Mapping soil attributes can lift pasture performance to new levels

Crop growers have used precision agriculture methods such as yield mapping for several years to help sort out issues such as why some parts of a paddock yield far greater than others.

Soil fertility, sodicity, acidity or sub soil toxicity are all factors responsible for different yields.

Precision Pastures is an example of a business specialising in assessing and mapping pasture paddocks based on two-hectare grids.

Milton Curkpatrick, director of the business, points out that carefully assessing pasture paddocks with science-based information, such as nutrient and pH, and mapping these can save farmers a lot of money and ensure expenditure is more accurately targeted.

For example its soil surveying and analysis commonly show pH across an area can vary from 4.3 to 5.5. In such a case lime application at a standard rate of 2.5 tonnes to the hectare would be wasted on the higher pH zones, may be ideal for some of the area and too low for the extreme low pH parts.

Its surveying data, converted by computer programs, provides clear zoning areas across a paddock with different categories of soil aspects such as pH or nutrient levels like phosphorus.

Contractors or individuals with appropriate programmed lime and fertiliser spreaders or drills can then be easily set to apply variable rates of lime or appropriate fertiliser across the paddock.

Most of us have pasture paddocks that are quite variable in soil pH and levels of various nutrients.

These differences commonly have a big bearing on productivity.

Precision agriculture along the lines covered by a business such as Precision Pastures does give us the capacity to address such variability that commonly costs lost productivity and sometimes wasted expenditure.

There naturally is a cost in seeking someone to properly assess pasture paddocks for issues like acidity and soil nutrient levels.

A common cost is about $20/ha.

But in a case where we may be planning $50/ha fertiliser application or $160/ha lime application that cost is, I believe, likely to be excellent value. Improved knowledge of aspects such as soil pH sulphur and phosphorus are only useful if carefully related to “best available” interpretation.

Also, by using soil analysis techniques deemed the most appropriate via extensive Australian research is also important. For example Precision Pastures uses the well-recognised calcium chloride pH test, the Colwell phosphate test and the KCL40 sulphur test, all recognised as most-useful general tests in their respective categories.

Phosphate analysis also includes PBI index (phosphorus buffering Index), a valuable measure to help determine appropriate pasture phosphorus requirements.

Correct lime rates not only depend on soil pH but also texture (more lime to make a change on heavier textured soils) as well as pasture species being used. Clearly more knowledge of soil features is just part of planning towards ensuring the pasture reaches its potential rather than just uniform treatment across extremely variable soil.

Next week. Stored soil water forever key to Australian agriculture.