تاثیر شیوه‎های مختلف ذخیرۀ نزولات باران بر رطوبت خاک و خصوصیات رویشی نهال‎های مغیر acacia oerfota (forssk.) schweinf (مطالعۀ موردی: حوزۀ آبخیز معرف و زوجی دهگین استان هرمزگان)

با جمع آوری آب باران و ذخیره سازی آن با استفاده از شیوه های مختلف ذخیرۀ نزولات آسمانی در مناطق خشک کشور، اراضی فاقد پتانسیل کشاورزی، در جهت ایجاد پوشش گیاهی به کار گرفته می شود که در نتیجۀ آن، کاهش تبخیر، رواناب و اتلاف آب و افزایش ذخیرۀ آب زیرزمینی حاصل خواهد شد. هدف از این تحقیق، تاثیر شیوه های مختلف ذخیرۀ نزولات آسمانی بر حفظ رطوبت خاک و برخی از خصوصیات رویشی نهال های بومی گونۀ مغیر (acacia oerfota (forssk.) schweinf) در حوزۀ زوجی و معرف دهگین استان هرمزگان است. خصوصیات رویشی و کیفی نهال ها شش ماه پس از تولید، اندازه گیری و سپس به سامانه های آبگیر باران هلالی، لوزی، پیتینگ و شاهد انتقال یافت. چاله هایی با ابعاد40 ×40 ×40 سانتی متر در وسط سامانه های هلالی، پیتینگ و انتهای ضلع سامانۀ لوزی جهت کاشت نهال ها حفر شد. همۀ سامانه ها عمود در جهت شیب احداث شده است. شایان ذکر است برای پلات شاهد نیز در منطقه ای هم شیب با سایر سامانه ها و فاصلۀ متوسط 2 متر از یکدیگر، چاله های کاشت نهال حفر شد. چهار ماه پس از کاشت نهال در دورۀ بارش و ثبت پنج واقعۀ بارندگی، خصوصیات رویشی و کیفی نهال ها در سامانه ها و همچنین رطوبت خاک 24 ساعت پس از هر بارش بررسی و با استفاده از آنالیز واریانس دوطرفه مقایسه شد. درجۀ شادابی نهال ها در شاهد با مقدار 2.86 در درجۀ متوسط طبقه بندی قرار گرفته و به طور معنی داری کمتر از مقدار آن در شیوه های مختلف جمع آوری نزولات آسمانی بود. میانگین رویش قطری و ارتفاعی در سامانۀ هلالی 1.95 میلی‌متر و 10.12 سانتی متر بود که اختلاف معنی داری با شاهد در سطح 5% داشت. این نتایج نشان می دهد این اختلاف رویش تصادفی نبوده بلکه تحت‌تاثیر شیوه های مختلف ذخیرۀ نزولات آسمانی است. درصد رطوبت در سامانه های هلالی، لوزی، پیتینگ و شاهد (24 ساعت پس از بارش) به ترتیب 13.46، 11.95، 11.5 و 10.34 درصد بود که اختلاف معنی داری با یکدیگر داشتند. بنابراین اختلاف رطوبت، واقعی بوده و ناشی از عملکرد شیوه های مختلف ذخیرۀ نزولات آسمانی است. نتایج همبستگی بین خصوصیات رویشی و رطوبت خاک با استفاده از ضریب همبستگی پیرسون نیز نشان داد رطوبت خاک با احتمال 99%، اثر مستقیم مثبتی بر قطر یقه و ارتفاع نهال ها دارد. طبق نتایج، در شرایط طبیعی در منطقۀ دهگین، سامانۀ هلالی با بهبود بهتر ذخیرۀ نزولات و کاهش اتلاف آب و درنتیجه افزایش رطوبت خاک در مقایسه با شاهد، میکروکلیمای مناسب تری را برای رویش گیاه فراهم می کند.

Investigating the Effects of Different Methods of Precipitation Storage on Soil moisture and Growth Characteristics of Acacia Oerfota (Forssk) Schweinf Seedlings: A Case study of Paired Watershed of Dehgin, Hormozgan Province

Introduction: water is necessary for human, animal and vegetation lives. Therefore, providing sufficient water is an undeniable necessity for sustaining creatures rsquo; lives. Development of water supplies, thus, should occur in such a way as to keep the hydrological balance and biological functions of all ecosystems which is crucial for marginal lands. Precipitation storage is the general name for all different techniques used for collecting runoff and rain water to be saved in the soil profile or tanks and be used for growing trees and crops and developing them in dry lands. The precipitation storage is applied for afforestation in arid and semiarid regions whose rainfall rates are not enough to sustain a good seedling or tree growth. Precipitation storage can increase the rate of planting trees in drought regions through the collection of rainfall, and runoff enhancement. Therefore, these techniques could compensate for the lack of soil moisture and help overcome good spells in critical growing stages, securing good water for plant when rainfall is erratic. This study, therefore, sought to investigate the effect of different precipitation storage techniques on preserving soil moisture and some growth characteristics of Acacia oerfota (Forssk.) Schweinf seedlings in Paired watershed of Dehgin, Hormozgan province. Material and methods: Paired watershed of Dehgin is one of the sub watersheds of Esteghlal dam in Minab, Hormozgan province. Having collected Acacia oerfota seeds in the summer of 2018, they were planted in plastic pots. Collar diameter, stem height and quality characteristics of seedlings were measured. Seedlings were then planted with three replications (three blocks) in four treatments (diamondshape micro catchment, semicircular bunds, pitting, and control). following four months and five rainfall events, growth and quality characteristics of seedlings were measured in different precipitation storage techniques and the collected data were analyzed, using twoway analyses at the level of 95%. Soil moisture was measured based on different precipitation storage techniques and control, and the extracted data were analyzed by twoway analyses. The relationship between soil moisture, collar diameter and stem height were also measured via Pearson's correlations. Results: the results of the study indicated that the seedling vitality with the amount of 2.86 was significantly lower in control than it was in different precipitation storage techniques. Collar diameter of seedlings in semicircular bunds (1.95 mm) was higher than what it was in diamondshape micro catchment, pitting and control (0.92, 0.88 and 0.89 mm). Height growth in semicircular bunds with the amount of 10.12 cm was significantly higher than that in control with the amount of 6.2 cm. These significant differences were due to the function of different precipitation storage techniques. Soil moisture percentage in all treatments was reported as being different (p<0.05). The amounts of soil moisture were 13.46%, 11.95%, 11.5% and 10.34% in diamondshape micro catchment, semicircular bunds, pitting, and control respectively. It was also found that soil moisture had positive direct effect on collar diameter and seedling height (p<0.01). Discussion and Conclusion: Vitality and establishment of tree seedlings depend on soil conditions and available moisture. As rain water is free of salts and other minerals that may harm plants and prevent their growth, it deemed great for plant growth. Considering the fact that rain water percolates into the soil, it forces salt down and away from root zone, allowing roots to grow better and making them tolerate more severe drought. The construction of diamondshape micro catchments, semicircular bunds and pitting in the study region, and collection of rain water and runoff led to the increase in soil moisture by improving infiltration rate, and thus facilitated plant growth. On the other hand, as plants require large quantities of water for growth, water was used during photosynthesis to produce carbohydrate as a necessary element for plant growth. Moreover, it is evident that leaves are important organs for photosynthesis and play an important role in survival and growth of plants. As the findings of the current study showed, soil moisture was higher in control method. It could thus be concluded that lower growth in control is due to lower moisture.The results of this study indicated that precipitation storage techniques were highly crucial for the soil moisture storage to improve vegetation in arid and semiarid areas and increase their growth and vitality. It was also found that soil moisture content and also growth characteristics of droughttolerant seedlings of Acacia oerfota, were higher in semicircular bunds than those in control and other precipitation storage methods. These seedlings have suitable shoots and large green leaves without dieback in dry climate of Dehgin, resulted from the rain water and runoff collected through precipitation storage techniques and absorbed by plants. Moreover, among all treatments, semicircular bunds were the best precipitation storage methods for afforestation and pasture improvement in the studied region.