Highlights:

  • Flooded soils impact oxygen levels in soils. However, a balance needs to be maintained between working soils to assist in aeration and minimising compaction from use of heavy equipment if soils are too wet.
  • Ideally, 50 percent of the soils’ pore space should be filled with air for good root growth.

  • Replanting the damaged or lost crop may not be the best option. Consider a crop rotation, cover crop or green manure crop to help the soil recover.

  • The net photosynthesis of a crop can be significantly impacted after only 24 hours of inundation.

  • Mycorrhizal colonies are not heavily impacted by flooding, but root growth is still inhibited in short term inundation periods (8 hours).

  • Soil microbiota is resilient to flooding for periods of up to three weeks and can generally be expected to recover within three weeks post floods and is typically not influenced by soil type.

  • Conditions that increase the soil microbiota resiliency include the presence of high organic content and carbon.

Key information and source (all articles and research papers are from experiences and research in the USA):

Management considerations for post flooding soils

Iowa State University, USA

Key Points:

  • Several changes take place when soil is flooded for an extended period of time that can be carried into the next season.
  • Flooded soils may experience what is called "post flood syndrome," similar to the fallow syndrome.
  • Crops planted after a fallow or flood period may grow poorly.
  • Flooded soils may encounter problems caused by the reduction of soil arbuscular mycorrhizae (AM) fungi colonisation rates in the following season.
  • Physical-chemical-biological changes in soil such as aggregate stability, soil structure, pH etc., can be significant if there is no growing crop.
  • This research shows that growing plants, such as cover crops, row crops and other crops, can increase AM recolonisation and ultimately the availability of phosphorous.
  • AM fungi inoculation of soil may not be feasible.
  • Once soils become aerobic, soil micro flora will recovery naturally.
  • Flooded soils may indicate an average phosphorus soil test levels and low AM population.

Land leveling and sand cleaning –

  • Sand removal depends on the depth of accumulation.
  • Sand up to a few inches in depth (i.e. 5-10 cm deep) can be incorporated into the soil using normal field operations. Otherwise, minimum soil disturbance is advisable.
  • If sand is up to 15cm in depth, then mouldboard plough to a depth twice the sand depth to incorporate it into the soil.
  • If sand is 20-60cm deep, it is advisable to consider spreading it to areas with less sand and incorporate it with special deep tillage equipment. It is not advisable to move sand to fill lower or severely eroded areas in the field without proper topsoil to cover the sand.
  • For sand more than 60cm deep, evaluate the cost of removing or stockpiling sand.
  • In the case of severe erosion and deep cuts, topsoil from surrounding fields should be used to fill such areas.

Dealing with flooded vegetable fields

Cornell University, USA:

Key Points: 

  • Corn may have a short-term reduction in root and leaf growth rates within 1-12 hours, but tend to recover quickly 2-3 days after water has drained away.
  • If flooding in corn lasts less than 48 hours, crop injury should be limited. Look for new leaf growth 3-5 days after water drains from the field.
  • Excess moisture in early corn development retards root development.
  • When six-inch corn was flooded for 24, 48 and 72 hours corn yields were reduced 18, 22, and 32% at a low nitrogen (N) fertilizer level.
  • At a high N level, these reductions ranged from 19 to 14 % one year and when corn at a height of 30 inches was flooded for 24 and 96 hours, yields were reduced 14 to 30 %
  • When flooded near silking, no reduction in yield occurred at a high N level, but yield reductions up to 16% occurred with 96 hours of flooding at the low level of N.
  • Higher levels of N may help reduce yield losses in flooded corn crops.
  • Flooding of a short duration, less than 48 hours should have a minor impact on yield in vegetable crops.
  • Flooding for 48 to 72 hours may result in more significant yield losses.
  • Two actions that may assist with flood recovery: 1) as soon as the soil can be worked, till the soil to break up sealed surfaces and allow air to enter the soil, and 2) side dress with nitrogen, perhaps during the tillage operation or, if conditions do not allow for soil applications, apply a foliar application. Speak with a qualified agronomist to see if this is recommend for your situation and appropriate rates of application.
  • Consider a cover crop/ green manure crop instead of your typical plantings.

The effect of repeated short-term flooding on Mycorrhizal survival in snap bean roots*. (Phaseolus vulgaris L.)

Hort Science Vol 41 (Issue 3) June 2006

Key Points: 

  • Flooding did not affect survival of mycorrhizal colonies established before the first flood event.
  • Percent root colonisation in flooded vs non-flooded treatments was not significantly different at either 31 or 50 days after planting.
  • Three weekly floods beginning at 13 days after planting did not inhibit initial mycorrhizal colonisation.
  • Each test flood duration was 8 hours.
  • At 31 days after planting, the two periodic short-term flood events significantly reduced root length below that of non-flooded plants.

*Note- flood period was of a short duration and plants were in potting mix, not soil which may have influenced the ability of the mycorrhizal to spread during the first flood simulation.

Flooding reduces gas exchange and growth in snap bean (Phaseolus vulgaris L.)

Hort Science Vol 26 (Issue 4) April 1991

Key Points: 

  • The net photosynthesis of plants flooded for 1 day was 17% lower than that of the control (not flooded) and it reaches near zero in plants flooded for 7 days.
  • After recovering for 7 days, none of the flooded plants regained gas exchange activities on par with the control.
  • Overall, even 1 day of flooding reduced photosynthesis in snap bean and caused a decrease in dry weight of the plant. The extent of decrease, increased with the duration of flooding.

Impact of flooding on the soil microbiota

Environmental Challenges Volume 4 August 2021

Key Points: 

  • The soil microbiota is resilient to stagnant flooding up to 15 days.
  • Three weeks of recovery period post flooding allows microbiota to recover.
  • The resiliency of soil microbiota is independent of the soil type.
  • Three weeks incubation recovery time for soil microbiota based on previous studies.
  • Soil microbiota recovers within 3 weeks even after up to 15 days submerged in floodwaters.

Farming after a flood

Successful Farming

Key Points: 

  • Prolonged soil exposure to standing water can convert phosphorus (P) into unavailable forms. If planting corn/maize, it is best to start with P at planting. P in the soil will convert to available P during the growing season.
  • Soils recover faster with living roots growing in it. If you can't plant your normal crop, consider a cover crop.
  • Chicken or cow manures may help re-establish soil microbiota, earthworms and beneficial nematodes.
  • Soil microbiota is likely to recover within 3-4 weeks and mycorrhizal fungi is likely to have been minimally impacted.

References

Al-Kaisi M. 2019. Management considerations for post flooding soils. Integrated Crop Management News, Iowa State University Extension and Outreach, USA. [accessed 28 March 2024] https://crops.extension.iastate.edu/cropnews/2019/03/management-considerations-post-flooding-soils

Johnston G. 2012. Farming after a flood. Successful Farming, USA. [accessed 28 March 2024] https://www.agriculture.com/farm-management/farming-after-a-flood_298-ar22297

Reiners S. 2019. Dealing with flooded vegetable fields. Cornell University, USA. [accessed 28 March 2024] https://www.westoxfordallotments.org/wp-content/uploads/2019/11/Dealing-with-Flooded-Vegetable-Fields.pdf

Shah A, Shah S, Shah V. 2021. Impact of flooding on the soil microbiota. Environmental Challenges. 4: 100134. [accessed 28 March 2024] https://www.sciencedirect.com/science/article/pii/S266701002100113X

Sah S, Reed S, Jayachandran K, Dunn C, Fisher JB. 2006. The effect of repeated short term flooding on mycorrhizal survival in snap bean roots. Hort Science. 41 (3): 598-602 [accessed 28 March 2024] https://journals.ashs.org/hortsci/view/journals/hortsci/41/3/article-p598.xml?rskey=7kxhzF&result=1&tab_body=pdf

Singh BP, Tucker KA, Sutton JD, Bhardwaj HL. 1991. Flooding reduces gas exchange and growth in snap beans. Hort Science. 26 (4): 372-373 [accessed 28 March 2024] https://journals.ashs.org/hortsci/view/journals/hortsci/26/4/article-p372.xml?rskey=N9EGoz&result=19&tab_body=pdf

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