مرکز منطقه ای اطلاع رساني علوم و فناوري - ارائه الگوي برآورد تلفات تبخير و بادبردگي درسيستم آبياري باراني كلاسيك ثابت با آبپاش متحرك

چكيده لاتين :

Introduction The sustainability of irrigated agriculture depends on the consistency of high irrigation efficiency. During a sprinkler irrigation, a relevant part of the water discharged by the irrigation system does not reach the crop canopy. This unaccounted water is referred to as "wind drift and evaporation losses" or "spray losses" (Ls), and is expressed as a percentage of the gross volume of irrigation water. In hot and semi-arid areas, these losses would be significant. Thus a proper understanding of the factors affecting spray losses (Ls) in different sprinkler irrigation systems is important for developing water conservation strategies. Trimmer (1987) developed an equation based on the nomograph of Frost and Schwalen (1955) that enables the user to estimate the percentage of evaporation loss during sprinkler irrigation as a function of the sprinkler characteristics, the operating pressure, and the climate factors. The magnitude of the losses can be very relevant under certain conditions. While some authors reported losses of 5-10% under a moderate evaporative demand (Keller and Bliesner, 1990), others signaled maximum losses of 30% (Spurgeon et al., 1983). Spurgeon et al. (1983) reported that hot, dry, and windy conditions eould cause spray losses from sprinkler irrigation systems to approach 30% of the water applied. In the hot and semi-arid meteorological conditions of Zaragoza (Spain) the average spray losses for the experimental moving lateral amounted to 9.8% during the day and 5.0% during the night (Playan et al., 2005). Objective The objective of this paper is to propose a mathematical equation for correct and exact estimation by characterizing Ls under different weather conditions for semi-portable hand-move sprinkler systems in the hot and semi-arid conditions of the Khouzestan province. Methodology The selected irrigation system is in the southeastern part of the Khouzestan province in Iran, 50°17ʹ37" east and 30"30ʹ45" north. The standard ISO 7749/2 (1990) and ASAE S398.1 (2001) have been taken into account to determine Ls. To conduct tests, a pumping set is supplied from a deep well. Weather conditions (e.g. dry bulb temperature, wet bulb temperature, and wind speed) are collected through a weather station, located 50 m away from the test site. This information is all registered with a fiveminute frequency. For the analysis of Ls in the hot and semi-arid conditions, 40 tests have been carried out at operating pressures from 45 to 50 m. The impact sprinkler used in outdoor single-sprinkler tests is the VYR155 with the temal nozzles of 11*6.3*3.2mm. The statistical analysis of Ls was carried out using the SPSS and Excel software packages. The relative error (AMRE), the standard error (S.E.), and the coefficient of pearson (Rʹ) were used for equation obtained from the regression model. Results and Discussion In this study the wind speed ranged from 0 to 6.77 mis, the air temperature ranged from 21.4 to 44.9"c, the relative humidity ranged from 11.8 to 80%, and the vapour pressure deficit ranged from 0.63 to 8.42 kpa, The maximum Ls in the worst meteorological condition in the southern region of Khouzcstan province was 26.8% at 13 to 15 oʹclock, when the relative humidity was the lowest and the air temperature, the wind speed, and the vapour pressure deficit were the highest. The best condition was attained when the irrigation is done at night, during early morning, or early evening, In this case, Ls is usually smaller than 1-2%. The results switching irrigation from day to night reduced Ls strongly, A new equation is introduced in this research for estimating Ls under the hot and semi-arid conditions. The best regression coefficient (Rʹ) was obtained with the nonlinear multiple regression modeL This model was performed to evaluate how the meteorological variables could explain Ls. Wind and vapour pressure defieit were the most explicative variables. The analysis with SPSS showed whole terms of the model resulted highly significant (P ~0,05), The fit parameters as well as the expression of the model were: Ls=5.4*wn·6 +7.4*(e, _eJJ · 45 -6.1 (1) (Rʹ ~ 0,94 , S,E ~ 2,0 ,AMRE ~ 0,23) where Ls is the spray losses (%), W is the wind speed (mls), e, - e" is the vapour pressure deficit (kPa), Losses estimated from the Frost and Schwalen (1955) method were compared to the values of the field measurements. The comparison of results showed that the Ls values estimated from the Frost and Schwalen (1955) method were 6% less than the field values or the values of simulated Ls with the equation (1) moderately, Phocaides (2000) suggests that in winds of over 3.5 rn/s, sprinkling is not recommended. The above obtained equation showes that Ls exceeded 21.9% when the wind speed and vapour pressure deficit increase more than 3.5 m/s and 6 kpa, respectively. Therefore, to avoid excessive Ls, sprinkler irrigation systems should not be operated in the early afternoon hours in the summer or windy conditions. The amount of loss would be very small (mainly 1% to 2%) for operation during night time, early morning, and early evening hours.