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Evapotranspiration and Simulation of Soil Water Movement in Small Area Vegetation

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Evapotranspiration and Simulation of Soil Water Movement in Small Area Vegetation INTERNATIONAL Agrophysics www.international-agrophysics.org Int. Agrophys., 2013, 27, 445-453 doi: 10.2478/intag-2013-0015 Evapotranspiration and simulation of soil water movement in small area vegetation C. Paraskevas1, P. Georgiou1*, A. Ilias2, A. Panoras2, and C. Babajimopoulos1 1Department of Hydraulics, Soil Science and Agricultural Engineering, Aristotle University of Thessaloniki, 54124, Thessaloniki, Greece 2Land Reclamation Institute, National Agricultural Research Foundation, 57400, Sindos, Greece Received May 14, 2012; accepted December 12, 2012 A b s t r a c t. In Greece, crops are frequently cultivated in Frequently, fields in Greece are very small (<1 000 m2) small isolated areas in close proximity to roads and bare soils and representing typical non-standard conditions. Under these therefore evapotranspiration is affected by local advection. Under circumstances, the crops are growing under conditions of these circumstances, oasis effect conditions are present and evapo- the oasis effect resulting in very high evapotranspiration transpiration is higher than what is expected. In this paper, the evapotranspiration and soil water dynamics of a cotton crop culti- values. Increased evapotranspiration is also observed at the vated in small areas under the oasis effect is studied. To this end, upwind series of crops resulting in lower yields since these two isolated free-drainage lysimeters cultivated with cotton in the series obtain the same amount of water as the interior series. year 2007 were used. Soil moisture of the soil profile of both the Therefore, the overall yield is reduced because of the lysimeters was monitored with two capacitance water content pro- non-satisfactory yield of the upwind series. bes. The soil water balance method was used to estimate crop eva- The climatic definition of the ‘oasis effect’ or ‘cold potranspiration and corresponding crop coefficients in one of the island effect’ refers to the phenomenon of a cooling effect two lysimeters. These coefficients were 75% larger than the caused by vegetation (Givoni, 1991; Potchter et al., 2008). FAO-56 crop coefficients at the mid-season stage. The FAO-56 and the derived crop coefficients were used for the simulation of According to Oke (1987) this cooling effect is due to the fact the water dynamics in the second lysimeter by the SWBACROS that the energy required for evaporation (QE) is more than model. The derived crop coefficients for these conditions produced that supplied by radiation (Q*). It has been observed that the much better results than the FAO-56 crop coefficients. The results ratio QE/Q* can be as large as 2.5 over an irrigated field of were improved when crop coefficient value equal to 2.5 was used cotton (Lemon et al., 1957). Kai et al. (1997) also explained for the mid-season stage. the cooling effect by the difference of the energy balance K e y w o r d s: modelling soil water flow, evapotranspiration, between oasis and the surrounding area. The oasis effect oasis-effect, crop coefficients phenomenon is observed in different climates and urban or INTRODUCTION rural conditions (Oke, 1987; Potchter et al., 2008; Spronken- Smith et al., 2000). Therefore, the use of the term ‘oasis Crop evapotranspiration (ETc) can be calculated under effect’ has a wider definition than the classical term standard or non-standard conditions and various (Potchter et al., 2008). management practices. Standard conditions refer to crops According to Oke (1987) any cool moist surface domi- grown in large fields under non-limiting agronomic and soil nated by larger scale warmer, drier surroundings has the conditions. Non-standard conditions and various manage- characteristics of an oasis effect situation: a lake in an area ment practices refer to management and environmental with a dry summer climate; an urban park; an isolated tree in conditions that deviate from standard conditions such as salt a street or on open bare ground etc. A common characteristic toxicity, pests, diseases, surface mulches, small areas vege- of all these cases is that evaporation rates are higher than tation etc. (Allen et al., 1998). those from extensive areas of the same composition. *Corresponding author e-mail: [email protected] © 2013 Institute of Agrophysics, Polish Academy of Sciences 446 C. PARASKEVAS et al. Exchange of energy and matter, especially heat and wa- Thessaloniki, Greece, during the cultivation period of 2007 ter, is dominant in the interaction between oasis and desert under conditions of the oasis effect. The oasis effect is (Zhang and Huang, 2004). The soil water content and the ensured by the fact that this small field (surface area of 90 atmospheric humidity over the oasis are influenced and modi- m2) is isolated from any other crops. Currently, a dirt road fied, resulting in larger values of evapotranspiration than the and an area of bare soil extend around the field. Additionally net radiation (Oke, 1981). Oke (1979) observed that the ac- the building of the Land Reclamation Institute and a small tual evapotranspiration of an irrigated suburban lawn (ap- group of trees were at a distance of 50 m from the lysimeters. 2 proximately 160 m ) markedly exceeds the potential value The two lysimeters have a surface area of 4 m2 and 20 cm set by Priestley and Taylor (1972). thick concrete walls. The lysimeters were filled with dis- Spornken-Smith et al. (2000) observed that evaporation turbed soil to a depth of 90 cm. Below that depth, there was from an urban park was 130% higher than that from a rural a layer of about 30 cm consisting of coarse material (sand grass site. Eigenmann et al. (2011) also observed high va- and gravels) for collection of percolating water. lues of evapotranspiration in a number of maize fields in This field was planted with cotton and all the cultivating Germany caused by the oasis effect. practices common in the plain of Thessaloniki were im- In this paper, the evapotranspiration and the soil water plemented throughout the cultivation period. Sowing of dynamics of a cotton crop cultivated in two free-drainage cotton took place on the 11th of May 2007 (day of the year – lysimeters under conditions of the oasis effect were studied. DOY 131). Three rows of plants were planted in each lysi- Lysimeters provide a direct measurement of evapotrans- meter, one in the middle and two rows at a distance of 70 cm piration (ET) and they are frequently used to study climatic on each side of the central row. The estimated plant density effects on ET and to evaluate ET estimating procedures. was 1950 plants per 100 m2. The soil was fertilized on the Irrigation scheduling requires estimation of the fre- 18th of May with a composite fertilizer 21-8-11 N-P-K+0.5 quency of watering and the time variation of the available to Zn. The plants were harvested on the 25th September 2007 the plants soil water. The quality of the water that returns to (DOY 268). It was observed that the four plant growth sta- water receivers, the accumulation of salts to the root zone, ges had the following durations: initial stage – 21 days, crop the evaporation and the root water uptake, and the contami- development stage – 45 days, mid-season stage – 49 days, nation of the surface and ground water depend on the re- and late season stage – 23 days. distribution of the water in the unsaturated zone. Therefore, Climatic data were obtained from an automatic weather an integrated methodology for the study of the soil water station (AWS) that was located on a small grass field close to movement in the unsaturated zone is required for more the lysimeters in hourly intervals. Sensors measuring air efficient water management in this zone. Toward this task temperature (T), relative humidity (RH), solar radiation many mathematical models for the simulation of the water (Rs), wind speed (u2), and rainfall (R) were included in the dynamics in the unsaturated zone of cultivated soils have station. All sensors were placed 2 m above the soil surface. been developed and can be found in the international Daily meteorological data were used to calculate the re- literature. ference evapotranspiration (ETo) according to the FAO-56 The objectives of this paper were: Penman-Monteith equation (Allen et al., 1998). Even – estimation of the evapotranspiration of a cotton crop though total precipitation was high enough to cover a large cultivated in two free-drainage lysimeters under condi- part of the plant water needs, the rain was unevenly distri- tions of the oasis effect; buted throughout the cultivation period and only a very small – estimation of the crop coefficients under conditions of the part of the plant needs was fulfilled. In particular, preci- oasis effect and their comparison there of with the pitation of 205.6 mm was observed during the months of FAO-56 coefficients under standard conditions (Allen et May and June. About 152 mm out of the 205.6 mm dropped al., 1998); in few hours on three consecutive days with very severe – simulation of the water movement in a lysimeter field intensity. Due to this high intensity, most of the water ran off cultivated with cotton with the mathematical model SWBACROS (Babajimopoulos et al., 1995) throughout the lysimeters because of the small height of the surrounding the cultivating period. In this simulation, the crop coeffi- walls. The rest of precipitation was observed in August cients estimated in this paper and the FAO-56 coefficients (66.2 mm) and September (24.0 mm). were used. Additionally, a very high value of 2.5 for the The effective rainfall at daily time steps was calculated mid-season stage was used. using the Curve Number (CN) method. The Curve Number is a dimensionless parameter indicating the runoff response characteristics of an area and related to land use, land MATERIALS AND METHODS treatment, hydrological condition, hydrological soil group, Experimental data were obtained in two pre-existing and antecedent soil moisture (AMC) (Bos et al., 2009).
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