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Öğe Dependence of zeta potential and soil hydraulic conductivity on adsorbed cation and aqueous phase properties(Soil Sci Soc Amer, 2004) Aydin, M; Yano, T; Kilic, SThis paper deals with the effects of pH, electrolyte concentration, and exchangeable Na percentage (ESP) on electrophoretic mobility (EM)/zeta potential (zetap) of clay particles and hydraulic conductivity (HC) of the clay/sand mixtures. The soils taken from Japan and Kazakhstan were used for obtaining clay fractions. For EM determinations, clay suspensions were prepared at a concentration of 4 g of clay per 100 mL of distilled water (DW) or electrolyte solution. The electrophoretic mobilities were measured using Burton apparatus with water-cooling system and converted into p. For HC measurements, clay/sand mixtures were designated 16:84. Columns of these mixtures were prepared by packing 120 g of mixtures into 50-mm diameter plastic cylinders to a bulk density of about 1.4 g cm(-3). Results showed clearly that the mobility was very sensitive to the ion valence adsorbed on the clay. The negative electrophoretic mobilities of homoionic Na-Ariake soil (AS) clay and Na-Kzyl-Orda soil (KS) clay were 2.13 X 10(-8) and 2.14 X 10(-8) m(2) s(-1) V-1, respectively, whereas Ca clays flocculated. The p values of AS clay and KS clay, as a function of the ESP, varied between -12.83 and -26.84 mV, and -5.68 and -27.00 mV, respectively, at ESP > 30. Although the smectitic AS clay was less sensitive than the micaceous KS clay to pH changes during electrophoresis experiment, its HC also was affected by pH changes. Decreased pH from 7 to 5 could easily result in two to three times high HC values for both clay/sand mixtures. The EM of both soil clays was similar at pH 10 to 12, and exchangeable Na percentages 90 to 100. Sharp increases in EM and decreases in HC of AS clay were observed at exchangeable Na percentages 50 and 60, respectively. Similar trends related to EM were also obtained for the KS clay. However, salt concentration of the suspension solution did not have consistent effect on the EM values. This behavior of the clays was consistent with HC observation. The results indicated that HC of the clay/sand mixtures could he correlated to p. The saturated HC of the mixtures was found to change as an exponential function of the zetap of clay particles.Öğe Evapotranspiration of orange trees in greenhouse lysimeters(Springer, 2003) Yang, SL; Aydin, M; Yano, T; Li, XEight-year-old Murcott orange trees (Citrus sinensis (L.) Murcott) grown in greenhouse lysimeters filled with sandy soil were used to investigate seasonal variations in daily and hourly evapotranspiration. The study was conducted in Japan during the summer of 2000 and the winter of 2001. Weighing lysimeters of 1.5 in diameter and 1.6 in depth (three replications) planted with a tree were irrigated when average soil moisture in 0-120 cm of soil depth was depleted to below 70% of the field capacity (FC). Evapotranspiration (ET) showed significant seasonal variations. Average ET rate exceeded 4.4 mm/day in the summer period, and dropped to 0.6 mm/day in the winter months. The average seasonal crop coefficient (KC) was 0.91 and 0.75 during the summer and winter periods, respectively. Hourly variations in ET exhibited a time difference with season. The time of maximum ET was 0900 hours for winter and 1200 hours for summer; Moreover, some evaporative losses of soil water occurred even during the night in both summer and winter seasons. Soil evaporation (E) was 33% of ET during the winter period; while E was only 11% of ET during summer. Maximum water uptake by the trees was found at a depth of 30-60 cm, and soil water depletion was observed in the 0-120 cm depth of the profile during the summer period. However, during the winter season, water depletion occurred only from 0-30 cm depth of the soil profile.Öğe History of rainfed agriculture in Turkey(Soil Conservation & Watershed Management Research Center, 1997) Aydin, M; Kiliç, STurkey, like most other Mediterranean countries, is an arid and semi-arid country. Turkey is also experiencing a population boom. This increase in population has led people to boost agricultural production by cultivating marginal land. In fact, until 1970, increases in food crop production were caused mostly by increases in the area of land that was cleared and cultivated. After 1970, with the help of more sophisticated techniques and more modern equipment, farmers aimed to conserve the moisture in the soil profile and produce greater yields by controlling the time of tilling, how many times a year soil was disturbed, and how deeply soil was cultivated. For a time; these new farming practices appeared to resolve Turkey's agricultural production problems. Between 1970 and 1990 while the area cultivated in wheat increased by only 9 % wheat production increased by 90 %. Nevertheless, Turkish farmers had much to learn about contending with periods of low rainfall, such as in 1989, when wheat production declined by 20 % from the year before. By the early 1990s, the increasing rate of production clearly showed that it was time to establish new guidelines for sustainable agriculture, particularly in the nation's dry regions. Indeed lack of rain during the growing season on the Central Plateau and other semiarid regions of Turkey poses the greatest challenge to the nation's agriculturalists. To address the pressing need for water the Turkish government launched the Southeastern Anatolian Development Project in 1987. The project covers an area of 74,000 km(2), roughly equal to one-tenth of Turkey's land surface. The project consists of 13 subprojects on the Euphrates and Tigris rivers.Öğe Short term effects of saline irrigation on evapotranspiration from lysimeter-grown citrus trees(Elsevier, 2002) Yang, SL; Yano, T; Aydin, M; Kitamura, Y; Takeuchi, SEight-year-old Murcott orange trees grown in greenhouse lysimeters filled with sandy soil were subjected to irrigation with saline water to investigate the influence of salinity on daily evapotranspiration (ET). The study was conducted in Japan from 1 August to 15 September 2000. The study duration was divided into three periods of about 2 weeks each. In period I, all lysimeters. planted with a tree were irrigated with 60 mm of non-saline water at the water content of 70% of field capacity (FC). Salinity treatments for period II started on 14 August. The treatments during period II were as follows: Lysimeter 1 (L1) had 32 nun non-saline water with an electrical conductivity (EC1) of 1.0 dS/m applied. At the same time Lysimeter 2 (L2) had 32 mm of saline water with an EC1 of 8.6 dS/m applied when the water content decreased to 70% of FC. Lysimeter 3 (L3) had 16 mm saline water (EC1 = 8.6 dS/m) applied at 85% of FC. The irrigation amounts during period II were equal to those corresponding to 1.2 times of water required to reach FC. Treatments in period III were the same as in period I. Daily ET was similar for all weighing lysimeters during period 1, The average relative ET for L2 and L3 with respect to L1 (L2/L1 and L3/L1) were similar during this period, with a mean value of 0.99. During period II. ET from L1 was consistently higher than that from L2 and L3. In addition, L3 with a higher irrigation frequency because of irrigation at higher soil water content resulted in higher ET than L2. The average relative ET of period II was 0.71 and 0. 88 for both L2 and L3, During the last half of period III, reductions occurred in the ET differences between the saline treatments (L2 and U) and non-saline control (L1). Evaporation rates from soil did not exceed 0.7 mm per day. Transpiration rates from L1. L2 and L3 during period II varied between 6.3 and 3,1 mm per day. 4.5 and 2.2 mm per day, and 5.8 and 3.0 mm per day, respectively. The results reflected a tangible difference of water extraction by roots from individual soil layers. Maximum water uptake by these trees was observed at layer of 30-60 cm. Nevertheless. no clear differences in water extraction pattern between trees were observed. Approximately, 95% of drainage occurred during the first 2 days following irrigation. The electrical conductivity of soil water (ECs) and the electrical conductivity of drainage water (ECD) for the saline water treatments (L2 and L3). compared to the control (L1) were significantly different during period II. ECs values were 2-5 times higher in saline treatments compared to the control treatment. After irrigating trees with saline water. ECs increased from 5 to 14 and 16 dS/m in L2 and L3, respectively. Similarly, in both saline treatments. ECD values were greatly increased after irrigation. During period III, ECD values increased from 5 to 8 dS/m in L2, and from 3 to 11 dS/m in L3. By contrast. ECs declined from 14 to 5 dS/m in L2. and from 16 to 3 dS/m in L3 over the same period. (C) 2002 Elsevier Science B.V All. rights reserved.Öğe Spatial and temporal variations in diurnal CO2 fluxes of different Mediterranean ecosystems in Turkey(Royal Soc Chemistry, 2005) Evrendilek, F; Ben-Asher, J; Aydin, M; Çelik, IDiurnal rates of net CO2 assimilation (P-N) and soil respiration (R-h) in the summer were measured in six Mediterranean ecosystems through an automatic continuous monitoring system. The six sites include a typical evergreen Pinus pinea L. forest with two co-occurring sclerophyllous shrubs (Pistacia terebinthus L. and Phillyrea latifiolia L.), citrus (Citrus Union L.), corn (Zea mays L.), cotton (Gossypium hirsutum L.), soybean (Glycine max L.) and vineyard (Vitis vinifera L.). All six sites exhibited similar behaviour in that low soil water availability and high evaporative demand not only depressed P-N and R-h, rates, but also changed the diurnal time course of their peak rates. Except for P. terebinthus and corn, P-N rates of all the species peaked in the morning (7:30-9:30), and R-h, rates in all the sites were higher during the night than during the day (p < 0.05). Mean rates of net ecosystem emission (NEE) Of CO2 to the atmosphere were highest (-23.9 mu mol CO2 m(-2) s(-1)) in the corn site and lowest (-0.6 mu mol CO2 m(-2) s(-1)) in the vineyard site. On average, all six ecosystems were a net source of CO2 to the atmosphere, due to R-h effluxes exceeding P-N rates. Net CO2 assimilation and R-h explained 25% (for corn) to 87% (for citrus) of the diurnal fluctuations of the atmospheric CO2 concentration. Multiple linear regression (MLR) models accounted for 42% (P. pinea) to 95% (cotton) of diurnal variations in P-N rates and 30% (forest) to 92% (citrus) of diurnal variations in R-h rates (p <= 0.001). The dependence of diurnal P-N and R-h rates on water vapour pressure deficit and soil water deficit for dry and hot summer days appeared to be major and needs to be re-examined for biogeochemical models of climate change effects on CO2 dynamics of Mediterranean ecosystems.Öğe Test of a simple model for estimating evaporation from bare soils in different environments(Elsevier Science Bv, 2005) Aydin, M; Yang, SL; Kurt, N; Yano, TA simplified model originally proposed by Aydin [Aydin, M., 1998a. A new model for predicting evaporation from bare field soil. In: Proceedings of the International Symposium and second Chinese National Conference on Rainwater Utilization, Xuzhou-Jiangsu, China, pp. 283-287] for estimating actual evaporation from bare soils was tested under different environmental conditions. Field experiments were carried out on clay soils in a semi-arid region of Turkey. A sandy soil column-experiment in a drying chamber and a study with the same sand media in a greenhouse were conducted at Arid Land Research Center, Tottori University, Japan, in order to test the performance of the model. The model is based on the relations among potential and actual soil evaporation and soil-water potential at the top surface layer of the soil, with some simplifying assumptions. Input parameters of the model are simple and relatively obtainable viz. climatic parameters for the calculations of potential soil evaporation and matric potential measured near the soil surface. Despite some differences between calculated and measured soil evaporation, the agreement was reasonable at all sites. This agreement seems to support the model assumptions, and the model is potentially valuable, but the objective measurement of soil-water potential near the surface of the profile is difficult, especially for a drier upper layer. (C) 2004 Elsevier B.V. All rights reserved.
