Wednesday, September 8, 2010

Soil Myths #3: Clay Breaker is not always your best friend

Too much gypsum can be a pain in the butt! Gypsum (calcium sulphate dihydrate: CaSO4.2H2O) or more commonly known as Clay Breaker, when used in large quantities can cause all sorts of problems. I was reminded of this in the last week as I worked on adapting a method to deal with gypsum interfering in nutrient measurements. Too much gypsum makes it difficult to measure nutrients, such as nitrogen. Gypsum is a type of salt, and for humans, plants and soil to much salt can be bad for health. So why are we recommended to use Clay Breaker? Do you really need Clay Breaker for your yard? Or are the Fertiliser companies ripping you off?

Why use Clay Breaker?

Clay Breakers or Gypsum are used to literally break-down clay. Traditionally, gypsum was used on heavy sodic clays in agricultural environments. These clays have a high content of sodium which reduces the porosity and water retention of soils, and hence plant growth. Soil scientists call this problem Sodicity. The calcium present in the Clay Breaker swaps with the sodium in the soil, and helps to bind the soil together. It improves porosity and water retention of soil, and thus plant growth also improves.

In your own backyard, you would use Clay Breaker in a similar way. People often use Clay Breaker when starting or improving a garden. In Australia, including Canberra, we often have heavy clay soils in our backyards. Gardens can be sparse, as there is not enough water in the soil for even grass to grow! So, when thinking about putting in a veggie or other garden, Clay Breaker comes to mind as a way of getting more moisture into the soil and improving plant growth. However, it isn't always the best option...

Example of a sodic soil; with a hard surface that plants can't get through!

Why is Clay Breaker not always the best option? 

Gypsum targets a specific type of soil, not necessarily the one in your backyard. Gypsum is great for targetting problems of sodic soils. However, not all clays are sodic! In fact, in Australia most sodic soils are found in river terraces, plains and in drainage areas; areas where sodium builds up from water movement and where sodium is naturally occuring. Some researchers say Sodic Soils make up about 28% of Australia. This means that the soil in your backyard may not necessarily be sodic. In fact, your soil may actually have heaps of calcium to help bind it, and this is when Gypsum may cause problems!

Gypsum can be unkind to your plants. Soils have a natural amount of salts present; natural salts of Calcium, Magnesium, Iron, Sodium etc. When you add Gypsum, you increase the salt content of the soil. If you add too much Gypsum, you can cause your soil to become too salty. When this happens, many plants refuse to grow or some start to grow and then wither and die. They are intolerant to the amount of salt in the soil as a result of the Gypsum application. 

But do not fear!! It actually may be another problem causing your clay to have poor plant growth, and there are other ways of fixing it.  First, you can work out what is wrong with your soil, and then what to add to get better plant growth.

Does your backyard look like this? 
You may have a problem with compaction and carbon!

What other problems could it be and what can I do about it? 

If Gypsum is not what you need to use in your Garden, how can you tell and what else can it be? You can do a few tests on your soil to work out the problem and how to solve it!

Step 1: Is it Sodicity?
  • Pull out your pH kit. If it has a pH greater than 7 (basic), it may be sodic.
  • Now, get a dish and add 1cm deep of rain or bottle water. Place 3 pieces of soil (about 1.5cm diameter) into the dish and leave for 5 minutes. If the water goes cloudy, then it is likely to be Sodic. Follow the Cure below. If your soil falls apart or does nothing, go to Step 2. 
Cure: Add 500g of Gypsum per meter square and gently hoe into your soil. If you aren't noticing any results after 6-12 months, try adding a reduced volume of 100g. Take care to use it sparingly, or you may get problems with salinity! Don't be suprised if you have a failed crop immediately after Gypsum use. You need about 6-12 months for the Gypsum to naturally integrate with the soil and for the salinity to reduce. In addition, you can also add some organic matter (below) for nutrients and improving soil structure.

Sodic soil with Gypsum added (white flecks). 
This soil is very saline and has only a few plants growing in it.

Step 2: Is it Carbon and Compaction (or both)?
  • Get a dish and add 1cm deep of rain or bottle water. Place 3 pieces of soil (about 1.5cm diameter) into the dish and leave for 5 minutes. If the peds fall apart or stay solid (but you still can't get anything to grow), then the problem is probably compaction and a lack of organic matter. 
  • Now for the hoe test! Get a shovel or hoe and try to dig a hole. If you are able to dig a bit of a hole without too much strain you probably have a Carbon problem. If the hole is really hard to dig, and you can bearly go down a few centimeters, the problem is Compaction. Check out the Cures for each below.
Carbon Cure: Low carbon means soil does not bind together, and water holding is reduced. It also means there are less soil bugs and nutrients for your plans. Replacing carbon through mulches is the best way to improve this problem! Add a mixture of Mulches to your garden and rake/hoe in. You can get some guidelines about Mulch mixes from a previous post: Mulch ain't Mulch. You will need to leave it 6-12 months before you see any really good results! Growth and productivity may be a bit slow to begin with.

Compaction Cure: Compaction usually happens with house construction. Heavy machinery tamper down soil, and reduce the ability of soil to hold water, roots to get into the soil and bugs to cycle nutrients. The best way to deal with this is a bit of Hard Yakka, mixed with some organic matter! Get out the hoe and the shovel and dig as deep as you can!!! If you can, get a loan of a rotary hoe and get nice and deep! But don't forget to check Dial before you Dig first! Add some mulch mix (as above), and double it!! Again, it may take some time to see results, but it will happen.

And if you still want to use Clay Breaker anyway, limit it to 100-200g per meter square. Otherwise you  may risk killing your plants!

Sodic soil (middle) with no treatment and with different treatments of Gypsum and Mulches.

Before you go for the bag of Clay Breaker, ask yourself 'Do I really need this?' Don't give into the fertiliser companies! You may not need Gypsum/Clay Breaker, and in fact, you may be killing your plants. Instead, do a few tests and work out if you need to use Clay Breaker, or if you need some Organic Matter!

For more info on Sodic Soils, check out this neat Guide by Central West CMA.   And if you want to get some more Info on your soil, gypsum application and Sodicity, you can send it away to a lab for analysis. Always happy to answer questions.

Happy Spring Gardening!

Monday, September 6, 2010

Spring is here, so get those shovels digging!

For us lucky people in the Southern Hemisphere, Spring has arrived. Sort of. Although we have had a few days of mild weather, we have also had lashings of cold and wet-windy storms. Many of us have not seen this much rain for over 10 years.

Regardless of the ups-and-downs of the beginning of Spring, we can start getting excited about our Summer crops! With the good weather, warmer days, nice moist soil, now is the perfect time to work on your Veggie Garden. And if you are a first time Veggie-Producer, you can check out some courses in your area:

If you are in Canberra, the Environment Centre is offering a Permaculture Course.

Topics covered are based on permaculture principles and include:
planning, soil, composting, water, 'where and when to grow what' and
finally ....harvesting !

Dates: 18-Sep-2010 and 25-Sep-2010
Time: 10.00-2.30pm
Teacher: Barbara Schreiner
Where: Canberra Environment and Sustainability Resource Centre Cnr
Lawson Circuit and Lennox Crossing, Acton
Cost: $180
Bring: A light lunch...tea/coffee provided
Bookings: info(@)
Payment: In advance by Direct Fund Transfer, cheque or cash.

You can check out your local Growers Society for courses and land:
Canberra Organic Growers
Australian-wide Community Gardens

... and don't forget you can always get some good advice on Garden Blog Networks, such as
Aussie Gardening
Sowing Seeds with Christine Milne 
Peter Cundall's Veggie Patch

Now, I have just got to work on my box-garden. The winter has taken the toll on the veggies (cold soil = no harvest). Hoping they will perk-up with the warmer weather and will get some peas, cauliflower, broccoli and spinach before I plant my summer veggies.

Happy digging!