Posts Tagged ‘dairy farming’

Farm dam water filter – the results are in!

Saturday, March 11th, 2017

On our farm we require good quality water for jobs like cleaning in the dairy. We built a water filter that would be capable of treating a large volume of dam water so that it could be used to top up our rain water tank through dry periods. The design can be seen Low tech farm dam water filter.

In a slow media filter water passes slowly down through a filter medium. In our filter we used rockwool. The rockwool acts as a trap for sediment. Over time a layer of micro-organisms, mainly bacteria, builds up on top of the media. These trap and digest organic contaminants in the water. So it is a type of biological filter. Slow media filters have a simple design and have been used in many places mainly as a cheap and easy to make filter to improve drinking water. Studies have shown that they are effective in reducing turbidity and reducing bacteria and organic matter contamination in water.

A new filter needs to have water run through it for some time to condition the filter. This allows the biofilm to develop and for the filter to become effective.

Test results:

At the time of testing the dam water entering the filter was of reasonable quality. The turbidity was slightly elevated and fresh organic matter was in the low to moderate range. Coliform bacteria and total aerobic bacteria levels were elevated.

We tested before filter and after filter samples starting from day 2 after the filter was started. The tests were for coliform bacteria, total aerobic bacteria, turbidity, humic material by UV absorption and fresh or readily degradable organic matter by permanganate oxidation. Humic materials often give water from dams or creeks pale yellow or brown colours.

On day 2 before and after coliform and total aerobic bacteria counts were high and showed very little difference.

After operating for 8 days, filtered samples showed a 68% reduction in coliform bacteria.

After 18 days there was a 96% reduction in coliforms and 50% reduction in total aerobic bacteria.

At day 20 there was a 21% reduction in turbidity, 44% reduction in fresh organic matter and 15% reduction in UV absorbance.

Coliform bacteria are a large group of bacteria that are naturally present in water and soils. The group also includes some species that can cause illness. Therefore they are often used as indicators of water quality with higher than normal levels indicating possible contamination.

Slow media filter supplying water on a dairy farm

A slow media filter made from 2 x 200 L barrels on a dairy farm. The filter treats over 1000 L of dam water each day which is then used to top up a rainwater tank.

Maintenance: Our filter has now run for 6 weeks without any problems. We expect that at some later time the biofilm may build up and perhaps restrict the flow of water. There is a drain plug installed just above the biofilm layer which will allow some of the biofilm to be removed.

How the idea can be extended: If more filtered water is required then another filter with its own float valve and connection to the source water could be added. Both could then feed into the one collection barrel. A slow media filter could also be used to maintain the quality of water in a tank. In this case the filter would continuously take water from the tank, treat it then put the water back into the tank. The same type of filter could be installed in a gravity fed farm water supply. If the source water can be fed in by gravity and the treated water can be run off to below the filter then no pressurised water or pumps are needed.

A slow media filter is a low cost and low tech but effective way to improve the quality of surface water such as creek and dam water on farms.

Low tech filter for farm dam water

Friday, March 10th, 2017

Farm dam water is challenging to treat because it typically has high overall bacteria levels, is often discoloured by humic materials, has elevated turbidity and often has elevated levels of fresh organic matter.

On our dairy farm we rely on dam water through the dry months. The dam water is pumped to a holding tank near the dairy and is used as wash down water in the dairy and for drinking water for cows.

Dam on dairy farm in South Gippsland

Dam on a dairy farm in South Gippsland. The dam collects water from surrounding paddocks that are grazed by dairy cows. In this water bacteria levels are elevated and fresh organic matter is slightly elevated.

Water from a rain water tank is used to wash cows, clusters and to do the final rinse and clean. During summer the rainwater tank is occasionally topped up with the dam water. We needed a filter to treat about 1000 L each day of the dam water to improve the quality of the top up water.

Slow media filters are a simple low-tech method for treating poor quality water. We built a slow media filter out of two plastic 200 L barrels.

The main barrel has a few inches of clean gravel in the bottom. Horticultural grade rockwool was added up to about 2/3 the barrel height. The rockwool sits on a piece of woven shademesh to stop it mixing with the gravel. A manifold of PVC pipe with multiple drill holes sits within the gravel layer. It is glued to a riser pipe inside the barrel that exits just above the rockwool layer.

The filter is kept full of water by a float valve that lets in pressurised dam water. A valve on the outlet restricts the flow of water out of the filter. This both slows the flow of water in the filter and maintains a ‘head’ of water above the rockwool.

Slow media filter on a dairy farm.

Dam water enters the filter through a float valve. A valve on the outlet is opened just enough to allow a small flow through the filter. There is always water above the biofilm layer.

Over time a layer of microorganisms called a biofilm mainly made up by bacteria develops on the surface of the rockwool. Our filter has a biofilm surface area of 0.25 sq meters and has an output of 0.8 L each minute. Most of the work in a slow media filter is done by the biofilm layer which catches particles and digests organic material.

The second barrel catches the treated water. It has an automatic sump pump that periodically pumps the treated water out into the dairy rainwater tank. Even running at this low rate the filter treats around 1150 L each day.

The total cost of setting up the filter including fittings, rockwool and sump pump was under AU$200.

References:

Guchi, Ephrem. “Review on Slow Sand Filtration in Removing Microbial Contamination and Particles from Drinking Water.” American Journal of Food and Nutrition 3.2 (2015): 47-55.

Our new farm

Tuesday, December 8th, 2015

After a lot of searching we finally found a new home for our calves, 173 acres in Ranceby in South Gippsland.

 

Feeding cows

Feeding out hay to the milkers in the first Winter. This is not ideal especially under wet conditions.

 

The previous owners Robin and Deb McKinnon were very helpful in showing us their production figures, explaining how the farm worked and then allowing us to move some machinery and cows early.

There are some steep paddocks but most is gently undulating. About 2/3 of the farm is accessible with a tractor. We ran production and financial models on the farm and the figures showed that it was viable.

The Strzeleckis were originally under the sea so the soil is derived from sediments. It is a gray coloured loam with poor structure. When its dry weather the soil is dusty and when it rains it turns to mud.

Our family shares the farm jobs which spreads the load and makes it manageable.

We bought the existing herd and have bought in new milkers. As at December 2015 we still have 20% of the herd yet to calve. This should bring the total cows in the vat to around 95. We were aiming for 110 cows but it seems that the existing cows are doing better than anticipated so that has made up some of the difference.

Moving yearlings back to their paddock

Moving our wandering yearlings back to their home paddock. The farm has extensive shelterbelts of Southern Blue Gums. There are also many of the now uncommon Strzelecki Gums on the property.

 

Sustainable farming – what is it?

Wednesday, March 19th, 2014

Yesterday as a guest of Trevor and Anne-Marie Mills and the Western Port Catchment Landcare Network I attended a field day on the Mills’ dairy farm at Drouin South.

Amongst the principles of sustainable agriculture are that farming should:

– provide an amenable lifestyle for the farmer & family

– protect and enhance the productive capacity of the farm

– protect and nurture the natural environment and reduce environmental impacts

Judging by these criteria, the Mills have gone a long way to creating a sustainable farm. Much of this has been achieved by thinking ‘outside the square’ and often going against conventional thinking. For example T & A-M have fenced off and replanted many of the drainage areas and watercourses on the farm. Water is now piped to stock high up in each paddock. The result; less contamination of water, less nutrient runoff and cleaner water for the cows to drink.

The South Gippsland area was originally heavily forested and early accounts have detailed the diversity of wildlife that once existed. Now with areas on the farm returning to natural vegetation, some of the native animals are also returning. Happily these areas are often those that would be less productive and difficult to manage. The photos below taken from the same spot approx 5 years apart show the dramatic change around a natural waterway.

Before and after watercourse revegetation on the Mills Farm at Drouin South. By excluding stock from wet gullies significant improvements have been made to the quality of water flowing from the farm and as drinking water for stock. Approx 5 years between photos. Courtesy of T & A-M Mills and WPCLN.

Before and after watercourse revegetation on the Mills Farm at Drouin South. By excluding stock from wet gullies significant improvements have been made to the quality of water flowing from the farm and as drinking water for stock. Approx 5 years between photos. Courtesy of T & A-M Mills and WPCLN.

The WPCLN as part of their involvment in the property have been monitoring water quality and this has provided valuable feedback for farm planning.

On the farm management side T & A-M have adopted a rotational grazing system that takes advantage of the natural productivity of the soil and facilitates nutrient cycling whilst protecting against overgrazing and damage to pasture. The result, an increase in productivity which has meant that the herd size can be reduced whilst maintaining production.

I was especially interested to hear how Trevor had cut back on use of urea as a nitrogen fertilizer. This came about because he saw that the urea was favouring grass growth and supressing clovers. Now clovers are thriving and producing nitrogen naturally!

I think that soil testing still has a role to play on this farm. Particularly if it is done in a way that provides a better understanding of management effects on soil processes and the dynamics of nutrient movement around the property as well as off the property as natural losses and in farm products.

Judging by the attendance at the field day there is a lot of interest in sustainable farming and land management. The Mills farm is an excellent example for all to see that shows how productive farming can go hand in hand with protecting and enhancing environmental quality.

Farm water supply investigation

Saturday, January 25th, 2014

A preliminary investigation was carried out on the quality of water in two dams on a dairy farm in West Gippsland. The dams are a short distance apart in the same gully. The Upper dam is spring fed and can overflow into the Lower dam. The water was tested during summer. At that time the flow into the Upper dam had decreased and the water level was falling. The Lower dam was still fairly full.

The dams are in an elevated position and drain approximately 10 ha. The surrounding land is pasture.

Farm dam in West Gippsland. The Upper dam in this study. Water is pumped around the farm for drinking water for stock and also for washdown water in the dairy.

Farm dam in West Gippsland. The Upper dam in this study. Water is pumped around the farm for drinking water for stock.

There are many waterbirds on the dams – mainly ducks. Cows have access to both dams and commonly drink at the water’s edge. The water in both dams has a pale yellow-brown colour. There is significant attached bacterial – fungal mats clearly visible in shallow water.  One significant observation was that were no visible micro crustaceans.

Dam CO2 EC Turbidity Reactive C ORP*
ppm microS/cm FTU mg/L mV
Upper 18 289 11.5 0.5 207
elevated sl. elevated sl. cloudy moderate OK
Lower 5.8 738 3.5 0.5 205
moderate elevated clear moderate OK
* oxidation reduction potential

Some key findings are: Dissociated carbon dioxide was high in the Upper dam. The water is fairly clear in both dams with the Upper dam water just slightly cloudy. Overall salts as conductivity are elevated in the Lower dam. Both dams have oxidizing potential (a surrogate for oxygen level) within the desirable range.

Reactive or relatively fresh organic matter was estimated by permanganate digestion. In both dams reactive organic matter was in the moderately elevated range. Humic material in dams can be measured indirectly by UV absorbance. In both dams the UV absorbance was high, around 65%.

The pH of the Upper dam was 7.2 and pH of the Lower dam was 6.8. A pH buffer system analysis of the Upper dam gives a calculated pH of 6.7. This suggested the scenario of a falling pH (water becoming more acidic) as the carbon dioxide level rises. In this case the rise in carbon dioxide is being most likely caused by increasing organic matter decomposition. See organic matter figures below.

A pH buffer system analysis for the Lower dam gives theoretical pH of 7.84. This suggests that carbon dioxide level in this water is falling and this will cause the pH to slowly rise (the water will become more alkaline).

Farm dam in West Gippsland. This is the Lower dam in the study. Some physical and chemical factors show some improvement compared to the Upper dam. However there levels of the 3 key bacteria water quality indicator groups are twice the levels compared to the Upper dam.

Farm dam in West Gippsland. This is the Lower dam in the study. Some levels of physical and chemical factors are more favourable compared to the Upper dam. However the levels of 3 key bacteria water quality indicator groups are around twice the levels of the Upper dam.

Dam E. coli coliforms TC*
CFU’s / 100 ml CFU’s / 100 ml CFU’s / 100 ml
Upper 440 3317 53281
elevated** high moderate
Lower 960 7119 118274
elevated** elevated** sl. elevated
* aerobic plate count
** indicates contamination

For both dams the high  E coli level taken along with the high coliform levels indicate some fecal contamination of the water. Total aerobic bacteria level is approximately in the moderate range for exposed waters.

The main quality issue in both dams is elevated reactive organic matter levels and elevated E coli bacteria levels. There is some evidence that processes in the Lower dam are at least slowing deterioration of water quality. However on the negative side, levels of bacteria are significantly higher in the Lower dam.

Ideally in a study like this it would be useful to test the source water, in this case the spring water entering the dams. Unfortunately the spring was not accessible. There was also no other dam on the property to provide a comparison.

Acidity and major nutrients in dairy farm soil

Tuesday, 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).

Results:

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?

Tuesday, 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).

Results:

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?

References:

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 http://msucares.com/crops/soils/phosphorus.html Nov, 2013.

Phosphorus fractions in soil diagram.

Effluent management on a dairy farm

Saturday, 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 http://www.dpi.vic.gov.au/agriculture/dairy/pastures-management/fertilising-dairy-pastures/chapter-13, November 2013.

Organic matter in dairy farm pasture

Tuesday, 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.

Results.

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.

References.

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