Nutrient balance is key to a happy and healthy lifestyle. Similar to humans, plants also require balanced nutrients. Plant nutrients can be classified into macronutrients and micronutrients.
Plants require much larger quantities of macronutrients than micronutrients. For every 1kg of plant dry weight, more than 1g of macronutrients are required, whereas for micronutrients, less than 0.1g.
However, this is not to say that micronutrients are less important than macronutrients.
Micronutrients and macronutrients are like black and white keys on pianos. Both are essential for harmony; plants require both types of nutrients and in the right balance to thrive.
What are micronutrients?
Common micronutrients, such as iron (Fe), zinc (Zn), boron (B), copper (Cu), and manganese (Mn), play vital roles in plant growth and metabolism.
Micronutrients are the building blocks of plant enzymes and the core engine of photosynthesis, where plants absorb carbon dioxide from the atmosphere and store it in plant tissue as dry matter. This translates into yields, such as fruits and leafy greens, to be harvested from our garden.
Micronutrient deficiencies
Most common fertilisers on the market contain only macronutrients, such as nitrogen (N), phosphorus (P), and potassium (K).
However, the continuous use of fertilisers containing only macronutrients (N, P, and K) can potentially have a detrimental long-term impact on soil micronutrient status, resulting in nutrient imbalance and plant micronutrient deficiency, ultimately affecting plant yield.
Micronutrient deficiencies can be detected by visual symptoms in crops and by conducting soil and plant tissue testing.Deficiency symptomsIf sweet corn is planted in a garden, it is important to monitor micronutrient deficiency, primarily in the leaves, as an early indicator of Zn deficiency.
The visible symptoms of micronutrient deficiency in plants can be corrected through gardening practices, such as spraying the leaf surface with liquid micronutrient fertilisers and applying compost to increase the soil micronutrient status.
Correction of micronutrient deficiencyFoliar fertiliser (leaf spraying) is a practical and economical method for correcting micronutrient deficiencies in plants.
Foliar application is more efficient, as it quickly supplies micronutrients during critical growth stages. Studies have shown that supplying micronutrients during the reproductive stages boosts fruit yield in tomatoes, eggplants, and sweet corn.
Practical advice on micronutrients
Zinc is important for enzyme activation related to regulating plant growth, such as the production of chlorophyll and proteins in plants. Iron, copper, manganese, and chlorine (Cl) activate enzymes involved in respiration and photosynthesis. Boron is vital for plant cell metabolism and cell division.
When deficiency symptoms are observed on a case-by-case basis, gardeners need to strategise to correct the micronutrient deficiencies. Gardeners can purchase micronutrient products from fertiliser dealers in the form of concentrates.
For example, a bottle of concentrated liquid (minimum volume of one litre) contains a combination of essential micronutrients suitable for vegetables and fruits.
Please read the instructions written on the bottle for the correct dilution ratio to ensure efficient application of micronutrients to the targeted soils and leaves.
Micronutrients are usually applied as band applications within rows at planting.
Micronutrients such as Cu, Fe, Mn, and Zn can bind to soil particles because of their positive charge and are soluble under our country’s acidic soil conditions.
For foliar application, B and Cl are subject to leaching below the plant rooting zone; therefore, it is advisable for both B and Cl to be applied via leaf spraying.
Gardeners can regularly apply organic matter, such as composted garden waste, to sustain soil micronutrient reservoirs, taking advantage of the positive link between organic carbon and soil micronutrient levels.
Micronutrients and human health
Micronutrient deficiencies in edible plant tissues (fruits or leaves) can potentially cause serious human health issues.
Micronutrient malnutrition, such as deficiency in iron and zinc, commonly occurs in women and children in developing countries. Therefore, humans require micronutrients to maintain health.
Micronutrient malnutrition is a major global health challenge.
According to an official report in 2021 by Unicef Malaysia, millions of children in developing countries suffer from micronutrient malnutrition.
So, do not underestimate the importance of micronutrients in fruits and vegetables. The availability of micronutrients in fruits and vegetables depends on the soil micronutrient status over the entire plant growth cycle, which continuously affects human health.
As gardeners, we must ensure the proper application of fertilisers, whether it be soil-based or foliar, to cultivate nutritious fruits and vegetables. The saying, “Healthy soils for healthy plants for healthy humans” is a reminder of the importance of proper soil management.
Dr Arina Shairah Abdul Sukor is a senior lecturer at the Dept of Land Management, Faculty of Agriculture, Universiti Putra Malaysia. Her expertise is in Soil Fertility Management.