Waterlogging in soil occurs when the root zone becomes saturated, and the air between the soil particles is replaced with water. This can result from heavy localised rains, flood waters slowly flowing across the landscape, a rising water table or a combination of all three. The persistence of the waterlogging is influenced by local topography and drainage properties of the soil.

Compacted soils and soils with shallow impermeable layers are particularly prone to waterlogging. Compaction is generally more of an issue in soils with high clay content, especially soils with a high sodium-to-calcium ratio.

Waterlogging may continue even after surface water has dissipated, particularly in clay soils and soils with a shallow impermeable layer below soil surface. Digging a hole or installing a test well can help monitor the water table and degree of waterlogging.

It is best to re-direct any traffic movements and defer cultivation while the soil is very wet to prevent soil compaction. Only work the soil once the excess water has drained away, but care is needed as cultivation has the potential to pulverise the soil and create further damage to soil structure. 

Identifying issues created by waterlogged soils

The Australian Wine Research Institute (AWRI) noted that waterlogging is known to increase the impact of soil salinity. Salts in the subsoil can move up the profile into surface soils and the rootzone area through rising water tables and flooding, becoming highly concentrated and causing damage to roots, especially as the soil dries out.  When a lack of oxygen impairs root function, plants have difficulty keeping sodium and chloride out of the roots, and they end up accumulating more salt than usual.

A gypsum (calcium sulphate) application onto the soil can assist with displacing sodium from the soil profile and, as a result, will improve the soil's structural stability.

AWRI noted that waterlogging can cause changes in soil pH, which can then affect the availability of some nutrients.  In the right conditions, an agricultural lime application may be considered if soil pH needs to be corrected, based on a soil lab test result.

Gypsum improves soil structure

Adding gypsum (calcium sulphate) to the soil can assist with improving soil structure. One of the many the benefits is the sulphate in gypsum binds with phosphorus, reducing leaching from the soil.

 With greater stability of soil organic matter and the creation of soil aggregates may assist with water penetration through the soil profile due to soil structure improvements. Increasing soil integrity and reducing soil crusting will result in more rapid seed emergence.

Soil micro- organisms and earth worm activity, which aids in soil aeration and macropore formation, does best in soil with moderate moisture and high calcium levels (The Biological Farmer).

Talk to your local fertiliser advisor about gypsum applications based on a recent soil lab test result to improve soil structure. 

Gypsum – It all starts with healthy soil. Gypsum is BioGro certified.

References

Australian Wine Research Institute, Managing Waterlogged vineyards fact sheet, Govt of Western Aust, Dept of Primary Industries, Agriculture and Food, Bulletin 4666 Managing Waterlogged Dispersive soils, 2022

Use of gypsum on soil where needed can make agriculture more sustainable, A Wallace, 11 Nov 2008

The Biological Farmer, Gary Zimmer with Leilani Zimmer- Durand, 2nd edition 2017. Publisher is Acres USA.

Bulletin 945: Gypsum as an agricultural amendment, General use guidelines; W Dick, L Chen, Ohio State University.