Role of Zinc in Citrus Production

Zinc and fruit number

Zinc deficiency significantly reduces growth and yield potential. Low zinc levels reduce fruit number per tree, as trials with navel oranges in Egypt show.

Zinc and fruit weight

Low zinc levels, though to a lesser extent than fruit number, reduce fruit size, resulting in decreased yields.

Soil and foliar applications

Soil and foliar applications are both effective in increasing yield. In some studies in oranges and grapefruit, researchers have also reported increases in juice content from use of Zn.

Zinc and TSS

Zinc increases TSS in fruit, as can be seen on the example above, on Valencia oranges in Chile.

Zinc and vitamin C

Zinc also increases the ascorbic acid content of the fruit. Under severe Zn deficiency, fruits may be misshapen and have low juice content – the juice present also lacks taste.

Zinc and twig dieback

Deficiency symptoms first appear as chlorotic leaf spots ('mottle leaf') and/or white interveinal areas with green veins. New leaves are significantly stunted and often occur in rosettes because the twig internodes are shortened. Twig die back can be corrected using foliar sprays, as image above shows (Kinnow mandarim, India).

See more on Citrus Growth Stages.

General guidelines for Zinc application

The main roles of zinc are as a cofactor of enzymes and involvement in the production of growth regulators responsible for internode elongation and chloroplast development. Zinc deficiency significantly reduces growth and yield potential. Low zinc levels reduce fruit number per tree and, to a lesser extent fruit size, resulting in decreased yields. Soil and foliar applications are both effective in increasing citrus production yield.

Zinc deficiencies in Citrus

Zinc deficiency symptoms in citrus first appear as chlorotic leaf spots ('mottle leaf') and/or white interveinal areas with green veins. New leaves are significantly stunted and often occur in rosettes because the twig internodes are shortened. Twig die back can be corrected using foliar sprays. Zn deficiency is most common on sandy soils which have inherently low levels of zinc, and under conditions of high soil Ph and high soil moisture content.

Soils that are mechanically leveled and have variable topsoil organic matters are particularly prone to zinc deficiency. Soil applications are more effective on low pH soils than high pH soils. Foliar zinc sprays applied after flowering are most effective in controlling zinc deficiencies. Use tissue analysis to check for deficiencies.