The Loam Ranger – Using testing to improve management

SESL Australia

Loam Ranger logoDear Loam Ranger,

What’s the point of testing?

Testing of soil, foliage and water is an essential tool in the care and maintenance of turf and crops.

There are two stages in using testing: first, getting the basic chemical conditions right for optimal growth (getting it right); and second, devising and tuning fertiliser programs (keeping it right). Different types of testing are used in each stage.

Getting the basic balance right

The basic balance of soil chemistry can be summarised as in the following table:

Analyte

Optimum range

pH in water

5.5-7.5

pH in calcium chloride (CaCl2)

5.3-6.3

Sodium (as % of CEC)

<15% (preferably <5%)

Potassium (as % of CEC)

5%-15%

Calcium (as % of CEC)

65%-75%

Magnesium (as % of CEC)

15%-25%

Ca/Mg ratio

3-6

Adjusting these few determinants to the optimum level is the first and most basic task in improving a soil and ensuring that plants respond to normal feeding programs. These factors are corrected by reference to the following table:

 

 

 

pH in CaCl2

 

 

 

Too acidic

5.3-6.3

Too alkaline

 

>6

Add magnesite or dolomite

Add Epsom salts

Add Epsom salts + iron sulphate or ag sulphur

Ca/Mg ratio

3-6

Add 50/50 dolomite-lime mix

No action

Add iron sulphate or ag sulphur

 

<3

Add lime

Add gypsum

Add gypsum + iron sulphate or ag sulphur

Where sodium levels are too high we usually recommend gypsum, but where soil is also acidic (low pH), a mixture of lime and gypsum is preferable.

The quantities of ameliorants to add depend on the size of the CEC, the buffering capacity of the soil and the cost of materials.

The need to acidify soils is less common than the need to lime them. Agricultural sulphur is 4 times more acidifying than iron sulphate and is used only where a significant amount of alkali (high pH) must be neutralised. As neither contains calcium, it can be necessary to additionally apply gypsum to an alkaline sodic soil.

What to test for

The nutrients commonly tested for are phosphorus (P), nitrogen (N), sulphur (S) and trace elements.

Although P is often deficient in unimproved soils, it is not true that all Australian soils are low in P, especially if a soil has been used and fertilised for many years. We often find excessive amounts of P due to an overemphasis on P in maintenance feed programs. The following table explains how to interpret the results of the Bray No. 1 method of P analysis:

mg/kg of P

Suitability of P level in soil

0-5

Inadequate for all but some native plants

5-10

Adequate for park trees, pasture and fairway grassing

10-20

Adequate for mass plantings and good-looking turf

20-40

Suitable for most turf; upper end adequate for high-quality turf

40-80

Annuals and bedding plants, high-quality turf

>80

Excessive in almost all situations

The supply of N and S is very difficult to predict from soil testing. Foliar analysis is a better method of identifying the N and S status of a plant. Spring foliar sampling gives the most accurate results.

Gross trace element deficiencies can be identified in soil tests, but only foliar testing can reveal how much the plants have been able to take up. Just because trace elements are present in a soil does not automatically mean that they are available to plants.

When to test

Testing for basic properties (top table) should occur every midwinter.

To calibrate and improve feeding programs, collect foliage samples at least once a year, ideally in late spring, when the effects of early fertiliser programs will be seen. The best method is to take samples with plastic gloves and clean stainless steel scissors. At least 150 g fresh weight is required by most labs.

Water testing

The most important reasons for testing water are:

  • to assess salinity and general properties of irrigation water
  • to assess nutrient runoff rates and thus achieve more efficient fertiliser timing and use.

All land-based industries are under pressure to improve their environmental credentials. Soil, foliage and water testing can be used to minimise fertiliser inputs while maintaining growth. This not only improves environmental performance, but also reduces fertiliser costs and wastage.

Further information

Every situation is different. Call us for specific information on testing in your situation.