The key to healthy, productive pastures has traditionally been seen in terms of species selection and the application of basic fertilisers such as acid treated phosphorus, limestone, and urea in more intensive situations. However a growing number of early adopters are also looking more closely at the broader nutritional picture in conjunction
with soil biology to increase production and reduce costs. The aim is to translate a greater understanding of soil fertility factors into healthy productive livestock and a healthier bottom line.

Soil Nutrition – Balance is Everything

Nutrition of the soil has perhaps been over-simplified on many occasions when dealing with pasture soils. Longer term fertility, and total soil/animal nutrition is often a casualty in the pursuit of cheap inputs with a promise of big results. This is certainly true when we overlook the total mineral package an animal requires for health and high production and forget that in a grazing situation this fundamentally must come from the soil. All growth and reproductive success, as well as most animal ailments, are related to minerals being either adequate or deficient in the food the animal is consuming – the pasture.

A good example is zinc and copper – both elements are often extremely deficient in Australian soils and both elements are directly related to animal health and productivity. A soil deficiency of these elements can cause significant economic loss, yet only a small percentage of growers actually apply zinc and copper to pasture soils.

Soil tests to ascertain deficiencies are perhaps not as popular as they could be.

Acid treated phosphorus applications, although yielding a short term boost, are prone to locking up into insoluble compounds with aluminum and iron at low pH and calcium at higher pH values. These insoluble compounds are not plant available and so nothing like the full fertiliser package is delivered to the pasture. Phosphorus clays and citrate soluble phosphorus materials are generally a better choice for pastures as they rely on weak microbial acids to liberate phosphorus ions for plant uptake. By this natural process the phosphorus is used by the plant as it becomes available through biological activity and as such does not lock up into compounds of greater insolubility.

Calcium applications in the form of limestone can also be a problem when the other cautions such as magnesium and potassium are not taken into consideration. Lime recommendations are unfortunately still often given on incorrect assumptions based on soil pH alone. It must be remembered that magnesium and potassium have a greater influence on soil pH than calcium. As such the relative proportions of calcium, magnesium and/or potassium need to be considered in any recommendation.

Applying calcitic limestone to soils where magnesium or potassium are already low will only exacerbate the deficiency of these elements. The pH may look good, however there will be an imbalance and an induced deficiency. Maintaining the balance of cations is the goal and pH is only a vague reflection of this balance. A good soil test will give the grazier the full nutritional picture.

Soil Biology – The Final Frontier

The management of the microscopic organisms dwelling in our soil has recently been gaining much attention as producers search to marry sustainability with profitability. The benefits of maintaining a healthy microbial soil food web have been well established by many researchers and growers, revealing benefits such as improved nutrient and water storage, reduced leaching of nitrates and calcium, improved plant vigor and improved pasture nutrition.

Materials that yield slow release carbon in the form of humic acid (the active component of organic matter) such as good composts and brown coal (known as lignite, leonardite or raw humate) have shown significant increases in microbial growth and activity in most Australian soils. When combined with slow release soil correcting minerals (based on a soil test) such as limestone, dolomite, magnesite, phosphate clays and trace elements etc, the increased microbial stimulation in turn increases the solubility of these materials. In effect this means that lower rates can be applied to achieve the same sustained pasture response.

A more holistic approach to pasture management is required to create soils that are on a rising plan of fertility rather than declining fertility as is often seen. The aim is to increase production while reducing overall production cost by utilizing our improved knowledge of soil fertility. Correcting soil nutrition coupled with biological stimulation is the key. The simple fertility equation is as follows;

Carbon/ humate materials stimulate soil microbes soil correcting minerals added to avoid deficiencies

Increase in availability of soil minerals to the plant via microbial activity .

Livestock benefit from the increased pasture nutrition over an extended period of time..