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February 2010

Welcome to the February 2010 edition of Fertile Minds, the newsletter of Sydney Environmental & Soil Laboratory.

In this new-look issue (we’ve used a new template for the e-mail newsletter) we highlight the fact that the world is running out of phosphorus.

If you have any questions you would like answered in Fertile Minds, please write to info@sesl.com.au. 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 – Reducing soil pH
• A looming phosphorus crisis
• Topdressing turf
• Benzo[a]pyrene – a carcinogen in smoke
• Did you know ... ? – Parafield Stormwater Harvesting Facility, SA

The Loam Ranger – Reducing soil pH

Dear Loam Ranger,

My turfgrass soil shows a pH of above 7. I know that the best pH range is 6 to 7. Should I try to reduce it, and how?

It is not always easy to reduce the pH of an alkaline soil; it depends on how much lime is present. Whether you even need to depends on what you are growing. Some problems can be managed just with fertiliser.

Alkalinity in urban areas usually occurs when lime (calcium carbonate) is present in or has been added to the soil. Some soils are naturally limey (e.g. coastal sands containing shell grit), and some become limey as a result of too much lime or, quite commonly, the presence of crushed concrete or cement.

Naturally alkaline soils are more common in arid and semi-arid regions, but can also occur in wetter regions on chalk or limestone parent materials or when shell grit is present. Such soils are called calcareous soils.

These are two main ways gardeners and farmers can lower soil pH: by adding iron sulphate or elemental sulphur (called ag sulphur). To destroy 100 g of lime requires 32 g of ag S or 278 g of iron sulphate. Iron sulphate is purely chemical in its reaction, whereas acidification by ag S is biological, requiring S-oxidising bacteria, which use the energy released from the S and from organic matter, and in the process release sulphuric acid (H₂SO₄). This requires 6–8 weeks to occur in good soil moisture conditions.

Click here for advice on when and when not to try to lower soil pH (750 words, 3 minutes)

A looming phosphorus crisis

We’ve all heard of “peak oil”: the situation in which half of all oil reserves have already been extracted and used, and prices will henceforth go up. But of far more concern for agriculture is “peak phosphorus”. Unlike oil, for which substitutes are available, there is no substitute for phosphorus (P). And we’re slowly running out.

P is one of several essential elements for all life. As an element, it cannot be manufactured, only extracted. Unlike nitrogen, which can be pulled from the atmosphere (either by factories or by legumes), economically extractable P is found in only a dozen countries, 5 of which produce 75% of world output: Morocco (with around half of all reserves, much of it in occupied Western Sahara), China, the USA and Russia.

According to research cited by the Global Phosphorus Research Initiative (GPRI), current high-grade reserves will be depleted within 50 to 100 years, and peak P production could occur by 2030. Prices are already increasing quickly: the price of rock phosphate increased from US$50/t in 2007 to US$350/t in 2008 (a factor of 7 times, or a 600% increase).

Click here for information on why we’re running out of P and what we can do (850 words, 3 minutes)

Topdressing turf

Topdressing refers to the layering of sand and soil over turf. (For farmers and nurserymen it usually refers to the application of fertilisers to a standing crop.) Topdressing of turf is used for four main reasons:

• To restore the level of a surface after play or subsidence has altered it.
• To adjust the soil texture so as to improve compaction resistance: usually to create or maintain a coarse particle size range.
• To control thatch or the organic matter content at the surface, so as to increase speed, bounce and resistance.
• To build up soil depth.

Topdressing is often combined with coring and dethatching operations in sports field maintenance and renovation.

Click here for advice on how to topdress (1350 words, 7 minutes)

Benzo[a]pyrene – a carcinogen in smoke

You need to read this article if:

• you work as a volunteer bushfire fighter
• you work in a smoky environment
• you work in the commercial compost industry
• you work with recycled soils or in soil remediation
• you are exposed to tar, pitch, asphalt, soot, carbon black, crude paraffin, coal or coke
• you work regularly with a char grill or a charcoal barbecue.

Such work can expose you to benzo[a]pyrene (abbreviated BaP), a naturally occurring dangerous chemical that forms as a result of incomplete combustion of both fossil fuels and bushland. BaP is mutagenic and highly carcinogenic: that is, it causes cancer. In fact, BaP was recognised in 1933 to be the component of coal tar responsible for cancers of the scrotum suffered by chimney sweeps in 18th century England.

Click here for advice on how to avoid exposure (700 words, 3 minutes)

Did you know ... ? – Parafield Stormwater Harvesting Facility, SA

An innovative project in Adelaide was begun in 1999 to recharge groundwater with stormwater runoff that was previously lost to sea. Stormwater is often polluted with human and animal wastes. The project aimed to prevent the loss of the fresh water to the sea, clean it, store it for industrial use and irrigation, conserve drinking water, and support wildlife.

The Parafield Stormwater Harvesting Facility, as it became, arose from concerns of G. H. Michell & Sons, Australia’s largest wool processing company, over the rising costs of fresh water to wash its wool and of wastewater disposal. The company did not want to relocate, at the cost of 700 local jobs. Instead, the City of Salisbury Council created a series of weirs and wetlands to harvest the stormwater for use in place of fresh water.

Click here for details of the project and how much water has been saved (650 words, 2 minutes)