You cannot consider fertilisers without knowledge of the soil. The key points will only be touched on here. See further reading for more information.
- In geological terms, New Zealand it's a very young country, with major ash storms from volcanos being deposited as recently as 1300AD.
- NZ Soils have all been surveyed, described, and mapped by what used to be the government's Soil Survey.
- Soils arise from the underlying rock after being broken down by climatic factors such as water freezing into ice and expanding in cracks.
- Soils can also be formed in other places and moved by wind, water (rivers) and ice (glaciers).
What kind of soils are there in New Zealand?
- The classification of soils is very descriptive and is mainly based on colour.
- Then within the broad types listed below, there are local types, named after districts or areas.
- So knowledge of your farm's soil classification is very important in getting best value from your fertiliser investment.
- Ash or allophonic soils (from volcanic parent material)
- " Yellow-brown loams (Waikato, Taranaki)
- " Red brown loams, granular clays, loams (Northland, Waikato).
- " Poorly-drained (gley) soils formed from volcanic ash (Waikato).
- Sedimentary soils - formed from sedimentary rock
- " Yellow-brown earths or brown soils (Southland).
- " Yellow-grey earth or pallic soils (Manawatu, South Otago).
- " Yellow-brown sands (Manawatu, Northland).
- " Gley podsol (Pakahi) soils.
- Pumice soils (from volcanic parent material)
- " Yellow brown pumice soils and gley soils formed from raw pumice (Bay of Plenty, Central Plateau).
Peat or organic soils
- These have little or no mineral matter and are made from plant and forest residues (Waikato).
How can you find out what soils you have ?
- Landcare portal http://lris.scinfo.org.nz/
- Waikato Regional Council website http://www.waikatoregion.govt.nz/Services/Regional-services/For-schools/Resources-for-teachers/Classroom-units/Soils-and-us/
Soil texture - is it important?
- The texture of a soil is a key component in classifying soils.
- There is a long list of classes of soil based on texture.
- Texture is decided by testing the soil in the top layer where the plant roots grow. Below that are rocks and boulders.
- Soils are made up of sand, silt, and clay particles - all less than 2mm. It's the proportion of these components which determine soil texture.
- Sand - between 2.0 and 0.06mm
- Silt - between 0.06 and 0.002mm
- Clay - less than 0.002mm
Why is soil structure important?
It gives a good guide to:
- Soil water - its retention and release to plants.
- Soil structure - its development and stability.
- Nutrient retention and availability to plants.
- Activity and retention of residual soil-acting herbicides.
- Erosion potential by wind and water.
- Stickiness and ease of cultivation.
- Drainage characteristics and suitability for mole draining.
- Cropping suitability.
- Soil temperature changes.
- Stocking capacity - pugging risks.
Which enterprise for which soil type?
- Some farming enterprises are better suited to particular soils - if you have a choice.
- If you don't have a choice, then you need to understand the challenges involved. An example is where dairy farmers provide standoff pads in winter on fertile wet soils.
- It's become a very high priority to choose an enterprise that does not damage the delicate 'crumb structure' of the soil by 'pugging' to allow water to drain through and air to reach plant roots.
- Pugging smears the soil crumbs so the structure is damaged and may take a very long time to be restored.
- You need to talk to a consultant about which enterprise is best for you.
Special thanks to my former MAF colleague, Dr AHC Roberts, now Chief Scientific Officer at Ravensdown for helpful comment and permission to use his AgResearch information, and to my former fellow student and UK soil consultant, Dr Tom Batey from Aberdeen.