Search

The experiment was conducted in a polyethylene greenhouse at the experimental farm of Tuscia University, central Italy. The aim of this study was to determine yield, water requirement and water use efficiency (WUE) of a zucchini squash (Cucurbita pepo L. cv ‘Afrodite’) in relation to the method of culture: soil versus closed soilless systems using three growing media (cocofiber, perlite and pumice). The increment rate was higher in soilless in comparison with soil. During the growing cycle, the water use in soil (256 L m) was higher compared with the water requirements of plants grown respectively in cocofiber (221 L m), perlite (200 L m) and pumice (185 L m). Marketable fresh fruit weight per unit of transpired water was more pronounced in closed soilless in comparison to the soil culture as indicated by the slope values of the regression equations: pumice (32.6 g L), perilte (28.3 g L), cocofiber (25.5 g L) and soil (21.2 g L). The yield water use efficiency calculated on fresh weight basis ranged from 4.3 to 28.5 g kg for pumice, 13.0 to 26.4 g kg for cocofiber, 3.9 to 23.4 g kg for perlite and 1.0 to 13.1 g kg for soil culture. The results demonstrated that the growers may improve, yield, water requirement and water use efficiency by switching from soil to closed soilless culture. INTRODUCTION Water is fast becoming an economically scarce resource in many areas of the world especially in arid and semi-arid regions (Gregory, 1984), such as the Mediterranean. Nonetheless, a large amount of water is consumed in the process of plant biomass production, and water is one of the main components of the fresh biomass especially in horticulture (Baille, 2001). The term water use efficiency (WUE) is commonly used to quantify this fact. WUE can be defined in four different ways: (i) photosynthetic WUE as the ratio of leaf net assimilation (μmol CO2 ms) and leaf transpiration (μmol H2O ms); (ii) transpiration WUE as the ratio of cumulative harvested biomass (g) to cumulative transpiration (T) used by the crop; (iii) evapotranspiration WUE as the ratio of harvested biomass (g) to cumulative evapotranspiration (ET); (iv) effective WUE of the cropping system, which is the harvested biomass, divided by the total amount of water supplied to the crop (Steduto, 1996; Raviv and Blom, 2001). The agricultural and horticultural industries will be faced to the challenge of justifying and proving that they really need the amount water that they use. In other words, growers have to be prepared to use less water, implying that they have to improve the methods, techniques and management practices they presently apply in the processes related to agricultural production. Furthermore, they have to use water taking into account the more strict environmental regulations that are now prevailing in most of the developed countries. In this aspect, the development throughout the world of greenhouse soilless crops is very encouraging. The combination greenhouse hydroponics is a clear example of how horticulture could meet the objectives of a sustainable horticulture, with a more efficient use of inputs: water and fertilizers (Tognoni et al., 2001). The yield-related water use efficiency can be increased by three main ways: (i) by increasing the physiological and transpirational efficiencies, by manipulating the environment (greenhouse, soilless culture) in order to get a faster growth and development with the same amount of transpired water. (ii) Reduce the Proc. IS on Soilless Cult. and Hydroponics Ed: M. Urrestarazu Gavilan Acta Hort. 697 ISHS 2005 82 evaporation component of ET, by mulching, or by using artificial substrates in containers or bags, that reduced significantly the area of evaporating soil. (iii) Reduce the water loss due to drainage and run-off, by recycling part of totality of the nutrient solution (Baille, 2001). Starting from the above considerations, the aim of this study was to determine, the yield, the water requirement and water use efficiency of zucchini squash cultivar in relation to the method of culture: soil vs. soilless in plastic greenhouse conditions. MATERIALS AND METHODS The experiment was carried out in a polyethylene 400 m greenhouse situated at the experimental farm of Tuscia University, central Italy (latitude 42° 25' N, longitude 12° 08' E, altitude 310 m). Inside the greenhouse, ventilation was provided automatically when the air temperature exceeded 25°C. A randomized complete block design with four replicates (ten plants per replicates) was used to compare four substrates: perlite (Perlite Italiana), pumice (Europumice) and cocofiber (Cocco Ter), and soil (control). The texture of the two expanded minerals (perlite and pumice) was respectively between 3-5 and 5-10 mm, while the organic substrate (cocofiber) had the following characteristics: pH 5.4-6.0; CE 216 meq 100g; organic carbon 48%; organic N 2.5%. Physicals and chemicals characteristics of soil were: sand-loam-clay (43-25-32%), CEC 25 meq 100 g, 1 g kgtotal N, 9 mg kg P (Olsen method), and ammonium acetate extractable nutrients as follow: 2.8 g kg Ca, 0.35 g kg Mg, 1.1 g kg K, 225 mg kg Na, 20 mg kg Fe, 43 mg kg 1 Mn, 1.3 mg kg Cu, 0.9 mg kg Zn. Soilless plants were placed in single plastic channel benches (section 26×12 cm; length 5m with a slope of 1.5%). Benches were recovered with a polyethylene film to avoid evaporation. Plastic mulching was also adopted in soil culture to eliminate the loose of water by evaporation. Seeds of “Afrodite” hybrid (Syngenta) were germinated in vermiculite on 10 March 2001, the plants remained in the seed pots until the two true leaf stage. The seedlings were transplanted 13 days after planting (23 March) into cocofiber, pumice, perlite, and soil at a plant density of 2.1 plants m. Harvesting started on 3 May and fruits were subsequently picked every 2 days until the final harvest (6 June). Plants grown in soilless and soil culture were fertilized with the following nutrient solution (mg L): N-NO3 (160), S (26), P (13), Cl (57), K (150), Ca (122), Mg (59), Na (50), Fe (3), Mn (0.8), Cu (0.07), Zn (0.1), B(0.3), Mo (0.05). The EC values were kept within the range of 1.8 to 2.0 dS m, while the pH of the solution was maintained between 5.8 and 6.3 by adding an acid mixture with the same anionic proportions as the nutrient solution. In soilless systems, nutrient solution was pumped from independent tanks (one tank per experimental unit) through a drip irrigation system with one emitter per plant and an emitter flow rate of 2L·h. The excess of the nutritive solution was recycled for the entire growing cycle. In both soilless and soil systems, irrigation scheduling was performed using electronic low-tension tensiometers (LT-Irrometer). Tensiometers were connected to an electronic programmer that controlled the beginning of irrigation (-5 kPa and -30 kPa in soilless and soil treatments respectively), the end of irrigation (-1 kPa), which correspond to high and low tension set points for the major part of media (Kiehl et al., 1992). During the growing cycle, the water requirement of the crop was monitored daily on soilless and soil systems by a flowmeter. Fresh weight of marketable fruits, fruit number, was recorded 3 times per week on four plants per plot during the fruiting period (40 days after transplanting). Fruits were harvested when they reached marketable quality (over 12 cm); fruit that was less than 12 cm was considered unmarketable. The effective water use efficiency (WUE, g kg) was calculated as the marketable fresh weight fruit yield (g m) divided by the total of water supplied to the crop (kg m) (Raviv and Blom, 2001). Linear and non-linear regression analysis was performed using the GraphPad Prism package (1999). Differences between the slopes of linear regressions were examined by testing the homogeneity of regression coefficients (Gomez and Gomez, 1983). RESULTS AND DISCUSSION Fruit Yield The duration of the cultural cycle was 73 days. With regard to marketable fruit fresh weight, the regression analysis gave a strong linear relationship between the marketable fresh

This study describes an application of Systematic Variation method (SV) for optimizing cation proportions (K, Ca, Mg, Na) and the total element concentration of hydroponically-grown tomatoes. A randomized complete-block design with 5 replications (3 plants per experimental unit) was used to compare a factorial combination of 4 proportions of K:Ca:Mg:Na and 2 total concentrations of elements (30 and 60 meq L-1). Each of the cation proportion treatment was defined by a high proportion of one cation (V=0.64) and an equally low proportion of the others (v=0.12) for a total amount of one (V + 3v = 1). The highest total and marketable yield were obtained in treatment with high proportion of K (avg. 2.94 and 2.72 kg plant-1, respectively) and Ca (avg. 2.84 and 2.65 kg plant-1, respectively), while treatments with high proportion of Mg (avg. 2.59 and 2.22 kg plant-1, respectively) and Na (avg. 2.21 and 2.09 kg plant-1, respectively) gave the lowest values. The highest incidence of blossomend rot was observed in treatments with high proportion of Mg and K (avg. 10.8 % and 3.7 % of total yield, respectively). Fruit quality (soluble solids, titratable acidity, EC) improved by increasing the proportion of K and Na and the total concentration. The SV method showed that for maximise the marketable yield it is necessary to include a large amount of K and Ca in the nutrient solution.