Keywords: growing media, N fertilization, containerized cell-trays, post-harvest, Leafy Vegetable Production, LVP, ready-to-eat products

Transcription

1 Rocket (Eruca sativa Mill.) and Corn Salad (Valerianella olitoria L.): Production and Shelf-life of Two Leafy Vegetables Grown in a Soilless Culture System S. Nicola, J. Hoeberechts and E. Fontana Dipartimento di Agronomia Selvicoltura e Gestione del Territorio Università di Torino Via Leonardo da Vinci 44 I Grugliasco (TO) Italy silvana.nicola@unito.it Keywords: growing media, N fertilization, containerized cell-trays, post-harvest, Leafy Vegetable Production, LVP, ready-to-eat products Abstract Fresh-cut products are fresh vegetables and fruits, previously washed and cut, packaged and sealed in bags or containers, and marketed as ready-to-eat or ready-tocook products. Consequently, the products present a high added-value and, therefore, are highly appreciated by the consumers. Recently, Italy is experiencing a booming interest in high quality and tasty ready-to-eat vegetables. Therefore, studies on postharvest shelf-life and quality of typical Italian salads are necessary. Using soilless culture system (SCS) avoids soil contamination of the leaves, facilitating the production of clean material at harvest, and consequently the reduction of many washing treatments. Plants of rocket (Eruca sativa Mill.) and corn salad (Valerianella olitoria L.) were grown for Leafy Vegetable Production (LVP) in different containerized celltrays (40 or 160 cells), using different growing media (rockwool or peat and perlite), and different nitrogen concentrations in the nutrient solution (30 and 120 mmol L -1 N). At sampling, leaves were cut and weighed, assigned a Quality Index (QI: 100%, 75%, 50%, 25% and 0%), according to marketable values, packaged in commercial plastic boxes, and stored in a cool chamber at 4 C for the post-harvest shelf-life phase. Evaluation of post-harvest quality was assessed by variations of fresh and dry weight over time (0, 2, 4 and 6 days after storage) and values of QI (at 0, 2, 4 and 6 days of storage). Fresh mass and QI decreased over time for both species, as expected. However, the values decreased less in plants that were grown in 40-cell trays filled with peat and perlite and fertilized with 30 mmol L -1 of N than in plants that were grown under the other experimented conditions. The QI indicated that rocket and corn salad can be grown with the tested SCS system to obtain high quality ready-to-eat salads. INTRODUCTION Rocket (Eruca sativa Mill.) is an herbaceous species spontaneous in the entire Mediterranean basin and in Asia, already cultivated by ancient Romans. Its cultivation area has expanded in the last years in many Mediterranean countries because of the growing interest of consumers (Pimpini and Enzo, 1997). In Italy, thanks to the geographical position and to the latitude, rocket is present in many Regions all year long. In Veneto, Campania, Lazio, Puglia, Lombardia, Abruzzo, Sardegna and Piemonte, where rocket production plays an important role, surfaces cultivated are expanding both as open field and protected cultivation. Corn salad (Valerianella olitoria L.) is an herbaceous species spontaneous in the entire Mediterranean basin, largely diffused in Europe and America where it is appreciated for its good taste and dietary characteristics. It is either an annual or a biennial plant according to sowing period, and could be cultivated during the whole year with repeated sowings. In Italy, protected cultivation surface is 52 ha: the greatest Proc. XXVI IHC Protected Cultivation 2002 Ed. A.P. Papadopoulos Acta Hort. 633, ISHS 2004 Publication supported by Can. Int. Dev. Agency (CIDA) 509

2 production is obtained in Lombardia (30 ha), then in Piemonte (10 ha) and in Liguria (9 ha) (Tesi, 1990). In the last years, research has been conducted on rocket and corn salad cultivation in open field conditions. However, cultivation with soilless culture systems (SCS) of these two leafy vegetables is expanding more and more: in fact, SCS represents a valid alternative to traditional cultivation techniques because of the qualitative characteristics of the final product. Leafy vegetables can be commercialized fresh, previously-washed and cut, packaged and sealed in bags or containers, and marketed as ready-to-eat or ready-to-cook products, becoming products with a high added-value. Studies on postharvest shelf-life and quality of typical Italian salads are necessary to obtain fresh leaves, proper to ready-to-eat market. For this reason, it is necessary to optimize every production phase. SCS could represent the solution, because the full control of the inputs that they give might contribute to high production standardization quality of the vegetable. Besides, using mineral and sterile media, with low environmental impact, may be an alternative to the soil fumigation practice, which takes usually place during traditional vegetable crop production in open field. In addition, the short growing cycle of the greenhouse-grown vegetables reduces chances of parasite attacks and disease spread throughout the crop. The SCS avoids soil parts to reach the leaves, allowing the production of clean material at harvest, and consequently the reduction of many washing treatments. The general objective of the work was to set up a SCS to grow young leafy vegetables (leafy vegetable production, LVP), such as rocket and corn salad for fresh-cut products of high quality and long shelf-life. Above all, the general goal was to compare different growing practices and management in order to achieve the production of high quality ready-to-eat salads, in terms of hygiene, commercial standards and shelf-life. MATERIALS AND METHODS The experiments were conducted in 1999 at the Experimental Center of the University of Turin, in Carmagnola (TO), in a glasshouse provided with environmental control for temperature and light. Maximum and minimum temperatures were registered by a hygrothermograph, and were 35 C and 5 C respectively. Plants grew in styrofoam containerized cell-trays applying the ebb-and-flow irrigation system (Thomas, 1993) (Fig. 1). The bench was equipped with galvanized sheet iron tanks (1350 x 605 x 200 mm), in which trays could be sub-irrigated and then suspended on metal wires, so that water could drip. At each ebb-and-flow irrigation, water was raised to the level of the trays, maintained for about 1-2 hours according to plant needs and then freed by opening the tank taps. Two growing media were tested: 1) 100% hydrophilic rockwool (Grodan ), and 2) a mix of peat ( Rekiva, 90% organic matter on D.M., 52% organic C of biological origin and 0.2% organic N) and perlite ( Peralit 25, expanded perlite with great granulometry), in the ratio 3:1 (v/v). Peat was amended with lime (1% in weight) to correct the ph. Two cell-tray sizes were used: 1) 40 cell-trays (cell shaped as upset frustum of cone: cell apical and basal diameters: 55 mm and 40 mm) and 2) 160 cell-trays (cell apical and basal diameters: 27 and 10 mm). In 40-cell trays and in 160-cell trays 8 and 2 seeds were respectively sown in order to obtain an equal plant density per m 2. Two N levels were supplied in the nutrient solution (Table 1): 1) 30 mmol L -1 N 2) 120 mmol L -1 N. The total number of treatments was 2 (media) x 2 (trays) x 2 (N levels) = 8. The statistical design was a split-plot design with 4 randomized blocks, with N as main-plot factor and media x cell-tray as sub-plot factor. Sowings took place on 3 June (corn salad) and on 7 June (rocket), using 510

3 respectively RS (Royal Sluis) and an unselected line of rocket. Trays were incubated in a growth chamber at 19 C for 48 hours and at 23 C for 96 hours, respectively for rocket and corn salad, then transferred into the greenhouse and arranged on the bench according to the statistical design. During the experiments, plants were fertilized weekly for a total of 4 fertilizations per experiment; fertilizations ended 10 days before harvesting. At every fertilization, 40 L of nutrient solution were poured in each tank. At 2 nd and 4 th fertilization, 3 g L -1 of Micral (microelements) were added to the nutrient solution. Rocket was harvested on 21 July, cutting leaves at 20 mm above the substrate; corn salad was harvested on 23 July, cutting manually the hypocotyls. At harvest, plant quality of each tray was visually evaluated by an index (Quality Index), ranking 100, 75, 50, 25 and 0%, according to the product marketable level; biometrical measurements on leaves were done. Samples from each tray were prepared: 12 plants were weighed and leaf area was measured with Delta T Area meter MK2, then samples were oven dried at 70 C for 2 days. Leaf dry weight was measured with a scale, and dry matter was determined. The remaining plants were divided in 4 samples, then weighed, packaged in plastic boxes, closed with film for food and put in refrigerator at 4 C to study product post-harvest shelf-life. Every 2 days after harvesting, refrigerated samples were weighed, visually evaluated by the Quality Index, and then put again in the refrigerator, except one sample that was oven dried at 70 C for 2 days. Analysis of variance was performed on collected data. Quality Index was statistically assessed by D of Somers non parametric tests. RESULTS The soilless culture system with ebb-and-flow irrigation resulted to be an efficient cultivation system to grow high quality, homogeneous, clean and marketable rocket and corn salad plants. Rocket. Treatments affected the biometrical parameters of rocket salad. Interactions among the factors were not statistically significant, while the main factors affected plant growth (Table 2). Leaf area was affected by media and trays, dry matter by media and N, fresh weight by media and trays. The greatest leaf area was reached by plants grown in peat and perlite media mix ( cm 2, 12-plant samples), regardless of the other factors, as well as the greatest fresh weight (21.86 g, 12-plant samples) (Table 3). Plants produced more leaf area and fresh weight when growing in peat and perlite media mix than in rockwool, and more when growing in 40-cell trays than in 160-cell trays. Dry matter accumulation was less in leaves of plants growing in peat and perlite media mix than in those growing in rockwool, and less in plants fertilized with 30 mmol L -1 than in those fertilized with 120 mmol L -1. Rockwool media gave in general the worst results on rocket production. During shelf-life phase fresh weight decreased over time, while dry matter increased (Table 4), indicating a normal and progressive loss of leaf turgor. The average quality index during post-harvest is outlined in Table 5. Given the contingency table, with the frequency of each quality category within each post-harvest date, the D of Somers test revealed that the QI significantly decreased over time. After six days of storage the QI was about 16%. Corn salad. Leaf area and fresh weight were statistically influenced by the different treatments, in particular by the interaction media x trays x N. Dry matter was not affected by treatments. Results of the analysis of variance are presented in Table 6. The largest leaf area was obtained by plants grown in 40-cell trays, with peat and perlite mix, and with 120 mmol L -1 N (Table 7). Rockwool medium in general did not enhance leaf area production, while peat and perlite media mix was in general favorable, confirming the positive effect of this medium also in corn salad growth. Using 40-cell trays increased leaf area if the medium was a mix of peat and perlite, especially when 120 mmol L -1 N were supplied. The greatest fresh mass was obtained using 40-cell trays, again if the plants were growing in peat and perlite mix, and with 120 mmol L -1 (18.81 g per 12-plant sample). The use of 160-cell trays was not, in general, convenient, besides some positive 511

4 effect on leaf area and fresh mass production, when plants grew in peat and perlite and were fertilized with 30 mmol L -1. The same growing conditions influenced both leaf area and fresh weight, pointing out a direct relation between leaf area and weight, without affecting the final dry matter. During post-harvest shelf-life, fresh weight decreased over time (Table 8), indicating a normal and progressive leaf loss of turgor. Corn salad contained less dry matter than rocket at harvest (see Table 4), but the dry matter increased over time, reaching 6 days after storage similar values as in rocket (ca 15%). Quality indices during the post-harvest period are given in Table 9. Given the contingency table, with the frequency of each quality category within each post-harvest date, the D of Somers test revealed that the QI significantly decreased over time, as it happened for rocket. However, QI of corn salad was much higher at harvest (ca 96%) than rocket (ca 61%, Table 5), and it was still around 47% after 4 days of storage, while in rocket decreased more dramatically. This would suggest that in the case of corn salad there was a better plant material at harvest, which conditioned the post-harvest quality. DISCUSSION AND CONCLUSIONS First results from these experiments indicated the possibilities of obtaining good quality fresh production of rocket and corn salad in a soilless culture system. The 40-cell trays in a mix of peat and perlite gave the overall best results, while rockwool gave bad results in terms of plant quality. To obtain a great fresh mass in terms of both leaf area and fresh weight N concentrations could be around 30 mmol L -1. In general, the maximum shelf-life of fresh-cut vegetables is 5-7 days from packaging; the present research indicated that a 4-day shelf-life period is recommended. Further investigations will be conducted to determine nitrate content in leafy vegetables, to introduce cultural techniques that permit a low N supply. Among the factors that influenced LVP is the media mix composition. The choice of the media is very important for plant growth: mixing different types of components (i.e. peat, vermiculite, perlite, rockwool), enriched with fertilizer, determines the physical and chemical properties of the substrate, thus affecting root growth and the whole plant growth, causing different mass partitioning (Nicola, 1998; Nicola and Cantliffe, 1996a). Cell-tray size has a great influence on leaf production (Nicola and Cantliffe, 1996c). Greater availability of medium for root system development causes leaf higher quality at the end of the cultural cycle, apart from the fact that more plants had been sown in the same cell (Lynch, 1995). In the same conditions of planting density, that means competition for light and other inputs (i.e. water and mineral elements), it could be supposed that roots in any case take advantage of bigger medium volume to explore. In conclusion, results of these first experiments permitted us to verify the effects of non-traditional irrigation systems (ebb-and-flow) on leafy vegetable production. Besides, a cultural system with a low environmental impact and suitable to use in farms has been improved. Cultural systems adopting sub-irrigation had given excellent results as regards qualitative plant growth in many researches; they respect the environment because water and fertilizer use is limited if compared to traditional overhead irrigation systems (Nicola and Cantliffe, 1996b). In addition, the introduction of these irrigation systems in soilless culture permits the use of closed-systems with no environmental impact, in comparison with open-systems, the ones in use in Italy but with higher environmental impact (Gysi and von Allmen, 1997). At the Experimental Center of the University of Turin series of experiments have been carried out with the general objective of studying soilless culture systems to grow leafy vegetables. The short growing cycle of the greenhouse-grown vegetables did not allow parasite attacks and disease spread throughout the crop; at harvest, plants were already clean because sub-irrigated, ready to packaging or requiring a minimum washing. 512

5 ACKNOWLEDGEMENTS Research financed by Regione Piemonte, Project L impiego del sistema di crescita fuori suolo in colture protette ad alto valore aggiunto, Thanks to professor Marco Acutis, University of Milan, for statistical assistance. The authors have equally contributed to the research and to the manuscript. Literature Cited Caponigro, V. and Piro, F Requisiti della materia prima per la IV gamma. L Informatore agrario 19: Gysi, C. and von Allmen, F Lamb s lettuce in different growing media in closed recirculating soilless culture. Acta Hort. 450: Lynch, J Root architecture and plant productivity. Plant Physiol. 109:7-13. Nicola, S Transplant Production and Performance: Understanding Root Systems to improve Seedling quality. Hort. Technol. 8(4): Nicola, S. and Cantliffe, D.J. 1996a. Fertilizer content of the medium enhances lettuce transplant growth. Proc. FSHS Annual Meeting, 3-5 November, 1996, Orlando, Florida, USA. p.61. Nicola, S. and Cantliffe, D.J. 1996b. Irrigation methods and photoperiod are essential for optimum lettuce transplant growth during winter in Florida. Citrus and Vegetable Magazine October: Nicola, S. and Cantliffe, D.J. 1996c. Increasing cell size and reducing medium compression enhance lettuce transplant quality and field production. Hort. Sci. 31: Pimpini, F. and Enzo, M La coltura della rucola negli ambienti veneti. Colture protette 4: Tesi, R Valerianella (Valerianella locusta Laterr.). p.927. In: V.V. Bianco and F. Pimpini (eds.), Orticoltura, Patron Editore, Bologna. Thomas, B Overview of the Speedling, Incorporated, Transplant Industry Operation. Hort. Technol. 3(4): Tables Table 1. Nutrient solution composition. 30 mm/l N treatment g L mm/l N treatment g L -1 NH 4 NO NH 4 NO KNO KNO MgSO 4.7H 2 O MgSO 4.7H 2 O KH 2 PO KH 2 PO MICRAL MICRAL

6 Table 2. Analysis of variance of rocket with the P values presented. Source of variation Leaf area Dry matter Fresh weight Media <0.001 <0.001 <0.001 Trays N media N trays Media trays N media trays error 1 N Table 3. Leaf area, fresh weight and dry matter of rocket at harvest (significant main effects). Leaf area (cm 2 ) Fresh Weight (g) Dry matter (%) Media Peat + Perlite Media Peat + Perlite Rockwool Rockwool Significance (P) <0.001 <0.001 Significance (P) <0.001 Trays N (cell number) (mmol -1 ) Significance (P) Significance (P) Table 4. Effects of post-harvest on fresh weight and dry matter of rocket. Post-harvest (days) Fresh weight (g) Dry matter (%) Significance (P) <

7 Table 5. Effects of post-harvest on Quality Index of rocket (SD = standard deviation). Post-harvest (days) QI SD Total D of Somers test: Significance (P) <0.001 Table 6. Analysis of variance of corn salad with the P values presented. Source of variation Leaf area Fresh weight Dry matter Media <0.001 < Trays <0.001 < N media N trays Media trays < N media trays <0.001 < error 1 N Table 7. Leaf area and fresh weight of corn salad with Standard Deviation (SD) at harvest (significant interaction N x Media x Trays, P < 0.001). N (mm L -1 ) Media Trays Leaf area SD Fresh weight SD (cell number) (cm 2 ) Leaf area (g) Fresh weight Peat Perlite Rockwool Peat Perlite Rockwool Table 8. Effects of post-harvest on fresh weight and dry matter of corn salad. Post-harvest (days) Fresh weight (g) Dry matter (%) Significance (P) <0.001 <

8 Table 9. Effects of post-harvest on Quality Index of corn salad (SD = standard deviation). Post-harvest (days) QI SD Total D of Somers test: Significance (P) <0.001 Figurese CULTIVATION HARVESTING View of the bench with the growing plants Trays with rocket ready to harvesting View of the benches after harvesting: the irrigation tanks and the different trays and media are visible CONSERVATION Rocket salad in plastic boxes ready for cool chamber Fig. 1. Overview of plant growth and post-harvest setting. 516