Acidity and major nutrients in dairy farm soil

December 3rd, 2013

What is the connection between soil pH, acidity, nutrients and amount of lime required to raise the soil pH?

When we think of soil acidity most people think of pH. But pH is a measure of active acidity which can be measured with a meter, test strips or indicator solution or powder. In simple terms they measure hydrogen ions in water that’s in the soil.

But there is a ‘pool’ of acidity that is held in the soil. This is called exchangeable acidity and it creates a balance with pH in the soil solution.

An important property of soils is their ability to hold nutrients such as calcium, magnesium and potassium and make them available to plants. This is called the ‘exchange’ capacity and it is generally larger for soils with more clays and organic matter. But this capacity can be partly taken up by exchangeable acidity.

For agricultural soils generally, as pH increases (less hydrogen ions), exchangeable acidity decreases. But also with increasing pH the total exchange capacity of the soil increases and this capacity is taken up with a larger proportion of desirable nutrients. In soils with pH around 5.5 to 7 exchangeable acidity should taper off as pH rises with more of the available exchange capacity occupied by nutrients.

Soil samples were taken on a West Gippsland dairy farm at the same 3 sites described in previous entries. Exchangeable acidity was extracted with KCl salt solution. Exchangeable calcium and magnesium were extracted using Double Acid (Mehlich 1).


Exchangeable Exchangeable Exchangeable

acidity calcium magnesium
Site pH meq% meq% meq%
1 5.5 0.76 7.24 0.93
2 6 0.13 17.00 2.46
3 6 0.32 26.10 9.83

Typical figures for exchangeable acidity reported for other soils range from 0.5 to 1 meq% so Sites 2 and 3 have low exchangeable acidity.

Typical values for exchangeable calcium can range from 0.23 to 12.5 meq%. Typical values for exchangeable magnesium range from 0.25 to 4.2 meq%. Calcium levels are moderate at Site 1 to high at Sites 2 and 3. Magnesium levels are low / moderate at Site 1, moderate at Site 2 and high at Site 3.

West Gippland dairy farm Site 1. Of 3 sites tested on this farm, Site 1 has lowest pH, organic matter, phosphorus, calcium and magnesium. But exchangeable acidity is highest here.

West Gippland dairy farm Site 1. Of 3 sites tested on this farm, Site 1 has the lowest pH, organic matter, phosphorus, calcium and magnesium and it has the highest exchangeable acidity.

The unit meq% used to express acidity and nutrients is designed to allow a direct comparison between the amounts of each held on exchange sites in the soil. It also provides the mechanism for working out how much lime to apply to soil.

As lime is applied to soil it slowly reacts with the soil acidity. The active (pH) acidity is constantly replenished from the exchangeable acidity but in the process some of the calcium (and magnesium for Dolomite type lime) becomes attached to the exchange sites. The lime will displace some of the exchangeable acidity. This raises the proportion of desirable nutrients to acidity and in doing so, raises the pH.

One approach for working out how much lime to apply to raise the pH is to calculate how much would be required to neutralize the exchangeable acidity. At least this takes the guess work out of liming. Tests like the ones shown here can be used to monitor progress.

Another related approach is to estimate or measure the occupied exchange capacity then by using a diagram of pH vs exchange capacity decide the percentage change required to raise the pH a particular amount. See the reference below for more details.

So far, tests for organic matter, pH and some major nutrients have shown significant differences in fertility between paddocks on a dairy farm.

Further reading: Soil test interpretations by Apps Labs.

How much phosphorus is in dairy farm soil?

November 26th, 2013

How much phosphorus is there in farm soils?

I’m in the process of carrying out a quick assessment of soils on a dairy farm in West Gippsland. Phosphorus use is an increasingly important topic from a $ cost as well as environmental perspective.

In this study samples were taken from the same sites previously tested for soil organic matter. One sample was taken at each site in a core between the surface and 10 cm. One subsample was prepared after mixing the soil for each core. Phosphorus was extracted using Mehlich 3 extractant.

Mehlich 3 is a widely used extractant for several nutrients suitable for alkaline as well as neutral to acidic soils. It will extract a proportion of the inorganic forms of phosphorus. Mehlich 3 extractable P has been found to correlate well with a number of other indicators for more readily ‘plant available’ or potentially available phosphorus (Moody et al 2013).


Site Colour Organic matter pH Phosphate ppm
1 Grey low 5.5 27
2 Red-brown medium 6 36
3 Red-brown high 6 632

Phosphate measurements at other locations taken by Apps Laboratories (using Mehlich 3) have ranged from 23 ppm for Gembrook pasture through to 385 ppm for a well composted garden soil. Generally phosphate levels around 30 ppm are considered low and levels around 150 ppm high. The phosphate levels at sites 1 and 2 are low but the phosphate level at site 3 is very high. Some further tests might be useful to find if this applies to the whole paddock. Information on fertilizer history could also be helpful.

Dairy cows grazing on mixed species pasture in West Gippsland. Levels of more readily available phosphorus can vary widely between paddocks.
Dairy cows grazing on mixed species pasture in West Gippsland. Levels of more readily available phosphorus can vary widely between paddocks.

In soils, phosphorus is thought to be present in around 4 ‘pools’. Readily available P is dissolved ready for plant uptake. This amount can last between 1/2 to 3 days for average crops. Some P is temporarily attracted to and held by soil minerals (called adsorbed P). Some P is held in organic forms in the soil organic matter. Adsorbed and organic P form moderately available P and phosphorus moves slowly between these pools and soluble P. Up to 70% of the available P can be held in organic form. However some P finds its way into more permanent ‘bound up’ or ‘occluded’ pools in the soil minerals. This phosphorus is only released again very slowly so is in effect ‘lost’. The total amount of P in soils may be much larger than the amount recovered by extractants like Mehlich 3. Much of this is in the ‘occluded’ pool.

Challenge problem: A pasture contains 30 ppm Mehlich 3 extractable phosphate – a low value. This is close to 9.8 ppm phosphorus (P). This part is done – each hectare contains approximtely 9.8 Kg of P (down to 10 cm). Is this amount of P adequate for the milk produced in a year assuming that 1000 L of milk contains approx 1 Kg of P? For the non dairy farmers some approximate figures that will help are stocking rate 2 cows / ha, production 6000 L / yr / cow. What assumptions have to be made and what factors are missing in this calculation?


Moody, P.W. et al. 2013. Soil phosphorus tests I: What soil phosphorus pools and processes do they measure? Crop and Pasture Science 64(5) 461-468.

Phosphorus fertility. Mississippi Agricultural and Forestry Experiment Station. Downloaded from Nov, 2013.

Phosphorus fractions in soil diagram.

Effluent management on a dairy farm

November 9th, 2013

For the last few weeks I’ve been visiting a dairy farm in West Gippsland to learn a bit more about how dairy farms work. It’s also an opportunity to apply some ideas about soil and water management in a practical context.

Cows can deposit around 8 – 10% of manure and urine output around the milking shed and yards. Manure and urine contains significant amounts of major nutrients including nitrogen, phosphorous and potassium.

On many farms this manure is often washed directly into specially contructed waste retention dams. A typical setup is a sedimentation dam sometimes followed by an aeration dam.

Sedimentation dam for dairy waste on a farm in West Gippsland. Water is washed into the dam from the milking shed and yards without treatment.

Sedimentation dam for dairy waste on a farm in West Gippsland. Water is washed into the dam from the milking shed and yards without treatment.

The picture shows a sedimentation dam on the WG farm. There is a thick crust of manure on top which means that conditions in the dam are most likely anaerobic. At this dam I didn’t want to get too close in case I became part of the waste system! Therefore I didn’t get a sample!

In an anaerobic dam the organic matter itself provides oxygen to help drive the other processes that eventually break down most of the organic matter into methane, hydrogen, carbon dioxide and ammonia. But the disadvantage of this method is that energy in the organic matter is lost (as methane) and importantly nitrogen is lost (as ammonia).

The overflow from the sedimentation dam on the farm enters a second aeration dam. What can we expect the water quality to be in this type of dam? There shouldn’t be much nitrogen but what other nutrients will be present?

Dairy farm aeration dam in West Gippsland. Water flows into this dam from an uphill sediantation dam that takes waste directly from the dairy.

Dairy farm aeration dam in West Gippsland. Water flows into this dam from an uphill sedimentation dam that takes waste directly from the dairy.

The aeration dam is just below the sedimentation dam. The overflow pipe can be seen in the picture. The water has a brown colour and a slightly unpleasant smell. Here are some water quality tests done in the Apps Labs lab: Dissociated carbon dioxide 13.5 ppm (elevated); Turbidity (unfiltered) 57 FTU (high); Turbidity filtered (0.45 micron) 19.8 FTU (still high); pH 7.1 (very slightly on the alkaline side); UV absorbance 99.2% (very high dissolved humic materials); Conductivity 1459 microS/cm (elevated salts); redox potential (ORP) -44.7 mV (anaerobic, and that’s at the surface).

Nitrate and nitrite were checked using screening tests. Both were at low levels or absent. That’s expected anyway because nitrates usually don’t exist in low oxygen conditions and nitrites usually form from nitrates under reducing conditions. Phosphate was checked using two different test kits. One showed phosphate over 30 ppm. The other showed phosphate as 43 ppm. Both these levels are very high.

There may be significantly more phosphate present in the two dams than the amount measured as some is likely to be held in the sediments.

What about nitrogen? Ammonia – nitrogen in the aeration dam was 0.44 ppm. This is higher than normally found in natural waters but is not excessive. At pH 7 around 0.4% of this nitrogen can be expected to be in the ammonia form as opposed to the ammonium form. This is not good for water life because the ammonia form is harmful. In general as water becomes more alkaline, an increasing amount of any total ammonia nitrogen present is likely to be in the ammonia form. This same amount of ammonia nitrogen, is roughly equivalent to 2 ppm nitrogen as nitrate. This is slightly elevated for natural waters so the nitrogen in the ammonia form probably doesn’t account for all the nitrogen in the original manure entering the two dams.

What is the best way to use dairy effluent to capture maximum nutrient value?

The following web resource provides detailed figures on tests done on dairy effluent dams and suggests way to reuse the nutrients in the effluent:

DPI Victoria 2013, Using dairy effluent as a fertilizer. Downloaded from, November 2013.

Organic matter in dairy farm pasture

October 22nd, 2013

The benefits of organic matter in soil are well known. Organic matter improves factors including water holding capacity, nutrient holding capacity and structure. But organic matter can be made up of more longer lasting humus through partially broken down material to fresh material from plants and animals that has recently entered the soil. This fresh reactive fraction is more likely to be a major supplier of nitrogen to a pasture as it is broken down.

How much of each is likely to be present in a pasture soil? A recent study, Culman et al, 2012, has found that permanganate oxidizable carbon in soils correlates well with widely used measurements of microbial biomass and particulate organic matter. Permanganate oxidizable carbon is also a good indicator of variation in management and environmental factors.

Dairy farm pasture in West Gippland, Site 2 of the study. The paddock is elevated and the soils has a characteristic reddish-brown colour.

Dairy farm pasture in West Gippsland, Site 2 of the study. The paddock is elevated and the soils has a characteristic reddish-brown colour.

It is relatively cheap and easy to measure the reactive fraction of soil organic matter by permanganate digestion. A simplified method is outlined in detail in the Archive for March, 2012.

In a preliminary study soil was sampled at three sites on a dairy farm in West Gippsland.

Site 1: Pasture soil mid way down a slope, known to be poorly drained. Mixed pasture species including some perennial ryegrass and poorly developed white clover. pH measured at approx 5.5. The soil has a heavy texture but becomes powdery when dry.

Site 2: Elevated pasture with mixed species. Chosen for its contrast to Site 1.  More typical West Gippsland red-brown soil. Distinct crumb structure with pH around 6. This is the site in the picture.

Site 3: Another red-brown soil in an elevated position considered to have good pasture. pH approx 6. Good crumb structure.

Partially dried samples were sieved to remove roots. Two tests were carried out: digestion with 30% hydrogen peroxide for a ‘total’ organic matter measurement and, digestion with potassium permanganate for a reactive organic fraction.


Organic matter Reactive Total % reactive Approx
Site total w/w % org C ppm org C ppm org C level *
1 5.3 865 29293 2.9 low
2 7.2 1025.5 39751 2.5 moderate
3 9.5 2085.6 52014 3.9 high

* representative values can be seen by following the SOM Method link in the Archive for March, 2012  ‘A simple test  for reactive soil organic matter’.

Across the farm, levels of total and reactive organic soil matter varied from low to high. The lowest at Site 1 and the highest at Site 3. The percentage of total organic matter weight for dry weight in the soils ranges from 5.3 to 9.5.

The percentage of reactive soil organic matter was significantly higher at Site 3 (3.9% of total). However a meta-analysis of a range of figures for total and reactive soil C from the Archive for March, 2012 shows that typically the reactive component ranges from 3.8 % to 10.6 %. Therefore overall, soils on the dairy farm in this study have low or lower than expected levels of reactive soil organic matter.

This study has provided some comparative figures for soil organic matter fractions on a dairy farm. Reliability will be improved with more tests per paddock and wider testing over the farm will be useful as part of pasture and feed management on the farm. Many of the factors that determine organic matter levels in the soil can be identified like grazing, pasture, crop and fertilizer history. This information along with tests for key nutrients can help to better understand how the current situation has developed.


Culman et al, 2012, Permanganate oxidizable carbon reflects a processed fraction that is sensitive to management, 2012, Soil Science Society of America Journal.

My tank drinking water smells, what can I do?

December 31st, 2012

One of the frequent problems seen in water tanks is smelly water. This can occur in above and below ground tanks and includes rain water tanks. People often describe the smell of their water as musty, decaying or like ammonia or rotten eggs. It can be just a little bit off-putting or in some cases can be very unpleasant. In any case its hard to drink and wash in smelly water.

The ammonia or rotten egg smell is a give away for anaerobic conditions. In other words poorly aerated water.  The first test to do when investigating smelly tank water is a redox test. Redox or oxidation reduction potential is an indicator of oxygenation and unlike oxygen level tests redox can also show very anaerobic conditions.

Tests from one underground tank with smelly water showed that redox was 145 mV just below the water surface. Generally redox in the 200 – 250 mV range is commonly seen and acceptable for drinking water. Below 0 mV is definitely not good. So 145 mV was a little low but not too bad. However at the kitchen tap where water is drawn from deep in the tank the redox was -58 mV. Now that is bad! It indicates anaerobic water. This water had an unpleasant ‘eggy’ smell.

testing being carried out on a below ground concrete rain water tank. The tank is dug into a slope with no barrier to stop runoff running onto the tank.

Testing being carried out on a below ground concrete rain water tank. The tank is dug into a slope and risks contamination because the tank is level with the ground on the uphill side.

Checklist for smelly tanks:

  • is there runoff entering the tank?
  • have you been on holidays or have you just bought the property?
  • do the downpipes from the roof go underground then come back up before the tank?

What can be done about smelly water? If the smell can be traced to anaerobic conditions the simplest thing to do is direct the stream from a garden hose back into the tank. Just ripple the water and try to get a slow circulating movement happening in the water.  There’s no need to do anything too drastic like emptying the tank or throwing in handfulls of chlorine. All you need to do is get oxygen back into the water to reverse the reactions that created the smells in the first place. As a safeguard think about installing a cartridge water filter, one that has an activated carbon cartridge. That will help to remove some of the smells and will be good insurance against any future contamination. The Basic Water Quality Test from Apps Laboratories is designed to test water quality factors and can be used to trouble shoot water quality problems. Apps Labs also supplies rural and farm water filters.

Filters for farm water supplies.

December 8th, 2012

Not all water quality problems for farm and rural drinking water can be solved by simple filters. However there is a lot that can be done to improve drinking water quality. Its often a matter of being proactive in case contamination occurs. Dual cartridge systems are easy to install and can often be fitted under the kitchen sink. The choice of cartridges depends on the source of the water.

Above ground or well protected rainwater tanks usually don’t build up bacteria levels but they can develop undesirable smells if poorly aerated. Use a sediment cartridge and a 5 micron carbon cartridge. At Apps Laboratories we have selected some dual cartridge combinations that can be applied to different situations. See them at Drinking water systems.

If you have to backup your water supply from a creek or dam then use a sediment cartridge plus a finer carbon cartridge, one that is designed to reduce waterborne protozoan pathogens. Your carbon cartridge should reduce some turbidity so that UV treatment can be added. UV is very effective against bacteria provided there is not too much dissolved organic matter in the water. Ask Apps Laboratories for a Basic water quality test.

Many farms source water from fairly protected situations like springs or bores. But there may be fine silt or sediment and a risk from bacteria. Again a fine carbon cartridge like the KX Matrikx Cr1 is recommended. The second cartridge will be a special ceramic cartridge such as the Doulton Sterasyl. Ceramic cartridges are very effective at reducing bacteria. At Apps Laboratories we have tested ceramic cartridges and the results are reported in Ceramic cartridge test.

Doulton Sterasyl ceramic cartridge for bacteria reduction.

Doulton Sterasyl ceramic cartridge for bacteria reduction.

For more details on Rural and farm drinking water systems please see Rural and farm systems.

Reducing water hardness by lime softening

November 28th, 2012

Water hardness is caused by high calcium and magnesium levels. However a water test is needed to find out how much hardness is accounted for by bicarbonates, called temporary hardness and how much is composed of sulphates and chlorides (permanent hardness). For a discussion of alkalinity and hardness please see Water test interpretations.

Lime softening uses calcium hydroxide to raise the pH of the water to reduce temporary hardness. At around pH 10 calcium is precipitated and at around pH 11.5 magnesium is precipitated.

Laboratoriy trial of lime softenin.

Calcium hydroxide ready to be added to a sample of hard water in a laboratory trial.

The theoretical dose of lime can be calculated from water test results. In practice the dose of calcium hydroxide and final pH adjustment needs to be tested on actual samples in laboratory trials. Too little lime will only reduce calcium. Too much will create an imbalance of calcium and magnesium in the final sample and will make pH adjustment more difficult.

In the Apps Laboratories lab we were successful in significantly reducing the hardness in a bore water sample from a rural property. After several trials we arrived at a lime dose that achieved a good final balance of salts and hardness.

EC Hardness Calcium Magnesium
microS/cm ppm CaCO3 mg/L mg/L
Untreated 1630 769 72 139
Treated 586 162 34 18.5

Calcium and magnesium precipitate formed after dosing with lime. If the dose is right the 'fluffy' precipitate settles quickly.

Calcium and magnesium precipitate formed after dosing with lime. If the dose is right the 'fluffy' precipitate settles quickly.

Mt Erica trip 2012

July 29th, 2012

Another successful trip up Mt Erica this year. As you can see conditions were a bit wintery. But hey, we’re tough. We can battle through blizzards and snow drifts .. as long as there is a warm fire we can retreat to back at the Hut!

Mount Erica summit 2012There was plenty of hot discussion about the issues of the day and we resolved a few problems of national significance .. but we forgot to write it down!

There are a few memorial plaques appearing around the rock outcrops. One of the newer ones our group helped to install was for Graham Cook. Graham was a Senior Sergeant of Police at Morwell and Moe and was involved in numerous searches in the High Country during his career.

On Sunday morning a fresh light blanket of snow lay around the Hut, a sight not seen by some for quite a while.

A simple test for reactive soil organic matter.

March 20th, 2012

Of all the factors that can be measured in soil, fresh, reactive or labile organic matter is one of the more important. Its a tool that can be used to monitor seasonal changes that depend on strategies like cover crops, composting and residue retention. This test can be valuable for home gardens, horticulture, pastures or cropping.

A test for soil organic matter that shows the change in colour of a potassium permanganate solution is useful for quick comparisons. I’ve been working on an improved method that uses a relatively inexpensive colorimeter. Also there’s a spreadsheet calculator that handles all the necessary calculations even for soils with a wide range of organic matter content.

Soil organic matter is essential for good growth and flowering in vegetable gardens.

Soil organic matter is essential for good growth and flowering in vegetable gardens.

A description of the method can be found at SOM method. The calculations are in a Excel spreadsheet here SOM calculations.

As yet there is no kit available but if anyone wants help getting setup please let me know.

How much organic matter is in your soil?

September 2nd, 2011

Of all the factors that can be measured in soils, organic matter (OM) is probably the most useful and critical. This test measures the fresh or labile organic matter in soil. This organic matter supplies nutrients to plants because it is the food for microorganisms which in turn release nutrients like phosphorus and nitrogen.

Some tests like high temperature degradation or acid / dichromate digestion measure total or resistant organic matter. This is important for nutrient holding capacity, water holding capacity and soil structure. These tests are slightly difficult and can be slightly dangerous – been there, done that! Peroxide digestion tends to measure labile and perhaps more resistant SOM.

Potassium permanganate (KPM) is an oxidant that is safe to use. As the KPM oxidizes the OM it loses its purple / magenta colour. In the lab I use 0.2 M KPM stock solution with an added flocculant. The sample can be weighed or measured by volume (2.5 mls). The stock solution is diluted x 10 and then shaken with the soil by hand for a short time. So the method is simple and easy to carry out.

I tested 5 soils from around my property. A good compost, vegetable garden soil, soil from an old strawberry patch, soil from a paddock where very little fertilizer or compost had been added, and sub soil from an excavation. The soil in Gembrook is mostly a highly oxidized iron based soil that has a reddish colour. The results are below.

Permanganate digestion of labile organic matter in soils
Five soils from compost (left) to subsoil (right) were extracted using potassium permanganate. Soils with high labile organic matter remove most of the purple permanganate colour.

The compost sample is on the left – very high OM, then from L – R vegetable garden, unfertilized paddock, old strawberry patch, subsoil. The big surprise was that the old strawberry patch soil had relatively high labile OM, slightly more than the vegetable garden. The subsoil (on the right) had almost no OM. The unfertilized paddock (centre) had relatively low OM.

The change in colour provides a simple way to compare the OM in samples. In the lab I used a photometer to read the absorbance of the solutions at 570 nm. This method needs a calibration curve but the end result is more accurate. The amount of carbon in the OM can be related back to the amount of KPM used up (based on a simple assumption). Therefore this method can give a reading for organic carbon in gm/kg. Then that can be converted to a value for OM (organic C is about 55% of OM). Its even possible to estimate the amount of nitrogen that could be potentially released from the OM because the C : N ratio is usually , based on soil type, between 10 : 1 and 33 : 1.

The amount of fresh OM in soils is related more directly to soil fertility factors like microbial respiration and biomass and to factors that can be linked to soil management like reduced tillage, green manures etc.

The inspiration for my exploration was Weil, Ray, et al 2003, Estimating active carbon for soil quality assessment: A simplified method for laboratory and field use.

There are many good articles on soil organic matter available on the web including this one: Hoorman and Islam, 2010,  Understanding soil microbes and nutrient cycling. Ohio State University Agriculture and Natural Resources Fact Sheet SAG-16-10