Investigation of the Effect Soil particles size on the Currency Time Domain Reflectometry for water content measurement
محورهای موضوعی : Irrigation and Drainage
عیسی معروف پور
1
(دانشگاه کردستان، گروه مهندسی آب، کردستان، ایران.)
مینا بهزادی نسب
2
(شرکت آب منطقه‌ای کردستان،کردستان، ایران.)
کلید واژه: Calibration, بافت خاک, TDR, Soil texture, کالیبراسیون,
چکیده مقاله :
This study carried out on the provided textures at laboratory. The provided textures were infusedinside the PVC cylinder with 30cm height and 25cm diameter. The studied textures were loamysand, sandy loam, sandy clay-loam, clay loam and clay. After 24 hours of saturation, the soil watercontent of the samples was measured by oven-dry gravimetric and TDR methods. For each texturesat any stage of measurement the determination of moisture and di-electric constant were done atthree capture windows and with three repetitions. In each day the moisture measurement of eachtexture was carried out by these two methods until a moisture range was determined. The results ofthis research show that: 1- For all soil textures the measured moisture at the capture windows of 20ns has more accuracy compared to the other capture windows. and TDR device can not measure thesoil water content at capture window of 40 ns. 2- For loamy-sand and sandy-loam textures when themoisture was less than 20% and also for other textures for total range of measurement, the TDRdevice measured the moisture values less than the gravimetric method. This difference is increasedwhen the soil ranged from light to heavy textures. 3- From the statistical view at probably level of1% there is not difference between the measured value of moisture by TDR device and gravimetricmethod. 4- For the all textures the fitted regression lines have high regression coefficient.
این تحقیق در شرایط آزمایشگاهی روی بافت‌های دست‌خورده که درون گلدان‌هایی از جنس پی وی سی به ارتفاع و قطر متوسط 300 ×250 میلی‌متر انجام گرفت. خاک‌های مورد استفاده، شن‌لومی، لوم‌شنی، لوم رسی‌شنی، لوم‌رسی و رسی با سه تکرار بودند. پس از حدود 24 ساعت از اشباع شدن هر بافت، اندازه‌گیری رطوبت به روش وزنی و با استفاده از TDR انجام شد. در این تحقیق تعیین رطوبت و ثابت دی‌الکتریک درسه پنجره برداشت و در سه تکرار برای هر بافت در هر نوبت اندازه‌گیری، صورت گرفت. عمل اندازه‌گیری رطوبت با این دو روش هر روز انجام گرفت تا اینکه یک محدوده رطوبتی برای هر بافت تعیین شد. نتایج این تحقیق نشان داد که: 1- در تمامی بافت‌های مورد مطالعه مقادیر رطوبتی اندازه‌گیری شده در پنجره اندازه‌گیری 20 نانو ثانیه از دقت بالاتری برخوردار بودند و دستگاه TDR قابلیت اندازه‌گیری رطوبت در پنجره 40 نانو ثانیه را نداشت. 2- دستگاه TDR در دو بافت شن‌لومی و لوم شنی در رطوبت کمتر از 20 درصد و در مابقی بافت‌ها در کل دامنه اندازه‌گیری، میزان رطوبت را کمتر از روش وزنی اندازه‌گیری می‌کند که با سنگین‌تر شدن بافت این تفاوت بیشتر شده است. 3- از نظر آماری در سطح یک درصد بین مقادیر رطوبتی اندازه‌گیری شده توسط TDR و روش وزنی تفاوت معنی‌داری مشاهده نشده است. 4- خطوط رگرسیونی برازش یافته بر مقادیر رطوبتی در تمام بافت‌ها دارای ضریب همبستگی بالایی بود.
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