WHAT IS IT? WHAT DOES IT TELL US?

Soil texture reveals the sand, silt and clay proportions in the soil

Soil texture is commonly assessed ‘by feel’; laboratory methods are available but time consuming.

The lighter the texture (sandier the soil) the lower the nutrient holding capacity; smaller quantities of nutrients should be applied more frequently. Texture also relates to many physical and biological indicators.

Critical nutrient ranges for some tests will vary with soil texture. The soil cation exchange capacity (CEC)¹² provides an indication of soil texture (low CEC, light, sandy soil; high CEC, heavier, more clay based soil).

• measured in a 1:5 soil:water and/or 1:5 soil:CaCl₂ (calcium chloride) solution.

WHAT IS IT? WHAT DOES IT TELL US?

pH reveals whether a soil is acid (pH <6.9), neutral (pH 7) or alkaline (pH >7.1). It informs about potential chemical, physical and biological soil properties.

The pH water value may vary by as much as 0.6 units throughout the year. It is lower in dry soils. Soil salinity increases the pH_(water) reading.

pH (CaCl₂) is more consistent throughout the year and usually about 0.5-0.8 pH units lower than pH_(water).

WHAT IS A GOOD LEVEL OR RANGE?

A range of 4.5-6.5 (measured in a calcium chloride (CaCl₂) solution or 5.2-7.2 as measured in water (H₂O)is suitable for most pasture species.¹³

WHAT DOES IT MEAN IF THE RESULTS ARE NOT IN THE DESIRED RANGE?

Different pasture species have different tolerances to acidity. Species such as ryegrass and clover tend to be more tolerant of acidity than pastures of lucerne.

Nodulation on legume pastures is significantly inhibited by acidity; although some pastures may be tolerant of acidity, the availability, uptake and/or balance of nutrients is affected (see Figure 2 in Appendix 1); as the pH drops below pHCaCl₂ 5.5, levels of available, toxic aluminium in the soil increase; this leads to phosphorus fixing. Also, the populations of soil organisms change, organic matter breakdown may be hampered leading to an accumulation on the soil surface and levels of available nutrients.

NB. The seasonal or salinity variation of pH_(water) can affect automated recommendations for fertilisers, particularly lime.

Acid subsoils can be a significant source of persistent acidity in pasture systems.

See Appendix 1 for more information on the effects of acidity.

HOW TO CHANGE OR MANAGE IT?

Although some soils exhibit alkalinity, acidity tends to be the greatest issue in Tasmanian farming systems.

pH can be increased by using lime (calcium carbonate) or dolomite (magnesium carbonate). In both products, it is the carbonate that changes the pH not the calcium (Ca) or magnesium (Mg). The effectiveness of agricultural lime is a combination of ‘fineness’ and ‘purity’ (termed neutralisation value). The finer and purer, the less is needed.

pH can be lowered by elemental sulphur, if a rapid change is required.

Some fertilisers such as urea or ammonium (e.g., in ammonium sulphate or MAP) reduce the soil pH. Gypsum does not change the pH.

See Appendix 1 for more information on managing acidity.

Electrical conductivity (EC)

• measured in a 1:5 soil : water solution or in a ‘saturated paste extract’ (EC_SE).

WHAT IS IT? WHAT DOES IT TELL US?

EC measures the electrical current through the soil, which gives an indication of soil salinity. EC increases as salt content in the soil increases. Some labs multiply EC 1:5 by a factor between 6 and 13, depending on texture to report EC_SE (Appendix 1).

Salinity measurements in the top 10 cm tend to be lower in winter and higher in summer due to rainfall.

WHAT IS A GOOD LEVEL OR RANGE?

Soils with EC_SE above 1.5 [dS/m] are high in soluble salts.

For all pasture species < 1 [dS/m] = [mS/cm] = 1500 [μS/cm] = 960 [ppm]

WHAT DOES IT MEAN IF THE RESULTS ARE NOT IN THE DESIRED RANGE?

Plant water uptake is impeded with increasing salinity; plants take up toxic levels of sodium (Na) and chloride (Cl) if salt (NaCl) is the EC issue. Potassium uptake is repressed by sodium uptake; calcium (Ca), phosphorus (P) and boron (B) uptake may be reduced.

Increases in salinity can result in significantly poorer outcomes for pasture growth. Some pastures have better tolerance to salinity than others. See Appendix 1 for further information.¹⁴

Elevated levels of soil Cl (indicated by EC e.g., in 1:5 soil/water extract) can enhance cadmium (Cd) absorption by sensitive forage and pasture species (e.g., lupins, legumes, and brassicas). Cadmium (Cd) is a toxic, regulated¹⁵ heavy metal. Cadmium can inhibit kidney and liver function in livestock.

HOW TO CHANGE OR MANAGE IT?

Drainage, taking water off the paddock, strategic, deep-rooted plantings, growing

different varieties or species, carefully managing irrigation, if used, increase soil

calcium levels and potassium (K) inputs, increase organic matter levels.

A catchment wide approach may be needed to lower water tables. Avoid fertilisers containing high levels of chloride (Cl) such as Muriate of Potash (MOP) or some gypsum sources. Check the salt index of fertilisers, especially for sensitive pastures. Minimising trace element deficiencies also assists in reducing cadmium uptake by pastures and hence animals.¹⁶

• Cl [mg/kg]

WHAT IS IT? WHAT DOES IT TELL US?

Cl adds to soil ionic strength and thus salinity; plants require very small amounts of Cl. Chloride deficiency has not been recorded in Australia.

WHAT IS A GOOD LEVEL OR RANGE?

Critical levels for salinity are:

<120 [mg/kg] sands to sandy loam

<180 [mg/kg] loam to clay loam

<300 [mg/kg] clays

WHAT DOES IT MEAN IF THE RESULTS ARE NOT IN THE DESIRED RANGE?

Plant water uptake is impeded with increasing salinity; plants take up toxic levels of sodium (Na) and chloride (Cl) if salt (NaCl) is the EC issue. Potassium uptake is repressed by sodium uptake; calcium (Ca), phosphorus (P) and boron (B) uptake may be reduced.

Increases in salinity can result in significantly poorer outcomes for pasture growth. Some pastures have better tolerance to salinity than others. See Appendix 1 for further information.14

Elevated levels of soil Cl (indicated by EC e.g., in 1:5 soil/water extract) can enhance cadmium (Cd) absorption by sensitive forage and pasture species (e.g., lupins, legumes, and brassicas). Cadmium (Cd) is a toxic, regulated15 heavy metal. Cadmium can inhibit kidney and liver function in livestock.

HOW TO CHANGE OR MANAGE IT?

Drainage, taking water off the paddock, strategic, deep-rooted plantings, growing different varieties or species, carefully managing irrigation, if used, increase soil calcium levels and potassium (K) inputs, increase organic matter levels.

A catchment wide approach may be needed to lower water tables. Avoid fertilisers containing high levels of chloride (Cl) such as Muriate of Potash (MOP) or some gypsum sources. Check the salt index of fertilisers, especially for sensitive

pastures. Minimising trace element deficiencies also assists in reducing cadmium uptake by pastures and hence animals.16

The ratio of the EC 1:5 (dS/m) and ESP (exchangeable sodium percentage, Na%)

WHAT IS IT? WHAT DOES IT TELL US?

Information about potential:

• Water infiltration rates
• Water holding capacity
• Oxygen supply to roots and soil life
• Nutrient use efficiency
• Structural stability (erosion and compaction risks)

WHAT IS A GOOD LEVEL OR RANGE?

ESI is the ratio of the electrochemical conductivity (EC1:5 - dS/m) to exchangeable sodium percentage (ESP). Critical values for crops have not been established (yet), however an indicative value of >0.05 is given for Australian soils. Soils with an index of <0.05 have the potential to disperse.

WHAT DOES IT MEAN IF THE RESULTS ARE NOT IN THE DESIRED RANGE?

A low ESI can mean poor:

• Water infiltration rates
• Water holding capacity
• Oxygen supply to roots and soil life
• Nutrient use efficiency
• Structural stability (erosion and compaction risks).

HOW TO CHANGE OR MANAGE IT?

An economically viable response to gypsum and/or lime can be expected where ESI values are at or below 0.05. The best results will be achieved if the gypsum is dissolved prior to application.

Ensure the gypsum does not contain high levels of sodium and or chloride.

Organic carbon (OC) %

Organic matter (OM) % (OC x 2 = OM¹⁷)

WHAT IS IT? WHAT DOES IT TELL US?

OC or OM give information about soil function: soil chemical, physical and biological conditions, disease suppression potential and buffering against toxic elements or substances. OM is an essential food source for soil organisms; soils with high OM / OC usually have higher soil microbial populations and good nutrient holding and cycling ability.

WHAT IS A GOOD LEVEL OR RANGE?

A good approach is to keep soil as close as possible to levels that are typical for comparable soil types (or texture) and climate in the area. For perennial pastures on Tasmanian soil types see Appendix 2. Measurements of organic carbon tend to be higher during times of increased microbial activity in spring and early summer and lower with decreased activity during winter.

Rainfall, temperature, and soil type are correlated with levels of organic carbon. Organic carbon is directly correlated with clay content.

WHAT DOES IT MEAN IF THE RESULTS ARE NOT IN THE DESIRED RANGE?

Lower organic carbon than typical for the soil type and climate means reduced water and nutrient holding capacity, lower diversity of soil organisms, less nutrient cycling of animal waste, poorer drainage, poorer root growth and potentially a higher risk of erosion and compaction.

HOW TO CHANGE OR MANAGE IT?

It is possible to increase organic carbon by minimising overgrazing, increasing pasture growth, while reducing stocking rates and improving dung recycling through dung beetles and biological activity.

See Appendix 2 for more information on organic carbon.

Use methods recommended by carbon farming (CFI) with specific reference to your climate, and especially for your region and crops. Refer to EPA and food safety regulations when using soil amendments containing manures; do not use biosolids without EPA permit.

(C/N) Ratio = Total Carbon % / Total Nitrogen %

WHAT IS IT? WHAT DOES IT TELL US?

Indicates whether nitrogen will be fixed or released when microorganisms break down organic matter, Organic matter contains around 45-50% carbon; it contains nitrogen (N), and also phosphorous (P) and sulphur (S).

WHAT IS A GOOD LEVEL OR RANGE?

High C/N ratio = >25

Medium C/N ratio = 11-24

Low C/N ratio = <10

WHAT DOES IT MEAN IF THE RESULTS ARE NOT IN THE DESIRED RANGE?

If the C/N ratio is too high (excess carbon), nutrient cycling slows down; microbes will compete with pastures for nitrogen (nitrogen fixing or draw down). If the C/N ratio is low the soil contains excess nitrogen, which may be lost from the root zone through leaching, or as nitrous oxide gas (greenhouse gas).

HOW TO CHANGE OR MANAGE IT?

If C/N is too high, add nitrogen fertilisers of the right type and amount, at the right time to reduce N drawn down by microbes; If C/N is low, reduce N fertilisers or use small amount more often; high carbon amendments may be added to the soil so that microbes ‘fix’ excess N when breaking these down (wood or bark, straw).

Total Nitrogen (N) % (used to calculate the C/N ratio). Often abbreviated as TN.

WHAT IS IT? WHAT DOES IT TELL US?

A measure of the total amount of N in the soil in all forms, not just what is available to plants.

Indication of a soil’s long-term nitrogen supplying capacity (potentially mineralisable nitrogen). About 5% of TN (0-10 cm depth) is mineralised per year. This fluctuates depending on soil type, soil health and climatic conditions.

Deep testing of Total N is required to get a more accurate picture of potential N in the soil profile.

WHAT IS A GOOD LEVEL OR RANGE?

Less than 0.10% is regarded as low, while over 0.25% is high. Ideally, TN should be > 0.15

WHAT DOES IT MEAN IF THE RESULTS ARE NOT IN THE DESIRED RANGE?

Low levels of TN mean that the soil will not provide much free nitrogen via mineralisation; pasture legumes and fertiliser applications need to provide most of the nitrogen plants require (i.e., fertiliser N inputs + legume fixing inputs = pasture N removal rates).

High TN levels mean that the N mineralisation potential is high and nitrogen fertiliser inputs can be cut down especially when mineralisation conditions are good (good soil moisture, soil temperatures between 15 and 28^oC).

Nitrogen fixing of legumes is limited in extremely acid soils.

HOW TO CHANGE OR MANAGE IT?

Assess legume N fixing performance. Assess nutrient cycling from urine and manure e.g., dung beetle performance.

Adjust fertiliser programs so that supplied N from soil and fertilisers match N needs/ removal rates of pastures and fodder crops at different growth stages.

Monitor available N in the root zone (N-check or ‘deep’ soil N) and biomass removal to make good decisions on nitrogen management.

When applying N fertilisers, ensure you understand which type will give the best results in your specific situation to avoid gaseous losses, leaching and runoff as well as soil acidification.

• Available nitrogen: Nitrate (NO₃) and ammonium (NO₄)
• ‘deep soil N’ [mg/kg] or ‘N-check’ [kg/ha]

WHAT IS IT? WHAT DOES IT TELL US?

Readily available root zone nitrogen that needs to be included in nitrogen budgets.

Levels are reported as NO₃-N and NH₄-N or NO₃ and NH₄. Below are conversion factors to convert reported levels.

N x 4.42 = NO₃

N x 1.29 = NH₄

NO₃ x 0.226 = NO₃- N

NH₄x 0.777 = NH₄- N

WHAT IS A GOOD LEVEL OR RANGE?

Depends on pasture composition, stocking rate, and dry matter removal <25 [kg N/ha] may be low, > 100 [kg N/ha] may be high

WHAT DOES IT MEAN IF THE RESULTS ARE NOT IN THE DESIRED RANGE?

If available nitrogen is lower than needed to maintain dry matter removal, pastures can be degraded. Ryegrass may not persist. Topping up with nitrogen fertiliser is required; types, amounts, number of applications and timing vary with pasture composition, stocking rates, and dry matter removal.

HOW TO CHANGE OR MANAGE IT?

Available nitrogen reserves should be checked using the suitable test(s) e.g. Deep Soil N or N-check before (re)-planting and or before a pasture/fodder crop grows rapidly. A nitrogen budget should be used to determine application times and amounts per application; plant testing can be used to monitor.

Nitrate (NO₃) [mg/ kg] dry soil extract of topsoil

WHAT IS IT? WHAT DOES IT TELL US?

Indicates available nitrate to sampling depth, poor indicator compared to deeper testing.

WHAT IS A GOOD LEVEL OR RANGE?

Given that the test is not indicative of the amount of N available to the pasture or fodder crop, levels are not included here.

WHAT DOES IT MEAN IF THE RESULTS ARE NOT IN THE DESIRED RANGE?

The topsoil may be sandy, or low in organic carbon if nitrate levels are low or the pH may be low, preventing OM from breaking down; if they are high, fertiliser may just have been applied or OM levels and mineralisation conditions are good.

High concentrations of nitrate in the soil can result in nitrate staggers in animals for certain pasture types, especially in spring/early summer and under overcast conditions. Toxic levels are a result of high nitrate uptake and low conversion to ammonium due to low light conditions as the responsible plant enzyme is light dependent.

Perennial ryegrass, fescue, cocksfoot, and white clover are NOT of concern in the accumulation of toxic levels of nitrate.¹⁸

HOW TO CHANGE OR MANAGE IT?

See above re using the best tests for checking on available nitrate or total nitrogen and managing N. Calculating nitrogen use efficiency (NUE%) is one way of checking whether N is used well.

Remove livestock from susceptible pastures during high risk times (high soil nitrate, warming soil temperatures, overcast conditions).

Phosphorus (P) [mg/kg]

WHAT IS IT? WHAT DOES IT TELL US?

‘Extractable’ phosphorus in the soil, loosely indicating potential P availability, however, actual available P will depend on soil type and root distribution (P is mostly immobile). Several tests are offered, some estimate P availability better than others.¹⁹

WHAT IS A GOOD LEVEL OR RANGE?

Desirable levels vary with pasture composition, and dry matter removal or stocking rate. In many cases, texture, pH, and other elements affect results and desirable ranges.

WHAT DOES IT MEAN IF THE RESULTS ARE NOT IN THE DESIRED RANGE?

No matter which test is used, inadequate P supply leads to reduced plant function, poor root growth, and increased risk of pest and disease attack. P is especially important for early establishment of root systems.

Low or high pH increases the binding of P to the soil, and can result in deficiencies if not corrected. Low pH e.g. < 5.5 and or high soil iron levels will lead to the formation of insoluble aluminium and iron phosphates; high pH > 7 usually indicates high levels of calcium in the soil, leading to insoluble calcium phosphates.

Some soil microbes can utilise the insoluble phosphates and make the P available to plants when their bodies decompose.

HOW TO CHANGE OR MANAGE IT?

In all cases, the application of fertilisers and or manures is used to increase soil P levels.

Frequent or heavy use of manures can lead to elevated soil P levels and eventually leaching and or run-off. Monitoring is highly recommended!

P monitoring is especially important (and a legal requirement in many states) if biosolids are applied or high P recycled water or effluent is used.

The environmental risk can be assessed using the Phosphorus environmental risk index (PERI) or the Mehlich 3 P saturation ratio (M3 PSR) (Appendix 3).

High P applications reduce Zinc uptake.

[mg/kg] – most commonly used test

WHAT IS IT? WHAT DOES IT TELL US?

Soils high in free lime (calcareous soils pH >7) generally ‘lock up’ most of the soil P; this reduces the accuracy of this test. A recent review rated the much-used test as inferior to others.²⁰ PBI should be measured in conjunction with Colwell P to assess how much P is in the labile pool.

WHAT IS A GOOD LEVEL OR RANGE?

Varies with soil type, levels < 30 [mg/kg] is usually marginal or low, levels 30-45 [mg/kg] are generally adequate, >45 [mg/kg] are considered high; Colwell P levels should be higher in heavier soils.

See Appendix 3 for optimum levels for Tasmanian soil types.

WHAT DOES IT MEAN IF THE RESULTS ARE NOT IN THE DESIRED RANGE?

No matter which test is used, inadequate P supply leads to reduced plant function, poor root growth, and increased risk of pest and disease attack. P is especially important for early establishment of root systems.

Low or high pH increases the binding of P to the soil, and can result in deficiencies if not corrected. Low pH e.g. < 5.5 and or high soil iron levels will lead to the formation of insoluble aluminium and iron phosphates; high pH > 7 usually indicates high levels of calcium in the soil, leading to insoluble calcium phosphates.

Some soil microbes can utilise the insoluble phosphates and make the P available to plants when their bodies decompose.

HOW TO CHANGE OR MANAGE IT?

In all cases, the application of fertilisers and or manures is used to increase soil P levels.

Frequent or heavy use of manures can lead to elevated soil P levels and eventually leaching and or run-off. Monitoring is highly recommended!

P monitoring is especially important (and a legal requirement in many states) if biosolids are applied or high P recycled water or effluent is used.

The environmental risk can be assessed using the Phosphorus environmental risk index (PERI) or the Mehlich 3 P saturation ratio (M3 PSR) (Appendix 3).

High P applications reduce Zinc uptake.

[mg/kg] – use above pH 6, definitely > pH 7

WHAT IS IT? WHAT DOES IT TELL US?

Soils high in free aluminium and iron (e.g., Ferrosol soils pH < 5.5) generally ‘lock up’ most of the soil P, this reduces the accuracy of this test.

WHAT IS A GOOD LEVEL OR RANGE?

For pastures, < 10 [mg/kg] is usually low, > 50 [mg/kg] is often considered high.

The Making Better Fertiliser Decisions guidelines places the critical value as 15 [mg/kg], with a range of 14-17 [mg/kg] based on the national dataset.

WHAT DOES IT MEAN IF THE RESULTS ARE NOT IN THE DESIRED RANGE?

No matter which test is used, inadequate P supply leads to reduced plant function, poor root growth, and increased risk of pest and disease attack. P is especially important for early establishment of root systems.

Low or high pH increases the binding of P to the soil, and can result in deficiencies if not corrected. Low pH e.g. < 5.5 and or high soil iron levels will lead to the formation of insoluble aluminium and iron phosphates; high pH > 7 usually indicates high levels of calcium in the soil, leading to insoluble calcium phosphates.

Some soil microbes can utilise the insoluble phosphates and make the P available to plants when their bodies decompose.

HOW TO CHANGE OR MANAGE IT?

In all cases, the application of fertilisers and or manures is used to increase soil P levels.

Frequent or heavy use of manures can lead to elevated soil P levels and eventually leaching and or run-off. Monitoring is highly recommended!

P monitoring is especially important (and a legal requirement in many states) if biosolids are applied or high P recycled water or effluent is used.

The environmental risk can be assessed using the Phosphorus environmental risk index (PERI) or the Mehlich 3 P saturation ratio (M3 PSR) (Appendix 3).

High P applications reduce Zinc uptake.

Mehlich 3 (M3) P [mg/kg] – use below pH 7.5

WHAT IS IT? WHAT DOES IT TELL US?

Used over a wider pH range; The M3 multi- element soil test has gained popularity nationally and internationally.

Moreover, its measurement performance for P has improved rapidly across the past 7 years, more so than the other soil P tests mentioned here.

WHAT IS A GOOD LEVEL OR RANGE?

< 25 is usually low, > 60 is usually high.²¹

WHAT DOES IT MEAN IF THE RESULTS ARE NOT IN THE DESIRED RANGE?

No matter which test is used, inadequate P supply leads to reduced plant function, poor root growth, and increased risk of pest and disease attack. P is especially important for early establishment of root systems.

Low or high pH increases the binding of P to the soil, and can result in deficiencies if not corrected. Low pH e.g. < 5.5 and or high soil iron levels will lead to the formation of insoluble aluminium and iron phosphates; high pH > 7 usually indicates high levels of calcium in the soil, leading to insoluble calcium phosphates.

Some soil microbes can utilise the insoluble phosphates and make the P available to plants when their bodies decompose.

HOW TO CHANGE OR MANAGE IT?

In all cases, the application of fertilisers and or manures is used to increase soil P levels.

Frequent or heavy use of manures can lead to elevated soil P levels and eventually leaching and or run-off. Monitoring is highly recommended!

P monitoring is especially important (and a legal requirement in many states) if biosolids are applied or high P recycled water or effluent is used.

The environmental risk can be assessed using the Phosphorus environmental risk index (PERI) or the Mehlich 3 P saturation ratio (M3 PSR) (Appendix 3).

High P applications reduce Zinc uptake.

[mg/kg] - use below pH 7.2

WHAT IS IT? WHAT DOES IT TELL US?

Bray P has most use in NSW. Its measurement performance in ASPAC inter-laboratory proficiency programs across two decades has been poor and inconsistent; it cannot be recommended, even with acidic soils.

WHAT IS A GOOD LEVEL OR RANGE?

< 15 [mg/kg] is usually low, > 25 [mg/kg] is usually high.

WHAT DOES IT MEAN IF THE RESULTS ARE NOT IN THE DESIRED RANGE?

No matter which test is used, inadequate P supply leads to reduced plant function, poor root growth, and increased risk of pest and disease attack. P is especially important for early establishment of root systems.

Low or high pH increases the binding of P to the soil, and can result in deficiencies if not corrected. Low pH e.g. < 5.5 and or high soil iron levels will lead to the formation of insoluble aluminium and iron phosphates; high pH > 7 usually indicates high levels of calcium in the soil, leading to insoluble calcium phosphates.

Some soil microbes can utilise the insoluble phosphates and make the P available to plants when their bodies decompose.

HOW TO CHANGE OR MANAGE IT?

In all cases, the application of fertilisers and or manures is used to increase soil P levels.

Frequent or heavy use of manures can lead to elevated soil P levels and eventually leaching and or run-off. Monitoring is highly recommended!

P monitoring is especially important (and a legal requirement in many states) if biosolids are applied or high P recycled water or effluent is used.

The environmental risk can be assessed using the Phosphorus environmental risk index (PERI) or the Mehlich 3 P saturation ratio (M3 PSR) (Appendix 3).

High P applications reduce Zinc uptake.

- under development

WHAT IS IT? WHAT DOES IT TELL US?

How much P may be fixed by the soil and how much should be supplied via fertilisers or manures.

WHAT IS A GOOD LEVEL OR RANGE?

Further studies are needed, however preliminary studies²² showed that DGT tests are somewhat less reliable for perennial pasture systems than existing extraction methods in estimating how much P deep rooted pasture species are able to extract.

WHAT IS IT? WHAT DOES IT TELL US?

How much P may being fixed by the soil and how much should be supplied via fertilisers or manures, leaching risk.

WHAT IS A GOOD LEVEL OR RANGE?

Good PBI: < 140 (with rising PBI, P fixation potential increases, (Appendix 3).

WHAT DOES IT MEAN IF THE RESULTS ARE NOT IN THE DESIRED RANGE?

Reduced plant availability can indicate P is fixing by Ca at high pH > 7 or Fe and Al at low pH < 5.5. Soils with a very low PBI have a high risk of P leaching, and it is hard to increase soil P levels.

HOW TO CHANGE OR MANAGE IT?

Adjust fertiliser or manure rates according to the soil’s P fixing capacity.

WHAT IS IT? WHAT DOES IT TELL US?

How much P may be fixed by the soil and how much should be supplied via fertilisers or manures, leaching risk.

WHAT IS A GOOD LEVEL OR RANGE?

Good PSR: 0.062 - 0.2 (Appendix 3)

WHAT DOES IT MEAN IF THE RESULTS ARE NOT IN THE DESIRED RANGE?

PSR < 0.062: decreasing P availability to the pasture

> 0.2 indicates leaching risk.

HOW TO CHANGE OR MANAGE IT?

Adjust fertiliser or manure rates according to the soil’s P fixing capacity to stay within the agronomic and environmental optimum.

WHAT IS IT? WHAT DOES IT TELL US?

P leaching risk calculated from the available P (Colwell) and PBI.

WHAT IS A GOOD LEVEL OR RANGE?

Critical ratio value: 2 (Appendix 3)

WHAT DOES IT MEAN IF THE RESULTS ARE NOT IN THE DESIRED RANGE?

> 2 the risk of P movement in the soil and losses from the root zone increases.

HOW TO CHANGE OR MANAGE IT?

Reduce fertiliser or manure/biosolids/effluent inputs.

Sulphur (S) [mg/kg] – several methods in use

WHAT IS IT? WHAT DOES IT TELL US?

Potentially available S.

WHAT IS A GOOD LEVEL OR RANGE?

6 to 16 [mg/kg] is generally adequate, < 6 [mg/kg] is low, >16 [mg/kg] is high

WHAT DOES IT MEAN IF THE RESULTS ARE NOT IN THE DESIRED RANGE?

S is an important building block of proteins, so overall plant function is reduced if S uptake is low.

Pastures fertilised heavily with high analysis fertilisers as a P source (e.g., DAP and MAP) can become sulphur deficient.²³

HOW TO CHANGE OR MANAGE IT?

Use the sulphate form of fertilisers to build S in soils. Can use Single Super as a

phosphorus (SSP) source as it also supplies SO₄-S and Ca. If using SSP, monitor soil cadmium (Cd) levels.

Available potassium (K) [mg/kg] Different methods (e.g., Colwell, Skene, Mehlich 3) give similar but not identical results.

WHAT IS IT? WHAT DOES IT TELL US?

Potentially available K

Heavier soils usually have and require higher K levels; they also hold onto K better than lighter soils (clay > clay loam > sandy loam > sand

WHAT IS A GOOD LEVEL OR RANGE?

As a guide, < 109 [mg/kg] is low, > 182 [mg/kg] is usually high.

Optimum Collwell K for Pasture (0-100mm):

Sand 109-142 [mg/kg]

Sandy/silty loam 126-157 [mg/kg]

Sandy clay loam 127-173 [mg/kg]

Clay loam & clay 151-182 [mg/kg]

NB: most crops remove as much or more K from the soil as nitrogen.

WHAT DOES IT MEAN IF THE RESULTS ARE NOT IN THE DESIRED RANGE?

K is especially important for regulating transpiration in plants; low K can mean that plants lose water quickly. In dryland situations, plants that are low in K suffer water stress more readily. Sufficient K improves the ability for pasture to withstand dry periods.²⁴

High sodium (Na) and or magnesium (Mg) uptake depresses K uptake in plants (leading to cation imbalance).

High K depresses calcium (Ca) and Mg uptake in plants, increasing the risk of deficiencies in livestock, particularly cows.

High potassium uptake can have a negative effect on livestock such as:

• Impaired growth and development due to an imbalance in the ratio of nutrients, particularly calcium and magnesium, which can impair animal growth and development.
• Metabolic disorders such as grass tetany in ruminants.
• Palatability and digestibility of forage, leading to digestive disturbances such as diarrhoea and reduced feed intake.
• Reduced fertility and reproductive performance in livestock.

HOW TO CHANGE OR MANAGE IT?

In heavier soils K can be applied preplanting as per a K removal budget. K may

leach from the root zone in lighter soils depending on water movement. Foliar applications also work well.

Despite being a macronutrient, K applications are often forgotten. Monitor K levels in routine soil testing and apply fertiliser as necessary.

If effluent or biosolids are being used on farm, monitor levels of K applied to minimise risk of subsequent nutrient deficiencies and health problems in livestock.

(major exchangeable cations: Ca, Mg, K, Na and Al; hydrogen H and trace metals can also be counted as cations)

WHAT IS IT? WHAT DOES IT TELL US?

The CEC and cation proportions (%) give information about soil structure stability, nutrient availability and storage capacity, the soil pH and the potential soil response to fertiliser.

Cations have a positive charge.

WHAT IS A GOOD LEVEL OR RANGE?

CEC increases with the soil’s clay and organic matter content. CEC and soil texture are correlated, with lighter soils having lower CEC and heavier soils having higher CEC.

Low CEC < 5 [cmol/kg]

High CEC > 20 [cmol/kg]

Desirable levels for individual cations vary for different pastures and soil types.

[cmol/kg = meq/100g = meq%]

WHAT DOES IT MEAN IF THE RESULTS ARE NOT IN THE DESIRED RANGE?

All cations compete for uptake by plants, therefore an oversupply of one can reduce uptake of another (cation imbalance).

Elevated levels of ammonium ions (NH₄+) in soil solution compete for uptake with other nutrient cations, particularly Ca.

This tendency is enhanced when plants are forced to meet much of their mineral-N requirements from NH₄-N rather than NO₃-N. Low plant Ca concentrations are often a result.

HOW TO CHANGE OR MANAGE IT?

Low CEC means that the soil does not hold nutrients (with a positive charge) well.

Low CEC soil usually has a sandy texture with little clay and or organic matter.

Nutrients especially nitrogen, sulphur, boron and potassium can leach easily.

These soils need smaller quantities of nutrients applied more frequently than

heavier soils.

A high CEC usually indicates a higher fertility; the soil holds nutrients well and

OM accumulation can be greater than in low CEC, lighter soils.

Given organic matter has a higher CEC than clay, adding organic matter is a good way of increasing or maintaining CEC.

Exchangeable magnesium (Mg) [mg/ kg], [cmol/kg], % CEC

WHAT IS IT? WHAT DOES IT TELL US?

Potentially available Mg

CEC proportion (%), considering Al and H as part of CEC

WHAT IS A GOOD LEVEL OR RANGE?

200 – 400 [mg/kg]

A level of > 1.6 [cmol/kg] is sufficient for most pasture species.

10 – 15 % of total eCEC or CEC

The ratio of exchangeable Mg will not influence plant growth except for at extreme values.

WHAT DOES IT MEAN IF THE RESULTS ARE NOT IN THE DESIRED RANGE?

Soils high in Mg are usually hard setting when dry and sticky when wet; this is made worse if Na levels are also high (e.g., due to salinity or sodicity).

Low Mg means that plants will suffer from Mg deficiency and nutrient imbalance.

Low Mg can also result in livestock deficiencies (hypomagnesaemia) increasing the risk of milk fever and grass tetany in cattle, and grass staggers in sheep. Mg deficiency most often occurs when high levels of nitrogen interfere with Mg absorption in the rumen.²⁵

Livestock are particularly susceptible to hypomagnesaemia during lactation or late pregnancy.

HOW TO CHANGE OR MANAGE IT?

Low Mg levels can be corrected via a range of Mg fertilisers applied to soils or as foliar products. Dolomite contains Mg and can be used if a pH increase is needed as well.

Applying calcium fertilisers or gypsum can counteract high Mg levels. Make sure potassium availability and uptake are adequate when using Mg fertilisers.

Magnesium can be applied to hay to combat deficiencies in livestock.²⁶

Exchangeable potassium (K) [cmol/kg], % CEC

WHAT IS IT? WHAT DOES IT TELL US?

CEC proportion (%), considering Al and H as part of CEC

Potentially available K [mg/kg] is explained separately above.

WHAT IS A GOOD LEVEL OR RANGE?

Soil type related differences need to be considered, below is an overall rough guide:

0.3 – 0.6 [cmol/kg]27 across all soil types

>0.6 very high across all soil types

1 - 5 % of total eCEC or CEC

WHAT DOES IT MEAN IF THE RESULTS ARE NOT IN THE DESIRED RANGE?

K is especially important for regulating transpiration; low K can mean that plants lose water quickly. High sodium and or magnesium uptake depresses K uptake in plants (leading to cation imbalance).

HOW TO CHANGE OR MANAGE IT?

In heavier soils K can be applied preplanting as per a K removal budget²⁸. K may leach from the root zone in lighter soils depending on water movement. Foliar applications work well.

The removal of hay and silage can deplete large amounts of potassium from the soil. In pasture systems, potassium levels can be managed by stock movements as K is deposited in urine and dung. Applications of K fertilisers can also be used to increase potassium.

Fodder conservation can assist in reducing high potassium levels.

Exchangeable calcium (Ca) [mg/kg] [cmol/kg], % CEC

WHAT IS IT? WHAT DOES IT TELL US?

Potentially available Ca

CEC proportion (%), considering Al and H as part of CEC

WHAT IS A GOOD LEVEL OR RANGE?

6.0 – 20 meq/100g10

65 - 80% of total eCEC or CEC

The ratio of exchangeable Ca will not greatly influence plant growth except for at extreme values.

(Not all soil Ca methodology excludes solid- phase Ca from the apparent result so care is needed with choice of method and interpretation)

WHAT DOES IT MEAN IF THE RESULTS ARE NOT IN THE DESIRED RANGE?

Ca strengthens plants (cell walls) and is needed for developing tissues (shoot tips, buds, roots).

In the soil, it also helps to strengthen structure in many ways, and is the most dominant exchangeable cation.

HOW TO CHANGE OR MANAGE IT?

Plants need free Ca in the soil solution and rely on transpiration for uptake. Low soil solution Ca, dry or humid conditions hamper uptake. Ca can be applied via fertilisers with high soluble Ca content or applied as a foliar product. Ca is most commonly applied through routine liming applications. It does not move downwards in plants, only up with transpiration.

Ca deficiencies in perennial pastures are rare however if they present, they can cause serious diseases such as milk fever and grass tetany.

To improve soil Ca, lime and gypsum can be applied. More readily available forms of Ca in fertilisers should also be considered if a rapid response it required.

WHAT IS IT? WHAT DOES IT TELL US?

Presence of free carbonate in the soil which can increase the pH

WHAT IS A GOOD LEVEL OR RANGE?

Nil to slight: Non-calcareous

Moderate to high to very high: Calcareous

WHAT DOES IT MEAN IF THE RESULTS ARE NOT IN THE DESIRED RANGE?

N/A

HOW TO CHANGE OR MANAGE IT?

Use of acidifying fertilisers.

Exchangeable sodium (Na) [mg/kg] % CEC or ESP

WHAT IS IT? WHAT DOES IT TELL US?

Potentially available, toxic Na

CEC proportion (%), considering Al and H as part of CEC also called exchangeable sodium percentage ESP which is a measure of sodicity.

WHAT IS A GOOD LEVEL OR RANGE?

< 80 [mg/kg]

ESP < 4% of total eCEC or CEC or < 6% of total eCEC or CEC

Maximum recommended levels vary depending on soil type.

WHAT DOES IT MEAN IF THE RESULTS ARE NOT IN THE DESIRED RANGE?

Na is not a plant nutrient! It interferes with plant water uptake and soil structure.

High levels make the soil hard setting when dry and sticky when wet. Na competes with potassium (K) for plant uptake, so plants become K deficient and need extra K input.

Sodic soils lack structure and are highly erodible, with poor trafficability.

HOW TO CHANGE OR MANAGE IT?

High soil Na can be managed by increasing soil calcium (Ca) via lime or gypsum depending on pH. Paddocks high in Na should get extra soluble Ca fertiliser and extra K fertilisers.

Ammonium (NH₄) based fertilisers should be avoided. Improving organic matter levels is helpful to buffer the sodium effect.

Exchangeable aluminium (Al) [mg/kg] % CEC

WHAT IS IT? WHAT DOES IT TELL US?

Potentially available, toxic Al

Toxicity is usually associated with pH levels below 5.5 in soils which contain significant exchangeable aluminium.

WHAT IS A GOOD LEVEL OR RANGE?

< 1% CEC

Extractable Al is < 2 [mg/kg] for sensitive plants

WHAT DOES IT MEAN IF THE RESULTS ARE NOT IN THE DESIRED RANGE?

High Al levels will reduce root growth and can lead to toxicity symptoms. Plant species that are adapted to low pH soils usually have a higher tolerance to Al. Legume pastures perform poorly and struggle to fix nitrogen with high levels of aluminium.

HOW TO CHANGE OR MANAGE IT?

Increase pH (e.g., via lime or dolomite).

Increase levels of other cations, especially calcium (Ca).

Copper (Cu) [mg/kg] trace metal

WHAT IS IT? WHAT DOES IT TELL US?

Potentially available Cu

WHAT IS A GOOD LEVEL OR RANGE?

<0.3 [mg/kg] is considered low (1.0-2.0 [mg/kg] is considered adequate)

Less available/tied up in insoluble forms in high pH and calcareous soils, deficiencies can occur in dryer conditions.

WHAT DOES IT MEAN IF THE RESULTS ARE NOT IN THE DESIRED RANGE?

Reduced protein synthesis, reduced nitrogen (N) fixing by legumes.

In cattle, copper deficiency can result in many issues, such as rough coats, retarded growth, and diarrhoea. In sheep copper deficiency results mostly in wool abnormalities. Copper is especially important for ewes in lamb and lactation.

HOW TO CHANGE OR MANAGE IT?

Cu can be applied to soil or plants. Trace metals compete for uptake if not in balance in the soil.

Iron (Fe) [mg/kg] trace metal

WHAT IS IT? WHAT DOES IT TELL US?

Potentially available Fe

WHAT IS A GOOD LEVEL OR RANGE?

Soil tests do not accurately assess Fe deficiencies in the soil.

>5-30 [mg/kg] based on crop studies

EDTA values not available

Less available/tied up in insoluble forms in high pH and calcareous soils, can be worse in wet conditions.

WHAT DOES IT MEAN IF THE RESULTS ARE NOT IN THE DESIRED RANGE?

Reduced photosynthesis, respiration, and chlorophyll production. Iron deficiency is not common in pasture systems, however, can contribute to Cu deficiency. At low pH surplus Iron can cause deficiencies of other trace elements.

HOW TO CHANGE OR MANAGE IT?

Fe can be applied to soil or plants. Trace metals compete for uptake if not in balance in the soil.

Iron deficiency is not common in pasture systems. Addressing acidity through liming reduces the risk of iron imbalances.

Zinc (Zn) [mg/kg] trace metal

WHAT IS IT? WHAT DOES IT TELL US?

Potentially available Zn

WHAT IS A GOOD LEVEL OR RANGE?

0.13-0.55 [mg/kg] (1.0-2.0 [mg/kg])

Less available/more tied up in insoluble forms in high pH and calcareous soils.

WHAT DOES IT MEAN IF THE RESULTS ARE NOT IN THE DESIRED RANGE?

Carbohydrate metabolism and enzyme activation are affected (like manganese (Mn)).

In soils with a high pH, or that are limed regularly, availability of Zn may become deficient.

High P applications can reduce Zn uptake in plants.

In sheep and cattle, Zn deficiency presents as sub-optimal growth and fertility. Poor skin condition is also a sign of Zn deficiency.

HOW TO CHANGE OR MANAGE IT?

Zn can be applied to soil or plants. Trace metals compete for uptake if not in balance in the soil. High P applications reduce Zn uptake.

Manganese (Mn) [mg/ kg], trace metal Various methods used

WHAT IS IT? WHAT DOES IT TELL US?

Potentially available Mn

WHAT IS A GOOD LEVEL OR RANGE?

>50 [mg/kg] – using 0.01 M

CaCl₂ extraction method (SE NSW)

<102 [mg/kg] – using 0.005

M DTPA (pH 7.3) extraction method (SE QLD)

Less available/more tied up in insoluble forms in high pH and calcareous soils, deficiencies can occur in dryer conditions.

WHAT DOES IT MEAN IF THE RESULTS ARE NOT IN THE DESIRED RANGE?

Disturbed carbohydrate metabolism and energy transfer (like Zn). Some soils are naturally high in Mn, this can suppress the uptake of other metals.

Mn toxicity is more of a concern than Mn deficiency as pH declines, and Mn becomes more available. When pH <4.3 (CalCl₂), Mn becomes toxic to plants. Particularly susceptible are legumes and brassicas.

Oats are particularly sensitive to Mn deficiency, along with legume pastures such as sub clover, white clover, and lucerne.

In livestock, Mn deficiency is associated with sub-optimal growth and bone development, and infertility.

HOW TO CHANGE OR MANAGE IT?

Mn can be applied to soil or plants. Trace metal(s) compete for uptake if not in balance in the soil. If Mn uptake is too high, the other trace metal should be applied to correct the imbalance. Liming can reduce Mn availability and reduce toxicity.

Boron (B) hot water extraction [mg/kg] or indicative test for ‘plant-available’ B is hot CaCl2- extractable B

WHAT IS IT? WHAT DOES IT TELL US?

Potentially available boron

WHAT IS A GOOD LEVEL OR RANGE?

0.34-0.84 [mg/kg] not limiting for Lucerne (Central Tablelands, NSW)

WHAT DOES IT MEAN IF THE RESULTS ARE NOT IN THE DESIRED RANGE?

New tissues cannot develop normally and can die, roots and fruits crack.

Excessive amounts of boron are toxic to plants, however specific thresholds for pasture species have not been established.

HOW TO CHANGE OR MANAGE IT?

Plants rely on transpiration for B uptake. It can be applied to soil or plants. Care should be taken to ensure B applications do not lead to toxicity.

Molybdenum (Mo) - testing for extractable Mo is uncommon

WHAT IS IT? WHAT DOES IT TELL US?

Potentially available Mo, most Mo soil tests are not reliable, Rayment and Lyons (2011) published a method based on 0.01 M CaCl₂

WHAT IS A GOOD LEVEL OR RANGE?

As tests are unreliable optimal levels cannot be recommended.

WHAT DOES IT MEAN IF THE RESULTS ARE NOT IN THE DESIRED RANGE?

Mo deficiency results in reduced N assimilation and rhizobia function in legumes. Mo deficiency affects brassicas where leaf size is narrowed.

In livestock, Mo deficiency is not common. Of more concern is Cu deficiency induced by excess of Mo in herbage (molybdenosis). Molybdenosis results in reduced poor growth and reduced fertility.

HOW TO CHANGE OR MANAGE IT?

Mo can be applied to soil or plants. Care should be taken when applying Mo to paddocks to ensure Cu deficiency does not occur from high or frequent applications of Mo on all paddocks.

Soil tests for selenium are not commercially available

WHAT IS IT? WHAT DOES IT TELL US?

Potentially available selenium

Plant tissue and animal tests

WHAT IS A GOOD LEVEL OR RANGE?

In plant tissue <0.02 mg Se/kg DM is deficient. >0.05 is adequate for grazing livestock.

WHAT DOES IT MEAN IF THE RESULTS ARE NOT IN THE DESIRED RANGE?

Se appears to be not essential for plant growth.

Selenium deficiencies in livestock predispose them to white muscle disease and ill thrift.

HOW TO CHANGE OR MANAGE IT?

High and regular applications of superphosphate decreases the amount of selenium in pastures and subsequently animal uptake, contributing to predisposition of white muscle disease.

Stock drenching with Se supplements combats Se deficiency.

Se can also be applied granularly with superphosphate.

Rayment and Lyons method³⁰

WHAT IS IT? WHAT DOES IT TELL US?

Potentially available cobalt

Plant tissue and animal tests are preferred

WHAT IS A GOOD LEVEL OR RANGE?

In clover, 0.04mg Co/kg DM

Concentrations in plant tissue <0.10mg/kg dry weight is deficient.

Cobalt deficiency measured in blood serum as Vitamin B12 is most accurate.

WHAT DOES IT MEAN IF THE RESULTS ARE NOT IN THE DESIRED RANGE?

Cobalt in plants is only required by Rhizobia bacteria on nodules in legumes for vitamin B12 synthesis. Deficiency can affect N fixing efficiency.

In livestock, cobalt deficiency presents as weakness, similar to malnutrition. Cobalt intake directly influences vitamin B12 synthesis in the rumen.

Cobalt is critical when grazing Phalaris based pastures to reduce the risk of Phalaris staggers.

HOW TO CHANGE OR MANAGE IT?

Cobalt deficiency can be corrected in livestock with drenches, vaccines, or bullets.