Explaining the Origin of Zinc for Plants and Soil
Soil type and properties significantly influence the availability of zinc (Zn), a vital micronutrient for plants, in soil. The key factors include soil pH, organic matter content, and carbonate levels.
Zinc is most available in slightly acidic soils with a pH between about 5.0 and 7.0. At higher pH values (alkaline soils, pH > 7.0), zinc availability sharply decreases because zinc forms insoluble compounds such as zinc hydroxide [Zn(OH)₂] and zinc carbonate [ZnCO₃] which plants cannot absorb. This leads to zinc deficiency even if total zinc content is adequate.
Soils high in calcium carbonate (CaCO₃) reduce zinc solubility by precipitating zinc into unavailable forms, further limiting zinc uptake by plants. On the other hand, low organic matter levels correlate with lower zinc availability, as organic matter can chelate zinc and keep it in an available form for plant roots.
Different soil tests are used depending on soil pH to measure zinc availability accurately. The Bray test works best for neutral to acidic soils, Olsen test for alkaline soils, and Mehlich III test is suitable across most cropping soil pHs.
Acidic to neutral soils with adequate organic matter provide the best conditions for zinc availability, whereas alkaline, calcareous soils pose the greatest risk for zinc deficiency impacting crop growth and yield. Managing soil pH and organic matter, along with appropriate zinc fertilization guided by soil testing, helps prevent zinc deficiency in plants.
Sandy, highly weathered, or soils with low organic matter content are more prone to zinc deficiency. Eroded soils with low organic matter content also have a high risk of zinc deficiency. Soils with low organic matter or compacted soils that restrict root proliferation can limit zinc availability to plants.
Zinc is taken up by plants as the divalent cation, Zn2+. Once absorbed, zinc plays a crucial role in various cellular functions. It is involved in the production of chlorophyll, protein, and various enzymes, including alcohol dehydrogenase, carbonic anhydrase, and RNA polymerase. Zinc is also essential for the synthesis of tryptophan, an amino acid that is a precursor to the plant hormone indoleacetic acid.
Zinc deficiency in plants is common in calcareous, high pH, eroded, and levelled soils. This deficiency causes chlorosis, a type of leaf discolouration characterised by the yellowing of leaves, particularly between the veins, while the veins remain green. A zinc-deficient plant will have reduced hormone production, leading to shorter internodes and stunted leaf growth.
Zinc is taken up by various transporter proteins, including ZRT/IRT, HMA, VIT, NRAMP, MTP. Managing soil conditions and using appropriate zinc fertilization can help ensure that plants have the zinc they need for optimal growth and yield.
In the realm of both health-and-wellness and plant nutrition, zinc deficiency can have significant impacts. Soils with high calcium carbonate content, frequent in fitness-and-exercise activities like running or jogging outdoors, reduce zinc solubility and make it less available for plant absorption. Conversely, soils with high organic matter content facilitate zinc availability, promoting healthier plant growth and development.
