Last week we excavated some soil pits near Clare in the Mid North of South Australia. Some great fertile red soils cover a large area of the Mid North region of SA and from the surface all look very similar. However, upon opening up a number of pits it is readily apparent that there are many different soil profiles that constitute the soils of the Mid North.
The diverse range of subsoils that are present, even over a small area are quite amazing. From deep red loamy clay soils to red loams over shallow calcareous (limestone) subsoils (see photos above).
Each soil profile was interesting and all could be managed for profitable cropping returns, however as always very reliant on the timely rainfall events, with spring rainfall definitely being a limiting factor in the past few years.
When it comes to soil use efficiency and water use efficiency in all of these soils it was apparent that the soil structure is quite often the limiting factor to production. A majority of the soils in the area are very low in organic carbon, often less than 1.5% Organic Carbon.
No-Till in the are has certainly aided in reducing the soil carbon loss however when it comes to stabilising the soil the low organic matter present in the soil is reflected by the aggregate stability being so low.
The soils of the area are , in relative terms, structurally unstable with slaking and dispersion readily occurring (read the dispersion article for more information). This results in surface and or subsurface sealing which reduces water infiltration and drainage which directly impacts the crop performance, from germination right through to water accessibility late in the season.