بررسي تاثير تغييرات شوري آب زيرزميني كم عمق بر ضريب گياهي Kc ذرت

Investigation of shallow groundwater effects with different salinities on crop coefficients of Maize

براي بررسي ضرايب گياهي Kc ذرت تابستانه تحت شرايطي كه از آب زيرزميني كم عمق و شور در تامين بخشي از نياز آبي گياه استفاده مي‌شود، تحقيقي در لايسي‌مترهاي ستوني به قطر 8/0 و ارتفاع 2/1 متر انجام شد. سطح آب زيرزميني در لايسي‌مترها با استفاده از بطري ماريوت در عمق 6/0 متر ثابت نگه داشته شد. تيمارهاي مورد استفاده شامل سه سطح شوري آب زيرزميني معادل 5/2، 5 و‌ 5/7 دسي‌زيمنس بر متر و دو سطح آبياري معادل 100 و 70 درصد نياز آبياري محاسبه شد. آزمايش به صورت فاكتوريل و در قالب طرح پايه بلوك‌هاي كامل تصادفي با سه تكرار انجام شد. يك تيمار كشت ذرت بدون آب زيرزميني با سه تكرار و با آبياري كامل به عنوان تيمار شاهد در نظر گرفته شد. در اين پژوهش معادله مربوط به اجزا ضريب گياهي واقعي Kca، شامل ضريب مربوط به آبياري Kci و ضريب مربوط به آب زيرزميني Kcg، بر اساس معادله توازن حجم به دست آمد و منحني‌هاي مربوطه ترسيم شد. نتايج نشان داد كه ميزان مشاركت آب زيرزميني در سطح آبياري 100 درصد در شوري‌هاي كه ذكر شد به ترتيب 28/5، 61/4 و 76/3 درصد و با 70 درصد تامين نياز آبي، 00/25، 09/22 و 71/19 درصد بوده است. كه اين اختلاف در سطح 5 درصد معني‌دار است. منحني‌هاي ضريب گياهي واقعي و اجزا آن در دو حالت آبياري كامل و كم آبياري نيز از الگوي متفاوتي پيروي نمود.

To study the crop coefficients of summer maize a lysimeter experiment was conducted under conditions that shallow and saline groundwater contributes to supply required water. Twenty-four lysimeters each with 1.2 m depth and 0.8 m diameter were installed. Thereafter, maize was planted in each lysimeter. The depth of groundwater table in the lysimeters was set to 0.6 m by using Marriotte Bottles. In this experiment, Three groundwater salinity levels (2.5, 5 and 7.5 dS/m) with two irrigation levels (at 70% and 100% rates of evaporation from pan class A before irrigation period) were used. Soil water was replenished on a weekly basis. Factorial experiment was established in a randomized complete block design with three replications. In an individual treatment, maize was planted with full irrigation on one hand and no ground water (NGW) considered as the control treatment on the other hand and they both were replicated three times. In this study, the equation of actual crop coefficient Kca, and its components including Kci (the coefficient related to irrigation) and Kcg (the coefficient related to groundwater), was obtained based on the water balance equation. Then regression analyses were used to develop the Kci, Kcg and Kca crop coefficient curves for each salinity and irrigation treatments. The results indicated that the percent of groundwater contribution at full irrigation level were 5.28, 4.61 and 3.76 for each of three salinity treatments (abovementioned), and were 25, 22.09 and 19.71 respectively at deficit irrigation level, All differences were significant at the level of 0.05 in Duncan multiple range test. The curves of actual crop coefficient and curves of its components followed different patterns at full and deficit irrigation levels.