Addressing Post-Flood Soil Challenges in Walgett
We recently had the opportunity to work with a client from Walgett, who faced significant challenges on his property following a flood. As a dryland farmer, the season following a flood presents something of an opportunity with a full moisture profile.
Grower observations/problem
The client noticed that despite appearances of a full moisture profile, the expected productivity was not met. The plant available water they thought was there, was not.
Potential explanation
Initial thoughts were that ponded water from the flood has led to anaerobic conditions, which in turn have diminished organic carbon levels and soil biology at depth. This disturbance has adversely affected the soil's water dynamics, impacting the crop yield.
In field observations
Upon closer examination, we found the soil landscape to be a mixture of grey and black vertosols, displaying significant cracking—some wide enough to reach down to one's hip. The soil cores that were collected between the cracks showed minimal aggregation – they had very limited structure and minimal microporosity. There were clear signs of severe compaction in all cores, leading to our theory that the shear weight of the ponded water had caused widespread compaction. Coupled with the anaerobic conditions, it has resulted in severe limitations on plant-available water.
Solution
While mechanical loosening, such as ripping, could potentially alleviate the issue, it is not advisable under the current subsoil moisture conditions, which are too wet. Such an action could lead to smearing and further exacerbate water penetration issues. Instead, we recommend the cultivation of a tap-rooted crop that both fits within the farm's business model and can also overcome the compaction. The goal is to dry out the subsoil as much as possible before considering any mechanical intervention.
Additional Insights:
It's important to note that while bulk density is a common measure for compaction, its interpretation can be misleading in vertic soils, which exhibit shrink-swell behaviour. These soil types are particularly sensitive to moisture content, which can skew bulk density readings. Therefore, the most accurate diagnosis of compaction comes from collecting an intact core sample. By examining the aggregation of such a sample by breaking down the ped’s by hand we can gain a true understanding of the soil's condition.
Contact Us
If you need help with your soil management after a flood event then please get in touch.
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