Journal of Watershed Management Research

Introduction and objective: Soil erosion is a response to the increase in pressure on the earth, which is growing with the increase in population, and improper use of land and finally its abandonment causes soil loss and salinity or alkalinity. Abandoned rain-feds are one of the main sources of erosion in semi-arid areas, and in this regard, soil protection environmentally can be helpful. Quantitative and qualitative loss of soil in plowed rain-feds located on slopes is an aspect of land degradation that is considered a great threat to arid and semi-arid lands and has negative effects on food security. It is difficult to manage soil erosion in critical conditions and in areas prone to erosion, so the use of soil amendments is considered one of the inevitable solutions for soil protection. The control of runoff and soil loss has been investigated by using various amendments during the past years. The effect of biochar with various sources of primary biomass on erosion control and different soil properties has been the subject of extensive research in recent years. It is necessary to know the behavior, reactions, and changes of biochar in the fields of natural resources with the focus on erosion control for sustainable management. Following the laboratory studies of using organic amendments to control erosion, in this research, the effect of biochar in an abandoned rainfed area on reducing runoff and controlling soil loss caused by natural rainfall has been evaluated.
Material and methods: Biochar produced from the branches of Populus nigra species during the pyrolysis process at 420 degrees and in the ratio of 44% of the initial weight was added to USLE standard plots of 40.2 square meters established in a slope of the abandoned rainfed Zarrinehrood watershed, one of the largest watersheds of the Urmia Lake. Control and biochar treatments at the rate of 32.5 tons per hectare per plot were considered each with three replications. The experiment was conducted during 2.5 years under natural rainfall conditions. During this period, eight precipitation events that led to the production of runoff and sediment were recorded and measured. The runoff volume component was measured at the test site after the occurrence and completion of rainfall and runoff production. The soil loss component was calculated by measuring the amount of sediment in the runoff samples of the plots, and the sediment concentration component was also calculated from the ratio of these values in grams per liter.
Results: The present study was conducted to investigate the effectiveness of biochar amendment prepared from Populus nigra species branches in soil and water protection in the form of USLE test plots and under natural weather conditions in abandoned rain-feds. For this purpose, the components of runoff volume, soil loss, and sediment concentration were measured and calculated during the test period after effective rainfall events. The conservation percentage of biochar treatment for the runoff volume in the first to eighth events was 24.59, 20.92, 13.89, 17.82, 26.05, 10.07, 9.72, and 12.39 percent, respectively. On average, the biochar conservation treatment has been able to create limited and effective changes of 20% in the runoff volume component. Also, the percentage of protective changes in the soil loss component in the first to eighth event was 27/22, 24/44, 28/32, 23/57, 33/34, 18/33, 17/6, and 19/55, respectively. Also, the protection percentages in the sediment concentration component in the first to eighth events were 8% on average. The comparison of the average of the components among the treatments according to the experimental events was done using the paired samples T-test at a significance level of 99%, and the results of this test showed that the application of biochar amendment caused a significant reduction in the components of runoff volume and soil loss at a significant level of 99%. Also, the results of comparing the averages indicate that there is no significance in the sediment concentration component, which shows that the impact of soil loss was on the surface runoff volume component.
Conclusion: This research has been conducted with the aim of investigating the use of biochar amendment obtained from Populus nigra branches in reducing the volume of runoff, soil loss, and sediment concentration in abandoned rain-feds in the form of standard erosion plots and under natural weather conditions. Biochar amendment, which has had positive results in the field of soil protection and erosion control in most laboratory-scale studies, was tested in this study in the natural field and in USLE standard plots. In the investigation of the conservation percentages of the studied organic amendment in the components of runoff volume, soil loss, and sediment concentration, limited percentages of 20, 24, and 8% are observed, respectively. Also, there is a drop in conservation percentages in the spring season and in the second year of the study. The comparison of averages showed that the components of runoff volume and soil loss in the soil treated with biochar had a significant difference with these components in the control soil, therefore, according to the results of this study, the addition of biochar can be used to protect the soil of abandoned rain-feds be useful and effective in semi-arid areas. Due to the location of the plots in natural weather conditions and the field scale of the experiment, the complexity of such processes is increased, and therefore, the need to design studies on a larger time scale and smaller time intervals is necessary in order to obtain more accurate results.