How crops lodge?
Cereals lodge due to interactions between wind, rain and soil with the plant. The factors affecting wheat lodging are wind speed, rainfall, soil strength, soil residual nitrogen, sowing date and plant population.
If the stem buckles,lodging results. Wind force exerts leverage on the plant. Results in STEM lodging. Stem strength depends on stem diameter and the composition and width of the stem wall. Stem lodging occurs when the stem base has insufficient strength to hold the shoot up against leverage.
Rain decreases soil strength and anchorage. Anchorage depends on the spread and depth of the root plate
and the strength of surrounding soil.
Root lodging occurs when the root system has insufficient
anchorage to hold the plant up against leverage.
Costs of lodging:
On average, every three or four years widespread lodging occurs on up to 20% of the UK winter wheat area. Lodging has serious economic effects; yield is reduced and quality impaired, while combining and drying costs increase.
Economic loss is greatest when crops lodge early. Up to 75% of yield can be lost if crops lodge at ear emergence.
Later lodging has less effect on yield, but will impair quality characters such as Hagberg falling number. Lodged crops often require extra drying which can cost £3–£7.50/tonne.
Factors affecting wheat lodging:
Lodging risk increases as the wind leverage exerted on shoots rises. A 5kph increase in the maximum wind speed has the effectof reducing the varietal lodging resistance score by 1.
Just 6–11mm of rain in a day reduces soil surface strength and significantly increases the risk of root lodging. In a season with four extra days (compared with the farm’s average) when rainfall exceeds 7mm, the varietal lodging resistance score will effectively be reduced by 1.
Soil shear strength has a large impact on anchorage strength and has most effect on root lodging risk. Soils with good crumb structure, low clay content or high organic matter tend to provide less anchorage and hence crops are at a higher lodging risk. Soil strength also reduces significantly as moisture content increases.
Long growing seasons, high fertility sites or eyespot infection can increase lodging risk.The varietal lodging resistance score decreases by 0.5 points for each 1t/ha yield increase. Crops grown in fields with light and drought-prone soils tend to lodge less. Latitude influences sowing date and length of growing season which affects lodging risk.
Crop condition in spring can indicate future lodging risk.
Root lodging risk increases when plant population exceeds 200 plants/m2.
Stem lodging risk increases when the canopy at GS31 is large (green area index of 2 or more, or ground cover of >60%) as such crops tend to be weak-stemmed.
Assessing and managing risk:
To assess the likely threat of lodging to a specific crop, start with the resistance to lodging score for the variety in
The HGCA Recommended List® provides a combined root
and stem lodging resistance rating for each variety. Recent
research shows that husbandry affects root and stem
lodging to different extents.
Soil residual nitrogen:
The amount of nitrogen left in the soil after a previous
crop can significantly affect lodging risk. See ‘Further
information’ for references to RB209 and T516 which
provide details on calculating crop N need and soil
Early sowing leads to taller crops with a higher risk of both
root and stem lodging.They also have denser canopies and
often weaker stems. Adjustments (see right) are for
central England. In northern Britain treat score for end
September as zero.
Crops grown at higher plant populations have an increased
risk of root lodging due to reduced anchorage strength.
Stem strength is also reduced to some extent.
A variety’s risk of lodging is given on a 1–9 score. Varieties
with a score without PGR of 7 or less can be considered
High levels of soil N (SNS index 3 or above) promote thick, dense crop canopies that are more susceptible to stem
lodging. Each unit increase on the soil nitrogen supply (SNS) index reduces stem lodging resistance score by 1.5. The effect on root lodging is about 0.75. Early-sown crops (before October) are affected most by high soil N levels.
For each week’s delay in sowing, between mid-September
and early November, a crop’s lodging resistance score
increases by 0.5.
At plant populations of 200–400 plants/m2
, each increase
of 50 plants/m2 reduces stem lodging resistance score by
0.5 and root lodging by 1.0. Effects are greater below
Total lodging resistance score:
Early (pre–GS31) or excessive applications of nitrogen increase tiller numbers and reduce stem strength.This
increases the risk of both stem and root lodging. Nitrogen applications should always seek to optimise yield and quality.
A canopy management approach to nitrogen use (delayed and reduced applications) increases both root and stem
lodging resistance by 0.5 points. Delaying the first split where soil fertility is moderate or high is unlikely to affect yield.
Plant growth regulators:
Tall crops are more prone to root and stem lodging. Plant growth regulators shorten crops to reduce both lodging
risks to similar extents.
A single PGR application can increase both root and stem lodging resistance by 0.5 to 1.5, depending on variety and
Loosely-structured soils provide weak anchorage for crops. Spring rolling, in appropriate conditions, consolidates such soils to reduce root lodging risk.
Spring rolling before GS30 increases the root lodging resistance score by 1. Rolling after GS30 can damage the growing point.