A two-year greenhouse study was performed to determine the possibility of estimating the transpiration rate in hydroponically grown tomato on the basis of climate parameters. Transpiration rate, determined by the water balance method on different substrates, was compared to the transpiration rate calculated using the Penman Monteith equation. Regression analysis of the comparison of two different approaches to water consumption determination confirmed that the transpiration rate of greenhouse grown tomato for the studied area can be estimated with high accuracy (R2 > 0.95)

Davor Romić

Gabrijel Ondrašek

Ivo Stričević

Josip Borošić

Marija Romić

English

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113ORIGINAL SCIENTIFIC PAPERSummaryA two-year greenhouse study was performed to determine the possibility of estimating the transpiration rate in hydroponically grown tomato on the basis of climate parameters. Transpiration rate, determined by the water balance method on diff erent substrates, was compared to the transpiration rate calculated using the Penman-Monteith equation. Regression analysis of the comparison of two diff erent approaches to water consumption determination confi rmed that the transpiration rate of greenhouse grown tomato for the studied area can be estimated with high accuracy (R2 > 0.95).Key wordsPenman-Monteith equation, water balance method, hydroponic substratesAgriculturae Conspectus Scientifi cus | Vol. 72 (2007) No. 2 (113-116)Comparison of Transpiration Models in Tomato Soilless Culture Gabrijel ONDRAŠEK 1( )Davor ROMIĆ 1Josip BOROŠIĆ 2Marija ROMIĆ 1Ivo STRIČEVIĆ 11 University of Zagreb, Faculty of Agriculture, Department of Soil Amelioration, Svetošimunska 25, 10000 Zagreb, Croatia e-mail: gondrasek@agr.hr2 University of Zagreb, Faculty of Agriculture, Vegetable Crops Department, Svetošimunska 25, 10000 Zagreb, CroatiaReceived: April 13, 2006 | Accepted: February 7, 2007Agric. conspec. sci. Vol. 72 (2007) No. 2114 Gabrijel ONDRAŠEK, Davor ROMIĆ, Josip BOROŠIĆ, Marija ROMIĆ, Ivo STRIČEVIĆIntroductionAs the most intensive crop production, soilless cul-ture requires large quantities of water, oft en over 10,000 m3 ha-1 year-1 (Voogt, 1992; Duchein et al., 1995). Total water consumption (TWC) in open soilless culture can be divided into two segments - physiological and techno-logical consumption. Technological part (ca 20-30% of TWC) is the amount of water leached from the substrate due to gravitation and providing optimal moisture and aeration of the sub-strate, as well as preventing salt accumulation (Schon and Compton, 1997).Physiological segment (ca 70-80% of TWC) refers to the consumption by the plant, namely plant water uptake (PWU). Only a small part of absorbed water remains within the plant while the major part (> 90%) is released through the stomata as water vapour through the transpi-ration process (Li et al., 2001). Since these are large amounts of water, knowledge of transpiration rates of diff erent crops enables better and more rational management of water as a limited and in-applicable natural source. Transpiration models make it possible to estimate or calculate transpiration rates on the basis of climate and/or vegetative parameters.Th e main goal of this study was to compare and test tomato transpiration rates calculated by the transpiration model according to Penman-Monteith (P-M), adapted to greenhouse conditions, using tomato transpiration on dif-ferent substrates measured by the water balance method.Material and methodsExperimental settingTh e study of tomato grown in an open hydroponic system was conducted during 2001 and 2002 in a green-house (180 m2) located at the experimental station of the Faculty of Agriculture, University of Zagreb, Croatia. Th e greenhouse was equipped with an automatic heat-ing, ventilation and fertigation system. Tomato seedlings (Lycopersicon esculentum Mill. F1 Bell) were planted into PE bags (100x15x7.5 cm) fi lled with one of the tested sub-strates. Substrate bags were arranged in double rows with an average density of 3.1 plants per m2. A dropper was set up by each plant (2 l h-1) and the fl ow rate was checked month-ly. Fertigation drip management (rate and frequency) was equally applied in all treatments and it was adjusted to plant phenology and climate conditions in the greenhouse. Th e experiment was laid out according to the completely randomized block design in three treatments (rockwool, perlite and peat) and with three replicates. Th e experimen-tal plot consisted of three bags and the accounting plot comprised one bag with three tomato plants. Th e greenhouse was supplied with thermo- and hy-grologgers, which recorded the values of air temperature and humidity at one hour intervals. Water balance method Transpiration measurements were carried out in 2001 (15.04.-30.11.) and 2002 (01.03.-01.11.). Transpiration rate (T) on particular substrates was determined by the water balance method on the basis of the diff erence be-tween total water input (I) and output (O) (Romic, 1994; Romero-Aranda et al., 2001). Total I was measured by a fl ow meter installed on the main pipe, while drainage col-lectors were installed on each accounting plot for O cal-culation. Drainage quantity was measured twice a week. Disregarding the small evaporation area (0.006 m-2) of the rockwool cube into which tomato was transplanted, the dif-ference between I and O may represent the value of PWU, i.e. transpiration (T) (Romero-Aranda et al., 2001).T = I – O     (1)Penman-Monteith equationBesides direct measuring, transpiration rates were calculated using the Penman-Monteith model, adapted to greenhouse conditions (Stanghellini, 1987; Montero et al., 2001; Seginer, 2002):)/rr(1))(c/r()/rr(1)(R0.408TasaasS as ee                 (2)where  T - transpiration (mm day-1) Rs - external solar radiation (MJ m-2 day-1) ra - aerodynamic resistance (m s-1) rs - stomatal resistance (m s-1) es-ea - saturation vapour pressure defi cit (kPa) Δ - slope of vapour pressure curve (kPa ºC-1) τ - cover transmissivity of solar radiation  γ - psychrometric constant (kPa ºC-1) ρ - mean air density at constant pressure (kg m-3) c - specifi c heat of air at constant pressure (MJ kg-1 ºC-1).Rs was calculated on the basis of insulation duration (n) using the program CROPWAT ver. 5.7 (Smith, 1992). Insulation duration data were obtained from the mete-orological station Maksimir, Zagreb. It was assumed that the cover transmissivity of solar radiation (0.6) was con-stant and did not change during the trial period (Baille and Baille, 1994; Jolliet, 1994; Kittas et al., 1995). Mean air density (ρ), slope of saturation vapour pressure curve (Δ) for diff erent temperatures and specifi c heat of air (c) were considered as constants, as well as the psychrometric con-Agric. conspec. sci. Vol. 72 (2007) No. 2115Comparison of Transpiration Models in Tomato Soilless Culturestant (γ). Saturation vapour pressure defi cit (es-ea) repre-sents the diff erence between the mean saturation vapour pressure (es), related to air temperature and actual vapour pressure (ea), derived from relative humidity data according to Allen et al. (1998). In the P-M equation (Eq. 2), ra and rs represent the bulk aerodynamic and stomatal resistances of the leaves to vapour diff usion. Th e aerodynamic resistance value was considered as a constant (ra=200 s m-1) because of the comparatively large leaf area and low wind velocity in the greenhouse (Stanghellini, 1987; Kage et al., 2000). Stomatal resistance was calculated on the basis of external solar radiation (Boulard and Wang, 2000):)))50(05,0exp(11(200ss Rr   (3) Data processingTranspiration values, estimated according to P-M and directly measured using the water balance method, were calculated per decade and compared using a simple linear regression. All descriptive and procedural data process-ing was done using a statistical soft ware package (SAS, 2001). Results and discussionSince the nightly transpiration rate in the greenhouse can be negligible (Boulard and Wang, 2002), only daily values of climatic and vegetative parameters were used for research purposes (P-M equation), Table 1.Results of descriptive statistics given in Table 1 indicate that the climate conditions were fairly uniform in both trial years. Among the observed parameters, solar radia-tion varied the most in the two-year research period (CV= 41 and 43%). Relative humidity in the greenhouse varied the least, CV being 11% in 2001 and 15% in 2002.Data on directly measured transpiration were included into a simple linear regression model. In both trial years and with all three predictors, i.e. rockwool, perlite and peat, high coeffi  cients of determination (R2) with small diff erences between substrates were obtained (Figures 1 and 2). Th e model involving rockwool achieved the highest r-square value in both years (R2 = 0.98). Th is parameter, along with some others relating to macroelements and water balance (Ondrasek et al., 2004), confi rms that irrigation management was best adapted to tomato grown on rock-wool. Namely, irrigation applied in this trial involved the same amounts of water and identical irrigation intervals for all substrates. However, irrigation rates and intervals applied in soilless culture on substrates for the purpose of better water management should be adjusted not only to the plant growth, plant development stage, and climate parameters but also to the physical characteristics of the substrate. According to Biernbaum et al., (1999) and also  Parameter Rs (MJ/m2day) n (h) RH (%) T (°C) rs (m/s)  2001 2002 2001 2002 2001 2002 2001 2002 2001 2002 Minimum 5.5 4.7 3.3 2.2 41 30 9.8 9.6 201 202 Maximum 21.9 24.6 10.1 10.5 87.4 88.2 34.7 37.6 294 276 Mean 15.7 15.5 6.7 6.5 58.7 58.7 20.9 21.6 229 230 St. Deviation 6.3 6.7 2.5 2.7 5.5 5.3 4.5 4.7 38.9 28.4 C.V. % 41 43 37 41 11 15 31 32 17 12 Table 1. Descriptive statistics of climatic (Rs-solar radiation, n-sunshine duration, RH-relative humidity, T-air temperature) and vegetative parameters (rs- stomatal resistance)SQRT(ETPM) = 2,0649+0,105*ETPR2 = 0,954323456780 10 20 30 40 50 60ET P (mm/m2)SQRT(ETPM) = 2,0875+0,1011*ETTR2 = 0,960223456780 10 20 30 40 50 60ET T (mm/m2)SQRT(ETPM) = 2,0071+0,0999*ETRWR2 = 0,978623456780 10 20 30 40 50 6ET RW (mm/m2)SQRT(ET PM)(mm/m2)Figure 1. Comparison of the regression lines and associated statistical parameters between measured transpiration (TT-on peat, TRW-on rockwool, TP-on perlit) and predicted by the P-M equation (TPM) in 2001 (n=23)Agric. conspec. sci. Vol. 72 (2007) No. 2116 Gabrijel ONDRAŠEK, Davor ROMIĆ, Josip BOROŠIĆ, Marija ROMIĆ, Ivo STRIČEVIĆconfi rmed by our results, fertigation frequency on peat should be increased compared to other substrates less ca-pable of retaining available water. On the contrary, the amount and intervals of fertigation on perlite should be decreased compared to rockwool, which is more capable of accumulating water. According to Argo and Biernbaum (1995) and also confi rmed by our results, growing media with relatively higher water-holding capacity (e.i. rockwool and peat) required fewer (fert)irrigations than those with a lower water-holding capacity, like perlite.ConclusionsTh e two-year trial revealed that the same irrigation treatment in tomato hydroponic culture resulted in diff er-ent transpiration rates on diff erent substrates. It was also found that the external climate data in combination with the Penman-Monteith approach enable reliable prediction of water consumption by transpiration in tomato soilless culture in the studied area.ReferencesAllen R.G., Pereira L.S., Raes D., Martin S., 1998. Crop evapotranspiration. Guidelines for computing crop water requirements. FAO Irrig. and Drain. Paper 56, FAO, Rome, 300 pp.Baille M., Baille A., 1994. A simplifi ed model for predicting evapotranspiration rate of nine ornamental species vs climate factors and leaf area. Scientia Horticulturae, 59(3-4): 217-232.Biernbaum J., Argo W.R., Yelanich M.V., 1999. Water and nutrient management in peat-based media–a program review and perspective. Acta Hort., 481 (1), 103-111.Boulard T., Wang S., 2000. Greenhouse crop transpiration simulation from external climate conditions. Agricultural & Forest Meteorology, 100 (1), 25-34. Boulard, T., Wang, S., 2002. Experimental and numerical studies on the heterogeneity of crop transpiration in a plastic tunnel. Computers & Electronics in Agriculture, 34 (1-3), 173-190.Duchein M. C., Baille M., Baille A., 1995. Water use effi  ciency and nutrient consumption of a greenhouse rose crop grown in rockwool. Acta Hort. 408, 129-135.Jolliet O., 1994. Hortitrans, a model for predicting and optimizing humidity and transpiration in greenhouses. J. Agric. Eng. Res., 57: 23–37.Kage H., Krämer  M., Körner O., Fricke A., 2000. A simple model for predicting transpiration of greenhouse cucumber. Gartenbauwissenschaft . 65 (3), 107–114.Kittas C., Draoui B., Boulard T., 1995. Quantifi cation du taux d’aeration d’une serre a ouvrant continu en toiture. Agricultural & Forest Meteorology, 77: 95-111.Li YL., Stanghellini C., Challa H., 2001. Eff ect of electrical conductivity and transpiration on production of greenhouse tomato (Lycopersicon esculentum L.). Scientia Horticulturae. 88 (1), 11-29.Montero J. I. Antón A., Muñoz P., Lorenzo P., 2001. Transpiration from geranium grown under high temperatures and low humidities in greenhouses. Agricul. and forest meteorol. 107, 323-332.Ondrasek G., Romic D., Borosic J., 2004. Water and macroelements consumption in tomato solilles culture. Proceedings of the 39th Croatian Symposium on Agriculture with International Participation, Opatija, 367-368.Romic D., 1994. Navodnjavanje zaslanjenim vodama u agroekološkim uvjetima vranskog bazena. Ph.D. Dissertation. University of Zagreb, Croatia, 108pp.Romero-Aranda R., Soria T., Cuartero J., 2001. Tomato plant-water uptake and plant-water relationships under saline growth conditions. Plant Sci., 2 (160), 265-272. SAS., 2001. Statistical Analysis System for Windows, release 8.02. SAS Institute Inc., Cary, NC.Schon M. K., Peggy Compton M., 1997. Nitrogen and phosphorus requirements for rockwool-grown cucumbers trained with a double-steam method. HortTechnology, 7 (1), 33- 39.Seginer I., 2002. Th e Penman-Monteith evapotranspiration equation as an element in greenhouse ventilation design. Biosystems Engineering. 82 (4), 423-439.Smith M., 1992. Cropwat. A computer program for irrigation planning and management. FAO Irrig. and Drain. Paper 46, FAO, Rome, 126pp.Stanghellini C., 1987. Transpiration of greenhouse crops: an aid to climate management. Ph.D. Dissertation. Wageningen Agricultural University, Wageningen, 150 pp. Voogt W., 1992. Nutrient uptake of tomatoes during the growing period. Acta Hort. 307, 208-213.ETPM = 2,3224+0,9396*ETPR2 = 0,969601020304050600 10 20 30 40 50 60 70ETP (mm/m2)ETPM = 1,2246+0,9469*ETTR2 = 0,96460102030405060700 10 20 30 40 50 60 70ET T (mm/m2)ETPM = 2,11+0,8986*ETRWR2 = 0,97940102030405060700 10 20 30 40 50 60 70ET RW (mm/m2)ETPM (mm/m2)Figure 2. Comparison of the regression lines and associated statistical parameters between measured transpiration (TT-on peat, TRW-on rockwool, TP-on perlit) and predicted by the P-M equation (TPM) in 2002 (n=24)acs72_17

Comparison of Transpiration Models in Tomato Soilless Culture

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