Impact of waterlogging

  • Waterlogging reduces cane yield, with losses of about 0.5 t/ha per day when the water table is within 500 mm of the soil surface (Rudd and Chardon 1977).
  • The effect of waterlogging on cane yield has also been demonstrated more recently in the Herbert region (Salter et al. 2018).
  • Waterlogging stress is associated with anaerobic conditions (lack of oxygen) in the soil and the effect this has on root system function.
  • Waterlogging affects small less developed crops more than larger better developed crops.
  • Periods of waterlogging are also associated with high cloud cover and low solar radiation. A lack of sunlight limits the crops ability to grow and slows the rate at which soils dry out.
  • Waterlogging may occur for several months on some soils and only temporary on others. This depends on rainfall amount and duration, position in the landscape and the soils internal drainage characteristics.

Figure 1. Crop damage due to waterlogging in an experiment (image G. Park)

Figure 2. Roots are produced at the soil surface in response to waterlogging (image G. Park)

Figure 3. Cane yield in control and plots waterlogged for approximately 1 month in December (Early) or January-February (Late). Source: SRA project 2014046

 

  • Management practices to reduce the effect of waterlogging include:
    • Laser levelling to improve surface drainage.
    • Improving subsurface drainage systems.
    • Planting on mounds.
    • Planting or harvesting blocks prone to waterlogging earlier in the season to avoid waterlogging when the following crop is still small.
    • Where possible, irrigation should be used to ensure the crop is established and actively growing prior to the onset of the wet season.
    • Varieties with better waterlogging tolerance should be used on blocks that experience waterlogging regularly.
    • Fertiliser should be placed into the mound.
  • Improving the management of these blocks is a higher priority than adjusting fertiliser rates.

 

  • Denitrification occurs when soils are waterlogged. Nitrogen is lost from the soil as nitrous oxide (N2O) gas and/or di-nitrogen (N2) gas.
  • These losses can be substantial, and combined with a stressed root system, may limit the crops ability to acquire nitrogen.
  • The limitation on crop growth caused by waterlogging may result in a lower nitrogen requirement.
  • The two previous points highlight a complex situation where the crops ability to acquire nitrogen may be limited but the crops nitrogen requirement may not be high due to low growth potential.
  • In the SIX EASY STEPS program, soils with high organic carbon content have a high or very high nitrogen mineralisation index. Nitrogen fertiliser recommendations are reduced on these soils to account for the soils ability to mineralise nitrogen. However, soils with high organic carbon may also have high clay content and occur in low positions in the landscape prone to waterlogging. Therefore, in some cases nitrogen fertiliser recommendations for soils prone to waterlogging are already relatively low.

Determining an appropriate N rate

  • Management practices to reduce the impact of waterlogging on the crop are a higher priority than the adjustment of nitrogen fertiliser rates (see above).
  • The SIX EASY STEPS recommended rate should be used to guide nutrient application.
  • There may be an opportunity to reduce nitrogen rates for blocks that experience frequent prolonged waterlogging, where nitrogen responses are likely to be poor and crops are consistently low yielding due to the effect of waterlogging.
  • Reducing nitrogen rates may not be appropriate if the recommended rate is already low due to a high soil organic carbon content.
  • The weather/climate forecast, and its reliability, would need to be considered, as waterlogging may not be experienced.
  • If wanting  to make adjustments for waterlogged conditions, it is best to conduct an on-farm trial and consult a trusted advisor.
  • Guidance for conducting on-farm trials is included in the SIX EASY STEPS toolbox.
  • Only make small (10%) changes when assessing different nitrogen rates and use the results to build confidence in the new approach. Taking notes on the extent of waterlogging experienced during the trial and crop stage when waterlogging occurred will be critical for assessing results.
  • Leaf testing also provides a valuable method for checking on the adequacy of nutrient inputs.

 

Disclaimer:

Papers published from the Australian Society of Sugar Cane Technologists annual conference are also available at www.assct.com.au

 

Version: April 2020

 

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