Two-year study on the role of balanced fertilization on orange fruit yield increase and tolerance to frost in

One of the strategies for improving citrus yield and fruit tolerance to frost in citrus gardens is practicing balanced fertilization. So that if the concentration of each element is lower than the optimum concentration, the yield of the plant will be reduced. Therefore, the aim of this study was to investigate the role of optimum fertilizer application on increasing quantitative and qualitative yield of oranges and also resistance to cold stress.

In order to investigate the role of balanced fertilization on some of the characteristics of citrus fruits, including increased resistance to frost, a two-year trial was conducted on Thomson and Bloody Thomson with two treatments and five repetition in the years of 2016-17 and 2017-18 in a citrus garden in Neka city in Mazandaran province. treatments included, T1= control (Traditional fertilization method, i.e. every year in late autumn, 2 kg of urea, 1 kg of triple superphosphate per tree, along with animal manure under droppers) and T2= balanced fertilization according to the soil and leaf analysis results, i.e. every year in late autumn, 2 kg ammonium sulfate, 1.5 kg potassium sulfate 1 kg magnesium sulfate and 0.5 kg zinc sulfate mixed with animal manure and surface soil with deep placement under droppers. It should be noted that in both years, the same fertilizer sources were used. Also, in the summer of second year, for each tree, 0.5 kg of soluble potassium sulfate with zinc (SSOP+Zn-EDTA) was used in two split times (July and August).

The results revealed that a) In the first year, while the average yield in T1 for Thompson Blood Orange and Thompson Novell Orange were 40 and 75 kg, in T2, it increased up to 72 and 175 kg per tree and in the second year, also these figures were increased significantly from 80 and 140 kg and 155 and 305 kg per tree, respectively. In both years, the differences were significant at 1% level. The main reason for this performance in the second year was due to split application of SSOP+Zn during the summer. b) While the average dry matter percentage for Thompson Blood Orange and Thompson Novell Orange for the first year in T1 were 15.6 and 22%, in T2 they were increased to 17.1 and 24.4%, respectively. For the second year, they were increased from 18.1 and 22.3% in T1 to 20 and 25.2% in T2, respectively .c) While frost tolerance in Thompson Blood Orange and Thompson Novell Orange during the first year in were 0 and -1 degrees Celsius in T1, frost tolerance were increased in T2 up to -2 and -5 degrees Celsius. In the second year, these figures were changed from -1 and -3 to -4 and -9, respectively. One of the main reasons for this improvement in frost tolerance of citrus fruits was due to increase in their dry matter percentage and positive effects split application of K and Zn fertilizers.

While the superiority of balanced fertilization has been proven, it is highly recommended that for producing valuable citrus fruits, this practice should be generalized in all citrus gardens.