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October 2008
Welcome to the October edition of Fertile Minds, the monthly newsletter of Sydney Environmental & Soil Laboratory.
Did you know that plant nutrient deficiencies can be reducing yields even before symptoms appear? This is an important reason for having regular plant tissue tests, even if things look good. Heading off problems early can save you money later. One of our articles in this issue explain the benefits of early testing.
Another article looks at opportunities for growers to help fight global warming by locking up carbon in the soil.
If you have any questions you would like answered in Fertile Minds, please write to info@sesl.com.au. Or if you have any special requirements, we would be pleased to talk with you and tailor a package and price. Please contact the office on (02) 9980 6554 or write to us at info@sesl.com.au.
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In this issue
- The Loam Ranger – Mulches and soil improvers
- Plant tissue analysis – head off problems early
- Carbon burial
- Collecting irrigation water for testing
- Did you know ... ? – Oil and water do mix after all
The Loam Ranger – Mulches and soil improvers
Dear Loam Ranger,
We have a problem in a landscape largely composed of Lomandra in traffic islands and roundabouts. The plants are yellowish and failing to thrive. We have mulched with woodchip and fertilised normally and are wondering why the landscape is not looking better.
It is quite likely that the cause is nitrogen drawdown by the woody mulch, a commonly seen problem.
The solution is to apply 50 g/m2 of nitram to the surface mulch, water it in and assess the result in 1 month. Repeat if necessary.
Plant tissue analysis – head off problems early
The colour of a plant can be used as a crude indicator of a plant’s nutrient status. For example, green = healthy, yellow = unhealthy. But one problem with this technique is that once symptoms become visible, growth and yield have already been reduced – by as much as 15%. Colour changes also don’t tell you what is causing the problem. A plant that is yellowing may be deficient in nitrogen, sulphur or a combination of nutrients. Yellowing might also be caused by soil compaction or a disease organism.
Plant tissue analysis, while not a magical tool, is a wonderful aid when used with an up-to-date soil test and good field observations. The key in plant analysis is becoming familiar with it and using it regularly.
Tissue analysis is a particularly powerful tool for diagnosing trace element disorders. Both deficient and toxic levels of iron, manganese, zinc and copper can show up as interveinal chlorosis (yellowing between the veins, which remain green). Only tissue analysis can reveal the reason for the chlorosis.
Tissue analysis alone cannot tell us why a particular element may be at deficient or toxic levels. But combining it with a soil test can often reveal the reasons for the problem. For example, a high manganese content could well be explained by acidic soil pH.
Click here to read about the roles of plant tissue analysis (400 words, 2 minutes)
Carbon burial
We all know about global warming. The cause is the extra amounts of greenhouse gases that humans are pouring into the atmosphere. The two most significant of these are carbon dioxide (CO2) and methane (CH4). This article focuses on CO2.
Various strategies have been proposed to reduce the amount of CO2 in the atmosphere. Many focus on reducing our output, such as by moving from coal-fired power stations to solar energy, and replacing oil with biomass. Others focus on removing the CO2 that is already in the air, such as by reafforestation on a huge scale. This removal from circulation is called sequestration.
Can agriculture, horticulture and forestry make a significant contribution to carbon sequestration?
Click here to find out (850 words, 3 minutes)
Collecting irrigation water for testing
From time to time you will want your irrigation water analysed for nutrient and salt contents. You will need to collect a representative sample for testing.
Many different sources of water are used for irrigation, but they can be categorised into two kinds:
Running water: from a bore or spear point; from a river, stream or creek; or town water.
Still or pooled water: from a dam, tank or well.
Recycled water can be running or still.
The sampling technique you use – described below – will depend on the water source and your reason for testing. For example, if you want to assess the nutrient load in the water draining out of a glasshouse, you will collect running water. If you want to assess the nutrient load in your holding dam before you reuse the water, you will collect still water. But if you want to assess the nutrient load in that water as it is being reused in the glasshouse, you will collect running water.
Collecting samples
- Use a clean plastic or glass bottle.
- Rinse the bottle several times with the water that is to be sampled.
- If the water is running, take samples from the flowing stream.
- If the water is still, take subsamples at different locations and depths and combine them.
- Avoid any matter floating on the surface.
- Collect 200–300 mL for a full water test.
It is not necessary to refrigerate the sample unless you want it tested for nitrate, ammonium and phosphate. In this case, the sample should be either fresh (less than 24 hours since sampling) or refrigerated until it is delivered to the laboratory.
Make sure you label the bottle clearly with your name, the date and the source, and when you send it off to the lab, indicate what you want it tested for.
Did you know ... ? – Oil and water do mix after all
We all know that oil and water don’t mix. Either we have to shake them vigorously to make an emulsion, or we have to add a surfactant or detergent.
But in 2003, Professor Ric Pashley, then at the Australian National University, discovered that simply degassing water is enough to get water and oil to mix.
Water naturally contains dissolved gases, notably oxygen, nitrogen and carbon dioxide. Professor Pashley’s work suggests that these dissolved gases interfere with the water’s ability to be attracted electrostatically to the oil molecules.
Pashley began by degassing the water by repeatedly freezing and thawing it and drawing off the gases that were released. He has since developed a simpler process that uses semi-permeable membranes.
Degassing the oil as well greatly improves the results. Pashley found that simply mixing the oil and water and then degassing them led spontaneously to a cloudy emulsion.
This discovery could have important implications for agriculture and horticulture. Currently, hydrophobic chemicals and spray oils have to be mixed with a surfactant before they can be sprayed on crops. But surfactants can damage tissue surfaces. The development of a field technology to degas water could broaden the use of chemicals, particularly the non-toxic spray oils.
Even more importantly for human health, the direct mixing of drugs with water greatly expands the range of drugs that can be injected directly into the bloodstream.