Evaluation of the Interception Condition in Haloxylon Persicum Bunge and Calligonum Comosum L'Hér. Species and their Role on soil Conservation

Introduction and Objective
More than other biological and environmental factors, the water crisis reduces the production of plant ecosystems, especially in dry climates. For this reason, the evaluation and measurement of rain becomes more important, especially in arid and semi-arid regions where soil moisture is a limiting and effective factor on plant production (Sadeghi and Attard 2014). The proportion of precipitation which is converted to precipitation depends on three major parameters. It includes: plant characteristics, precipitation characteristics and evaporation conditions (Grits et al. 2010). The aim of the current research is the effect of the amount and intensity of precipitation and the percentage of the canopy density of the Calligonum comosum and Haloxylon persicum leaves in the climatic conditions of Birjand in the period (October 2018 to June 2019).
Materials and Methods
This research was conducted from October 2018 to June 2019 in Faculty of Agriculture and Natural Resources, University of Birjand. This area is located at 59' 63' 21 º East and 21' 43 º 32 North. The average annual rainfall of this area in the 50-year period was 170.8 mm (Derakhshan et al., 2014). In this research, the rate of canopy rainfall interception of H. persicum and C. comosum were measured. For this purpose, four replications with low to high crown cover density were selected. Taking into account the large and small diameter of the shrub, the percentage of the mass of the crown were measured. To collect rainwater under each species, tray-shaped containers with dimensions of 30 × 30 cm were used. Also, in order to calculate the effective area of the canopy of the species during autumn to spring, the surface of their canopy was photographed vertically. In order to analyze the data, correlation tests, analysis of variance and one-way analysis of variance (ANOVA) were used. All statistical tests were performed by SPSS software and graphs were drawn by Excel software.
Results and Discussion
comosum is a drought resistant species and it is spread in sandy hills in deserts. The results show that the highest amount of canopy rainfall interception belongs to spring season with the amount of 15.6 mm. Also, based on the Pearson correlation coefficient, there is a significant positive correlation between the amount of precipitation and the amount of rain at the level of 0.01 (R2=0.93). There is a significant positive correlation between the intensity of precipitation and the amount of interception at the level of 0.05 (R2=0.79) and there is a significant positive correlation between the intensity of precipitation and the percentage of interception at the level of 0.01 (R2=0.87). H. persicum has a high ability to absorb soil moisture due to its low osmotic potential. The results revealed that there is a significant positive correlation between the amount of precipitation and the amount of interception and the percentage of canopy mass with the amount of interception at the level of 0.05 (R=0.78 and R=0.71, respectively). Also, there is no significant relationship between the percentage of interception and any of the precipitation characteristics.
Conclusion and Suggestions
 The highest amount of interception belongs to C. comosum with a value of 15.6 mm and the lowest amount of interception is related to the H. persicum with 1.2 mm. The highest percentage of H. persicum is in February with 46% and the lowest percentage is 10% in December (p ≤ 0.05). Due to the density of leaves, H. persicum is more suitable for preventing floods and soil erosion, since more water is absorbed by the canopy and less water reaches the ground.