تعيين نياز آبي سيب زميني در اقليم هاي مختلف استان اصفهان

Determination of water requirement for potato in different climates ofIsfahan province

به منظور تعيين نياز آبي گياه سيب زميني در سه اقليم (خشك- زمستان سرد با دماي بالاي نقطه انجماد - تابستان گرم A-C-W)، (خشك- زمستان سرد با دماي برابر يا كمتر از صفر- تابستان گرم A-K-W) و (نيمه خشك- زمستان سرد با دماي برابر يا كمتر از صفر- تابستان گرم SA-K-W) در استان اصفهان، پژوهشي در سال1394-1393 با استفاده از طرح كاملاً تصادفي و با انتخاب مزارع نمونه در هر شهرستان انجام شد. تفاوت معني دار از نظر آب مصرفي و بهره‌وري آب بين شهرستان‌هاي مختلف وجود داشت. در اقليم A-C-W نياز آبي خالص دامنه‌اي از 4674 (مباركه) تا 5432 (اصفهان) متر مكعب در هكتار داشت. در اين اقليم دامنه‌ي بهره‌وري آب بر اساس سه شيوه آبياري قطره اي، آبياري باراني و آبياري جويچه اي به ترتيب برابر (5/77-4/03)، (5/04-3/52) و (4/28-2/99) كيلوگرم بر متر مكعب بود. در اقليم A-K-W مقدار آب خالص در هر هكتار از 4609 (نطنز) تا 5257 (شاهين شهر) متفاوت بود. در اقليم SA-K-W بيشترين نياز آبي (6426 متر مكعب) و كمترين بهره‌وري در آبياري جويچه‌اي (1/79كيلوگرم به ازاء هر متر مكعب آب) به ترتيب مربوط به شهرستان هاي تيران و دهاقان بود. به طور متوسط نياز آبي خالص سيب زميني در سه اقليم A-C-W، A-K-W و SA-K-W به ترتيب برابر 5044، 5078 و 5703 متر مكعب در هر هكتار محاسبه شد. بنابراين اگرچه اقليم SA-K-W مهم‌ترين اقليم توليد سيب زميني استان اصفهان محسوب مي‌شود ولي ميانگين‌هاي پايين عملكرد با وجود آب مصرفي زياد لزوم بازنگري عوامل مديريتي در اين اقليم را خاطر نشان مي‌سازد.

Introduction: Potato (Solanum tuberosum L.) is an annual and autotetraploid plant, which belongs to the family of Solanaceae. Global production of this crop was 385 million tons in 2014 with Asian countries approximately accounting for 40 % of the production (FAO, 2014). Potato requires 400 to 850 mm of irrigation water to grow, nevertheless, some researchers have reported that water needs of the crop could reach 900 mm (Carli et al., 2014). Potato crop, as a drought-sensitive plant, may suffer yield losses even under mild-water stress conditions due to its shallow rooting system and limited ability for recovery after water stress. Water use efficiency for potato can be defined as the ratio of the tuber yield to evapotranspiration. Water use efficiency in potato-based evapotranspiration has been reported to be 1.9 to 5.3 kg.m-3. There are considerable discrepancies in the values determined for the crop water requirement by major references such as national water document of Iran, the study of Farshi et al., (1997) and NETWAT software. This has become more problematic because of climate change in recent years. The aim of the study was to evaluate the potato crop water demand and to determine its water use efficiency at different phenological stages in Isfahan province. Materials and Methods: This research was carried out in 2014-2015 in two potato growing seasons (February /March sowing for temperate regions and May/ June sowing for cold regions) in different cities of Isfahan province where the cultivation of potato is prevalent. According to UNESCO methodology using agroclimatic zone map of Iran constructed based on three main criteria including moisture regime, winter and summer types, 28 climatic zones can be identified in Iran, of which, six zones encompass more than 90 % of the country. Accordingly, three main climatic zones can be distinguished for the cultivation of potatoes in Isfahan province, Crop evapotranspiration, which is influenced by weather conditions and plant growth stages, represents the amount of water required by a healthy plant on a farm without water restriction and was calculated from the following equation: ET crop=Σ Kci×EToi; where Kci and Etoi are crop coefficient, and the reference crop evapotranspiration, respectively. An unbalanced completely randomized design was used to analyze the data obtained from each potato cropping zone. The means were compared by Duncan’s multiple range tests at 5% probability level. Results and Discussion: Analysis of data for different cities located in three agro-climatic potato growing zones of A-C-W, A-K-W and SA-K-W in Isfahan province indicated that there were significant differences in water use rate and water productivity (P≤1%) and crop water consumption at different phenological stages (P≤5%). In the climate of A-C-W (including 6 cities), the highest and lowest water requirements were respectively associated with the cities of Isfahan (5432 m3) and Mobarake (4674 m3). Under this climate, water consumption based on three methods of drip, sprinkler and furrow irrigation was (4.03-5.30), (3.52-5.04), and (2.99-4.28) kg.m-3, respectively. These figures fall in the range of values reported by other researchers (4.9-9.3 kg.m-3). Water stress condition in the region is one of the reasons for high water productivity. In A-K-W climate (including 5 cities), the net water consumption per hectare ranged from 4609 m3 (Natanz) to 5257 m3 (Shahin Shahr). Under SA-K-W climate (including 10 cities), the highest water requirement (6426 m3) and the lowest water productivity under furrow irrigation (1.79 kg.m-3) were related to Tiran and Dehaghan, respectively. On average, the water requirement for potato production in three climates of A-C-W, A-K-W and SA-K-W was 5044, 5078 and 5703 m3.ha-1, respectively. Conclusions: According to our results, contrary to what is being promoted about the high water requirement of potato, if proper farm management is practiced and the water productivity is improved, potato similar to other crops can be included in rotations. Even under furrow irrigation, water productivity (expressed as kg.m-3) in three climates of A-C-W, A-K-W and SA-K-W was in a range of (2.99-3.94), (1.96-2.3) and (1.79-2.61), respectively. These figures are higher than what has been reported for cereal grains such as wheat and barley. This shows that external factors beyond farm and also policies related to potato production are more important limiting factors for potato than water requirement.