水灌溉指标的研究开展较少或没有进行,例如灌溉上限、灌溉次数等指标的研究尚属空白。节水灌溉所选择的蔬菜作物以番茄、黄瓜、茄子、辣椒等为主,而普遍栽培的蔬菜达60余种,关于大部分蔬菜作物节水灌溉指标的研究几乎没有进行。由于缺乏科学的理论指标,生产实际中仍然以“看天、看地、看庄稼”为灌溉管理手段。目前，我国蔬菜种植业已经作为一个农业中的领先行业由传统农业过渡到现代农业,迅速开展蔬菜等节水灌溉指标的研究显的更为紧迫和必要[7]。
参考文献
[1]赵英，郭旭新.节水灌溉新技术在温室生产中的应用与发展[J].农业工程技术(温室园艺) . 2007.(11)
[2]曾文艳.蔬菜节水灌溉技术[J].热带农业工程.2009.(06):44-45
[3] 汤丽玲等.不同灌溉与施氮措施对露地菜田土壤无机氮残留的影响[J]. 植物营养与肥料学报2002,8(3):282-287. [4] 马雪娇.水氮耦合对蔬菜-土壤系统中硝酸盐积累规律的影响[D].保定:河北农业大学,2003
[5] 于红梅等.不同水氮管理对蔬菜地硝态氮淋洗的影响[J].中国农业科学,2005,38(9):1849-1855. [6] 曾文艳.蔬菜节水灌溉技术[J].热带农业工程.2009.(06):44-45
[7]李建明，邹志荣，王晓燕.蔬菜节水灌溉指标的研究现状及存在问题[J].干旱地区农业研究,2000,18(2):118-123
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IRRIGATION
REQUIREMENTS OF VEGETABLES IN CRETE
GREENHOUSE
K. CHARTZBULAMIS and N. DROSOS NAGWEF,
Subtropical Plants and Olive Tree Instit.,73100 Chania, Crete, Greece Horticultural Research Station,
72200 Ierapetra, Crete, Greece
Abstract: Studies, over a number of years, were carried out in Crete ,Greece to determine the water consumptive uses of drip-irrigated vegetables (tomato, cucumber , eggplant and pepper) grown in unheated greenhouses. The amount of water applied and the irrigation frequency were controlled by tensiometers , so that soil water potential at a depth of 25 cm was maintained at values higher than -20 KPa . Maximum yields for an eight-month growing season (October to May) were obtained with seasonal water application of 260 mm for tomato,296 for pepper and 325 mm for eggplant .Cucumber was the most water-consuming crop, requiring 290mm of water application for 3.5 months growing season. The number of fruits per plant was mainly reduced with less water application. The crop maximum evapotranspiration (ETm) in October (at planting) was 0.2 of class A pan evaporation(Epan), located outside the greenhouse. This value remained almost constant until February, since crop growth and production are low due to low temperatures, and then increased gradually up to 1. 1xEpan, depending on the crop.
INTRODUCTION
Vegetable crops grown in greenhouses for out of season production are spreading in Greece, like in many areas of the world, since they ensure a relatively higher income to the farmers. On the island of Crete, where climatic conditions are favourable and heating is not usually required, about 46% of the total cultivated area in Greece is found. The main crops are cucumber (45%) and tomato (44%), while far behind are eggplants (5%) and pepper (3.8%). Water scarcity in many of the growing areas in the island, besides the increasing competition for municipal use, makes it necessary to optimise its use by the farmers.
The supply of the required water to the plant is of prime importance for its growth and economic production, especially into greenhouse, where irrigation is the unique source of water for the plant. Drip irrigation -which ensures efficient water use, improved fertiliser application, salinity control and labour saving-, is mainly used by our farmers but irrigation intervals and water volumes are usually set according to empirical criteria. Although a lot of papers deals with water requirements of greenhouse grown vegetables, the results are not applicable to our region, since they are referred to different climatic conditions (Sonneveld,1981;Frenz and Lechl, 198 1; Catzeflis,1 Sm), different growing season (Chiaranda and Zebri,1984, 1986; Hamar and Warms, 1986) or to heated greenhouse (Hiades,1988,1992).The objectives of these studies, carried out over 10 years, were to determine the water requirements of the main vegetable crops (tomato, cucumber, eggplant and pepper), and to relate them with class ‘A’ pan evaporation and solar radiation.
MATERIALS AND METHODS
The experiments were carried on in unheated greenhouses for two cropping seasons for each crop, at the experimental farm of Subtropical Plants & Olive Tree Institute of Chania , north-west of Crete, (for tomato and cucumber) and at Horticultural Research Station of Ierapetra, south-east of Crete (for eggplant and pepper). The following hybrids, widely used by our farmers, were used:‘Dombito’ for tomato, ‘Pepinex’ for cucumber, ‘Delica’ for eggplant and ‘Sonar’ for pepper. Information on plant population, planting dates and harvesting periods .are given in Table1.
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The top 40
cm soil layer of the greenhouse was amended, containing 60-68% sand 16-22% silt and 12-16% clay. Irrigation water was of good quality with electrical conductivity (ECw) of 0.3-0.6 dS.mˉ1. Cultivation cares (fertilisation, soil fumigation, and pruning, pest and disease control) were exactly the same for all treatments.
Plants were drip irrigated. For tomato and cucumber, the amount of water per irrigation and the frequency of water application were controlled by tensiometers installed at the depth of l5 and 30 cm. Irrigation was started when the soil water potential reached -20 KPa (treatment A), -40 KPa (treatment B) and -70 KPa (treatment C) at the depth of 15 cm, and was stopped when applied water reached at the depth of 30 cm. For eggplant and pepper the amounts of water tested were based on maximum evapotranspiration data obtained by the use of a tensiometer. It was assumed that maximum evapotranspiration (ETm) between two successive irrigations was calculated by the formula ETm= Iw -Dw, where Iw was the amount of irrigation water needed to keep the soil at field capacity (soil water potential higher than -20 KPa); and Dw was the amount of water drained at the soil depth of 45 cm. So , an electro-tensiometer was installed at the depth of 25 cm in order to pilot irrigation. Irrigation was started when soil water potential (SWP) reached at -20 KPa and stopped soon as applied water was reaching at the depth of 25 cm. Drainage at the depth of 45 cm, after a large amount of soil-water content measurements, was considered as negligible. Thus, maximum evapotranspiration was equal with the amount of irrigation water applied to keep SWP higher than -20 KPa, since drainage was zero at the soil depth of 45 cm. Four amounts of water were tested: 100% of ETm (treatment A), 85% of ETm (treatment B), 65% of ETm (treatment C) and 40% of ETm (treatment D). The frequency of irrigation ,determined also by electro- tensiometer , was the same for all treatments, but the corresponded water for B, C and D treatments was applied to plants the next day. Irrigation treatments began after plant establishment (fifteen days after transplanting). The experimental layout was complete randomised block design with four or six replications.
Evaporation from a Class A pan evaporimeter and the actual sunshine duration from a Campbel- Stokes sunshine recorder, located outside the greenhouse, 100 m far away, were recorded daily. The potential evapo-transpiration of the crop (ETP) was estimated using the formula:
where C1 is the penetration percentage in solar radiation for PE (0.8), Ra is the extra terrestrial radiation in mm, n is the mean actual sunshine duration in hr/day, N is the maximum possible sunshine duration in hy/day and a, b are constants (0.30 and 0.45 respectively). The mature fruits were harvested once or twice a week, and their number and weight were recorded.
RESULTS AND DISCUSSION
Crop yield response to different amounts of water applied is given in Fig. 1. For tomato, the highest yield(6.3 kg /plant) was achieved with a seasonal water application of 260 mm,while any further increase in water application did not increase yield. With less amount of applied water, fruit yield was reduced significantly, because fruits were smaller (Table 3).
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The same pattern was followed by cucumber, although water requirements were much higher than tomato, for a 3.5 months cropping season. The highest yields were obtained with 290m of water (Chartzoulakis and Michelakis, 1990), while application of 220 mm reduced yield significantly because of the formation of fewer fruits (Table 2). Eliades (1988)also reported less fruit formation with less water application for the cucumber, CV Maram , grown in a heated greenhouse.
For eggplant the highest yield(6.5 Kg/plant) was obtained with the treatments A and B, corresponding to seasonal water application of 380 and 325 mm respectively .Seasonal water application of 250 and 150 mm reduced the yield significantly in both growing seasons (Chartzoulakis and Drosos,1995). Although the fruit yield of A and B treatments was almost the same. The water use efficiency for harvested yield (kg of produced fruits per unit of applied water) of treatment B was higher (31.1 instead of 27.2 kg.mm-1); such a difference is significant for water sort area such as Crete. Eliades (1992) reported that the eggplant could grow successfully in a heated greenhouse for a 7-month period with as low as 285 mm of water.
For sweet pepper, the highest yield(4.4 Kg/plant) was obtained with300 mm of water, while less water application reduced the yield significantly. The effect of irrigation water applied on the number of marketable fruits harvested per plant is shown in Table 2. For cucumber, eggplant and pepper, less water application reduced significantly the number of fruits harvested per plant, while for tomato no reduction was observed.
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The water requirements of tomato, eggplant and pepper, when the soil water potential was kept higher than -20 ma, ranged between O.§ and 4.5 mm per day (Figure 2). Two periods can be distinguished from Figure 2 for the crop demand for irrigation water; a period characterized with low water requirements (October to February) because rates of plant growth and production are low due to low air temperatures (10 'C)inside the greenhouse. The second period from March to May is characterised by a fast increase of water requirements, due to the increase in the evaporative demand of the atmosphere and the faster rates of plant growth and production achieved under the optimum climatic conditions prevailing at that period. For cucumber, daily water requirements increased from March (at planting) up to June, while at fall cropping season,water requirements reached at a maximum (4.3 mm/day) at September, and then start to decline.
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