A complete soil test is an important first step to help restore the productivity of pastures. Most soil tests provide a breakdown of major and minor plant nutrients but many also profile the soil’s overall health, potential and fertility.
I was recently asked to visit a property in Gembrook east of Melbourne that was used to run horses. This was in February and the soil was very dry, around 3% moisture. At this level most biological activity in the soil ceases (more about this later). Now no-one expects a farm to be at its most productive during summer but its a good time to check on how well the soil and pasture is standing up to the stress of summer. Good indicators are the amount / proportion of bare ground, if there is any useable pasture left standing and the presence of weeds. Unfortunately this property showed signs of stress with little standing feed for the horses.
This is a higher rainfall area and soils are highly oxidized hence the red iron colour common in the area. On the positive side these soils have a good structure and are well aerated but they tend to be acidic and this is difficult for most plants.
Some results:
| Test | measured | preferred | comments |
| pH in water | 5.83 | 6 – 7 | too acidic |
| pH in CaCl2 | 5.04 | 5.4 – 6.4 | too acidic |
| Bulk density | 0.89 | ‘light’ soil | |
| Soil water | 3.1% | around 20% | very dry |
The soil is acidic as expected. The bulk density value shows that the soil is lightly textured and because the soil felt soft this suggests that there may be organic materials in the soil and the soil may be well aerated. By contrast some soils in West Gippsland have a heavy consistency like butter and when dried lose their structure and become powdery.
How much organic matter was in the soil?
| Test | measured | preferred | comments |
| Total organic C | 37184 ppm | 29000 – 52000 | moderate |
| Fresh organic C | 466.5 ppm | 860 – 2100 | very low |
| Proportion fresh org C | 1.23% | 2.9 – 3.9% | low |
The soil had moderate levels of organic matter but most is ‘older’ humic type organic matter. There is not much fresh organic matter present. Overall the picture is of little recent return of plant material to the soil. Is this important? Yes, because organic matter has a significant role in making nutrients such as phosphorus and sulphur available to plants – a very important role in these types of soils. Check my previous blog entries for some results and comments for dairy farm soils.
Complete soil tests are a cost effective management tool. Tests that cover all nutrients, many of the main physical factors and organic matter levels cost around AU$150. In future blog entries I will cover more of the test results from this Gembrook soil.