Soil Tests

WHY DO WE NEED TO TEST OUR SOIL?                                

The answer to this is simple; Do you know what is in your soil and the effect it is having on your crop just by looking at it?  I would suggest that you would be unable to.  It is possible to have a best guess, but to maximize productivity, it is essential to quantify the needs of your crop and the requirements of your soil.

            A soil test will enable one of our agronomists or certified consultants to develop a fertiliser program for your particular crop in your particular situation.  When developing a program there are several factors that need to be taken into consideration;

·         Crop type, Crop age (if applicable), Soil type, Soil structure, Surface drainage, Irrigation type, Fertiliser brand desired, Previous fertiliser history

With all of this information, it is possible to provide a confident fertiliser program that is specific for your crop and location.


Soil analysis is the foundation by which all our agronomic advice is derived. When combined with a range of analysis such as quick soil, water and SAP, it provides a complete picture of your crops nutrients – those locked up, those in reserve and those in circulation.

Hortus uses the following extraction methods for Complete soil: 
EC Electrical conductivity 1:5 soil-water 3A1
pH Soil pH, 1:5 soil-water 4A1
OC Organic Carbon - W&B 6A1
Total N Total N - Kjeldahl, steam distillation 7A1
Nitrate - N Water Soluble Nitrate N - autocolour 7B1
Colwell P Colwell Extractable P - manual 9B1
BSES P BSES Extractable P - 0.005 M H2SO4 9G1
PBI Phosphorus buffer index (with Colwell P) 9I2c
Ca Exchangeable Ca - 1M NH4OAc extract 15D3
Mg Exchangeable Mg - 1M NH4OAc extract 15D3
Na Exchangeable Na - 1M NH4OAc extract 15D3
K Exchangeable K - 1M NH4OAc extract 15D3
Al Exchangeable Al - 1M KCl extract 15G1
S KCl 40 Extractable S Blair et al5 10B1
Cl Water soluble Cl - potentiometric 5A1
Fe DTPA Extractable Fe 12A1
Cu DTPA Extractable Cu 12A1
Mn DTPA Extractable Mn 12A1
Zn DTPA Extractable Zn 12A1
B Extractable B - 0.01 M CaCl2 and 0.05 M Mannitol
Si Soluble Silica - 0.01 M CaCl2 13D1
BSES Si BSES Extractable Si - 0.005 M H2SO4


S1 COMPLETE soil: pH*(4A1),EC*(3A1), NO3-N*(7B1) , BSES P*(9G1), Colwell P*(9B1) K*,Ca*, Mg*, Na* (15D3) DTPA Zn*, Cu*, Mn*, Fe*(12A1) B, Cl*(5A1) S(10B1), OC%*(6A1), CEC, ESP, % base saturation, Ca:Mg, K:Mg ratio




 There is growing international interest1 - 5 in the Mehlich 3 (‘M3’) test, primarily because it is a

multi-element extraction. Since many elements can be determined from the one chemical

extraction, the resulting laboratory efficiencies can then be passed on to farmers and growers

through lower soil test charges.


The M3 test was originally developed in 1984 by Dr Adolph Mehlich6. It is very similar to the

Bray P-1 test7 (a dilute acid and fluoride extraction for assessing phosphate), but also has a

chelating agent (EDTA) to enhance the extraction of trace metals. This test is popular in the

United States8, and is used to assess phosphorus, potassium, calcium, magnesium, sodium,

manganese, zinc, copper, aluminium and boron.

Hortus Technical Services is pleased to offer the M3 soil test to complement our existing soil tests, by

providing useful additional information for little extra cost.


M3 Enhances Basic Soil Test

Many overseas laboratories offer only the M3 test, with pH, as their basic soil test profile.

However we have decided that cations (K, Ca, Mg and Na) and CEC obtained from the

ammonium acetate extraction must remain as part of our Basic Soil test, as many of our clients

find the CEC results and derived % Base Saturation data extremely useful.


Our clients also have comprehensive fertility histories of their properties based on the Colwell P

test, and so for the sake of continuity we are retaining the Colwell P test in our Complete Soil test.

Consequently we are offering the M3 test as an additional option with our current Complete Soil

test, to provide M3 determinations of P, Mn, Fe, Zn, Cu, and B.

Hortus Technical Services also offers an Extended M3 test (the above elements plus K, Ca, Mg, Na determined by the M3 method) for specific projects such as fertility mapping, where large

numbers of samples may be involved and the omission of the CEC and Colwell P data may be



Soil Phosphorus: M3 vs Colwell P

Soil testing services in Australia have been relatively unchanged for some 25 years. The Colwell test has been the dominant soil P test, with only a few alternative tests (Resin P, Bray) being performed.

While the Colwell test is internationally recognised as being a very good soil P test, some shortcomings have been identified with it:

• It does not include reactive phosphate rock (RPR) residues, and will therefore underestimate soil P status for properties with a history of RPR use.

• The pH of the soil affects the amount of P extracted by the Colwell method. High pH soils give lower Colwell P levels, whereas low pH soils will yield higher Colwell P levels,often over-estimating the soil P status.

• The Colwell test is also not “universal” in that the response curves vary with soil type, and this must be taken into account when interpreting the result.

The M 3-P test is very similar to the Bray P1 test, and gives essentially an identical P result. As an acid extractant, it will include RPR residues, in contrast to the alkaline Colwell test. But as for all acid extractants, the test can over-estimate P on recently formed soils (e.g. some sedimentary soils), due to dissolution of free apatite. Caution is therefore necessary when interpreting the M3-P levels for these soils.

Both tests have advantages, and limitations, and so we suggest that the M3-P result be regarded as being complementary to the Colwell P test, providing a second perspective on this important element.


Cations (K, Ca, Mg, Na)

 These are included in our M3 test. The M3 extractable cations showed very good correlations with ammonium acetate extractable cations, and normal range levels have been derived from these.


M3-Trace Metals (Manganese, Zinc, Copper and Iron)

 As with all soil trace element tests, the relationship between soil extractable levels and plant uptake is not strong. Interpretation should be made with caution, without undue weight being placed on the soil trace element levels.

In-house investigations have shown good correlations between the M3 test with the standard DTPA  test that is currently being used in Australia 10. Normal range levels

for the M3 trace metals have been cross-calibrated from this existing test.

We have also added cobalt into the standard M3 test, because of the importance

of this element in agriculture.



The hot water soluble boron (HWSB) test is regarded as the standard soil test for assessing B status. The M3-B test correlates well with the HWSB test at elevated levels. Like trace element tests in general, both the HWSB and M3-B tests are not particularly reliable. This is especially so at low levels, when B deficiency may be suspected. In contrast, both tests are more reliable at higher levels, to identify possible B toxicity, or to monitor soil B levels for B-loving crops (e.g. avocados, olives).

We believe the M3-B test can replace the HWSB test when the B levels are elevated (>1-2 ug/g). For lower levels, the relationship with the HWSB levels is poor, and we are not yet confident that these low-level M3-B results have any diagnostic value.


Method Outline

The Mehlich3 extractant is a mixture of ammonium fluoride, ammonium nitrate, EDTA and acetic and nitric acids

Soil is shaken in a volume of Mehlich3 extract (pH 2.6) and elements are analysed by AAS-ContrAA.


Expression of Results

The Mehlich3 results are expressed as mg/l of soil (i.e. ppm on a volume basis). The interpretive criteria used to

generate our bar graphs have primarily been derived by cross-calibration of the M3 test with currently offered tests.


Hortus Technical Services believes that this test will be particularly useful for the following situations:

• as a cost-effective soil test for fertility mapping;

• where soil trace element tests are required, e.g. for crops such as avocados

• as an additional soil P test, to complement the standard Colwell P test.

• to provide an indication of the sulphate and phosphate retention properties of the soil.


1 Burt, R.; Mays, M.D.; Benham, E.C. and Wilson, M.A. Phosphorus Characterisation and Correlation with Properties of Selected Benchmark Soils of the United States. Commun. Soil Sci. Plant Anal. 2002, 33, 117-141.

2 Buondonno, A.; Coppola, E.; Felleca, D. and Violante, P. comparing Tests for Soil Fertility: 1. Conversion Equations between Colwell and Mehlich 3 as Phosphorus Extractants for 120 Soils of South Italy. Commun. Soil Sci. Plant Anal. 1992, 23, 699-716.

3 Garcia, A.; de Iorio, A.F.; Barros, M.; Bargiela, M. and Rendina, A. Comparison of Soil Tests to Determine Micronutrient Status in Argentina Soils. Commun. Soil Sci. Plant Anal. 1997, 28, 1777-1792.

4 Zbiral, J. and Nemec, P. Integrating of Mehlich 3 Extractant into the Czech Soil Testing Scheme. Commun. Soil Sci. Plant Anal. 2000, 31, 2171-2182.

5 Fernandez Marcos, M.L.; Alvarez,, E. and Monterroso, C. Aluminium and Iron Estimated by Mehlich-3 Extractant in Mine Soils in Galicia, Northwest Spain. Commun. Soil Sci. Plant Anal. 1998, 29, 599-612.

6 Mehlich, A. Mehlich 3 Soil Test Extractant: A Modification of Mehlich 2 Extractant. Commun. Soil Sci. Plant Anal. 1984, 15,277-294.

7 Bray-1 P Extraction, Soil Analysis. Handbook of Reference Method,s, Soil and Plant Analysis Council, CRC Press. 1999, 70-73. 8 Mehlich No. 3 Extraction, Soil Analysis. Handbook of Reference Method,s, Soil and Plant Analysis Council, CRC Press. 1999, 100-104.

9 Colwell’s Sodium Bicarbonate Extraction, Soil Analysis. Handbook of Reference Method,s, Soil and Plant Analysis Council, CRC Press. 1999, 73-76.

10 Forbes, E.A. , Cobalt, copper and zinc in yellow-brown pumice soils under grazed, permanent pasture. Australia Journal of Agricultural Research. 1976, 153-164.

 Contact Details

For further information about any of the above tests please contact our office on 07 4132 5000 or

M3 Mehlich 3: pH*(4A1),EC*(3A1), NO3-N*(7B1) , PO4-P, K , Ca, Mg, Fe, Mn, Zn, Cu (M3)


S2 SUPER soil: S1 + NH4-N*(7C2), BSES Si*(13D1), Al*(15G1), H, PBI*(9i2c), PERI

S3 SUGAR soil: pH*(4A1),EC*(3A1), BSES P*(9G1),Colwell P*(9B1), PBI*(9i2c), K(Nitric), K*,Ca*,Mg*,Na* (15D3) DTPA Zn*,Cu*,Mn*,Fe*(12A1) S(10B1), OC%*(6A1) BSES Si*(13D1), Si (CaCL2), PERI

S10 Reef Wise: OC (6A1), Colwell P*(9B1), BSES-P (9G1), PBI (9i2c), PERI (compliant with 2010 Qld. gov. reefcare legislation)

S11 Reefwise Plus: S10 + pH (4A1), EC (3A1), K, Ca, Mg, Na (15D3) S (10B1) BSES Si (13D1)



Bio Soil: Soil Biology and Microbial Activity

S4 BIO Soil: S1 + Active Lactic Acid, Bacteria, Fungi, Yeast, Actinomycetes & Photosynthetic Bacteria

S5 Garden Soil: pH*, EC*(3A1), K*,Ca*, Mg*, Na* CEC, ESP, % base saturation, Ca:Mg, K:Mg ratios

This test is for the true soil scientist wishing to analyse soil biology and chemistry. Our analysis focuses on the “Active” components of the populations for each of five key biological indicator groups: Fungi / Yeasts / Lactic acid bacteria / Photosynthetic bacteria / Actinomycetes.

The results from this analysis are interpreted relative to the specific soil conditions identified in your Analysis Request Form (ARF), so that recommendations relate to the individual needs of the crop and its growing conditions.

The Hortus Bio Soil service is designed to analyse the microbiology present in soil samples and to develop appropriate responses to achieve desired levels and balances of soil microbiology to enable you to better manage and maintain a balanced and healthy soil.


QuickSoil Analysis

The original QuickSoil analysis developed in Australia and owned by Hortus Technical Services. Anything else is a compromise. Accurately monitoring your crops root zone is critical throughout your crops growth cycle.

S6 QUICK Soil / QUICK mix: pH, EC, NO3-N, K, Ca, Mg, Na, Cl (Liquid extraction of nutrients in solution for use during crop growth only)

S7 QUICK N: NH4-N (Ammonium N )

What is a QuickSoil Test?
QuickSoil nutrient tests were developed to enable the fast assessment of the readily available nutrients in the active root zone of a plant. Unlike conventional soil tests, the QuickSoil test is a monitoring tool, which is designed to examine immediate plant available nutrients only. The tests can be turned around to the client within 24 hours of arriving at the laboratory.


Potting Mix Analysis

Chemical - Physical - Quick

S8 Potting Mix - physical: NDI, AFP, Wettability, Bulk Density, WHC

S9 Potting Mix - chemical: pH, EC, NH4, NO3-N, P, K, Ca, Mg, Na, S, Cu, Zn, Mn ,Fe, Cl, B

S6 QUICK Soil / QUICK mix: pH, EC, NO3-N, K, Ca, Mg, Na, Cl (Liquid extraction of nutrients in solution for use during crop growth only)

What is a Potting Mix Test?
The success, or otherwise, of plants grown in potting mixes can be dictated by the physical and chemical properties of the media. Physical properties include the amount of air and water the mix can hold, and how well the media can support the plant. The chemical properties refer to the nutrients - how well the media holds the nutrients or their availability to the plant. Standard physical and chemical analyses are commonly required on unfertilised potting mixes, to determine if the basic mix conforms to Australian Standards.


Soil Sampling Procedures

Each sample should represent one major soil type. If the soil type changes within the block and you propose to fertilise those areas separately, then send separate samples from each area. If you do not propose to fertilise them separately, send only the major soil type.

The same argument applies for different varieties, if sampling is post-plant. If the variety changes within the block and you propose to fertilise the varieties separately, then send separate samples from each variety. If you do not propose to fertilise them separately, send only the major variety.

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Price List  General Price List

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