The adverse effects of floods can lead to both short term and long term soil health issues on the farm.
These effects often range from nutritional challenges to soil movement and even negative impacts on the soils microbial health.
With this in mind, let’s dive into the 5 incredibly adverse effects that floodwaters can have on the health of your soil.
When farmers think of soil leaching the first nutrient that comes to mind is nitrogen.
This is understandable as nitrogen is one of the core building blocks for life and as well as being the main driver behind plant biomass production.
With this in mind, a soil test after a significant flood event is an essential part of effectively planning for your up and coming season.
The test will need to cover deep N as well as a variety of micronutrients that are essential for healthy crop growth.
Under conditions where the soil is starved of oxygen, a process called denitrification occurs.
This process converts the plant-available forms of nitrogen into nitrogen gas effectively depleting the amount of nitrogen available for next years crop.
It’s important to keep a close eye on soil nitrogen levels particularly after a significant rain event.GRDC 2014 (Reducing Potential N Losses)
The process of mineralisation is an essential component of both farming and environmental ecosystems.
Mineralisation is effectively the conversion of organic forms of nutrients such as plant matter into forms that are available to plants.
Under flooded conditions, the levels of mineralisation dramatically decline as the percentage of water-filled poor spaces begins to exceed 60%.
It’s at this point where denitrification begins to become the dominant microbial process resulting in a net decline of plant-available nitrogen.
The relationship between water filled space (a measure of soil moisture availability) and relative amount of microbial activities.Soil Microbiology, Ecology & Biochemistry 4th Edition, Redrawn from Linn and Doran (1984).
The above graph shows the significant decline of nitrification and the steep incline of denitrification as the percentage of water-filled poor space exceeds 60%.
Compaction & Crusting
The presence of floodwater for an extended period can often result in compaction and crusting occurring particularly on soils with high clay content. During these conditions, cultivation may be necessary to aerate the soil.
Soil tests should also be conducted to assess how the soil profile may have changed while being submerged by floodwater.
Examples may include newly formed compaction layers as well as new layers forming due to erosion and soil mixing.
Nutrient deficiencies as a result of leaching are the first things that come to mind when planning for the next season.
Although an excess of certain nutrients can cause major problems for local growers. These nutrients are often in the forms of salts in areas of rising groundwater.
Evidence of salt toxicity often present as leaf burn and wilting due to a reduction in nutrient and water availability adding to the negative soil effects of floods.
That sums up the 5 incredibly adverse effects of floods on soil health. Soil tests will help alleviate the vast majority of these issues for the upcoming season.
When testing ensure that deep cores are taken to effectively capture any deep nitrogen storage as well as a snapshot of how the profile has changed as a direct result of the floods.