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April 2008
Welcome to the April edition of Fertile Minds, the monthly newsletter of Sydney Environmental & Soil Laboratory. A bit late, but we're catching up.
Winter is coming, and in this issue we begin a series of articles about using the down time to prepare for the growing season.
If there are specific topics that you would like covered, or you have a question for the Loam Ranger, please let us know at info@sesl.com.au.
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In this issue
- The Loam Ranger – Micronutrients for dryland pastures
- What is cation exchange capacity?
- Moisture retention and CEC in sandy soils
- Managing irrigation water quality
- Weed invasion
- Did you know ... ? – Coconut
New price list available
If you have not yet received your copy of our new price list, please click here.
As usual, if you have any special testing or consultancy requirements, we would be pleased to discuss them with you and tailor a package and price accordingly. Please contact the office on (02) 9980 6554 or info@sesl.com.au with your request.
The Loam Ranger – Micronutrients for dryland pastures
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Dear Loam Ranger, My neighbour said he increased his pasture growth by adding a trace element fertiliser. I’d like to do the same. What points do I need to know? Micronutrient (or trace element) requirements for pastures depend on soil type and are indicated by plant tissue analysis. A plant tissue analysis is an important step before you apply micronutrients, as you need to know which elements your pastures are not taking up. (There’s no point in paying good money for a fertiliser you don’t need.) |
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What is cation exchange capacity?
The cation exchange capacity (CEC) of a soil is its capacity to exchange cations between the soil particles and the soil solution (the water in the soil). It is determined by the negative electric charge on the surface of soil particles. This charge attracts the cations, restricting them from leaching away.
The phenomenon is called cation exchange because it is possible to exchange or displace one cation for another. For example, excessive use of ammonium fertiliser can displace calcium, leading to poor pH buffering and soil acidification. As plants take up nutrients from the soil, they exchange them for hydrogen, slowly acidifying the soil.
CEC is used as a measure of fertility and nutrient retention capacity, and indicates a soil’s capacity to protect groundwater from nutrient contamination. It also indicates a soil’s structural resilience, or shrink–swell potential: a low value (<20 meq/100 g) indicates that a soil will not recover from compaction, whereas a high value (>40 meq/100 g) indicates that soil structure will recover naturally.
Click here to learn how CEC is measured and how it works (500 words, 2 minutes)
Moisture retention and CEC in sandy soils
There can be good reasons for establishing turf or crops on sandy soil. In the case of elite sports fields, turf has to be able to handle heavy traffic, such as a football game, as soon as possible after a heavy downpour. Playing fields are ideally level, so rainwater will not run off quickly. Instead, it has to drain quickly into the soil, from where it can be carried away by subsoil drainage.
In the case of crops, some farmers have no choice but to crop on sand - particularly those in Western Australia.
But drainage for immediate access after rain must be balanced by the ability of the soil to grow the plants. Unfortunately for plant roots, sand has virtually no capacity to hold nutrients. Every watering or rainfall washes nutrients through the sand out of the reach of plant roots. This wastes money and pollutes groundwater.
Groundwater polluted with nutrients, especially nitrogen and phosphorus, can be poisonous (a lot of rural towns in Australia depend on bore water), and can flow through the subsoil until it reaches creeks and rivers, where it causes toxic algal blooms, killing fish and other aquatic animals and poisoning livestock that drink the water.
So it is essential to strike a balance between the ability of sandy soil to drain quickly and the need to stop nutrients from leaching down.
Managing irrigation water quality
Although it is possible to use water with a wide variety of characteristics for irrigation, as water quality declines, management procedures become more demanding, and the requirements of the soils and plants become more restrictive. Failure to match the soil with the water and the management type can result in damage to soils and plants.
Before you use any water for irrigation, you need to know what salts and how much are dissolved in it.
Click here to find out how to cope with saline irrigation water (1000 words, 4 minutes)
Weed invasion
The challenge for us all as we become increasingly urbanised is to develop sustainable lifestyles that will enable us to live in harmony with our bushland.
Many of our suburbs and towns adjoin some of the most biologically diverse, fragile and beautiful natural vegetation in the world. What we do in our gardens and public spaces has dramatically altered our natural environment. In particular, activities in built-up areas affect our downslope bushland, our National Parks, and our creeks and rivers.
Stormwater rushes off all our hard surfaces - roads, roofs, car parks, garages, factories and driveways - carrying with it the pollutants and detritus of everyday life. These include oils and chemicals, rubbish and organic litter, soil from cleared land, fertilisers, insecticides, herbicides, sewage from overflows, weed seeds and animal faeces.
This fast-flowing stormwater cocktail enters the bush, erodes the watercourses, silts up the creeks, and changes the nature of the soil. Many of the components of this urban runoff increase the nutrient levels in the soil. Most of our native plants are adapted to low nutrient conditions. But this moist, fertile soil favours the growth of weeds, and invasive species such as montbretia, blackberry and privet soon move in.
Click here to learn how we can fight bushland weeds (700 words, 3 minutes)
Did you know ... ? – Coconut
Coconut is probably the most completely utilized crop in the world. Nearly every part of the tree has a use:
Trunk – as timber for furniture and housing.
Fronds – as thatch roofing or woven into mats and walls.
Leaf stalks – as brooms and food skewers.
Leaf buds – as a salad vegetable, heart of palm (although collecting this kills the tree).
Husk – as coir, used to make doormats, rope and coco peat, a sustainable replacement for peat in horticulture.
Shell – as musical instruments, or burned for fuel or charcoal.
Flesh – eaten fresh (as coconut meat) or dried (as desiccated coconut); ground fresh and extracted to make coconut milk and coconut cream; or dried (to copra) for extraction of oil.
Juice – from unripe coconuts, drunk as a refreshing drink.
Sap – fermented into an alcoholic beverage called toddy, or boiled and evaporated to produce palm sugar.
Roots – for dye and medicines.
Click here to learn how coco peat is used in horticulture (500 words, 2 minutes)