Zucchini squash production in conven tional and organic cultivation systems

Organic production must be carried out following EU regulations and protocols. On the contrary, conventional cultivation instead can be carried out using the best agronomic approaches available and using the latest innovative resources. Organic cultivation is more widespread in permanent crops (olive and grape crops) than vegetable ones, and even less in protected cultivation systems, due to the high intensity production processes which render the appli­ cation of organic growing protocols more complex. The comparison between the two systems of cultivation, organic and conventional, is difficult because the two cultivation methods are often carried out in different farms and hence in different environmental conditions. Cultivation using the two methods was conducted in a greenhouse from November to March 2017/2018. Results demonstrated that the total fruit yield zucchini squash in organic cultivation was not significantly different to the conventional one (43.2 Mg ha­1 and 46.4 Mg ha­1, respectively). The agronomic inputs (fertilizers, fungicides, and insecti­ cides) were higher in the organic cultivation system than conventional one. The water use efficiency was higher in the conventional cultivation system (150.6 kg m­3 ha­1) compared to the organic one (147.6 kg m­3 ha­1). No statistically signifi­ cant differences were found for the fruit number per plant and for the mar­ ketable fruit at the end of the growing period. Significant differences for the harvest period were only detected for fresh weight, shape index, firmness, and titratable acidity. In conclusion, this work demonstrated that the organic sys­ tem required higher inputs compared to the conventional cultivation. The extensive experience of the grower allowed for comparable yields between the two systems.


Introduction
Both the demand for organic vegetables and cultivation areas have been increasing following market demand. Environmental benefits claimed by organic producers clearly contributed to building a positive consumer attitude towards organic. The primary request for organic pro duce is the absence of pesticide residuals or the presence of any agro chemical that is not allowed in the EUdefined organic protocols in regula tion n. 834/2007 and 889/2008, and more recently, n. 848/2018. Organic farming has become the fastestgrowing agricultural sector, accompanied by a constantly increasing con sumer demand for organic produce. The organic agri culture accounts for approximately 37.3 billion € in the European Union (EU) and it is the secondlargest single organic market in the world. In 2018, the coun tries with the largest organic agricultural areas were Spain (2.2 million hectares), France and Italy (2.0 mil lion hectares each) (Willer et al., 2020).
In Europe, the area dedicated to organic farming has increased in recent years, reaching 15.6 million hectares (Willer et al., 2020). The distribution of organic farmland by location is 15% in Spain, 12% in Italy, 11% in France, and 8% in Germany (Brzezina et al., 2017).
The total area of organic vegetables represents only 0.6% of the total area devoted to vegetables worldwide. Europe, with 184,373 ha, represents 47.6% of the total area and ranks first worldwide, fol lowed at a distance by North America (73,238 ha). Italy with 60,732 hectares is at the second place worldwide after the United States (Willer et al., 2020).
Quality and safety of organic produce must be guaranteed at harvest and during postharvest. The restricted use of pesticides and fungicides, and the predominant use of organic matter for fertilization during cultivation may increase the microorganism contamination of the product. The organic rules are stringently applied to vegetable production because the growing cycles are short and the rapid turnover of crops requires frequent soil tillage, with a negative effect on the soil structure and organic matter con tent. Soil fertility can be maintained by frequent organic material supply and adequate crop rotation (Watson et al., 2002).
Organic agriculture is considered one of the best alternatives for sustainable and good quality food production (Aninowski et al., 2020). The comparison between organic and conventional cultivation sys tems is very difficult to perform because the agro nomic management and strategies cannot be the same. Organic vegetable production must follow EU regulations, which outline specific protocols to follow and the agronomic choices are limited. Therefore, organic production is sometimes difficult, especially in environments with high levels of biotic stresses such as pests and diseases (Raigon et al., 2010). Agronomists can use only organic certified products and exploit the positive interactions among crops for controlling pests and diseases and for plant nutrition.
The conventional vegetable cultivation system has a wide range of choices and the experience of the agronomist can play an important role in increasing the yield and quality of the products. Conventional cropping systems follow innovative technologies and yearbyyear, new hybrids or cultivars can be adopt ed as well as new fertilizers, plant growth regulators, pesticides, etc. (Odegard and Van der Voet, 2014).
In organic cropping systems, the nutrients must be provided by certified organic fertilizers or through appropriate crop rotations (ThorupKristensen et al., 2012). In long term organic vegetable cultivation, the nutrients are provided by manure or by catch crops and intercrops. However, organic farming is strictly regulated by rules and laws thus allowing a better comparison of its performances with conventional farming methods, with and without the use of agro chemical inputs and/or the adoption of specific grow ing practices (Gomiero et al., 2011).
Organic farms which specialize in vegetable pro duction have more difficulty compared to farms involved in livestock and mixed production. These difficulties are represented by the lack of manure produced in the farms and the supply of organic mat ter must be provided by green manure that repre sents a loss of a cultivation cycle.
In many studies (Raviv, 2010;Campanelli and Canali, 2012;Rahmann et al., 2017) the great majori ty of organic systems are refer to open field condi tions; only recently such alternative organic systems of production have been tested in protected condi tions (Tittarelli et al., 2017). In fact, organic green house production is still a small sector of the organic industry and constitutes only a small proportion of total greenhouse production (Gamliel and Van Bruggen, 2016).
The different studies that have compared organic and conventional production systems have provided inconsistent results with regard to the sensorial qual ity and nutritive value of fruits (Bourn and Prescott, 2002;Lester, 2006;Zhao et al., 2006) but organically grown foods have lower pesticide residues (Trewavas, 2004). This is not surprising because com paring the effect of organic and conventional farming systems on fruit quality is inherently difficult due to the wide range of factors that can potentially affect crop composition such as climate, soil conditions, cul tivar, soil type, planting date, harvesting time, and growing seasons (Goldman et al., 1999;Adam, 2001;Magkos et al., 2003). In other studies, however, where organic vegetables were compared to conven tional ones, a higher concentration of health promot ing components has been found (Brandt and Mølgaard, 2001;Rembialkowska, 2003Rembialkowska, , 2007. Rembiałkowska (2000) found a higher content of total sugars in organically produced vegetables (car rots, sugar beet, red beetroot, potatoes, spinach, savoy cabbage). Hallmann (2012) showed that organ ic tomatoes presented a higher ratio of reducing sug ars/organic acids, and contained significantly more total sugars, vitamin C and total flavonoids, 3 quercetin rutinoside, and myricetin in comparison with the conventionallygrown fruits.
The main difference between conventional and organic cultivation systems is that conventional agri cultural systems are continuously evolving due to the introduction of innovative techniques, while organic cultivation must follow fixed protocols that are revised at an interval of several years. In general, organic farming is represented by an articulated series of variables related to the biotic and abiotic factors affecting growth and the final product (Lester and Saftner, 2011). The physical, chemical and bio logical/nutritional attributes of soils, the irrigation management and water quality, the crops/genotypes and the growing cycles, the harvesting, handling and storage methodologies are the main variables which affect organic and conventional produce quality.
Zucchini squash and pumpkins within the three major species of Cucurbita are important crops worldwide. In the Mediterranean region, and in par ticular in Italy, zucchini squash (Cucurbita pepo L.) is an important commercial crop, both in the open field and in the greenhouse. Zucchini squash is generally cultivated in soil under greenhouse conditions for off season production, but in the last years soilless culti vation has been strongly developed because it improves the product quality and increases plant defenses against diseases (Van Os et al., 2002). For these reasons, greenhouse zucchini crops are usually cultivated during two growing seasons (Spring Summer and SummerAutumn seasons) to respond to the high demand for this fresh vegetable in nation al and international markets (Rouphael and Colla, 2005).
The aim of this work was to compare the produc tivity and inputs (fertilizers, insecticides, and fungi cides) of conventional and organic zucchini squash cultivation systems carried out in a greenhouse. Both farms were in the same geographical area allowing for a comparison under reduced environmental inter ferences so that differences could be attributed to the crop management systems.

Greenhouse conditions
Zucchini squash (Cucurbita pepo L.) 'Sibilla' was grown under conventional and organic procedures, commonly adopted in the Sicily Region for zucchini squash production. The experiment was conducted in 2017/2018 in two 240 m 2 unheated polyethylene tunnels located in Syracuse (36°59.1' N, 15°12.6' E, 30 m above the sea level), Sicily, Italy: one devoted to organic (20 years under organic regime) and other to conventional horticulture systems. Plants were grown under natural light conditions. The mean tem perature was 16.5 °C and the mean relative humidity levels were 75.5%. The total radiation levels ranged from 4.5 to 14.6 MJ m 2 . Zucchini squash seedlings were transplanted at the twoleaf stage on 2 nd November 2017 for both methods of cultivation, in rows 1.1 m apart, with an alongrow spacing of 0.8 m, giving a planting density of 0.88 plant m 2 . Preliminarily, bottom fertilization was performed with cattle manure at a dose of 1500 kg ha 1 in organ ic system and a total amount of phosphorus (P 2 O 5 as triple super phosphate), and potassium (K 2 O as potassium sulfate) and onethird of the nitrogen (as ammonium sulfate) were applied for the convention al cultivation system. Specifically, 120 kg ha 1 of N, 45 kg ha 1 of P 2 O 5 , and 265 kg ha 1 of K 2 O were added.
The following products were used during the preparation of the soil and cultivation of the plants:
Similar types of machinery were used in both cul tivation systems. The final stage of cultivation involved the harvesting of zucchini squash fruits, which was performed manually and so did not affect the relative environmental performance of conven tional and organic systems (Table 1).

Organic cultivation system
The zucchini squash cultivation was performed following the procedures described in EU n. 834/2007 and 889/2008.
In this system Siveg GR and 6: 6: 12 Orga Kem were applied at 35 cm depth in pretransplant, respectively at doses of 400 and 1500 kg ha 1 ; after the spreading, the products were appropriately topped up.
During cultivation, fertigation and foliar applica tion were performed starting from the fourteenth day and at two weekintervals.

Sampling procedure and measurements
The fruits were harvested every two days and those obtained at the beginning, in the middle and at the end of the harvest were transported to the labo ratory of the Department of Agriculture, Food and Environment Science (Di3A) of Catania University (Italy), and immediately analyzed.
Agronomic data and fruit physical parameter from the greenhouse experiment such as plant pro ductivity, fruit weight, shape index, color, thickness epicarp etc. were measured. Water Use Efficiency (WUE) was calculated as yield/water consumed (kg m 3 ) (Yaghi et al., 2013).
The epicarp and mesocarp color was measured using a Chroma Meter CR200 (Konica Minolta, Japan) based on light reflectance. The color was expressed using the Commission Internationale de l'Eclairage (CIE) system where the L*, a* and b* val ues represent the lightness, greenred and blueyel low, respectively. The dry matter (DM) content was obtained by drying samples in a thermoventilated oven at 70°C to constant weight.
The firmness of the zucchini squash was mea sured using a compression test based on the resis tance of the fruit to deformation in the middle por tion using a texture analyzer (TA.XT2i, Stable Micro Systems Ltd., Godalming, UK) incorporating a 2 mm diameter probe. Eighteen recordings were per formed for each treatment. The values were expressed as the maximum shear force (N).
Defence against Oidium was carried out weekly with the use of Karma® 85 (3 kg ha 1 ), and Tiovit® JET (0.3 kg ha 1 ) after 34 days from the foliar fertilization.
Manual weed control was carried out twice, to eliminate the weeds that grew during the cultivation period.
The defence against Oidium was carried out weekly with the use Sulphur 95% (35 kg ha 1 ), after 3 4 days from the foliar fertilization (Fig. 1).

Conventional cultivation system
In this system Siveg GR and 6: 6: 12 Orga Kem, as for the organic system, were applied in pretrans plant, respectively at doses of 400 and 1500 kg ha 1 ; after the spreading, the products have been appro priately topped up. After transplanting, the following

Water use efficiency and external inputs
The water use efficiency (WUE) was higher in the conventional than in organic cultivation system with 150.6 and 147.6 kg m 3 ha 1 , respectively. In the con ventional production system, the amount of fertiliz ers used were 4.8 kg Mg 1 ha 1 and 0.3 L Mg 1 ha 1 , solid and liquid, respectively ( Table 2). The organic vegetable production showed higher fertilizers input compared with conventional cultivation system, with 11.4 kg t 1 ha 1 and 0.5 L t 1 ha 1 , solid and liquid, respectively. For plant protection purposes, solid fungicides were used in both growing systems.
The amount of fungicides used was almost indis tinguishable, with 0.11 kg Mg 1 ha 1 used in the con ventional cultivation system as compared to 0.12 kg Mg 1 ha 1 applied in the organic cultivation regime. Solid insecticides used were 103fold higher in organ ic cultivation system compared to the conventional one, while the liquid insecticides were 4.8fold higher in the organic compared to the conventional cultiva tion system.

Fruit quality parameters
During the cultivation period, three samples of  1, Atago CO., Ltd, Tokyo, Japan).

Statistical analysis
The experiment was conducted as a randomized completeblock design with three replications to compare two cultivation methods: conventional and organic. Each experimental unit consisted of six plants (18 plants for cultivation methods). The statis tical analyses were performed using CoStat version 6.311 (CoHortSoftware, Monterey, CA, USA); pair wise comparisons for productivity parameters were done using ttest for means of samples with unequal variances. Twoway ANOVA for quality and color parameters was used. The differences between the means were determined using Tukey's test (P<0.05). Interaction effects were calculated using the Tukey's test at a 5% level of significance.

Crop productivity
The harvest period lasted nine weeks, with the first and last harvest dates on the 16 th December 2016 and 7 th March 2017, respectively; in total, 57 harvests were done during this period for both culti vation methods. The average harvesting interval was 1.4 days during the cultivation period.
The total fruit yield of conventional zucchini squash was similar to the organic cultivation method (46.4 Mg ha 1 and 43.2 Mg ha 1 respectively) (Fig. 2). No statistically significant differences were found for the fruit number per plant at the end of the growing period (21.5 fruits plant 1 in conventional cultivation and 22.9 fruits plant 1 in organic cultivation). Similarly, no significant differences between the con ventional and organic cultivation were recorded for the marketable fruit yield plant: 4.1 and 3.8 kg plant 1 , respectively ( Table 2). The percentage of unmar ketable fruit weight was 3.5% and 2.6% in organic and conventional, respectively, without significant differences. fruits were taken for quality evaluation (one at the beginning, one approximately in the middle, and one at the end of production). Significant differences for fresh weight, shape index, firmness, and titratable acidity were only detected for the harvest period (Table 3). No signifi cant difference for dry biomass percentage was found (Table 3).

Method of cultivation
With regard to the total soluble solids content, the conventional cultivation method showed an effect of interaction (Cultivation methods x Harvesting time): the fruits of the plants cultivated using the organic method have maintained, for the entire cultivation period, higher values, while those harvested in conventional cultivation have shown a reduction at the end of the growing period (by 7%) (Table 3 and Fig. 3).
Measurements of surface color demonstrated sig nificant differences between the cultivation methods only with regard to L* mesocarp, which was reduced: the fruits obtained in the organic method have recorded a uniformity of the values, while those obtained in conventional cultivation method have shown lower values corresponding to the second har vest (Table 4 and Fig. 4).

Discussion and Conclusions
In greenhouses, where intensive cultivation sys tems are widely used, the differences between con ventional and organic approaches are especially evi dent. Organic production in greenhouse operations is a challenging task (Gamliel and Van Bruggen, 2016).
The production of vegetables in organic condi tions presents more technical challenges than con ventional cultivation, because many practices, such as the use of nonnatural agrochemicals, are not per mitted in organic production under the regulations of many countries (Raigon et al., 2010). Consequently, organic production is sometimes difficult, especially in environments with high levels of pests and disease pressure.
Organic cultivation systems that are specifically dedicated to the vegetable production do not have their own manure supply and must buy a majority of their most of agronomic inputs, as such as fertilizers, biocontrol agents, natural compounds, and biostimu lants for controlling pests and diseases and for plant nutrition from the market. Results demonstrate that Table 3 Quality parameters of zucchini squash grown under different cultivation methods Values are means of main effects of method of cultivation and harvesting period. The statistical analysis was twoway ANOVA; NS not significant; * significant at P<0.05; *** significant at P<0.001. The values in the same column followed by the same letter are not significantly different at P<0.05 (Tukey's test). the grower, after years of cultivation, found a wide range of agronomic inputs that allowed for the high est yield that was similar to the conventional farm.
In literature, it is wellknown that mineral ele ments released by the organic fertilizers are not promptly available and the lag of time may reduce growth and yield. This problem can be compensated by higher inputs of specific organic fertilizers and biostimulants.
The differences observed for crop yield between organic and conventional growing systems range from 5 to 34%, while on the average, organic cultiva tion can reach about 80% of the yield of conventional cultivation but with substantial variations depending on the growing system and site characteristics (De Ponti et al., 2012;Meier et al., 2015;Ciaccia et al., 2019). Some studies, however, point out that the effect of cultivation method disappears when the results are converted to absolute dry matter, because often differences are due to water content (Pieper and Barrett, 2009). The yield in organic cultivation system was about 30 Mg ha 1 and is similar to those observed in other open field cultivation experiments with yields averaging 30.7 Mg ha 1 (Conti et al., 2015). Colla et al. (2002) found similar results to our in tomato, with no differences in yield between the organic and conventional cultivation methods, whereas a lower yield was found in the organic grow ing system compared to the conventional one for zucchini (Maggio et al., 2013). A strong yield reduc tion of about 25% was observed in summer zucchini squash grown using organic fertilizers (Dasgan and Bozkoylu, 2007). Conventional mineral nutrition inputs can provide nutrients when plants really need them, while organic fertilizers or matrixes release nutrients following degradation kinetics that usually cannot promptly satisfy plant requirements. This longterm effect of the organic nutrient tools can slow down plant growth and negatively affect the yield. However, there is little information about nutritional and sensorial quality (aroma and volatile organic compounds between the two growing sys tems), and food safety of organic versus conventional crops (Gennaro and Quaglia, 2003).
Specific cultivars for organic cultivation are not available; in greenhouse tomato, the use of F 1 hybrid Values are means of main effects of method of cultivation and harvesting period. The statistical analysis was twoway ANOVA; NS not significant; * significant at P<0.05; *** significant at P<0.001. The values in the same column followed by the same letter are not significantly different at P<0.05 (Tukey's test). cultivars was beneficial to the organic system, being superior to nonhybrids (Santa Rosa et al., 2019) as normally occurs in conventional cultivation systems. Observation of consumer expectations on food quality presents the base for any successful food pro duction system and marketing scheme. This is also true for fruits and vegetables which are increasingly valued as an important part of the diet (Péneau et al., 2006).
Appearance, colour, texture, and aroma are arguably the most important criteria used by con sumers to evaluate the immediate quality of a prod uct and thus, persuade them to buy it (Ragaert et al., 2004). In our experiment, quality parameters were not significantly affected by cultivation systems. Between the two cultivation systems, differences in fruit colour, firmness, and titratable acidity, were found in relation to the harvesting date. In analogous comparison experiments, fruit color between organic and conventional cultivation showed higher L*, a*, and b* values in the organic cultivation system. These results can be ascribed to agronomic manage ment techniques but also to varieties and different geographical cultivation areas (Armesto et al., 2020).
Many studies on the quality of organic vegetables indicate a higher nutritional value and a higher con tent of biologically active compounds in agricultural crops from organic farming (Brandt and Mølgaard, 2001). In other related vegetable crops, such as tomato or pepper, it has also been found that pro duction under organic conditions has a significant effect on fruit composition, which normally consists of an increase in the content of antioxidants and min erals (Chassy et al., 2006;del Amor et al., 2008). For this reason, organic agriculture is considered one of the best alternatives for sustainable and good quality food production (Aninowski et al., 2020).
Our results highlighted that the main significant changes were observed in growth parameters. The product quality was mainly influenced by environ mental conditions that changed according to summer weather. Therefore, quality changes were visible at the different harvesting dates. It is known that veg etable crops have higher requirements compared to other crops and short cycles require appropriate agronomic management. The higher inputs do not always provide a better quality or higher yield in organic system. Metaanalysis performed on differ ent crops highlighted a wide variability among crops in both organic and conventional systems. The major ity showed higher inputs in conventional cultivations system (Seufert et al., 2012). However, the evalua tion of both systems can provide useful information only if the cultivations are performed in the same environments and differences can be really attrib uted to the agronomic managements.
Our results showed that zucchini squash crop can be grown in organic or conventional cultivation sys tems with no significant changes in fruit quality. The organic system reduced the yield even if higher inputs of agronomic tools were required for the crop management. As reported by Rouphael et al. (2015), understanding the functional links between cultural factors and physiological responses is an important requisite to enhance the quality of organic products.
The organic cultivation was able to give compara ble yield to conventional one under protected culti vation. Almost all the analysed qualitative parame ters of fruits were not statistically different between the two systems, except for the TSS and Lmesocarp, to underline the possibility to adopt organic proce dures also in greenhouse. The obtained results high lighted the difficulties of performing a comparison between these two cultivation systems because of the different variables that can change. Our study was carried out in a geographic area where the organic cultivation for vegetable crops has been long established and the contemporarily presence of organic and conventional cultivation systems allowed us to perform a scientific and reliable study. In con clusion, this work demonstrated that the organic sys tem required higher inputs compared to the conven tional cultivation system. The extensive experience of the grower allowed for comparable yields between the two systems. However, further evaluations should be performed for understanding the econom ic and environmental sustainability of zucchini squash production in the two cropping systems.