This season has again been a challenging one. Due to the dry and cold conditions crop growth, especially if the roots, has been restricted. This in turn reduces the crops ability to find nutrients, and the situation worsens if there are limited amounts in the soils. However, unlike macro nutrients like Nitrogen, Phosphorus, Sulphur and Potassium, micro nutrients can be applied fairly cost effectively. Also, the crop only requires very small amounts of these for optimum growth. Three of the most common micro nutrients are Zinc, Copper and Manganese. Here is a brief description of where and what to look out for to decide whether your crop is in need.
Zinc is one of the most common micronutrient deficiencies in agricultural crops. It is deficient across a wide range of soil types. Crops in soils with less than 0.3 mg/kg of zinc most likely require added zinc for optimum production. With highly alkaline soils, the critical level may be up to 0.8 mg/kg.
Deficiency Symptoms: Zinc deficiencies are difficult to diagnose. Cereals may not present any symptoms other than reduced top growth production. Visual symptoms often appear in the middle-aged leaves. Longitudinal pale green stripes appear on one or both sides of the mid-vein of the leaf. These develop into necrotic patches, which ultimately result in collapse of the leaf in the middle region.
Copper deficiency in South Australia is most commonly found in highly calcareous or ironstone soils, as well as in siliceous sandy soils with low levels of organic matter. High soil concentrations of other metals such as iron, magnesium and aluminium can also induce copper deficiency.
Deficiency Symptoms: Large losses in production from crops and pastures can occur without any visual deficiency symptoms. Visual symptoms in cereals include a general wilting (unrelated to moisture status) of the plant at tillering stage. Plants require copper for cell wall structure, so deficiencies can result in reduced stem strength. More severe deficiencies are characterised by the withering of the tips of leaves and incomplete head and grain formation. Crops suffering from copper deficiencies late in the season may incur significant reduction in grain production, as pollen production is affected.
Manganese deficiencies are most common in alkaline and calcareous soils but are particularly severe in crops and pastures grown on highly calcareous sands (60-85% free lime). It also occurs in slightly acid sandy soils, lateritic soils, peat soils and poorly drained soils.
Deficiency Symptoms: Manganese deficient cereal crops often have a patchy appearance with areas of poor growth. Severe deficiencies can even result in the death of the plant, and so can have a big impact on yields. As manganese is relatively immobile in the plant, symptoms initially appear on young leaves. Affected leaves turn pale green and have a limp or wilted appearance. Manganese deficiency can cause split or shrivelled grain in lupin pods and will delay maturity of deficient plants. In canola the whole of the deficient plant becomes paler. This yellowing is most prominent on the older leaves. The interveinal areas gradually turn yellow while the veins remain green.