Braškių vandens poreikio tyrimai Lietuvos Vidurio zonoje ; Strawberry water requirements in Middle Lithuania
LITHUANIAN UNIVERSITY OF AGRICULTURE Laima Taparauskien ė STRAWBERRY WATER REQUIREMENTS IN MIDDLE LITHUANIA Summary of doctoral dissertation Technological Sciences, Environmental Engineering and Landscape Management (04 T) Kaunas, 2005 The study was accomplished at the Lithuanian University of Agriculture in period of 2001-2004. Scientific supervisor: doc.dr. Zigmas Galminas (Lithuanian University of Agriculture, Technological Sciences, Environmental Engineering and Landscape Management 04 T) Thesis will be defended at scientific board of Environmental Engineering and Landscape Management, Lithuanian University of Agriculture: Chairman: doc.dr. Arvydas Povilaitis (Lithuanian University of Agriculture, Technological sciences, Environmental Engineering and Landscape Management – 04 T) Members: habil.dr. Saulius Vaikasas (Water Management Institute of Lithuanian University of Agriculture, Technological sciences, Environmental Engineering and Landscape Management – 04 T) prof. habil.dr. Juozas Ruseckas (Lithuanian Institute of forestry, Biomedical sciences, Forestry – 14 B) prof. habil.dr. Narimantas Titas Ždankus (Kaunas University of Technology, Technological sciences, Environmental Engineering and Landscape Management – 04 T) doc.dr.
Source : VDDB.LIBRARY.LT/FEDORA/GET/LT-ELABA-0001:E.02~2005~D_20060209_121629-10307/DS.005.1.01.ETD
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LITHUANIAN UNIVERSITY OF AGRICULTURE Laima Taparauskien ė STRAWBERRY WATER REQUIREMENTS IN MIDDLE LITHUANIA Summary of doctoral dissertation Technological Sciences, Environmental Engineering and Landscape Management (04 T) Kaunas, 2005
The study was accomplished at the Lithuanian University of Agriculture in period of 2001-2004. Scientific supervisor: doc.dr. Zigmas Galminas (Lithuanian University of Agriculture, Technological Sciences, Environmental Engineering and Landscape Management 04 T) Thesis will be defended at scientific board of Environmental Engineering and Landscape Management, Lithuanian University of Agriculture: Chairman: doc.dr. Arvydas Povilaitis (Lithuanian University of Agriculture, Technological sciences, Environmental Engineering and Landscape Management 04 T) Members: habil.dr. Saulius Vaikasas (Water Management Institute of Lithuanian University of Agriculture, Technological sciences, Environmental Engineering and Landscape Management 04 T) prof. habil.dr. Juozas Ruseckas (Lithuanian Institute of forestry, Biomedical sciences, Forestry 14 B) prof. habil.dr. Narimantas Titas dankus (Kaunas University of Technology, Technological sciences, Environmental Engineering and Landscape Management 04 T) doc.dr. Petras Punys (Lithuanian University of Agriculture, Technological sciences, Environmental Engineering and Landscape Management 04 T) Opponents: prof. habil.dr. Brunonas Gailiuis (Lithuanian Energy Institute, Technological Sciences, Environmental Engineering and Landscape Management 04 T) dr. Zenonas Strusevi č ius (Water Management Institute of Lithuanian University of Agriculture, Technological Sciences, Environmental Engineering and Landscape Management 04 T) The local discussion will be held at 11 a.m. on 27 December 2005 at the meeting of Environmental Engineering and Landscape Management board, 610 a. III rd building, Lithuanian University of Agriculture. Address: Universiteto st.10, LT 53607, Akademija, Kauno r., Lithuania. The summary of doctorial thesis was distributed on 27 of November 2005. The doctoral thesis is available at the libraries of Lithuanian University of Agriculture (Studentu 11, Akademija, Kaunas district) and Water Management Institute of Lithuanian University of Agriculture (Parko st.3, Vilainiai, K ė dainiai district).
LIETUVOS EM Ė S Ū KIO UNIVERSITETAS Laima Taparauskien ė BRAKI Ų VANDENS POREIKIO TYRIMAI LIETUVOS VIDURIO ZONOJE Daktaro disertacijos santrauka Technologijos mokslai, aplinkos ininerija ir kratotvarka (04 T) Kaunas, 2005
Disertacija rengta 2001-2004 metais Lietuvos em ė s ū kio universitete. Mokslinis vadovas : doc.dr. Zigmas Galminas (Lietuvos em ė s ū kio universitetas, technologijos mokslai, aplinkos ininerija ir kratotvarka 04 T) Disertacija ginama Lietuvos em ė s ū kio universiteto Aplinkos ininerijos ir kratotvarkos mokslo krypties taryboje: Pirmininkas: doc.dr. Arvydas Povilaitis (Lietuvos em ė s ū kio universitetas, technologijos mokslai, aplinkos ininerija ir kratotvarka 04 T) Nariai: habil.dr. Saulius Vaikasas (L Ū U Vandens ū kio institutas, technologijos mokslai, aplinkos ininerija ir kratotvarka 04 T) habil.dr. Juozas Ruseckas (Lietuvos mik ų institutas, biomedicinos mokslai, mikotyra 14 B) prof. habil.dr. Narimantas Titas dankus (Kauno technologijos universitetas, technologijos mokslai, aplinkos ininerija ir kratotvarka 04 T) doc. dr. Petras Punys (Lietuvos em ė s ū kio universitetas, Technologijos mokslai, aplinkos ininerija ir kratotvarka 04 T) Oponentai: prof. habil.dr. Brunonas Gailiuis (Lietuvos energetikos institutas, technologijos mokslai, aplinkos ininerija ir kratotvarka 04 T) dr. Zenonas Strusevi č ius (L Ū U Vandens ū kio institutas, technologijos mokslai, aplinkos ininerija ir kratotvarka 04 T) Disertacija bus ginama vieame Aplinkos ininerijos ir kratotvarkos mokslo krypties tarybos pos ė dyje, kuris vyks 2005 m. gruodio 27 d. 11 val. Lietuvos em ė s ū kio universitete, III r ū m ų 610 auditorijoje. Adresas: Universiteto g. 10, LT 53607, Akademija, Kauno r., Lietuva. Disertacijos santrauka isiuntin ė ta 2005 m. lapkri č io m ė n. 27 d. Disertacij ą galima peri ū r ė ti Lietuvos em ė s ū kio universiteto ir L Ū U Vandens ū kio instituto bibliotekose
INTRODUCTION Actuality: Restoration of Lithuanian independence, land reform, radically changed farming structure and strawberry growing potential has conditioned an increase of modern strawberry plantation. The Lithuanian strategy of agricultural development (20002006) forecasts that in order to meet consumers demand app 1112 thousand hectares of new trade gardens and berry-fields will have been planted until 2015 m. Such factors as cultural features, proper agricultural engineering, farm specialization and irrigation are deciding ones for fertility increase and competitiveness of strawberry (Strabioli, 1998, Afanasik et al., 2000). Strawberry is one of the most drought sensitive plants. Soil moisture deficit has a negative impact on strawberry growth, development, yield, berry size and persistency in winter time. In the recent decades the trend of instability of irrigation conditions has been evident in Lithuania. Now wet seasons appear every second -third year and every third -sixth year agriculture suffers from insufficient humidity. To reduce the negative impacts of this type both effective irrigation and land drainage systems are necessary. It has been stated by research that under Lithuanian climatic conditions it is necessary to irrigate not only during droughty and average humid periods but during more humid years as well (Dirse et al., 1984). Irrigation is a rather important precondition for the commercial cultivation of fruit and berries in Lithuania. The new farm structure requires new, mainly small -scale irrigation systems. The strawberry research results obtained in foreign countries show the positive effect of irrigation, however, there is no data available about the expedience of irrigation under Lithuanian climatic conditions. Lithuanian farmers grow strawberry without irrigation or apply foreign recommendations, which are not legitimated under Lithuanian conditions, so there is the need give scientific reasoning of the expedience of strawberry irrigation under Lithuanian climatic and new economical conditions. Actual evapotranspiration of irrigated fields is a crucial parameter, which has to be considered when making decisions on irrigation amount and timing (Mahrer, 1990). It is known that evapotranspiration (ET) makes 8090% from the total rainfall during the warm period of the year (Tumas, 1987, Lichasevich & Stelmach, 2002). Knowledge of the factors related with water consumption process allows understanding of stimulating water need forces of the plants and having evaluated them to provide and forecast irrigation regime that ensures optimal conditions of growth and productivity. Strawberry water consumption and the soil water dynamics during strawberry growing period stated performing pilot research and additional yield which had been got because of the irrigation influence allows to measure optimal irrigation regime of the strawberry based on research. This research is the basis for application of theoretical knowledge for creating new optimal technologies for strawberry growing. Research hypothesis: Soil water regime is one of the basic factors, which affects yield, berry size and others features of strawberry development. Establishment of strawberry water requirements and tendencies of actual evapotranspiration and relation with environmental (meteorological) conditions during vegetation period enables optimization of strawberry irrigation scheduling and specification of existing as well as modernization of new technologies of competitive strawberry production. Aim and tasks of the work : The aim of the work to investigate dynamics of strawberry evapotranspiration in the Middle Lithuania and in the course of experiments, with respect to development peculiarities and productivity, to determine optimal irrigation regime for the strawberry grown in loamy soils. The following steps have been taken to achieve this aim: - Conduction of lysimetric investigations in order to determine evapotranspiration of strawberries under natural climatic conditions and maintaining optimal soil moisture conditions with irrigation; - Analysis of reference evapotranspiration methods; determination of their interaction degree and evaluation of the possibilities to introduce reference evapotranspiration models in calculation of the evapotranspiration of strawberries;
- Quantitative evaluation of the influence of meteorological factors on the amount of the water consumed by strawberries and determination of their interaction degree; - Evaluation of soil moisture dynamics in strawberry field during vegetation and determination of optimal irrigation regime in loamy soils; - Determination of the influence of irrigation on strawberry yield and others indicators. Scientific novelty: Experimental investigations in the middle Lithuania have determined the following: - Strawberry water consumption during their growing period and its dependence on atmospheric conditions in optimal soil moisture conditions; - Relation of standard evaporation methods ( PenmanMontheith ) with ones applied in Lithuania and adjusted biological coefficient for calculation of strawberry evapotranspiration according to reference evapotranspiration; - Optimal irrigation regime in loamy soils, based on irrigation influence on the yield, fruit size, leaves area and runner production; - SWAP models adaptation for simulating of soil moisture dynamics in strawberry field. Practical importance of the work: The research has resulted in conclusions and proposals to be applied in projecting and maintaining of strawberry irrigation systems in the Middle Lithuania. The determined strawberry evapotranspiration dynamics during vegetation under the Lithuanian conditions enables to estimate strawberry water needs and, having applied optimal strawberry irrigation technologies, to receive higher strawberry yields up to 3 t/ha on average. Scope of dissertation: The dissertation consists of introduction, three chapters, conclusions and references. Text of dissertation is laid out in 146 pages with 40 figures and 27 tables . The first chapter of the work presents the review of general strawberry growing tendencies in Lithuania and all over the world, results of strawberry irrigation research in foreign countries, the results of irrigation research in Lithuania and the influence of irrigative melioration on crop development under Lithuanian climatic conditions, present situation and perspectives of irrigation systems. Conception and methods of evapotranspiration determination are discussed, the survey of evapotranspiration calculation methods that are applied in Lithuania and other countries is presented, the necessity of standard reference evapotranspiration method and its application possibilities under the Lithuanian climatic conditions are discussed. The second chapter of the work describes the object and methods of research. The investigations were carried out in the period of 2001-2004. The data of strawberry evapotranspiration that had been collected in the department of Land Reclamation (LUA) in the period of 1996-1999 was also used. Experimental investigations focused on Senga Sengana strawberry cultivar evapotranspiration dynamics, its dependence on meteorological factors and soil moisture dynamics in strawberry field. The investigations were carried out in the Middle Lithuania (the biggest agrarian zone 37.2% of total area). In this zone the present use and future priorities are first of all related with intensive agriculture, and it has favourable conditions for the formation of big-scale farmers and agricultural enterprises farms. On the basis of the distribution of the Lithuanian Republic territories into agrarian territories the characteristic localities (Birzai, Panevezys, Dotnuva, Kaunas and Kybartai) in the Middle Lithuania were selected. Comprehensive investigations of strawberry evapotranspiration and irrigation regime were conducted in Kaunas region. The geographical position of experimental plot corresponds to 54 ° 88 NL and 23 ° 09 EL. Location of the experiments belongs to the Middle Lithuania Lowland, limnoglacial clay and sand plain. The investigations were carried out in loamy soils as in Lithuania light loam and medium loam soils make 38.4% of farming lands. In the territory of investigations the soil was calcareus deeper gleyic leached soil, IDg4-k, (sod podzolic JP lv ), mechanical composition light loam on clay loam. The following experimental scheme was chosen for the irrigation regime field trials: watering rate that during vegetation changes depending on root development dynamics is the same in all
treatments of the experiment. In the first treatment the strawberry was watered when moisture in active soil layer (0-30 cm) was close to 70% of field capacity (FC), in the second treatment 80% FC. Irrigation efficiency was investigated in the control treatment under natural conditions. The maximum permissible soil moisture level was equated to the upper limit of optimal moisture FC. All field trials were done in three repetitions. Spray tips NAAN 5022 with the discharge of 0.63 m 3 /hour were used for watering. The area of experimental plots was 20 m 2 . Scheme of planting in rows, 0.8x0.3 m (plants number per 1 ha 41666 units). Methodic of investigations. Evapotranspiration was determined by the method of isolated monolith water balance, in direct way, during plant vegetation period (May-September). Weighing type of lysimeters, with soil monolith surface area of 1.0 m 2 and depth 1.1 m were used in the investigations. The lysimeters were weighed every 510 days. The experiments were carried out in three repetitions. The irrigation regime was investigated by the method of field experiments, aimed at the determination of the influence of one factor irrigation. Soil moisture reserves were investigated by the thermostatic method in three repetitions at every 10 cm to the depth of 60 cm. Soil samples were taken every ten days also before and after irrigation and after heavy precipitation (more 20 mm). Irrigation rate was calculated according to the formula of A. Kostiakov. Evaluation of meteorological conditions was based on the data registered at Kaunas Meteorological station (located in 1 km distance). Amount of precipitation was specified by using Tretiakov raingauges (in experimental plots). Humidity of the experimental period was evaluated according to Seleninov hydrothermal coefficient, relative hydrothermal coefficient unified at the department of Land Reclamation and humidity coefficient. Strawberry yield was determined by direct weight method in three repetitions. The method of washing was used to determine root mass. The amount of runners was determined according to the total amount in the plant and the number of rosettes. Computer programme Rootedge for leaves area measuring was used. Reference evapotranspiration was calculated according to the dependence on the sum of air moisture deficits ( Dirses) , that is used in Lithuania (Dirse & Seniunas, 1995) and according to Ivanov (Dirse, 1984), Blaney Criddle (Doorenbos & Pruitt, 1977), Turc (1961), Makkink (1957), Hargreaves (1994), FAORadiation (Doorenbos & Pruitt, 1977), classical Penman (1948), PriestleyTayler (1972), FAOPenman (Doorenbos & Pruitt, 1977), KimberlyPenman (Wright, 1982), FrerePopov (1979), PenmanMonteith (Allen et al., 1998) dependencies. The data of evaporation from water surface, measured with the pan evaporator GGI-3000 , was also used. Computer programme REF-ET was used for calculations. The method of regressive correlation analysis was used in analysis of interfactorial quantitative correlative relations and their strength. Computer programmes Statistica and SPSS were used in statistical data processing. Accuracy of evapotranspiration methods and fluctuations of the received results were analyzed by using statistical analysis methods standard error of estimates. Statistical evaluation of results from modeling and measurements was estimated according to average error, normalized root mean square error, modeling efficiency and normalized mean absolute error. The significance level of 0.05 was chosen for verification of statistical hypotheses. Research results and theirs analysis is presented in the third chapter in the following order: 1. Meteorological conditions in the research object (in the period of 1996-2004); 2. Investigation of strawberry evapotranspiration; 3. Analysis of strawberry evapotranspiration calculation methods; 4. Determination of strawberry irrigation scheduling; 5. Adaptation of SWAP model for simulation of soil moisture dynamics in strawberry field; 6. Analysis of irrigation influence on strawberry yield and others indicators; 7. Economical reasoning of strawberry irrigation; 1. Meteorological conditions in the research object (in the period of 1996-2004) Change of meteorological conditions corresponded to the general climatic condition characteristic to the Lithuanian territory and to the tendencies of distribution according to the humidity of
vegetation period (dry, wet, average humidity). Of the eight years of investigations three years were dry (1996, 1999 and 2002), one year was wet (2001) and four of average humidity. According to the average air temperature of many years two years of investigations were cool (1996 and 2004), two particularly warm (1999 and 2002) and four warm. Low air humidity deficit was observed in three years (1998, 2001 and 2004), average air moisture deficit in three years (1996, 1997 and 2003) and high air moisture deficit in two years of investigations (1999 and 2002). 2. Investigation of strawberry evapotranspiration Evapotranspiration under natural conditions in 1997 and in the period of 2001 2004 was investigated in order to determine the influence of irrigation on water consumption by strawberry. Under natural conditions in the period of May-August strawberry used 313 mm of water. The biggest water consumption 361 mm was determined in dry and warm year of 2002, while the lowest one 303 mm in 2001. In the years differing in climatic conditions strawberry consumed from 58 to 104 mm/month or on average 68 mm of water in May, 69 mm in June, 95 mm in July and 83 mm in August. The lowest evapotranspiration was observed in September 29 mm on average. In the year of average humidity (1997 and 2003, 2004) evapotranspiration dynamics was close to the dynamics of temperature changes. Correlation coefficient between strawberry evapotranspiration and average air temperature changed from 0.49 (in 1997) to 0.66 (in 2003). In the year of the highest humidity (2001) very strong dependence of evapotranspiration on air temperature was observed (r0.77). When no irrigation is applied precipitation is of great importance as the only source of moisture. However, in separate years of investigations no dependence of between evapotranspiration and amount of precipitation was determined. Under optimal soil moisture conditions strawberry consumed from 299 to 557 mm of water, or 366 mm on average, in the period of May August. Average evapotranspiration was 75 mm/month (changed from 63 (in 1999) to 125 mm/month (in 2002)). In eight years of investigations average evapotranspiration in June was 88 mm/month (changed from 55 to 130 mm/month). The biggest evapotranspiration per month was observed in July (on average 107 mm/month, changed from 68 (in 1996) to 143 (in 1999) mm/month), while in August average evapotranspiration was 97 mm/month (changed from 61 (in 1998) to 177 (in 2002) mm/month). In the period of 20012004 average evapotranspiration in September was 47 mm/month. Ten-day dynamics of strawberry evapotranspiration under optimal soil moisture conditions in years and months of the period of 19962004 is presented in Figure 1. 70 70 Min-Max Min-Max 60 25 60 25%-75% %-75% Median value Median value 50 50 40 40 30 30 20 20 10 10 0 0 1996 1997 1998 1999 2001 2002 2003* 2004 May June July August September Year of investigation Month of investigation Fig. 1 . Strawberry evapotranspiration under optimal soil moisture condition in 1996-2004 * the first year of growth In the period of investigations the average evapotranspiration of 10day period in May was 24 mm/decade, in June average evapotranspiration was 29 mm/decade, in July was 36 mm/decade, in August was 31 mm/decade and in September average evapotranspiration was 17 mm/decade. It has been established that in order to avoid stress conditions and to ensure optimal soil moisture conditions strawberry should be irrigated in the year of average humidity as short droughty periods negatively influences strawberry development. Under optimal soil moisture conditions 8
evapotranspiration depends only on thermal regime and plant biological characteristics. In the years of different thermal regime similar tendency of strawberry evapotranspiration is observed, while in the period of flowering and fruit ripening it differs slightly. In the course of investigations two phases of strawberry development are distinguished: the first phase is in May and June when strawberries are in flower, set and ripen fruits; the second important phase of strawberry development is in July and August when new summer leaves, bushes, runners and roots grow intensively. In the years of investigations the biggest water consumption was observed in July 30% of total consumed water. Water consumption percentage in May August was quite the same (2026%). Water consumption in September on average made 11% of the amount of water consumed in the period of May September. Strawberries evaporate 3 mm/day on average. In warmer and dryer years higher evapotranspiration was observed and reached 4.5 mm/day. Maximal evapotranspiration was 5.56 mm/day (in 2002). In the period of flowering average water consumption by strawberries was 2.6 mm/day, in the period of fruiting 3.2 mm/day. After harvesting the evaporation decreased to 2.3 mm/day. In the second part of July average strawberry evapotranspiration was 3.5 mm/day, in August it was equal to the average 3 mm/day. In different years of strawberry growing evapotranspiration was similar. In May of the first year of growth evapotranspiration was close to that of the strawberry of the third year of growth. Plant mass of the strawberry of the first year of growth developed more intensively in comparison to that of the strawberry of the third year of growth and this determined bigger strawberry evapotranspiration by 0.9 mm/day on average. It was established that strawberryplanting time had no significant influence on evapotranspiration in the second year of growth - the amount of water consumed by the strawberry that had been planted in spring was by up to 9% bigger than that consumed by the shoots that had been planted in summer (the same year). 3. Analysis of strawberry evapotranspiration calculation methods Evaluation of reference evapotranspiration methods was carried out in order to determine accuracy of different models and their suitability for calculation of strawberry evapotranspiration under the climatic conditions of the Middle Lithuania zone. Analysis of these different methods also determined the correlative relations of the dependency used under the Lithuanian climatic conditions to calculate reference evapotranspiration according to air moisture deficit ( Dirses ), PenmanMonteith method as the only standard method and evaporation from water surface (pan evaporator GGI-3000), their strength and standard errors. Dispersion of the calculated evapotranspiration in the period of investigations (20012004) is presented in Fig. 2. 90 80 Min-Max 70 25%-75% Median value 60 50 40 30 20 10 0
Method Fig. 2 . Dispersion of the reference evapotranspiration calculated according different methods in the period of investigations (2001 2004) The strongest deviations of the calculated evapotranspiration were determined by using temperature methods. However, having applied Hargreaves equation for calculations, reliable results were
received. From the equations attributed to radiation methods the reference evapotranspiration, calculated according to Turc equation, the most exactly conformed to the evapotranspiration, calculated according to the equations attributed to other methods. Comparison of the results obtained according to Dirses dependency and the ones calculated according to other equations showed that the smallest standard error of estimates ( SEE - 7.59 -7.70 mm/decade) (Fig. 3 a) was determined when PenmanMonteith dependency was used. Reference evapotranspiration calculated in wet and medium humid years differed by 2 -4%, while the values of very warm and dry period of 2002 calculated according to Dirses were significantly bigger than the evapotranspiration, calculated according to PenmanMonteith equation. The reference evapotranspiration, calculated according to combination methods, was bigger (by 4-28%) than that calculated according to Dirses ; while that calculated according to radiation Turc and Makkink smaller (by 2-16%) on average. Calculation according to Blaney-Criddle equation of temperature type determined the most bias; SEE was 13.8 mm/decade (Fig. 3 a). Dirses Dirses GGI-3000 15 IvanovGGI-3000 1 Ivanov 0.9 a) ASCE-PM 10 FAO-BC b) ASCE-PM FAO-BC 0.8 enman - Monteith 5 Turc enman - Monteith 0.7 Turc 0.6 0 0.5 Frere-Popov Mak k ink Frere-Popov ak k ink Kimber Penm 96 Hargreaves Kimber Penm 96 argreaves FAO-Penman FAO-24 Rd FAO-Penman FAO-24 Rd Priestley-Tayler Penman 48 Priestley-Tayler Penman 48 Dirses FAO-56 PM GGI-3000 Fig. 3. Interrelation of reference evapotranspiration methods Standard error of estimates (a); correlation (b) Comparison of the results received according to PenmanMonteith dependency with the results calculated according to other dependencies showed that the smallest deviations were obtained having used Turc , Hargreaves , PriestleyTayler . The biggest SEE of evapotranspiration was determined according to Ivanov and Blaney-Criddle equations, attributed to temperature methods; for combination methods according to FAOPenman equation. Having compared evapotranspiration and evaporation from water surface values according to PenmanMonteith equation the SEE was 7.2 mm/decade. Makkink dependency best corresponded to the results of pan evaporator, the biggest bias with the calculated values was determined when Blaney-Criddle equation had been used. Combination methods were determined to have the closest correlation with the remaining dependencies (r > 0.89). Of temperature methods Blaney-Criddle dependency had the closest relation with other methods. The evapotranspiration, calculated according to Dirses equation had the strongest relations with the evapotranspiration, determined according to Blaney-Criddle dependency (r0.86) (Fig. 3 b), although the obtained SEE was the biggest one. Strong direct linear relation (r0.82) existed between the values, calculated according to the recommended standard Penman - Monteith method and the evapotranspiration, calculated according to the sum of air moisture deficits ( Dirses ) (Fig. 3 b). Comparison of evaporation from water surface data with the calculated values determined strong relation, changing from 0.73 ( Priestley - Tayler ) to 0.86 ( Blaney-Criddle ), with the values, calculated according to Dirses determined strong relations (r 0.84). The PenmanMonteith reference evapotranspiration values versus the results of Dirses dependency and for evaporation from water surface is shown in Figure 4.
7070 60 ET o(PM) = 0.69 ET o(LT) + 9.64 ET o(PM) = 1.12 E o 0 R 2 = 0.669 6 R 2 = 0.688 50 r - 0.82 50 r - 0.83 4040 30 30 actual 20 20 with regression 10 10 coefficient 10 20 30 40 50 60 70 10 20 30 40 50 60 Reference evapotranspiration Pan evaporation E o ET o( LT) (Dirses) mm/decade ( GGI 3000 ) mm/decade - Fig. 4 . Penman Monteith reference evapotranspiration ( ET o(PM) ) versus Dirse reference evapotranspiration ( ET o(LT) ) and Pan evaporation ( E o ) (GGI3000) Application of reference evapotranspiration methods for calculation of strawberry evapotranspiration has been determined in the Middle Lithuania zone by the method of statistical regression analysis based on degree, trend and reliability of the dependency results. Dominance of direct linear relation has been established between strawberry evapotranspiration and the reference evapotranspiration. According to the correlation coefficient this relation changes from medium strong (r 0.50.7) to strong. As reference evapotranspiration evaluates climatic conditions, the specific characteristics of strawberry have been estimated by biological coefficient. Biological coefficients (Table 1) for Dirses dependency have been adjusted with respect to beginning of vegetation, sum of active temperatures (> 5 ° C) and stages of strawberry development. Table 1 . Strawberry biological coefficients for application of Dirse (LT) equation Sum of active (>5 ° C) temperatures (100 o C) 9,5 12 - 13 - 15 - 16 - 17 - 18 - > < 2 2-3 3-4 4-5 5-6 6 -7 97, -5 -12 13 15 16 17 18 19 19 0.55 0.6 0.75 0.90 1.0 1.05 1.0 0.9 0.95 1.0 0.9 0.8 0.7 0.6 0.5 At the beginning of vegetation the amount of evapotranspiration is determined by soil evaporation. When the sum of active temperatures reaches average value of 300 ° C strawberry begin blooming. The first berries ripen at average value of 500 ° C. The last berries are picked when sum of active temperatures is close to 800 ° C.Curve of biological coefficients for calculations according to PenmanMonteith dependency is based on stages of development and their duration from vegetation renewal. In 20012004 the period from vegetation renewal till inflorescence formation lasted for 2535 days. Average period of blooming lasted for 20 days and additional 10 days passed until formation of the first berries. Ripening lasted from 20 (in 2002) till 30 days. Biological coefficients should be chosen considering these development phases and their duration; the values are presented in Table 2. Table 2. Strawberry biological coefficients for application of Penman-Monteith method Number of decade from emergency 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 0.5 0.6 0.7 0.75 0.85 0.9 0.9 0.9 0.95 1 1.15 1.15 1.05 1 0.9 0.8 The part Influence of Meteorological Conditions on Strawberry Water Consumption determines dependence relations between strawberry evapotranspiration and meteorological conditions on the basis of experimental investigation data of many years. Air temperature, air humidity deficit, temperature at soil surface and at different soil layers, relative humidity and number of sunny hours have been analyzed. Having excluded the period of the strongest development of strawberry leaves (at the beginning of vegetation) the investigations of 2001-2004 have determined that the sum of air moisture deficits
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