 1%SSB, 3%SSB, and 3%RSB showed non-significant increases in available nitrate nitrogen (Table 4). Relative to the control treatment, the available nitrate nitrogen in the soil increased by 35%, 68%, 70%, 85%, 68%, 67%, 15%, 3%, 53%, 87%, 25%, and 93% for 1%WCB, 3%WCB, 5%WCB, 1%BLB, 3%BLB, 5%BLB, 1%SSB, 3%SSB, 5%SSB, 1%RSB, 3%RSB, and 5%RSB, respectively. The effectiveness of the treatments for the increase in available nitrate nitrogen values was in the order: 5%RSB > 1%RSB > 1%BLB > 5%WCB > 3%WCB > 3%BLB > 5%BLB > 5%SSB > 1%WCB > 3%RSB > 1%SSB > 3%SSB > control. The lowest concentration of available nitrate nitrogen was observed at the control treatment. However, the highest concentration was shown in the 5%RSB treatment (Table 4). The results obtained from this experiment also resulted in a non-significant increase in the available ammonium nitrogen by applying 3%WCB, 1%BLB, and 3%BLB treatments to saline soil compared to the control treatment, but adding 1%WCB, 1%SSB, 3%SSB, 5%SSB, 1%RSB, 3%RSB, and 5%RSB treatments caused a non-significant decrease in available ammonium nitrogen content compared to the control treatment (Table 4). Adding 3%WCB, 5%WCB, 1%BLB, 3%BLB, 5%BLB, 5%SSB, 1%RSB, and 5%RSB treatments caused a significant increase in the total available nitrogen (nitrate nitrogen + ammonium nitrogen) in the soil under study compared with the control treatment (Table 4). However, adding 1%WCB, 1%SSB, and 3%RSB resulted in a non-significant increase in total available nitrogen. On the other hand, applying 3%SSB to saline soil led to a non-significant decrease in total available nitrogen compared to the control treatment. Relative to the control treatment, the total available nitrogen in the soil increased by 14%, 41%, 34%, 43%, 34%, 33%, 7%, 24%, 41%, 11%, and 44% for 1%WCB, 3%WCB, 5%WCB, 1%BLB, 3%BLB, 5%BLB, 1%SSB, 5%SSB, 1%RSB, 3%RSB, and 5%RSB, respectively. The treatments under study can be ranked in the total available nitrogen increment of this saline soil in the order of 5%RSB > 1%BLB > 3%WCB > 1%RSB > 5%WCB > 3%BLB > 5%BLB > 5%SSB > 1%WCB > 3%RSB > 1%SSB > control > 3%SSB (Table 4). The lowest concentration of total available nitrogen was observed at the 3%SSB treatment. However, the highest concentration was shown in the 5%RSB treatment (Table 4).
After harvesting the arugula plant, the applications of 3%BLB, 5%BLB, 5%SSB, and 5%RSB treatments to saline soil significantly increased phosphorous availability compared to the control treatment (Fig. 2A). While applying 3%SSB and 3%RSB showed non-significant increases in phosphorous availability. On the other hand, adding 1%WCB, 3%WCB, 5%WCB, 1%BLB, 1%SSB, and 1%RSB, 3%RSB showed non-significant decrease in the phosphorous availability. Compared with the control treatment, the available phosphorus increased by 182%, 573%, 137%, 536%, 111%, and 222% for 3%BLB, 5%BLB, 3%SSB, 5%SSB, 3%RSB, and 5%RSB treatments, respectively. The effectiveness of the treatments in this study on the available phosphorus improvement was in the order of 5%BLB > 5%SSB > 5%RSB > 3%BLB > 3%SSB > 3%RSB > control > 1%SSB = 5%WCB > 1%WCB > 1%BLB > 3%WCB > 1%RSB (Fig. 2A). The lowest concentration of available phosphorus was observed at the 1%RSB treatment. Nevertheless, the highest concentration of available phosphorus was observed in saline soil with adding 5%BLB treatment.
Available phosphorus and potassium in saline sandy soil after harvesting arugula plant as affected by type and doses of biochar. Control: unamended soil; WCB, wood chips biochar; BLB: banana leaves biochar, SSB: sorghum stalks biochar, RSB: rice straw biochar. Biochar was applied at three doses 1%, 3%, and 5% (w/w). Different lowercase letters on each bar indicate the significant differences among treatments according to Tukey’s Honestly Significant Difference test at p ≤ 0.01. Vertical bars indicate the standard error of the mean (n = 3 replicates).
Potassium availability in saline soil increased significantly after the harvesting of arugula plant under applying 5%WCB, 1%BLB, 3%BLB, 5%BLB, 1%SSB, 3%SSB, 5%SSB, 1%RSB, 3%RSB, and 5%RSB compared to the control treatment (Fig. 2B). However, applying 1%WCB and 3%WCB resulted in a non-significant increase in potassium availability. The applied biochar treatments increased available K over the control by more pronounced percentages reaching 14%, 29%, 48%, 125%, 410%, 738%, 137%, 352%, 632%, 158%, 576%, and 849% for 1%WCB, 3%WCB, 5%WCB, 1%BLB, 3%BLB, 5%BLB, 1%SSB, 3%SSB, 5%SSB, 1%RSB, 3%RSB, and 5%RSB treatments, respectively. The effectiveness of the treatments in this study on the available potassium increase was in the order of 5%RSB > 5%BLB > 5%SSB > 3%RSB > 3%BLB > 3%SSB > 1%RSB > 1%SSB > 1%BLB > 5%WCB > 3%WCB > 1%WCB > control (Fig. 2B). The lowest concentration of available potassium was observed in the control treatment, whilst the highest value of available potassium in saline soil was noticed in the 5%RSB treatment.
Parameters growth of arugula plant
The results obtained from this experiment also resulted in a non-significant increase in the chlorophyll values under applying all treatments to the soil except 5%BLB treatment compared to the control treatment, but adding 5%BLB treatment showed a non-significant decrease in chlorophyll value compared to the control treatment (Table 5). A significant increase was observed in fresh and dry biomass of arugula plant grown in saline soil under applying 3%WCB, 5%WCB, 1%BLB, 3%BLB, 1%SSB, 3%SSB, 5%SSB, 1%RSB, 3%RSB, and 5%RSB treatments compared to the control treatment (Fig. 3A, B). However, adding 1%WCB and 5%BLB resulted in a non-significant increase in the fresh and dry biomass of the arugula plant. The relative increase in the fresh biomass of the arugula plant over the control treatment was 31%, 97%, 143%, 76%, 129%, 37%, 103%, 146%, 81%, 57%, 121%, and 97% for 1%WCB, 3%WCB, 5%WCB, 1%BLB, 3%BLB, 5%BLB, 1%SSB, 3%SSB, 5%SSB, 1%RSB, 3%RSB, and 5%RSB, respectively. The effectiveness of treatments in improving fresh biomass of arugula was in the order of 3%SSB > 5%WCB > 3%BLB > 3%RSB > 1%SSB > 5%RSB ≈ 3%WCB > 5%SSB > 1%BLB > 1%RSB > 5%BLB > 1%WCB > control (Fig. 3A). Relative to the control treatment, the dry biomass of the arugula plant increased by 42%, 166%, 236%, 125%, 201%, 26%, 168%, 224%, 117%, 87%, 201%, and 148% for 1%WCB, 3%WCB, 5%WCB, 1%BLB, 3%BLB, 5%BLB, 1%SSB, 3%SSB, 5%SSB, 1%RSB, 3%RSB, and 5%RSB, respectively. The treatments used in this soil showed improvements in the dry biomass of the arugula plant in the order of 5%WCB > 3%SSB > 3%RSB ≈ 3%BLB > 1%SSB > 3%WCB > 5%RSB > 1%BLB > 5%SSB > 1%RSB > 1%WCB > 5%BLB > control (Fig. 3B). The highest values of fresh and dry biomass of arugula plant were observed at the 5%WCB and 3%SSB applications, while the lowest values of fresh and dry biomass of arugula in this study were recorded for the control treatment.
Fresh and dry biomass of arugula plant grown in saline sandy soil as affected by type and doses of biochar. Control: unamended soil; WCB, wood chips biochar; BLB: banana leaves biochar, SSB: sorghum stalks biochar, RSB: rice straw biochar. Biochar was applied at three doses 1%, 3%, and 5% (w/w). Different lowercase letters on each bar indicate the significant differences among treatments according to Tukey’s Honestly Significant Difference test at p ≤ 0.01. Vertical bars indicate the standard error of the mean (n = 3 replicates).
The concentrations of nutrients in arugula plant
The applications of 3%WCB, 5%WCB, 1%BLB, 3%BLB, 5%BLB, 1%SSB, 3%SSB, 5%SSB, and 5%RSB to saline soil significantly increased nitrogen content in arugula plant compared with the control treatment. However, adding 1%WCB, 1%RSB, and 3%RSB treatments showed non-significant increases in nitrogen content in the arugula plant compared to the control treatment (Table 5). Adding 1%WCB, 3%WCB, 5%WCB, 1%BLB, 3%BLB, 5%BLB, 1%SSB, 3%SSB, 5%SSB, 1%RSB, 3%RSB, and 5%RSB treatments increased nitrogen concentration in arugula plant over the control by 12%, 108%, 69%, 80%, 67%, 67%, 92%, 80%, 64%, 13%, 8%, and 46%, respectively (Table 5). In this study, the effectiveness of the treatments in improving nitrogen content in arugula plant was in the order of 3%WCB > 1%SSB > 1%BLB = 3%SSB > 5%WCB > 3%BLB = 5%BLB > 5%SSB > 5%RSB > 1%RSB > 1%WCB > 3%RSB > control (Table 5). The lowest nitrogen content in the arugula plant was observed in the control treatment, whilst the highest nitrogen content in the arugula plant was noticed in the 3%WCB treatment.
A significant increase in phosphorus content occurred in arugula plant under applying 5%WCB, 1%BLB, 3%BLB, 5%BLB, 3%SSB, 5%SSB, and 5%RSB compared to the control treatment, on the other hand, the application of 1%WCB, 3%WCB, 1%SSB, 1%RSB, and 3%RSB caused an insignificant increase in phosphorus content in arugula plant (Table 5). Relative to the control treatment, phosphorus content in the arugula plant increased by 40%, 38%, 83%, 68%, 51%, 249%, 29%, 186%, 246%, 23%, 23%, 133% for the application of 1%WCB, 3%WCB, 5%WCB, 1%BLB, 3%BLB, 5%BLB, 1%SSB, 3%SSB, 5%SSB, 1%RSB, 3%RSB, and 5%RSB treatments, respectively. Therefore, all treatments increased the phosphorus content in the arugula plant in the order of 5%BLB > 5%SSB > 3%SSB > 5%RSB > 5%WCB > 1%BLB > 3%BLB > 1%WCB > 3%WCB > 1%SSB > 3%RSB > 1%RSB > control (Table 5). The lowest phosphorus content in the arugula plant was observed in the control treatment, whilst the highest phosphorus content in the arugula plant was noticed in the 5%BLB treatment.
The potassium content in the arugula plant grown in saline soil increased significantly with adding 3%BLB, 5%BLB, 3%SSB, 5%SSB, 3%RSB, and 5%RSB treatments compared with the control treatment. However, applying 1%WCB, 3%WCB, 5%WCB, and 1%SSB led to a non-significant increase in potassium content in the arugula plant. On the other hand, adding 1%BLB and 1%RSB showed a non-significant decrease in the potassium content in the arugula plant compared to the control treatment (Table 5). Relative to the control treatment, the potassium concentration in the arugula plant increased by 2%, 11%, 13%, 58%, 525%, 24%, 62%, 394%, 69%, and 399% with the addition of 1%WCB, 3%WCB, 5%WCB, 3%BLB, 5%BLB, 1%SSB, 3%SSB, 5%SSB, 3%RSB, and 5%RSB treatments, respectively. The effectiveness of treatments in improving potassium content in arugula was in the order of 5%BLB > 5%RSB > 5%SSB > 3%RSB > 3%SSB > 3%BLB > 1%SSB > 5%WCB > 3%WCB > 1%WCB > control > 1%BLB > 1%RSB (Table 5). The lowest potassium content in the arugula plant was observed in the 1%RSB treatment, whilst the highest potassium content in the arugula plant was noticed in the 5%BLB treatment.
Compared with the control treatment, adding 1%WCB, 3%WCB, 5%WCB, 1%BLB, 1%SSB, 3%SSB, and 1%RSB to saline soil significantly decreased the sodium content in the arugula plant. However, applying 3%BLB, 5%SSB, 3%RSB, and 5%RSB treatments resulted in a non-significant decrease in sodium content in the arugula plant (Table 5). Results showed that sodium concentration in the arugula plant decreased relative to the control treatment by 21%, 27%, 34%, 28%, 16%, 40%, 24%, 16%, 25%, 14%, and 13% for 1%WCB, 3%WCB, 5%WCB, 1%BLB, 3%BLB, 1%SSB, 3%SSB, 5%SSB, 1%RSB, 3%RSB, and 5%RSB treatments, respectively. On the other hand, applying 5%BLB to saline soil led to a significant increase in the sodium content in the arugula plant. Compared to the control, the 5%BLB addition increased sodium concentration in the arugula plant by 49%. The effectiveness of the treatments on sodium content in the arugula plant decrease was in the order of control > 5%RSB > 3%RSB > 5%SSB > 3%BLB > 1%WCB > 3%SSB > 1%RSB > 3%WCB > 1%BLB > 5%WCB > 1%SSB (Table 5). The lowest sodium content in the arugula plant was observed in the 1%SSB treatment, whilst the highest sodium content in the arugula plant was noticed in the 5%BLB treatment.
Nutrient uptake by arugula plant
A significant increase occurred in nitrogen uptake by arugula plant as a result of applying 3%WCB, 5%WCB, 1%BLB, 3%BLB, 1%SSB, 3%SSB, 5%SSB, 3%RSB, and 5%RSB treatments to saline soil compared to the control treatment. Meanwhile, applying 1%WCB, 5%BLB, and 1%RSB caused a non-significant increase in nitrogen uptake by the arugula plant (Fig. 4A). Results showed that the relative enhancements in of nitrogen uptake by arugula plant over the control were 59%, 453%, 471%, 305%, 403%, 110%, 418%, 483%, 257%, 112%, 225%, and 265% for 1%WCB, 3%WCB, 5%WCB, 1%BLB, 3%BLB, 5%BLB, 1%SSB, 3%SSB, 5%SSB, 1%RSB, 3%RSB, and 5%RSB treatments, respectively. The lowest nitrogen uptake by the arugula plant was observed in the control treatment, while the highest nitrogen uptake by the arugula plant was observed after adding 3%SSB treatment (Fig. 4A).
Nitrogen and phosphorus uptake by arugula plant grown in saline sandy soil as affected by type and doses of biochar; Control: unamended soil; WCB, wood chips biochar; BLB: banana leaves biochar, SSB: sorghum stalks biochar, RSB: rice straw biochar. Biochar was applied at three doses 1%, 3%, and 5% (w/w). Different lowercase letters on each bar indicate the significant differences among treatments according to Tukey’s Honestly Significant Difference test at p ≤ 0.01. Vertical bars indicate the standard error of the mean (n = 3 replicates).
Phosphorus and potassium uptake by arugula improved significantly with the applications of 3%WCB, 5%WCB, 1%BLB, 3%BLB, 5%BLB, 1%SSB, 3%SSB, 5%SSB, 3%RSB, and 5%RSB treatments to saline soil in comparison with the control treatment, while adding 1%WCB and 1%RSB treatments to this soil resulted in a non-significant increase in phosphorus and potassium uptake by the arugula plant compared to the control (Figs. 4B and 5A). Compared to the control, the biochar treatments of 1%WCB, 3%WCB, 5%WCB, 1%BLB, 3%BLB, 5%BLB, 1%SSB, 3%SSB, 5%SSB, 1%RSB, 3%RSB, and 5%RSB resulted in an increase in the phosphorus uptake by arugula plant by 100%, 269%, 518%, 280%, 357%, 343%, 248%, 833%, 657%, 132%, 275%, and 484%, respectively. The lowest phosphorus uptake by the arugula plant was observed in the control treatment, while the highest phosphorus uptake was noticed in the 3%SSB treatment (Fig. 4B). In addition, the relative increase in the potassium uptake by the arugula plant over the control was 44%, 197%, 282%, 126%, 379%, 688%, 234%, 425%, 975%, 86%, 408%, and 1135% for 1%WCB, 3%WCB, 5%WCB, 1%BLB, 3%BLB, 5%BLB, 1%SSB, 3%SSB, 5%SSB, 1%RSB, 3%RSB, and 5%RSB treatments, respectively. The lowest potassium uptake by the arugula plant was observed in the control treatment, while the highest potassium uptake was noticed when adding 5%RSB treatment (Fig. 5A).
Potassium and sodium uptake by arugula plant grown in saline sandy soil as affected by type and doses of biochar. Control: unamended soil; WCB, wood chips biochar; BLB: banana leaves biochar, SSB: sorghum stalks biochar, RSB: rice straw biochar. Biochar was applied at three doses 1%, 3%, and 5% (w/w). Different lowercase letters on each bar indicate the significant differences among treatments according to Tukey’s Honestly Significant Difference test at p ≤ 0.01. Vertical bars indicate the standard error of the mean (n = 3 replicates).
Sodium uptake by the arugula plant increased significantly with the applications of 3%WCB, 5%WCB, 3%BLB, 5%BLB, 3%SSB, 5%SSB, 3%RSB, and 5%RSB treatments to saline soil compared to the control treatment, while the addition of 1%WCB,1%BLB, 1%SSB, and 1%RSB treatments led to no significant increase in the sodium uptake by the arugula plant (Fig. 5B). Relative to the control, the sodium uptake by the arugula plant increased by 11%, 94%, 122%, 63%, 153%, 89%, 61%, 148%, 83%, 41%, 160%, and 116% with the biochar treatments as 1%WCB, 3%WCB, 5%WCB, 1%BLB, 3%BLB, 5%BLB, 1%SSB, 3%SSB, 5%SSB, 1%RSB, 3%RSB, and 5%RSB treatments, respectively. The lowest sodium uptake by the arugula plant was observed in the control treatment, while the highest sodium uptake content was noticed after adding 3%RSB treatment (Fig. 5B).
Potassium: sodium ratio increased significantly in arugula plant resulted from the applications of 5%WCB, 3%BLB, 5%BLB, 1%SSB, 3%SSB, 5%SSB, 3%RSB, and 5%RSB treatments to saline soil compared to the control treatment. On the other hand, applying 1%WCB, 3%WCB, 1%BLB, and 1%RSB treatments showed a non-significant increase in potassium: sodium ratio in the arugula plant compared to the control treatment (Table 5). Also, the potassium: sodium ratio in the arugula plant increased relative to the control treatment by 29%, 53%, 71%, 38%, 89%, 317%, 108%, 113%, 486%, 31%, 96%, and 473% for 1%WCB, 3%WCB, 5%WCB, 1%BLB, 3%BLB, 5%BLB, 1%SSB, 3%SSB, 5%SSB, 1%RSB, 3%RSB, and 5%RSB, respectively. The effectiveness of the treatments on potassium: sodium ratio in arugula plant increase was in the order of 5%SSB > 5%RSB > 5%BLB > 3%SSB > 1%SSB > 3%RSB > 3%BLB > 5%WCB > 3%WCB > 1%BLB > 1%RSB > 1%WCB > control. The lowest potassium: sodium ratio in the arugula plant was observed in the control treatment, while the highest potassium: sodium ratio in the arugula plant was noticed after applying 5%SSB treatment (Table 5).
Correlations between Biochar dose and plant growth parameters of arugula plant
Under applying wood chips biochar in saline soil, the correlation coefficients between biochar dose and fresh biomass, dry biomass, phosphorus uptake, and potassium uptake were positively and highly significant. Biochar dose was positively and significantly correlated with sodium uptake and potassium: sodium ratio. However, the correlation between biochar dose and nitrogen uptake was non-significant positive (Fig. 6A). Biochar dose was highly significant and positively correlated with potassium uptake under banana leaves biochar applications. Moreover, the correlation between the biochar dose and fresh biomass, dry biomass, phosphorus uptake, sodium uptake, and potassium: sodium ratio was positive and non-significant (Fig. 6B). In the presence of sorghum stalks biochar, biochar dose was significant and positively correlated with potassium uptake. Meanwhile, the correlation coefficients between biochar dose and fresh biomass, dry biomass, nitrogen uptake, phosphorus uptake, sodium uptake, and potassium: sodium ratio were non-significant positive (Fig. 6C). Under the application of rice straw biochar, the correlation coefficient between biochar dose and phosphorus was positive and highly significant. Biochar dose was positively significantly correlated with nitrogen uptake and potassium uptake. However, biochar dose and fresh biomass, dry biomass, sodium uptake, and potassium: sodium ratio had a non-significant positive correlation (Fig. 6D).
Pearson correlation analysis between biochar dose and plant growth parameters grown in saline sandy with (A) wood chips biochar, (B) banana leaves biochar, (C) sorghum stalks biochar, and (D) rice straw biochar. In the correlation analysis diagram, blue represented a positive correlation; and red represented a negative correlation. ***Correlation is significant at P ≤ 0.001; **Correlation is significant at P ≤ 0.01; *correlation is significant at P ≤ 0.05.