Saturday, 17 May 2008

pH, SALT AND OTHER SOIL THINGS

(Amongst this post are photos of what's happening in my garden today: Tony's fennel bulbs swelling, Chinese cabbage exploding with growth, Andrew's rainbow chard with the red stems, Joy's cos lettuce ready to have a leaf or two picked, and the last one is all the goodies from a post from last Wednesday.)

pH : This is a measure of the acidity /alkalinity of a substance. Plant growth is affected by soil pH because at different pH levels nutrients are either tied up in the soil and become unavailable to plants or are released and can be used by plants. Extremes of pH can cause the death of plants not suited to the conditions. Our locally-made testing kit (by Manutec) has a scale from 2 - 10. A reading of 6.5 - 7 is neutral. I would be aiming for a reading around 7 - 7.5 for my vegetable garden.









Today I decided to take some of my own advice and do a few pH tests around the vegie patch. I expected quite a range of results because my soil is generally pretty alkaline at about 8.5 but the vegetable garden has been built up in 2 terraces which vary in depth and over 18 years have had a lot of organic matter added to them. Rain has been scarce and our tap water is meant to be alkaline although when I tested it with a pool-stick it read 6.8.

The results of the 7 samples I took ranged in a seemingly random kind of way from 6 to 7.5. So the problem with my bok choy not growing was not a pH problem because both the good and bad bok choy soils had the same reading, which was around 7. I think 6 is a bit acidic for vegetables, in my limited experience, so I might get a bit of mushroom compost , which is more alkaline, to improve it during the next few months. Mushroom compost is the left-overs after the local mushroom growers have finished growing their mushrooms in it and can be bought from Heatcrete and other landscape supply yards by the trailer load. I would prefer not to bring in anything but it will be disposed of by the mushroom growers so we might as well use it. The ad in the yellow pages for our Adelaide mushroom compost says:
Genuine spent mushroom compost
Garden Mulch and Soil Conditioner
Organic - Natural - Environmentally Friendly - Pasteurised.
Saves Water, Inhibits Weeds, Promotes Plant Growth

I don't like the 'pasteurised' bit because it means all the lovely bacteria that were in it have been killed. To me if it is pasteurised it isn't organic. Killing is popular in most bought garden products and it is a shame they have to do it so no-one can sue them for making them sick. If you mix it with your genuine, home-made compost I think it will become alive again before too long. I could add a bit of garden lime to the soil instead but I don't like buying anything that comes in a plastic bag unless it is a particular sterile mix I use for seed raising in boxes. I could also make this but I don't - that is where I draw the line.


SALT

Here in South Australia, especially when things have been so dry and evaporation high, salt levels in the tap water are killing or damaging a lot of sensitive plants like exotics that come from wetter climes ( camelias, azaleas, gardenias etc) and if we don't get huge amounts of rain soon, the rising salinity of our soils will begin to affect vegetable growth too. If you have rain water, use it liberally to wash down those salts. A common sign of salt toxicity is the browning to a crisp of the tips of the oldest leaves. Plants in this state need to have a good soak, even with tap water, to remove the built-up salt from the root zone. If we are to keep growing food like these things at right, we are going to have to start looking for salt-tolerant vegetables to grow. There are a few natives we should adopt.
(Luckily we have had 46.5mm of rain since I wrote this. It is a good start but we have a long way to go).

...I wrote this a couple of days ago and at that time I had a whole lot of other things to add. Just now I can't really get enthused about anything worth saying except the obvious so I might as well just post it as it is. "Other soil things" will have to wait for another day. Life in the blog-lane is not always fun.

4 comments:

Anonymous said...

Hi Kate,
I love reading what you have to say about what goes on in and around Adelaide and the world. I find your thoughts and ideas are inspiring.
Your thoughts regarding salt tolerant veggies made me think that the wicking worm garden bed is not just a solution to our food growing issues regarding a lack of water but perhaps also with the PH and salt issues?
Independent researcher Colin Austin who looked at the problems of providing sustenance food in poor regions of the world, in sub-Saharan Africa such as Ethiopia for example, where lack of water is causing widespread hardship and even starvation has designed the simple technology of the wicking bed, developed for subsistence farmers in Africa. Is this a key for resolving the water crisis in our cities?
Water shortages are creating increasing pressure on food production. The wicking worm bed is a highly productive growing system which not only produces more food from limited water, but also recycles waste organic material to provide plant nutrient and capture carbon.

The essence is to form an underground reservoir of water contained by a waterproof liner below the surface. Alternatively tubs can also be set up, see “waterright.com.au” for details.

Problems would arise if the underground pond was routinely filled by applying water from the surface. The water percolating down through the soil would absorb nutrients which would accumulate in stagnant nutrient rich water in the pond. This would soon become anaerobic, starved of oxygen forming a toxic putrid mess which would inhibit plant growth.

This is resolved in the wicking bed system water by applying water to the bottom of the pond where it is pulled upwards to the roots of the plant by surface tension or wicking action. The water is now not stagnant but continuously moving from the base of the pond upwards to the roots.

The system gives the plant access to a continuous supply of water. There is minimal loss of water from either soaking into ground or from surface evaporation. This makes the system highly water efficient however plants need more than water, they need a balance of water air and nutrients.
Too much water is just as bad as not enough water. Root systems need oxygen. They also can emit gasses such as carbon dioxide and ethylene which act as growth inhibitors.

The wicking worm bed system correctly managed achieves this balance of water, air and nutrients.
The upward movement of the water by the wicking action can be significantly increased by incorporating additional organic material into the soil above the underground pond. Virtually any organic material will increase this wicking action. The condition of the soil is an important factor in the correct operation of the wicking bed. A heavy compacted clay soil is unlikely to be really effective. Incorporating organic material such as bagasse into the soil will help initially but this will gradually decompose with time.

Worms will naturally help condition the soil; however worms need to be fed continuously to survive on an ongoing basis. Worms do not eat organic material directly; there is a process in which the organic material is first broken down by a combination of micro biological actions, the result of bacteria, fungi, nematodes etc. The worms feed on the output from this microbiological activity and then add further microbiological activity form their guts which make a highly productive growing medium.
The concepts have been tested and proven many times over and now it just falls on local communities to find the will to experiment and grow good nutritional food using less water.
Creating carbon stores and benefitting from the social contact and sense of achievement, it seems to me to be a great thing to introduce to schools. I like it.

Happy harvesting!

Tina 

Kate said...

Thanks for all the lovely info Tina.The wicking bed is a great idea and one I am going to install in a difficult part of my vegetable garden in spring, ready for summer.Here is a link to Scarecrow's garden where I first saw the system: http://scarecrowsgarden.blogspot.com/2007/09/wickered-dreams.html

I think it would need to be dis-assembled in winter. I look forward to seeing what Scarecrow does with hers now we have had some rain.

Anonymous said...

Kate, I will have to let you know how my dads wicking beds go.. he has set his winter veggies up and so far so good. There is an overflow drainage hole to keep the level right when there is too much rain. Some people set up their beds in a bit of a terraced fasion to allow overflow to cascade down to the next level and the final overflow point can be a bit of a sump to encourage deeper seepage into the subsoil. Anyway it does seem to be quite a relevant solution to dry climate gardening. It is encouraging to know that there is likely to be a better harvest for my next attempt. Prior to my young one being around, I had time to put into gardening and adopted the no dig method which served me well but that was also prior to water restrictions. Restrictions are not likely to leave us and potentially will increase. Lets hope people are encouraged to grow their own food using simple time saving and water saving methods. Tina.

Deb said...

Re pH can varies a lot.Every soil has its own range. I'd stay away from mushroom compost & use a little lime. Several reasons but mainly Ca has a proven record of peventing plant disease & stronger plants.Biodynamic 500 is also known for balancing the pH.
Ps I had checked out the Diggers web site it has to be the most user unfriendly I've come accross 10+ MB to read a catalouge, I have better things to do!