This archive report was first published on 20 July 2019.
July 20, 2019 - A visit to a two-acre farm in the countryside left me impressed by the farmer's mastery of sustainable agricultural practices. Samuel, a teacher and farmer, had invited me to tour his farm, seeking to get things right. As we walked through the fields, I noticed the diversity of crops, which is essential for a farmer's income security.
The farm's soil had been tested, revealing a lack of major macro-nutrients. The three primary macronutrients required by plants are nitrogen for vegetative growth, phosphorus for root development, and potassium for flowering and fruiting. However, farmers often confuse the deficiency symptoms in crops, leading to incorrect identification and treatment.
For instance, the purpling in cabbages is due to a lack of nitrogen in the soil, not phosphorus as Samuel initially thought. Yellowing of crops is often mistaken for nitrogen deficiency, but it can be caused by various factors, including magnesium deficiency, which was evident in the tomato farm's leaves. Iron deficiency results in yellowing at the tip of the plants, typically in young seedlings grown in soilless media.
Phosphorus deficiency develops slowly, causing necrotic spots on older leaves and stunted growth. The deficiency can also lead to a distinct purpling of the stem and the underside of the leaves. In contrast, potassium deficiency causes the leaves' edges to appear burnt, and the plants to lodge, making them more susceptible to disease infestations.
Failure to take up nutrients is not solely due to their unavailability in the soil or media. Injured roots, waterlogging, dryness, acidic, or alkaline soils can also hinder nutrient absorption. The macronutrients are usually absorbed when the pH is slightly alkaline, while micronutrients are absorbed when the pH is slightly acidic.
Proper identification of deficiency symptoms is crucial for correct control. It's essential to determine if the symptoms are due to mobile or immobile nutrients, based on where they first appear in the plants. Mobile nutrients, such as nitrogen, phosphorus, potassium, and magnesium, can move from older to younger leaves. Immobile nutrients, like iron and zinc, do not move readily within the plants.
To prevent nutrient deficiencies, farmers should conduct soil analysis to determine the available nutrients. This helps in controlling the deficiencies' symptoms before the crop is affected. Seeking advice from experts is also crucial to determine the type and quantities of fertilisers to use during the production period, avoiding excess or inadequate application.
