A Study on Effects of Chemical Fertilizer and Organic Manures on Kiwifruit (Actinidia deliciosa, cv. Hayward) Quality during Cold Storage

 Consumers demand for organic products is increasing due to their awareness of health and nutritional quality. Organic manures maintain soil health and ecological balance of the region. Organic agriculture, as an alternative agricultural system to protect human health and the environment can improve the quality and storability of the product. Kiwifruit is one of the most important agricultural products in north of Iran, which plays an effective role in trade and employment of the people. Fertilization is one of the main factors affecting the yield and quality of kiwifruit. Growers use organic manures and chemical fertilizers in their orchard to achieve higher yields. It is necessary to study the effect of various organic manures available in the region on the nutrition of kiwifruit vines due to increase chemical fertilizer prices and the formation of the market for organic fruits. Therefore, the aim of this study was to compare the effect of using five types of organic manures and chemical fertilizer on the quality of Hayward kiwi fruit during cold storage.
 
 This research was conducted as randomized complete block design consisting six treatments (including complete chemical fertilizer, sheep manure, cow manure, chicken manure, vermicompost and azolla) on Hayward kiwifruit vines in orchard and factorial experiment with three replicates in cold storage during four years. The fruits were harvested at TSS: 6.5 (approximately mid-November) and then stored at 0.5 ° C and 90% RH for three months. Sampling was performed every month and physicochemical characteristics, including flesh color parameters (L*, C*, h◦), total soluble solids, titratable acidity, firmness and weight loss of fruit were measured. Sensory evaluation of fruits was also performed at the end of three months cold storage. Analysis of variance of the data was done using SAS 9.1 software. The significance of differences between the mean of treatments was determined by using Duncan’s test.
 
 The results showed the interaction between year, type of nutrition and cold storage period affected color indices, lightness and chroma. Lightness and chroma value didn’t show significant differences between organic and chemical fertilizer treatments. In addition, their value decreased during cold storage period, significantly. The chroma value indicates the degree of saturation of the green color and is associated with fruit firmness. The hue value was also influenced by the interaction between year and cold storage period and the simple effect of the nutrition type. The highest hue value was observed in chicken manure (108.63) and the lowest in vermicompost (107.66). The hue value decreased significantly after 90 days cold storage. According to the results, a decrease in fruit firmness, TA and an increase in TSS and TSS/TA were observed during cold storage irrespective of treatments. After 90 days, total soluble solids content was higher when organic fertilizers were applied. During the storage of kiwifruit, total soluble solids content increased, significantly. The titratable acidity value in organic fertilizer treatments was higher than chemical fertilizer after 90 days cold storage, significantly. Moreover, titratable acidity value decreased at the end of the cold storage period, significantly. The highest flesh fruit firmness was obtained in cow manure (8.74 kg/cm2) in forth year and chemical fertilizer treatment had the lowest flesh firmness (3.2 kg/cm2) in third year. Fruit lost firmness gradually during the cold storage period. However, no significant difference was found in maturity index (TSS/TA) between treatments. The TSS:TA ratio is highly increased after 90 days. Based on the results of the last two years, azolla, cow and chicken manures showed less weight loss percentage than chemical fertilizer treatment. Moreover, weight loss increased significantly during cold storage period in all treatments and years. Also the results of sensory analysis showed that fruits treated with vermicompost had a higher overall acceptance than other treatments.
 
 Generally, organic nutrition plays an important role in increasing the nutritional value and shelf life of kiwifruit cv.Hayward. Organically produced fruits had higher firmness than conventionally grown fruits during storage. Application of cow manure and vermicompost showed favorable effects on important properties of kiwi fruit such as firmness, weight loss, TSS, TA and sensory quality. Therefore, organic fruits will have better quality in the cold storage. As a result, it seems that by reducing the use of chemical fertilizers in the current orchards, kiwi production will be close to the standards defined for organic fruit.