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What can you do with waterlogged paddocks?

How do you make evidence-based decisions following excessive rain and slow soil water drainage? Where the crop is not a write-off, getting a handle on which areas of the paddock are in the best shape, and the yield potential for those areas is the most useful information to have.

Assessing crop condition

Split the paddock into zones visually (or using Normalised Difference Vegetation Index (NDVI) mapping). For example:

  • zone 1 –  few visible signs of waterlogging stress on plants
  • zone 2 –  plant growth or tiller numbers are clearly reduced and yellowing is evident but some recovery is likely
  • zone 3 –  plant and tiller numbers are dramatically reduced or a complete absence of crop.

The best potential for investment is in zone 1 where there is the least damage. These areas deserve the most scrutiny to get an evidence base for further investment to maximise 2016 profits.  Use quantitative methods to assess the condition of crop plants and their potential for response to additional fertiliser.

  • tiller counts to inform a revised N budget
  • tissue tests inform the nitrogen status of the crop and any likely micronutrient requirements. For nitrogen take whole plant samples and for micronutrients take samples from the youngest expanded leaves.
  • Look for actively growing roots to indicate that the crop is recovering from waterlogging and may benefit from applied N.
  • After the end of tillering, yield is unlikely to be responsive to N, but grain protein may be increased.

Zone 2 is likely to represent a small loss to a small profit.  Care should be taken when investing in these areas as it can increase risk exposure with limited upside. Zone 3 is not worth further investment to improve 2016 yields, and planning for the next season might warrant some extra investment in weed control and moisture conservation.

Fallow or write-off paddocks

Northern and southern regions:

  1. Keep the area free of weeds. This promotes the conservation of significant soil water stores and a disease break for the 2017 crop. At this late stage in the season, it’s likely this is the best option.
  2. Sow safflower – a very effective late sown crop in southern NSW requiring about 500mm of water to produce ~4 t/ha. Best yields are obtained where sowing occurs before mid-August. Farmers will need to do their research on this crop before sowing with regards to both crop management and marketing options and need to ensure herbicide residues from failed crops are considered.Visit this GRDC GrowNotes page on safflower agronomy.
  3. Sow either wheat or barley. However, timing is likely to be too late for this option given a short growing season and low grain prices.
  4. Sow forage that can be utilised by livestock very late in the season when other annual species have senesced. Very long season grazing canola varieties are an option but may present problems in terms of disease management in your cropping rotation. Arrotas arrowleaf clover can ensure both very late season grazing and nitrogen fixation for the following crop. Other pasture legume options are not likely to fix as much nitrogen as arrowleaf or to produce as much fodder.

Northern region only

  1. Sow mung beans, currently priced at around $1000 to $1200/tonne, rather than conserve the moisture for the 2017 winter crop. Purchase pure seed to avoid tan spot and halo blight which can be a problem with the varieties Jade-AU and Crystal. Planted on less than 100 mm of stored moisture with late follow-up rain, mung beans can grow as small plants with very few pods, making it hard to harvest and to know when best to desiccate.
  2. Consider dryland cotton, taking care with residual herbicide use prior to sowing, ensuring the correct time frame and rainfall have been exceeded. Also, ensure that the soil has also been through a wetting and drying cycle. Herbicides require a wetting and drying process to degrade in the soil. Waterlogged the soil may not have had enough aerobic conditions to degrade herbicides sufficiently.

Setting up for summer crops should include soil testing to determine available N levels for non-leguminous crops. Soil testing should be carried out at 0-60 centimetres. Where growers are interested in the timing of N application, samples can be separated into 0-30 and 30-60 cm.

This article was prepared in response to discussions between growers, advisors and researchers at the More Profit from Crop Nutrition Roadshows 2016.

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