There are two types of lodging in cereals. The most common type is root lodging, which usually occurs early in the season and causes leaning of the stems from the crown area because of disturbance to the root system. Stem lodging generally occurs later in the season, when the stem is more brittle as it approaches maturity. Stem internodes break while the roots are held tightly in hard or dry soil.
There are many factors affecting lodging and plenty of people who will adhere to the belief that each one in and of itself presents the greatest risk, but the whole issue comes down to achieving balance, says Elston Solberg, president of Agri-Trend Agrology Ltd.
“The thing that is always missing in the discussion is the concept of balance,” he says. “If you have way too much nitrogen on a crop relative to whatever other nutrients need to be there in balance, then, of course, the crop is going to fall down. Similarly, if you run into a really high yield potential year and you have areas in your field that are copper deficient then lignification of the straw becomes the issue and the crop falls down. The same with potassium, which is strongly correlated to lodging issues as well as many disease issues. But at the end of the day it is about balance. It’s not that N is bad and copper is good or potassium is great, it’s about the balance of those nutrients and how they help each other optimize yield and quality and prevent lodging.”
Variability may be the key term when talking about the relationship between nutrients of any kind and lodging. To make the most of variable rate technology that allows farmers to correct imbalances, they need to be certain of the situation they are dealing with. “Most of the farmers using variable rate N management credit it for reduced lodging on their farms,” says John Heard, crop nutrition specialist with Manitoba Agriculture, Food & Rural Initiatives. “Zone identification of yield potential, soil testing for N and a proper prescription map appear to offer major improvements in lodging management.”
Timing of lodging
Lodging will always have a negative effect on yield. Yield loss in lodged crops comes as a result of poor grain filling, head loss and bird damage. Lodging alters the plant’s growth and development, affecting flowering and interfering with photosynthesis and carbohydrate movement within the plant. It can interfere with the plant’s ability to extract nutrients and moisture from the soil, resulting in incomplete grain fill and smaller kernels. This can give yield losses of up to 40 per cent depending on the severity and timing of the lodging.
The amount of yield loss depends on the growth stage of the plant when lodging occurs:
Before flowering: Stems may regain their upright position if weather conditions are favourable. If not, the crop will have deformed heads and shrivelled kernels.
After flowering: Heads will not regain their upright position. Kernel numbers will not be affected, but the grain weight may be severely reduced depending on weather conditions.
After head emergence: Yield losses are greatest when a crop lodges during the 10 days following head emergence. Yield losses at this stage will range between 15 and 40 per cent.
After maturity: Yield will not be affected, but it may reduce the amount of harvestable grain. Neck breakage and the loss of the whole head can result with lodging at this stage and this can lead to severe harvest losses. In this case, straight combining will lead to higher losses than swathing.
Lodging and quality
Lodging can contribute to uneven maturity, a higher moisture content (necessitating drying of grain after harvest and increasing costs by up to 30 per cent) and a loss of quality due to sprouting and possible moulding. Test weight losses are typically eight per cent for wheat and barley and 15 per cent for oats. Grain protein content may increase by three to 20 per cent because photosynthesis and carbohydrate accumulation is disrupted. This can adversely affect the malting quality of barley.
Foliar diseases may increase due to a more humid microclimate within the lodged crop.
At harvest, lodging can seriously affect capacity, which can be reduced up to 25 per cent. The flattened crop and green, immature kernels mean the knife has to be run closer to the ground, requiring a slower combine speed. It also means that full length straw enters the combine and loss of unthreshed heads can double. All of which adds to harvest costs.
Causes of lodging
Lodging is usually caused because of a combination of morphological (structural) and environmental causes. Lodging can simply be as a result of adverse weather such as high winds, heavy rainfall or hail literally pushing the crop over. There are, however, a number of factors that will increase the risk of lodging.
Soil Type: Soil type can influence lodging. For example, the black soil zone has a high percentage of land with six or eight percent organic matter, which gives a larger reservoir of N for plants to draw on, thereby increasing the risk of lodging.
Manure: On soils where large amounts of manure are applied on a regular basis, (such as from feedlots or dairy operations), there can be a significant build up of N reserves.
Cultivar: Taller varieties tend to have weaker stems and will lodge easier than semi-dwarf varieties, which have stiffer straw. Plant height, stem thickness and straw density can all affect the ability of the plant to resist a lateral force. Changing plant height can have a big influence on lodging.
Roots: Lodging can result from failure of the root system, which if weak, can allow for the plant to be more easily broken or uprooted by force. A well-developed root system helps provide resistance to lodging by improving anchorage.
Disease: The occurrence of fungal diseases such as stem, leaf or stripe rust can increase incidences of lodging. The lush growth resulting from high fertilization (especially of N) and humid, moist conditions can drastically increase the risk of fungal disease. Root diseases, such as eyespot foot rot, strawbreaker foot rot and take-all can all contribute to lodging.
Pests: The wheat stem sawfly causes lodging in wheat. As there is no effective chemical control, experts suggest growing a semi solid stemmed variety. Hessian fly can cause lodging and kinking in wheat or barley crops.
Weather: How much N becomes available to the crop (whether from soil reserves or fertilizer application) depends on the weather. During high moisture conditions more N is released, so high moisture and humidity will contribute significantly to lodging.
Fertilization: High N fertilizer rates will increase the likelihood of lodging. Encouraging plants early on to become root dominant by fertilizing for good root development means there is less likelihood of the plant falling over than if the plant is over-fertilized early on, promoting excessive above ground vegetation, which results in the plant being top dominant. The lusher growth promoted by higher N fertilization, especially under cloudy and humid conditions, leads to more disease pressure from leaf, stem and stripe rust, which further weakens the plant.
Potassium levels: Potassium is one of the major nutrients that helps control water and solute movement in the plant. Straw from potassium deficient plants is more brittle and will have a greater tendency to lodge.
Copper: Copper deficient soils are susceptible to lodging. Copper plays a large role both in pollination of crops and also in lignifications or straw strength.
Seeding rates: Higher plant densities have been shown to increase lodging risk.
Tips to prevent lodging
If lodging occurs it is important to try and assess the crop to find out why it is lodging. Is it because the fertility is too high or because weather conditions have changed to make more N available from the organic matter in the soil? Could it be because you chose to grow a tall variety for silage or perhaps it is simply due to localized adverse weather?
Once you have a better idea of the cause you can try and reduce future lodging risks through a number of ways.
Reduce Seeding Rates: In general, high plant populations increase shading and produce greater internode elongation. If you have used normal (or increased) seeding rates previously and experienced lodging, try reducing seeding rates so that plants are around 2.5 centimetres apart and in row widths of 12 to 18 cm. If randomly seeded, the rate should result in 15 to 30 plants per square foot, depending on the rainfall usually received in the area. Earlier seeding during cooler conditions may reduce internode elongation.
Consider Seeding Depth: Crops seeded too deep have delayed emergence and crown root development, whereas too shallow seeding can lead to shallow root systems with reduced anchorage ability. The optimal seeding depth for cereals is generally 2.5 to five cm (one to two inches), if severe drought conditions are not present. Winter cereals (winter wheat, fall rye, winter triticale) should not be sown deeper than 2.5 cm to maintain winter hardiness. The seedbed should be firmed up to achieve good seed/soil contact, allowing for optimum seeding depth, plant spacing and plant population. Planting rows parallel to the direction of strong prevailing winds can reduce incidences of stem lodging.
Reduce N: Soil test to determine the amount of residual N and other elements present and fertilize accordingly. Consider reducing N rates at seeding based on a soil test and depending on spring moisture conditions. Abundant N during early growth stages promotes excessive tillering and extensive elongation of the lower stem internodes, whereas later applied N does not affect the stem internodes. When reducing N it is also important not to under-fertilize if there is a risk of mining out the organic matter present in the soil.
Spilt N applications: Some growers are using split applications of fertilizer to try and reduce lodging by reducing the N uptake and vegetative growth of the plants early on. The risks with split applications, however, are weather related. Too much rainfall may mean no opportunity to get on the fields at the right time to apply additional fertilizer. Conversely, if conditions are dry after the second application, the N will sit on the surface and there is an increased risk of N loss due to volatilization.
Choose semi-dwarf varieties: Cultivar selection can affect lodging. Go to semi-dwarf varieties with strong straw to reduce the lodging risk.
Consider crop rotation: It is important to take into account the amount of crop taken off in the previous year to help determine how much N was extracted or added. A cereal following peas, for example, may have sufficient N present to be able to reduce subsequent N applications. Crop rotation is also important for prevention of diseases such as common root rot, scald, net blotch and take-all, which can significantly increase the lodging risk by weakening the plants roots or stems. When a cereal crop is grown on a broad leaf crop stubble, such as canola or flax, the disease pressure is less severe. Careful rotations can help to lower protein levels in soft white spring wheat and malt barley. †