مقایسۀ تأثیر دو روش ذخیرۀ نزولات بر تغییرات رطوبت خاک و فیتوماس گیاهان علفی در مراتع استپی (مطالعۀ موردی: مراتع درمیان- استان خراسان جنوبی)

Introduction: Ninety percent of Iran surface is under arid and semi-arid climates. One of the most important of natural problems of rangelands in this climate is low rainfall. Along with the lack of rainfall, low permeability of soils in rangelands is also one of the issues that prevent the successful establishment of plants in rangelands. Therefore, it is necessary to perform a series of mechanical operations in order to make optimal use of wastewater and store rainfall.Introduction: Ninety percent of Iran's surface is under arid and semi-arid climates. However, low precipitation and low permeability of soils are considered as some of the most important natural problems of rangelands in such climates that prevent the successful establishment of plants. Therefore, it is necessary to perform a series of mechanical operations to make optimal use of wastewater and to store the rainfall.

Materials and Methods: a factorial experiment was performed via a completely randomized design with three replications and three treatments, including the rainfall storage structure (in five levels), soil depth (in two levels), and sampling season (in two levels) to compare the two methods of contour furrow and catchment crescents. Accordingly, a total of 60 soil samples were collected, which were immediately weighed after harvest and transferred to the soil science laboratory where their weight moisture content was measured individually. Moreover, a randomized systematic plot method was used to measure forage production and compare it to structural type treatments. In each of the treatments, two 100-meter transects were used at a distance of 100 meters from each other, and the total forage was harvested in 50 plots, whose weights were measured as grams per square meter.

Results: Analysis of variance of the collected data indicated that the main variables' (structure, depth, and sampling season) effect and the interaction effects (structure × depth, structure × sampling season, and structure × depth × sampling season) on the percentage of soil moisture were very significant. Moreover, there was a significant difference (P% 1) between the percentage of moisture's weight in the catchment crescent treatment with contour furrow, and between these two treatments with the other three ones (i.e., between catchment crescents, contour furrow, and control). The analysis of the data also suggested that when measured by the contour furrow method, the soil's moisture was 13.3% and 66.2% higher than the control treatment at the depth of 20-50 cm in the first and second sampling seasons, respectively. on the other hand, when measured by the catchment crescent method, the soil's moisture was 115.9% and 183% greater than that of the control treatment, respectively, indicating that the use of both catchment crescent and contour furrow methods increased moisture storage in deep soil.
Furthermore, the study's results showed that the catchment crescents method played a more effective role in soil water storage. It was also found that compared to the contour furrow method, moisture content was increased in the catchment crescents method by 90.5% and 70.4% in deep soil during the spring and autumn, respectively. Moreover, the results suggested that the amount of forage production was significantly different (P≥ 1%) in the catchment crescent treatment, the contour furrow treatment, and the other three treatments, and that the use of both precipitation storage methods increased forage production in the rangeland, with the production of herbaceous plants being increased by 126% in the contour furrow method and 378% in the catchment crescent method, compared to that of the control. Taking the obtained results into consideration, it could be said that the catchment crescent method was 110% more effective in increasing forage production than the contour furrow method.

Discussion and Conclusion: considering the direct relationship between the percentage of soil moisture and the amount of forage production in rangeland plants, it could be argued that increased moisture storage in the soil induced by the use of rainfall storage methods could have a great effect on increasing rangeland plant production, especially perennials. Taking this study's results into account, it can be said that an increase in moisture storage in deep soil because of the application of the catchment crescent method, and, therefore, its added effect on vegetation characteristics, indicates the higher efficiency of the method over the contour furrow one, for which two reasons can be offered: 1- In the catchment crescent method, the runoff is collected from a larger surface on the upstream slope of the crescents, which is then stored in a small area inside each catchment crescent; 2- The depth of the catchment crescent is more than that of the contour furrow (minimum 50 cm vs. maximum 25 cm), and therefore it stores more runoff inside, giving ample opportunities to the water stored in the catchment crescent so that it can penetrate deep into the soil. Therefore, it can be suggested that the relevant organizations use the catchment crescent method instead of the contour furrow one to store precipitation in the soil so that they can improve and rehabilitate the rangelands.

 
Materials and methods: In order to compare the two methods of contour furrow and catchment crescents, a factorial experiment in a completely randomized design with three treatments of rainfall storage structure (in five levels), soil depth (in two levels) and sampling season (in two levels) was conducted with three replications and a total of 60 soil samples were collected. Soil samples were weighed immediately after harvest and then transferred to the soil science laboratory and the weight moisture content of each was calculated. To measure forage production and compare it in structural type treatments, randomized systematic plot method was used. In each of the treatments, two 100-meter transects were used at a distance of 100 meters from each other and a total of forage in 50 plots was harvested and determined as grams per square meter.
 
Result: Analysis of variance of the obtained data shows that the effect of the main variable of structure, depth and sampling season and also the interaction effects: structure × depth, structure × sampling season and structure × depth × sampling season, on the percentage of soil moisture has become very significant or significant. There was a significant difference (P% 1) between the percentage of weight moisture in the catchment crescent treatment with contour furrow and also these two treatments with the other three treatments (between catchment crescents, between contour furrow and control). The data showed that the soil moisture at a depth of 20-50 cm and in the first and second seasons of sampling in the contour furrow method is 13.3% and 66.2% higher than the control treatment, respectively. Also, in the catchment crescent method, 115.9% and 183% is more than the control treatment, respectively. This means that the use of both catchment crescent and contour furrow methods has increased moisture storage in deep soil. Also, the results of the present study showed that in comparison between the two methods studied, the use of catchment crescents had a better role in soil water storage and in the spring and the autumn, respectively, it increased 90.5% and 70.4% of moisture in deep soil compared to the contour furrow method. On the other hand, the data of the present study showed that the amount of forage production in the catchment crescent treatment with the contour furrow treatment and the contour furrow treatment with the other three treatments had a significant difference (P≥ 1%).The results showed that the use of both methods of storage of rainfall increased forage production in the rangeland so that the production of herbaceous plants increased by 126% in the contour furrow method and 378% in the catchment crescent method compared to the control. Based on the data obtained in the present study, among the two methods of contour furrow and catchment crescent methods, the effect of catchment crescent method on increasing forage production was 110% greater than the contour furrow method.
 
Discussion and Conclusion: Since there is a direct relationship between the percentage of soil moisture and the amount of forage production of rangeland plants, so more moisture storage in the soil, which is due to the use of rainfall storage methods, has a great effect on increasing rangeland plant production, especially perennials. According to the obtained results, it can be stated that more moisture storage in deep soil and as a result, its additional effect on vegetation characteristics in using the catchment crescent method compared to contour furrow, shows the higher efficiency of this system than contour furrow system. This result has two reasons: 1- In the catchment crescent method, runoff from rainfall is collected from a larger surface, located on the upstream slope of the crescents, and is collected in a small area inside each catchment crescent. 2- The depth of the catchment crescent is more than the contour furrow (minimum 50 cm vs. maximum 25 cm) and therefore they store more runoff inside. This gives ample opportunity for water collected in the catchment crescent to penetrate deep into the soil. Therefore, it can be suggested that the responsible organizations, instead of using the contour furrow method, use the catchment crescent method to store precipitation in the soil in order to improve and rehabilitate rangelands.