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 simlified 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

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Mt Erica trip 2011

August 14th, 2011

Have just got back from the latest ex Rovers trips to Mt Erica. This year we had 6 starters. We were more adventurous with our walks this year, exploring round Mushroom Rocks and the NBW hut. Night-times were taken up reminiscing about the good old times like huddling around the tiny wood fire to keep warm. But things have changed, the Hut (Chalet) now has a gas stove, solar lighting and very tasteful drapes. However because of our ages alcohol is now only taken for medicinal purposes. Mushroom Rocks is still North of the Hut.

Mt Erica summit August 2011

Mt Erica summit August 2011

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Water pollution case study

February 16th, 2011

Contamination of waters by organic matter including manures is a type of water pollution. Excessive organic matter load in water is likely to cause a number of changes including:

Higher turbidity
High decomposition rate leading to elevated carbon dioxide and lowered oxygen,
Undesirable intermediate products of decompostion including nitrite and ammonia.
Elevated nutrient levels
Elevated dissolved organic matter
Elevated bacteria levels in general and specifically E coli if manures are present

The owner of this dam on a property north of Melbourne noticed an unpleasant smell coming from the dam. The water was also very discoloured.

Farm dam polluted by runoff. The owner has already fenced off the water to exclude stock.

Farm dam polluted by runoff. The owner has fenced off the water to exclude stock. But what is the source of the contamination?

Here are the test results for this dam: pH 6.8, ORP 217 mV (low end of desirable range), turbidity 624 FTU (very turbid), UV absorbance 40% at 1 : 25 dilution (very high), ammonia + ammonium 12.4 mg/L (high), carbon dioxide (dissociated fraction) 25.6 ppm (high), nitrate 8.9 mg/L (slightly elevated), nitrite 0.16 mg/L (any nitrite is undesirable), phosphate 16.9 mg/L (very high), E coli 13,100 CFU’s / 100 mls (very high), aerobic plate count 2,067,000 CFU’s / 100 mls (high).The indications are that there is an organic matter contamination problem – because of the E coli, probably from manure.

Here are the results from the drain in the foreground of the photo: pH 6.9, ORP -33 mV (very low, indicates low or depleted oxygen)), turbidity 976 FTU (very high levels of semi suspended particles), UV absorption 53% (high, at 1 : 25 dilution), ammonia 26.3 mg/L (high), carbon dioxide 42 ppm, nitrate and nitrite both 0, phosphate 27.3 mg/L (very high), E coli 14,900 CFU’s / 100 ml, aerobic plate count 1,553,000 CFU’s / 100 ml.

My brief interpretation: Decomposition in the runoff water is producing ammonia and carbon dioxide. As the water reaches the dam oxygenation levels increase slightly allowing some nitrate to be produced. However there is not enough oxygen to convert all the nitrogen decomposition products to nitrate hence there is some nitrite detectable in the water.

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Investigating water quality

January 22nd, 2011

Water quality standards like the Australian Drinking Water Guidelines often set the upper limit for contaminants like metals and organic chemicals. The Guidelines mention dozens if not hundreds of potential contaminants. But in many cases it is not clear at what level a particular chemical becomes a health hazard. For example it will depend on how much water is consumed over a given period and whether the contaminant has short or longer term effects. Arsenic is a contaminant that is thought to have longer term effects which are hard to quantify.

Dam near the Howqua River

This farm dam is in a fairly isolated location near Mansfield Victoria. The first step towards good quality dam water is to maintain a good vegetation cover in the catchment area.

Sometimes a customer wants a quick assessment of water quality. For example ‘is it safe to swim in a particular water body’? Its impossible to go through all the potential contaminants that might be present. Here are the results for a recent test. E coli 0, coliforms 0, aerobic plate count 141,000 (all CFU’s / 100 mls), pH 9, ORP 257 mV, dissolved organic carbon (as UVA) 12.5 ppm, EC 19.5 miliS/cm, turbidity 0 FTU. Would you swim in this water? The bacteria all tested absent or low, the oxidizing potential was within the acceptable range and the water was very clear. Its possible to find natural waters with at least one of those factors at the same level. But in the same sample the values for pH, DOC and EC sound alarm bells! Oddly enough the turbidity value (very clear water) in this case possibly indicated a problem because natural waters usually have some turbidity. The question went back to the customer, ‘Was there any obvious reason that they knew about for the unusual test results?’ It turned out that the water was from an artificial lake near an industrial area. Therefore the recommendation was that it would not be prudent to swim in that water.

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Water quality indicators

January 10th, 2010
Waterhole on a drying creek in Central Victoria

A waterhole on a drying creek in Central Victoria The water is very discoloured and has an earthy smell with abundant protozoans and a few algae The ORP value (oxygenation) has dropped to the low side of the desirable range.

At Apps Laboratories we measure a range of factors in water samples.  Some like dissolved metals can be compared directly to the Australian Water Quality  Guidelines. Others like salinity indicate what the water can be used for for example depending on the salt tolerance of irrigated crops. More often we want to give the landowner an idea of what is wrong with the water; an indicator of  ‘health’ or quality.

This gives a better understanding of management of the water or possible treatments. Here is what we found in a recent dam water sample. The water has a smell like compost and was discoloured green by algae. A quick check of ORP level showed very low oxygenation. High ammonia (unionized form) confirmed that there was probably high organic contamination of the water and that under low oxygen conditions some was being converted to ammonia. We also didn’t find any nitrates but this was expected because of the low oxygen. UVA absorbance was very high further suggesting high levels of organics in the water. The water also had elevated salts and a calculated significant sodium hazard.

Very high densities of algae usually indicate high nutrient inputs. The fact that we found some phosphate was a bit worrying as algae usually use up all the phosphate as they grow. Perhaps a check on the water coming into the dam would be recommended. The water was also very alkaline (pH 9.2). Algal blooms remove carbon dioxide especially during the day and send the pH upwards. At night the pH should return to more normal levels. There were two unusual characteristics of this water; the pH stayed high overnight and there was higher than expected alkalinity.  Some of this water is waste water from a food processing plant.

Overall the ‘quality’ was low and several problems were indicated both in the source water and in the stored water.

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Boosted reverse osmosis filter for farms

August 21st, 2009

One of the problems with many homes in rural areas is that there is not enough pressure from pressure pumps to run a reverse osmosis filter system. Reverse osmosis filters work by pushing water against a very fine membrane. Only a proportion of the water, usually 1/4 to 1/3 gets through, leaving behind most salts and other contaminants.  The rest of the water with the contaminants goes to waste.

A boosted RO system for rural homes.

A boosted RO system for rural homes.

RO systems are designed to remove a large proportion of most contaminants from water including salts and chemicals. The result is very clean water. RO works more efficiently with reasonably clean water like rain water tank or spring water.

The picture is of a boosted RO I made up. It is in the lab and produces rinsing water for the lab and also drinking water for the house. Output is about 108 l/d. It uses a 24 gpd membrane. 50 gpd membranes are also commonly used. The prefilter is just a 1 micron sediment cartridge. The second cartridge is a 1 micron carbon block cartridge. This cartridge is designed to reduce tastes, smells and protozoan pathogens. Here are some results for the lab RO system.

Before filter After filter
DOC* by UVA 254 nm 2.1 ppm 0
Conductivity 87 microS/cm 7.4 microS/cm

* DOC = Dissolved Organic Carbon. DOC is directly proportional to UVA at 254 nm for most waters. Here an estimate of DOC is made based on an approximate relationship derived from published data from a variety of waters.

There are no detectable dissolved organics getting through and the salts level has been significantly reduced. RO membranes can also reduce bacteria in the water but I haven’t tested bacteria reduction yet.

For a range of water filters to suit both town and country applications see Water Doctor water filters.

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Trip to Mt Erica

August 17th, 2009

Last weekend I joined a few of my ex Rover friends from the Yallourn Capt Hurley Rover Crew on a trip up “The Mountain”. The mountain is Mt Erica in Gippsland. Most of us are in our late 50’s or early 60’s. We have mostly known each other for over 40 years.

Mt Erica Aug 09

Our numbers were a bit down this year but here are the diehards at the summit of Mt Erica.

The Captain Hurley Rover crew built the JW McMahon hut on Mt Erica over many years starting from 1938. Its a basic but comfortable mountain retreat. It has given generations of scouts and other groups the opportunity to take time out in a relatively unspoilt and remote area in a safe way. From Mt Erica we can look down on the expansive Latrobe Valley with its several coal fired power stations. So close but a world away. The water on the mountain tends to be fairly clear with relatively low numbers of bacteria. In other similar hilly areas I’ve measured low organics in water using UV but this is mostly humic material.

There wasn’t much snow around this year. Global warming perhaps? Its often difficult to use scientific knowledge to prove that one factor is causing another so arguments tend to go round in circles. In the medical field there have been attempts to move towards a type of diagnosis that attempts to describe the patient’s current ’situation’ and to infer how the patient’s overall condition has developed. Its like trying to explain something and the explanation is a model that is further tested and refined. Part of that refinement is through the treatments themselves.  Perhaps environmental problems could be tackled the same way.

We spent a pleasant couple of days together with no electricity (well except for batteries to play the iPod), no emails, no showers and only the company of Boris the resident Lodge rat.

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ORP in water – what does it mean?

July 5th, 2009

Recently a couple of bore water samples came through the lab. By coincidence although they came from very different locations they had some distinct similarities. These were elevated dissociated carbon dioxide, elevated soluble iron and elevated manganese. But they both had another similarity – low ORP or redox value. The sample with the highest metal levels had an ORP of around 110 mV. In the other the ORP was around 160 mV. I usually expect ORP levels of between 200 – 400 mV in good quality water.

ORP is a measure of oxidizing capacity. A low ORP especially below 0 indicates reducing conditions. In the sample above with the lowest ORP I aerated the water with an aquarium pump for 5 hrs but could only get the ORP to around 300 mV. After that it slipped back to around 200 mV. What an ORP probe measures is the average effect of usually many different redox reactions pulling the mV value up and down. Oxygen supply is thought to mainly influence higher ORP values but lower values are created by reduction of oxygen supplying species (molecules / substances) such as sulphate and oxides of metals like iron and manganese.

For more detail on why measuring redox is important please see pH and ORP in water.

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What’s in water?

June 13th, 2009

Water testing is a little bit like problem solving. Most people want to know if there are any underlying issues that may affect their water quality. For example if there are higher than expected numbers of bacteria, if there are dissolved metals present or if there is any contamination from organic chemicals. Most test results are ‘indicators’ and go towards characterising water quality. They also give some ideas about both water treatment, for example by using water filters or, often more importantly water supply management.

There are a lot of things that can possibly be in water: algae and microorganisms, organic chemicals, metals, different salts and dissolved gases. But water is not a static system – it is a living (usually) system that has its own properties. One of the most useful tests I do in the lab is to measure carbon dioxide. Specifically its the dissociated fraction that is part of the pH buffer system. By also measuring alkalinity its possible to calculate a theoretical pH. Now when that’s compared to the actual pH some inferences can be made about factors that are affecting water quality. Something similar is done in medicine where analysis of the pH buffer system can indicate if a persons illness is affecting or originating from kidneys or lungs.

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