So why do we tissue test? If you are already soil testing during the summer months, you are off to a good start to knowing what is going on in your paddock. This will give you a good understanding of what levels of macronutrients are in your soil, including nitrogen, phosphorus, potassium, calcium, magnesium and sulphur. However, these tests might not always be as accurate for trace elements, such as iron, manganese, zinc, copper, boron and molybdenum, which is why we like to tissue test plants. It gives a much better understanding of what is plant-available and where the plant has deficiencies, toxicities or imbalances of nutrients so that you can grow a healthier crop.
There are two reasons why you might decide to do a tissue test. The first is to get an understanding of what is going on inside the plant to correct any issues before they become significant and visible symptoms appear. The second is when there are already visual symptoms in the crop, and you want to diagnose what is going on or confirm what you think you are seeing.
If you want to get some tissue testing done out at your place, get in touch with one of our agro’s today.
Below, we’ll look at a few examples of what each deficiency will look like in the crop.
Nitrogen is mobile in the plant and when deficient will be removed from older leaves to be put into the new growth, resulting in deficiency symptoms in older leaves. Thus symptoms will usually appear on the older lower leaves. Symptoms include leaf yellowing and reduced growth, and in nasty cases, the whole plant may turn yellow and then die.
Phosphorus is also mobile within the plant, so again will first be seen on older leaves. The leaves will become purple or reddish, as well as distorted or dead areas on the leaves.
Potassium deficiency affects many aspects of plant physiology and biochemistry, in particularly disturbing water economy of the plant and slowing growth and increasing respiration. Potassium is also a highly mobile nutrient, and symptoms will first show in the older leaves. The leaves become light yellow-green and later a marginal ‘scorch’ of the edges and the tips of the lower leaves.
Magnesium is mobile within the plant, meaning that symptoms are generally seen on older parts of the plant. In most species’ symptoms appear as interveinal yellow chlorosis of the lower leaves with leaf veins remaining green. This yellowing begins at the tip and margins and spreads towards the central vein.
Calcium is immobile in the plant phloem, so you can find deficiency symptoms appearing in new growth. Other symptoms of calcium deficiency include poor root growth, stunting, and a darkening root colour. Yellowing, blackening and death of growing points and leaf tips can occur.
Sulphur is generally immobile in the plant phloem, meaning that sulphur will not be readily mobilized from the lower leaves and translocated to the upper growing leaves. Symptoms will appear as stunted growth and yellowing on the new leaves with a slight upward rolling of young leaves may occur.
Iron deficiency is most often seen on young leaves because it does not move readily in the plant. The symptoms first appear between the veins on leaves while the veins remain green.
Boron deficient plants exhibit brittle abnormal growth at shoot tips, and one of the earliest symptoms is the failure of root tips to elongate normally. These tips can become swollen and discoloured. Leaves can have various symptoms including drying, thickening, distortion, wilting and chlorotic or necrotic spotting.
In grasses and cereals, symptoms generally appear in the centre of middle-aged to older leaves and oily grey-green patches which become necrotic and gradually extend to the leaf margins. A change in the colour to greyish-green with interveinal chlorosis and necrotic spotting on upper leaf surfaces can also occur. Symptoms often appear in cold, wet weather but disappear as the temperature rises in spring.
Copper is very immobile in the soil and is held strongly by organic matter and on clay colloids, meaning it is not very available to plants. Symptoms will vary on the crop; however, younger leaves will usually be the worst affected. The plant may wilt and lack firmness, as well as leaf rolling, bending and crinkling can be seen. In cereals, leaf tips turn light green to cream in colour.
In wheat and barley deficiency commonly appears wilted or limp, with the younger leaves showing these symptoms first. Interveinal chlorosis appears first, and leaf colour rapidly changes to pale yellow. White or grey flecks appear at the base of the leaf, and eventually, the leaf may die. Manganese is more mobile in oats, so the first symptoms will be grey flecks on mature leaves, eventually joining into lesions and then turning pale brown while collapsing.
Legumes will show deficiencies as general paleness and stunted growth, which are similar to the symptoms when nitrogen is deficient. The nodules will be green or pale lacking in their red pigment. Canola plants are less tolerant of deficiencies and will show leaf distortions. In wheat leaves will be pale and may have necrotic areas, this can be patchy across a paddock.