Zinc is required in small but critical amounts, especially in plantation cops. Among the micronutrients, Zn is the most limiting nutrient associated with Plantation crops. However, the role of zinc is much debated in coffee Agroforestry, despite scientific evidence that clearly points out to the fact that zinc plays a vital role in plant metabolism and nutrient uptake. It is an important component of the enzyme systems that are responsible for the physiological role. Zinc fertilizer increases crop yield and improves water uptake, resulting in healthier, stronger crops.
Advantages of Zinc
Zinc (Zn) ions have both beneficial and toxic effects on plant cells.
Zinc is an essential component of various enzymes that are required for growth hormones and many more metabolic processes
Zinc aids the synthesis of plant-growth substances and enzyme systems, and is essential for promoting certain metabolic reactions, which are particularly critical in the early growth stages.
The leaf-to-shoot ratio is well balanced with optimum levels of zinc availability.
Zinc application enhances fruit set.
Zinc induces tolerance to coffee exposed to low temperatures.
Carbohydrate, protein and chlorophyll formation is significantly reduced in zinc-deficient plants.
Zinc improves flower bud development in all varieties of coffee.
Zinc brings about qualitative and quantitative change in coffee clusters.
Zinc plays a pivotal function in the plant response to pests and diseases.
Low levels of zinc can stunt growth, minimize reproductive sites, and can reduce yields in all crops due to the stunting growth of roots and tissues.
The physiological stress caused by Zn deficiency results in the development of abnormalities in plants. In the case of severe ‘acute’ Zn deficiency, visible symptoms include stunted growth, chlorosis of leaves, small leaves, and spikelet sterility.
Zn deficiency reduces growth, tolerance to heat stress, and chlorophyll synthesis.
Natural sources of zinc
Zinc exists naturally in rocks. The amount of zinc present in the soil depends on the parent materials of that soil. Sandy and highly leached acid soils generally have low plant-available zinc. Mineral soils with low soil organic matter also exhibit zinc deficiency. In contrast, soils originating from igneous rocks are higher in zinc. Plants take up zinc as the divalent ionic form (Zn2+) and chelated zinc.
Zinc Availability In Soils
Several research projects have focused on the use of this nutrient, and much of the following information is based on the results of that research. Scientific Literature clearly spells out that Zn is known to occur in soil in a number of discrete chemical forms differing in their solubility and availability to plants. Zn exists as five distinct pools in soils viz., water soluble, exchangeable, adsorbed, chelated or complexed Zn. These pools differ in strength (or reversibility) and therefore in their susceptibility to plant uptake, leaching and extractability. The equilibrium among different pools is influenced by pH, concentration of Zn and other cations, particularly iron and manganese.
Coarse, sandy soils and peat soils with low zinc reserves and low organic matter can be more prone to zinc deficiency.
Zinc is primarily taken up by the plant via diffusion and root interception. Limits to these mechanisms can lead to reduced uptake and zinc deficiency.
Excessively wet soils reduce the ability of plants to uptake zinc.
Soils, where topsoil has been removed, are more prone to zinc deficiency due to the higher presence of calcium carbonate and organic matter.
High levels of phosphorous can reduce the availability of zinc.
Organic matter adds zinc and can increase zinc availability. Low levels of nitrogen can reduce a plant’s ability for uptake of zinc.
Factors Causing Zinc Deficiency
Zinc deficiency has increased with the introduction of modern varieties, crop intensification, and increased Zn removal through multiple crops.
The main soil factors responsible for causing Zn deficiency are low total contents of Zn, high pH, high contents of calcite, high concentrations of bicarbonate ions and salts, and high levels of available phosphorus.
Excess of fertilization can remove zinc from soils, which becomes unavailable to coffee. Zinc is used along with other nutrients like nitrogen, phosphorus, and potassium. When these elements are in short supply, this will result in depleting the amounts of zinc available to plants.
Influence of soil pH on Zinc Availability
The solubility of Zn decreases with increasing pH. For instance, in the range of 5.5 to 7.0 the concentration of Zn in the soil solution may decrease 30 to 45 times for each unit increase in soil pH.
Poultry Manure And Zinc
The application of poultry manure can add a considerable amount of zinc to the soil. For example, broiler litter contains 0.01-0.50 lb zinc/ton, and laying hen litter contains an average of 0.15 lb zinc/ton.
Types of Deficiency Symptoms
The various different types of symptoms are:
Necrotic Spots on Leaves
Bronzing of Leaves
Rosetting of Leaves
Stunting of Plants
Zinc Deficiency in Plants
It’s hard to tell the difference between zinc deficiency and other trace elements or micronutrient deficiencies by looking at the plant because they all have similar symptoms. The main difference is that chlorosis due to zinc deficiency begins on the lower leaves, while chlorosis due to a shortage of iron, manganese, or molybdenum begins on the upper leaves.
Zinc Deficiency in Soil
Foliar sprays fix the problem for the plant but they don’t fix the problem in the soil. This usually includes working chelated zinc into the soil. In addition to adding zinc to the soil, you should add compost or other organic matter to sandy soil to help the soil manage zinc better. Cut back on high-phosphorus fertilizers because they reduce the amount of zinc available to the plants.
Zinc deficiency is the most common micronutrient deficiency, affecting more than 50% of the world’s Agricultural soils. The availability of Zn to plants is hampered by its immobile nature and adverse soil conditions. Thus, Zn deficiency is observed even though a high amount is available in the soil. Judicious application of fertilizer Zn helps increase crop production as well as it helps enrichment of Zn in plant organs including grains.
Anand T Pereira and Geeta N Pereira. 2009. Shade Grown Ecofriendly Indian Coffee. Volume-1.
Zinc – An Indispensable Micronutrient
The Role of Zinc
Zinc for crop production
A Role for Zinc in Plant Defense
Importance of Zinc for Arabica