Archive for the ‘Horses’ Category

Farm soil testing – major nutrients

Tuesday, May 6th, 2014

Up to now we’ve looked at some of the main physical factors in the soil at the Gembrook horse property. Now its time to look at the other main nutrients and the soil’s fertility.

Soils have an ability to loosely hold nutrients to prevent leaching and to make them slowly available to plants. This applies mostly to the positively charged nutrients like calcium, magnesium and potassium. This is called the Cation exchange capacity and it depends on the type of clays but is higher in good structured soils like loams. Because organic matter also holds these same nutrients the amount of organic matter affects CEC.

This soil has a CEC of 17.76 meq%. This value is around mid range with sandy soils at around 1 meq% and organic soils around 30 meq%.

Nutrients are assessed in terms of absolute level, relative proportions, percent of nutrient holding capacity and levels compared to non nutrients and acidity.

Major nutrients weight for weight in the soil.

Nutrient Result Recommended range Level

ppm ppm
calcium 1859 1200 – 2000 good
magnesium 297.5 150 – 300 good
potassium 400.7 180 – 300 high
Horses at Gembrook eating hay during Autumn. Good nutrition is essential for growing or working horses and this can start with good quality pasture. A soil test can identify problems that can lead to nutritionally poor pasture and further health problems.

These horses at Gembrook are being fed hay during Autumn. Good nutrition is essential for growing or working horses and this starts with good quality pasture. A soil test can identify problems that can lead to nutritionally poor pasture.

The overall level of the major nutrients calcium, magnesium and potassium is good but a look at the makeup of the exchange capacity tells a different story.

Nutrients as proportion of (CEC) with comparison to non nutrients
Nutrient % of nutrient Recommended Level
holding capacity range
calcium 52.3 60 – 70 low
magnesium 13.8 12 – 20 ok
potassium 5.8 4 – 6 ok
Non nutrients
sodium 1 < 4 ok
exchangeable acidity 27 13 – 20 too high

The proportions (of CEC) of calcium and magnesium are low. At the same time, exchangeable acidity proportion of CEC is very high. So the soil has a too high proportion of acidity taking the place of more desirable nutrients. Its like saying, the soil has the capacity to hold more nutrients but they are not there. Instead, their place is being taken by acidity.

For similar soils, the higher the exchangeable acidity, the lower the pH.

Another way to look at this is to say that in this soil desirable nutrients (plus some low levels of sodium) occupy 73% of available capacity. This figure is called the base saturation. The base saturation represents the proportion of nutrient holding capacity CEC that is actually occupied by desirable nutrients. Around 80 – 87 % is considered desirable. The non desirable proportion is exchangeable acidity.

Sulphur was also measured in this soil. The result was 17.6 ppm. Around 10 – 40 ppm is considered desirable so the sulphur level was OK.

To change the pH of the soil some of the exchangeable acidity will need to be neutralized. This has to be done gradually, usually by applying lime. As the lime neutralizes the acidity, calcium and magnesium (if using dolomite lime) slowly occupy more of the exchange capacity and will slowly raise the pH by increasing the base saturation.

How can I improve the pasture on my farm?

Tuesday, March 11th, 2014

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.

Horse paddock in Gembrook. A complete soil test is the first step towards re-establishing a good feed base for horses.

Horse paddock in Gembrook. A complete soil test is the first step towards re-establishing a good feed base for 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.