Fertilisation is one of the biggest costs of maize production. Farmers generally base their maize fertilisation decisions on the targeted yield in combination with soil sample results, the soil potential, climatic conditions and production practices. The goal is to ensure that the plant has access to the nutrients it needs when it needs it.
According to the Fertiliser Association of South Africa’s Fertiliser Handbook, one ton of maize will remove about 15 kg of nitrogen (N), 3 kg of phosphorus (P), 4 kg potassium (K), 0,5 kg calcium (Ca), 0,5 kg magnesium (Mg) and 4,5 kg sulphur (S).
This can be multiplied by the targeted yield to establish how much fertiliser would be required to reach that target. To produce a three-ton yield, for example, would then require the availability of 45 kg of nitrogen, 9 kg of phosphorus, 12 kg potassium, 1,5 kg calcium and 13,5 kg sulphur.
Soil samples should be taken to determine how much fertiliser is available to the plant and how much should be added.
Soil nutrients levels can be built with the use of synthetic fertilisers as well as through the use of compost, compost teas manure, crop rotation and mixed cover cropping. Interestingly, farmers using regenerative agricultural practices in the United States have found that they can get away with fewer pesticides and synthetic fertiliser the healthier their systems become.
Some of their results are also turning traditional fertiliser recommendations on its head, with the argument being that these recommendations were made for a different type of system than the “healthy” holistic system with which these farmers work.
Nutritional Shortages
Symptoms of nutritional shortages are difficult to identify and can easily be mistaken for diseases. Farmers should for this reason make use of a production or chemical consultant to help them determine the origin of a problem, as nutritional problems cannot be fixed with disease management practices and vice versa.
Like diseases, nutritional shortages, depending on the type of deficiency, may negatively impact plant growth, yields and production quality. Plants may also become stressed rendering them more vulnerable to diseases. Too much of a specific nutrient, however, is also problematic as it will usually hinder the uptake of other essential nutrients.
Symptoms
Farmers should regularly scout plants and take leaf samples to identify nutritional problems before they get out of hand. Here are some of the signs of deficiencies, according to Grain SA.
Nitrogen shortages are usually associated with the yellowing and browning of leaves, starting from the tip to the mid-rib to form an inverted “V” pattern. It affects older leaves first and may cause the leaves to die. On the cob itself, it may result in the tip having no or flinty seed. Nitrogen will have a negative impact on plant growth and flowering.
Potassium shortages manifests in the yellowing of leaf edges, that later become scorched, starting from the tip of the leaves. Shortages first appear on older leaves at the bottom of the plant, spreading upwards as the situation worsens. The deficiency will lead to reduced straw and stalk strength, causing plants to fall over more easily. It will also have a negative impact on maize quality, since potassium is important for the formation of protein, sugar and starch.
Phosphorus shortages manifests as the purpling of leaves on specifically young plants and results in delayed maturity, reduced flowering and seed production. The root system of these plants are also poorly developed, which has a negative impact on the plant’s ability to absorb nutrients and water.
Magnesium shortages manifests as yellow streaks between the veins of leaves that later become beaded. Shortages will result in poor and stunted growth, since magnesium plays an important role in chlorophyll formation.
Plants suffering from Zinc shortages will be stunted and present with yellow streaks or bands on their leaves.
Molybdenum (MO) shortages manifests on leaf tips and edges of young plants becoming scorched. The leaves in general are narrow and light green in colour. The deficiency may result in poor grain set and premature germination of seed on the ear.