Determining the Efficiency of Silicon Fertilizer and Branch Pruning on Greenhouse Eggplant Yield and Post-harvest Shelf Life

    Silicon (Si) is not an essential element for the growth of plants, but its role in improving the yield by reducing the environmental stresses and crop durability is very important. Despite the abundance of Si in the soil, the amount of dissolved Si available for herbal absorption might be limited. Therefore, using this useful element through foliar application can be effective in the growth of the plants such as eggplant. On the other hand, profitability is dependent on the high yield and quality per unit area in producing greenhouse vegetables.

    To study the effect of foliar application of Si fertilizer from the source of Khazra Chelated Silicon (commercial brand, contains 2% chelated silicon for plant at pH 3 to 11 and no silicate in the form of salt) in different stages of the growth of eggplant and bush pruning in hybrid eggplant, a greenhouse experiment was conducted in a soil environment as a split-plot in a randomized complete block design with 3 replications in Minab region. In this experiment, the consumption of Si fertilizer as the main factor at 4 levels (0 and 2 per thousand in the vegetative phase, 2 per thousand in the reproductive phase and 2 per thousand at the two vegetative and reproductive phases) and the type of pruning as a sub-factor in 4 levels (two-branch training system, three-branch training system, four-branch training system and no training system) were applied. Eggplant seeds were transplanted in an environment containing sphagnum in November and then at four-leaf stage they were transferred to the main field in December. The distance between the rows was one meter and the distance between the plants in the row was 45 cm. After positioning the plant in the greenhouse and reaching the appropriate growth, pruning and foliar application of Si fertilizer began and in the treatment without fertilizer, spraying with pure water was used. Silicon fertilizer was sprayed on the eggplant leaves according to the instructions recommended by the manufacturer every eight days.  Once the eggplants reached a suitable reproductive growth and started fruiting, fruit thickness, fruit length, the weight of each fruit, the number of the fruits on each plant, and finally the yield of each plant were recorded in each pick. To evaluate the effect of Si on the durability of eggplant after picking, 3 fruits harvested from each treatment were first weighed by a digital scale, and then kept at room temperature for 2 weeks and after two weeks, the weight of each fruit was measured again. Based on two recorded weights, the percentage of fruit weight loss was calculated. Furthermore, to evaluate the effect of silicon fertilizer and plant pruning on resistance to fungal diseases, scores, from 1 to 9, were given to the plants in each treatment. Plants without any fungal infection were assigned a score of 1, and completely infected plants were assigned a score of 9.

    The results showed that pruning improved the fruit length, the plant height, the fruit weight in each plant, and the plant yield and reduced the percentage of fungal infection in the plant. Moreover, the silicon foliar application positively affected the number of the fruits in each plant and increased the durability of fruits after harvesting. Silicon foliar application in the two vegetative and reproductive stages together and plant pruning in a four-branch way resulted in maximum plant yield, improved crop quality, and improved greenhouse management. The intensity of fungal infection was affected by different levels of silicon, plant pruning, and the interaction of the two factors at a probability level of five percent. Comparison of interaction averages showed that pruning and foliar application in vegetative and reproductive stages together significantly reduced fungal infection in the greenhouse. The highest intensity of fungal infection was related to plants without pruning and lack of silicon. Pruning improves airflow and modulates humidity in the plant canopy and as a result eliminates the proper conditions for fungal growth. Silicon also prevents fungal penetration into plant cells by depositing in the plant cell wall and strengthening plant tissue, and as a result inhibits fungal growth in the plant. Marschner (2012) reported that silicon would increase resistance to fungal and bacterial diseases and pests. Plant diseases are a major threat to agricultural production because they cause a serious loss of yield and quality of the crop. Numerous studies have reported that Si is effective in controlling diseases caused by fungal and bacterial pathogens in various plant species. Furthermore, given that one of the challenges for producers to deliver high-quality crops to the target market is their durability after harvesting, it seems that silicon foliar application at the two vegetative and reproductive stages might be effective to overcome such a challenge. Choosing a training system depends to a large extent on the ease of work in the greenhouse, the production system, and the superiority of the production rate. On the other hand, a significant increase in yield and crop quality was reported for barley, rice, sugarcane, tomato, cucumber, soybean, and bamboo due to Si consumption during the growth. Another important feature of silicon is that it increases plant damage under biological and non-biological stress conditions as well as resistance against stress.

    According to the results, four-branch training system of eggplant and also silicon foliar application in the two vegetative and reproductive phases of greenhouse eggplant improved the yield components and increased the durability after harvesting. Pruning the plant into four branches also improved yields. Therefore, using silicon with four-branch training system is recommended, especially in traditional greenhouses without proper ventilation systems.