كمّي‌سازي پارامترهاي نفوذ آب به خاك با استفاده از مقياس‌سازي

Quantification of soil water infiltration parameters using scaling

براي كمّي‌سازي و آناليز تغييرپذيري پارامترهاي نفوذ آب به خاك در يك پهنه وسيع، در چهار هزار هكتار از اراضي دشت كوار شيراز و در 161 سايت در يك شبكه منظم 500×500 متري، نفوذ آب به خاك با استفاده از استوانه‌هاي دوگانه اندازه‌گيري شد. داده‌هاي حاصله به سه مدل نفوذ آب به خاك برازش داده شد. مدل دو پارامتري فيليپ با بالاترين ضريب تبيين به عنوان بهترين مدل انتخاب شد. سرعت نفوذ پايه با ميانگين 69/6، از 11/1 تا 11/31 سانتي‌متر بر ساعت متغير بود. ضريب جذبي و انتقالي مدل فوق تغييرات گسترده‌اي داشت. اين دو پارامتر به ترتيب بر اساس عامل مقياس‌سازي S? و A? محاسبه شد و داده‌هاي نفوذ آب به خاك مقياس‌بندي شد. مقياس‌سازي حاصله از A?، بهتر از مقياس‌سازي S? بود. سپس فاكتور مقياس‌سازي بهينه (opt?) با روش حداقل مربعات به دست آمد. فاكتورهاي مقياس‌سازي بر اساس ميانگين حسابي، هندسي و هارموني S? و A?، نيز براي مقياس‌سازي محاسبه شدند. نتايج نشان داد مقياس‌بندي داده‌هاي نفوذ آب به خاك بر اساس فاكتور مقياس‌‌سازي opt? و فاكتورهاي مقياس‌سازي حاصل از ميانگين هارموني S? و A? بهتر از ديگر فاكتورهاي مقياس‌سازي بودند.

Quantitative description of infiltration process is needed for both irrigated and rainfed agriculture for optimal management and designs purposes. The most difficult task in the field, however, is to determine the spatial variability of infiltration process, which is of great importance for precision agriculture. The objective of this study was to quantify spatial variability of infiltration models by using scaling in Kavar plain, east of Shiraz, Iran. A number of 161 infiltration experiments were conducted on a systematic squared grid pattern with 500*500m over the 4000 ha area, using double-ring method. The observed infiltration data from all the experimental sites were fitted to three selected infiltration models. The best-fitted model for individual sites was identified. Using the least-squares technique, the Philip model was selected as the best model to describe infiltration process. Infiltration rates of the area generally indicated low basic infiltration rates (1.11–31.11 cm hr?1) for most sites, and average amount of them was 6.69 cm hr?1. The parameters of Philip model (S and A) showed a wide variation among the test sites. The sorptivity-based scaling factor ?S and the transmissivity-based scaling factor ?A were computed and the observed infiltration data were scaled. Scaling achieved through ?A was found better than through ?S. Optimum scaling factors ?opt were then obtained by the least-squares. Scaling factors based on the arithmetic, geometric and harmonic means of ?S and ?A were also computed for scaling. It was found that ?opt and the scaling factor based on harmonic mean of ?S and ?A scaled the infiltration data more effectively (lowest sum of squares error) than other scaling factors.