LandWISE offers post-flood soil management advice

Date: 30.03.2023

LandWISE has compiled some useful New Zealand and international resources around post-flood soil management

Know what the flood has done in your paddocks or blocks

This information is available at landwise.org.nz and is a collection of resources to help growers make decisions about repairing, rebuilding or developing their soils, following flood events such as Cyclone Gabrielle.

Included in this is dealing with sediment covered paddocks and revegetating cropping soils after a flood.

In a nutshell:

Each situation is unique but principles apply
Take time to breathe – plan, prepare, act for best results
Know what the flood has done in your paddocks or blocks
Did water site for more than 3 days?
Was the site scoured?
Has sediment been deposited?
Check your drainage – poor drainage will slow recovery
Flood sediment is typically unstructured, with varying depths and textures
Sandier where water moves quicker, clay where water ponds
Nutrient status and pH variable, so soil testing and amendment helpful
Soil drying rate depends largely on texture – plan around that for sowing drier first, wet last
Anaerobic soil not good for seed, but cultivation will rapidly help
Medium depth sediment (5 – 20cm) best cultivated to mix with topsoil below
Deeper silt deposits (>20 cm) appear best cultivated when dried enough – lighter tractors preferred
Surveys showed annual crops e.g. oats, ryecorn, annual ryegrass grew well
Legumes can be beneficial especially in ongoing fertiliser applications not intended
Mulching cover crop s when mature may help build soil organic matter
Think about the crops likely to planted when selecting species for covers
Get something going as soon as sensible to avoid dry soil blowing and to start rebuilding soil structure