Influence of vermicompost and sheep manure on mechanical properties of tomato fruit

Abstract Mechanical properties of the horticultural products play an important role in improving the products quality and storage life after harvesting and also reducing product waste. Recently, using organic fertilizers has increasing trend for producing high‐quality products as well as improvement of soil quality. Two of the best options to produce organic material and sustainability of agricultural production are vermicompost and sheep manure. The present study relied on determination of mechanical properties through pressure and shear tests. Vermicompost and sheep manure were used separately to fertilize the soil. After planting tomato seeds and harvesting, tomato fruits were analyzed by a universal test machine. The results showed that vermicompost was a better fertilizer than sheep manure due to its more appropriate carbon to nitrogen ratio (C/N), acidity, and salinity. Also, in the pressure test, the maximum force required for bruise of tomato produced with vermicompost (41.5N) was more than that of control sample (no fertilizer) and sheep manure. In the shearing test, the maximum force required for shearing tomato produced with vermicompost (58.60 N) was lower than that of control sample (no fertilizer) and sheep manure. The findings of this study can be used to reduce the amount of waste at different stages of tomato production and supply including the design and optimization of processing and transportation equipment.

Vermicompost as a type of biological fertilizer is produced through a continuous and slow passage of decaying organic materials in the gastrointestinal tract of some earthworm species. When passing through the earthworm body, the materials are impregnated with the gastrointestinal mucosa, vitamins and enzymes before defecation. Thus, it is used as an enriched and very useful organic fertilizer that improves the quality and fertility of the soil (Haribhushan et al., 2013;Smith, 1998). Rochana, Sawaneg, Patma, and Bunyong (2006) stated that vermicompost leads to improve the size of the soil pores and increase soil porosity and thus the water holding capacity of the soil. Kashem, Sarker, Hossain, and Islam (2015) investigated the effects of vermicompost and mineral fertilizers on the vegetative growth and production of tomato fruit. They reported that the relationship between vermicompost use during the growth period and plant height, leaf number, shoot and root dry weights, and number of fruits was highly significant at 5% probability level. Feibert, Shock, Barnum, and Saunders (1995) observed that using 15 tons of compost per hectare could increase onion crop yield by 15%.
The researchers believed that the enhanced crop yield was due to nutrition improvement and increasing permeability and ventilation as well as the microbial activity in plant root zone. Cook, Keeling, and Bloxham (1997) reported that using vermicompost in a spring barely field caused to increase the plant's dry matter by 25% and it also increased the number of buds per plant. In organic cultivation, El Gendy, Hosni, Omer, and Reham (2001) stated that vermicompost improved the qualitative and quantitative performance of basil plant. It was reported that using vermicompost not only enhances the growth and germination of plants (Atiyeh et al., 2000;Joshi & Vig, 2010;Truong & Wang, 2015) but also enhances the growth of seedling vegetables (Bachman & Metzeger, 1998).
Tomato is the edible fruit of the Solanum lycopersicum which belongs to Solanaceae family. It is one of the most common commercial vegetables in the world. Due to low levels of fat, calorie, and free cholesterol and high levels of A, B, and C vitamins and carotene and lycopene, tomato fruit and its products are considered as healthy foods in human beings' daily diets (Alam, Rahman, Mamun, Ahmad, & Islam, 2006;Ghaffari, RezaGhassemzadeh, Sadeghi, & Alijani, 2015;Heuvelink, 2005). Tomato is one of the most important horticultural products in different parts of Iran.
Compared to other crops, tomato fruit has high waste due to high moisture content up to 90% (Gould, 2013;Heuvelink, 2005).
Knowing the mechanical properties of tomato is useful to predict the conditions result in mechanical damage, and it is very important in optimization of processing machinery. In this regard, researchers have shown that there is a linear relationship between tomato's mechanical properties and its vulnerability (R 2 = 0.78) (Desmet et al., 2004). Proper nutrition of the horticultural products plays an important role in reducing waste and improving the quality of the products and their storage life after harvesting (Kays, 1991;Wills, McGlasson, Graham, & Joyce, 2007). So according to above and also due to the importance of theoretical knowledge about the reducing agricultural waste and the lack of reporting on tomato waste, the authors decided to investigate the effect of vermicompost and sheep manure on the mechanical properties of tomato. Each treatment was experimented with three replications. For that, 6 plots with area of 2 m 2 were prepared. Fertilizers were mixed with soil at the depth of 15 cm with amount of 1 kg in each plot with area of 2 m 2 (5 tons per hectare). All variables such as irrigation, temperature, fighting against pests and diseases, weed control, and light were the same for all treatments during the growing period.

| MATERIAL S AND ME THODS
In each plot, three tomatoes were planted at the distance of 30 cm from each other. The ripped tomatoes were hand-picked, cleaned manually, and stored in an environment with the temperature of 11-12°C. The tomatoes were transferred from the storage place to the laboratory about one hour before determining mechanical properties. To determine the mechanical properties of tomato fruit, two tests, that is, pressure (compress) and shear test, were performed. To do so, a universal testing machine (Model: Z 0.5; Zwick/Roell company, Germany) was used ( Figure 2). The mechanical properties were tested on three samples of tomato for each plot.
Pressure test was conducted under vertical loading according to the ASTMD 790-03 standard in room temperature at the loading rate of 20 mm/min. At the same loading rate, the shear test was done using a flat edge blade with thickness of 1.4 mm and the blade angle of 30° was used according to DIN53294 standard ( Figure 3).
The universal testing machine was simultaneously connected to a computer to collect data.
In this research, SAS 9.4 software was used to analyze and perform statistical operations based on completely randomized design. Also, the mean comparison between treatments was done based on LSD test.

| RE SULTS AND D ISCUSS I ON
The results of chemical analysis of the vermicompost and sheep manure have been given in Table 1. The results indicated that carbon to nitrogen ratio is more appropriate in vermicompost compared to sheep manure.
Thus, using vermicompost as a fertilizer would provide better and more facilitative conditions for the plant to absorb nutritious elements.
The ability to absorb nutrients is highly dependent on the pH, and the proper pH range for the crops is between 6.5 and 7.5.
According to the results of this study, vermicompost has more neutral pH compared to sheep manure and using a high amount of that has not detrimental effects on the soil and plants.
Moreover, vermicompost is odorless and its impurity is much lower than sheep manure. The EC of the vermicompost is modified much more than the sheep manure and is at such a desirable level that it does not contaminate the soil. In addition, it decreases the salinity stress so causes to avoid change of the amount and types of the regulating metabolites of plant growth and thus decrease its effects on the growth rate.  Table 2. The results show that the effect of fertilizer type on mechanical properties of tomatoes was significant in the pressure test at 1% probability level. This result indicates that it can be said that there is a significant difference between the mean treatments with 99% confidence.
The mechanical properties of tomato determined through pressure test have been listed in Table 3. In this table, the values of the peak force required to the failure of the tomato fruit, deformation in peak force, and the energy to reach the peak force under pressure test have been provided.
The mean values of the peak force, deformation, and the energy to reach the peak force under pressure test were 30.60 N, 13.45 mm, and 207.65 N/mm, respectively, for the fruits produced without fertilizer (control samples), 34.03 N, 14.11 mm, and 223.31 N/mm, respectively, for the fruits produced by sheep manure and 41.50 N, 24.80 mm, and 712.13 N/mm, respectively, for the fruits produced by vermicompost fertilizer. The results showed that the peak force of tomato produced using vermicompost was 45.05% and 42.44% more than that of control sample (no fertilizer) and sheep manure, respectively. Also, the deformation was more in vermicompost. So, the energy performed to reach the peak force of the tomato fruit produced by vermicompost was higher than that of control sample (no fertilizer) and sheep manure. This is due to rich nutrients in vermicompost that gradually provides the plant requirements, and this makes the soil more fertile and yields higher-quality products. Therefore, it is   Table 4. The results showed that the effect of fertilizer type at the 1% probability level on the shear test of tomatoes was significant.

| CON CLUS IONS
In the present study, pressure and shear properties of tomato fruit produced using control sample (no fertilizer), vermicompost, and sheep manure were determined. The pressure properties of the tomato fruits produced by vermicompost were higher than that of control sample (no fertilizer) and sheep manure whereas the shearing properties of the fruits produced by vermicompost were lower than that of control sample (no fertilizer) and sheep manure. It was concluded that vermicompost can be used to improve the mechanical properties and then reduce the amount of waste at different stages of tomato production and supply including.

ACK N OWLED G M ENTS
The authors thank Ilam University for partial support of this study.

CO N FLI C T O F I NTE R E S T
The authors have declared no conflict of interest.

E TH I C A L R E V I E W
This study does not involve any human or animal testing.