cornucopia
The Permacultivator - Journal of Cool Climate Permaculture
Back to the
Journal Index

Soil

A series of articles on aspects of soil important in Permaculture

 
 
 
 

Soil Texture

TYPE

WHEN DRY

WHEN WET

SAND

Loose, single grains which look and feel the hand, the soil mass gritty. If squeezed in falls apart when the pressure is released.

When squeezed in the hand it forms a cast which crumbles when touched. It will not form a ribbon between thumb and finger.

SANDY LOAM

Aggregates easily crushed; very faint ‘velvety’ feeling initially, but with continued rubbing, gritty sand feeling dominates.

Forms a cast which bears careful handling without breaking. Does not form a ribbon between thumb and finger. Rubbed surface is rough.

LOAM

Aggregates are readily crushed under moderate pressure; clods can be quite firm. When pulverised, has a lovely velvety feel that becomes gritty with continued rubbing. Casts bear careful handling.

Casts can be handled quite freely without breaking up. Very slight tendency to ribbon between thumb and finger. Rubbed surface is rough.

SILT LOAM

Aggregates are firm but may be crushed under moderate pressure. Clods are firm to hard.Smooth, flour-like feel dominates when soil is pulverised.

Casts can be freely handled without breaking. Very slight tendency to ribbon between thumb and finger. Rubbed surface has a broken or rippled surface.

CLAY LOAM

Very firm aggregates and hard clods that strongly resist crushing by hand. When pulverised, soil takes on a somewhat gritty feeling due to harshness of the small aggregates present.

Cast can bear much handling without breaking up. Forms a ribbon between thumb and finger which feels slightly gritty when dampened and rubbed.Soil is plastic, sticky and puddles easily.

CLAY

Aggregates are hard;clods are extremely hard and resist crushing by hand. When pulverised, has a grit-like texture due to the harshness of numerous very small aggregates which persist.

Casts bear considerable handling without any breakage. Forms a flexible ribbon between thumb and finger and retains the plasticity when elongated. Rubbed surface has a very smooth, satin feeling. Sticky and easily puddled.

Soil Moisture

Soil moisture is critical for plant growth and hence food production.

In a permaculture system it is encouraged

The following table is provided to assist growers with determining how much water is present and how much is available to plants.

Determining the Moisture Content of Soil

Amount of readily Available Moisture for Plants
SAND
SANDY LOAM
CLAY LOAM
CLAY
Close to 0% Little or no moisture available. Dry, loose flows through fingers. Dry, Loose, flows through fingers. Dry clods that break down into powder. Hard baked, cracked surface. Hard clods difficult to break.
50% or less Approaching time to irrigate. Still appears dry, will not form ball. Still appears dry, will not form ball. Crumbly, but will bold in ball with pressure. Somewhat pliable will ball under pressure.
50% to 70% Enough available moisture. Same as sand under 50%. hold together. Tends to ball, but will not be slick. Forms ball plastic, may when squeezed. Forms ball, will ooze between fingers
75% to field capacity, Plenty of available moisture. Tends to stick together slightly, forms weak ball. Forms weak ball, breaks easily, is not slick. Forms ball and is pliable, becomes slick. Easily oozes out between fingers, feels slick.
Field capacity Will not hold more water. No free water, but moisture is left on hand. Same as sand. Same as sand. Same as sand.
Above field capacity. Soil is waterlogged. Free water appears when soil is in hand. Free water will be released with bounced Can squeeze out water. kneading. Puddles form on surface.

Weeds as Soil Indicators

With the summer growth comes the inevitable growth of a variety of "plants out of place" as some would call weeds. These can serve to indicate the condition of the soil in which they are growing.

Soil Indication

Amaranth Amaranthus Retroflexus Healthy aerated soil
Bracken Pteridium Esculentum Nitrogen deficiency
Chickweed Stellaria media Healthy slightly acid soil, rich in copper, iron, manganese, potassium
Dandelion Taraxacum officinale Earthworms
Dock    
Curled dock Rumex crispus  
Mud dock R. bidens  
Swamp dock R. Brownii Acid soil rich in iron, poor drainage
Fat hen Chenopodium Album Well balanced soil
Horehound Marrubium vulgare Shows naturally dry soil
Ink Weed Phytolacca Octandra Rich fertilised soil
Nettles Urtica Urens - annual  
  U Dioica, U Incisa - perennials Poor soil, may need iron, sulphur, nitrogen
Sorrel Rumex acetosella Acid soil

Soil Temperature and Germination

If you are wondering about the strange season we are experiencing the following table might indicate why germnation rates have been unusually low and growth rates have been slow. The table shows the differences in the number of days for seeds to germinate and seddlings to appear for seeds planted at a uniform 12mm depth.

SEED GERMINATION No. of days to appearance

Soil temperature in degrees Celsius

Crop 0 5 10 15 20 25 30 35 40
Asparagus 53 24 15 10 11 19 28    
Bean 16 11 8 6 6        
Cabbage 15 9 6 4 3        
Capscium 25 12 8 8 9        
Carrot 51 17 10 7 6 6 8    
Cauliflower 19 10 6 5 4        
Celery 57 26 14 9          
Corn 22 12 7 4 4 3      
Cucumber 13 6 4 3 3        
Eggplant 13 8 5            
Lettuce 49 15 7 4 3 2 2    
Okra 27 17 12 7 6 6      
Onion 135 31 13 7 5 4 4 12  
Parsley 29 17 14 13 12        
Parsnip 171 57 27 19 14 15 32    
Pea 36 13 9 7 6 6      
Radish 29 11 6 4 3 3      
Rockmelon 8 4 3            
Silverbeet 42 17 10 6 5 4 4    
Spinach 62 22 12 7 6 5 6    
Tomato 43 14 8 6 6 9      
Turnip 5 3 2 1 1 1 2    
Watermelon 12 5 4 3          

Soil Analysis

from Debbie Hebbard

Accurate information on your soil can lead to effective decisions. A professional chemical soil analysis is the way to obtain full data. It is not a cheap exercise so you need to consider the benefits. Trace element deficiencies and major nutrient imbalances can be dealt with precisely and hence cost effectively. SWEP Analytical Services, 43 Neasham Drive, Dandenong, VIC 3175, was recommended by Pat Coleby at her talk.

This firm includes cobalt, sulphur, hydrogen, and boron, but not selenium, at present. They provide an easy to understand analysis, and are most helpful in discussing results. They can, if asked, when specific land use is indicated, give the desired quantities of each mineral needed. The cost for one analysis is $100 per sample, sent with the sample - it takes about four days - for the result to be returned.

A soil sample is taken from the top 8 cms of soil, from several locations on the farm (whatever size) or one paddock, these are then thoroughly mixed, any growing matter removed and a sample bag of about half a kilogramme is sent for analysis. Where there is several soil types it may be advantageous to take and send more than one sample.

Soil and pH

WHAT IS pH?

pH is the term used to explain the acidity or alkalinity of the soil. Although the chemistry behind the concept of pH is complex, a basic understanding of its role can be of great benefit to the gardener. Very acidic soils lack organic matter, while aluminium and manganese can reach toxic levels, and phosphorus may become inaccessable. At the other extreme very alkaline soils destroy the humus content and soil structure while concentrating mineral salts to toxic levels, nutrient deficiencies can also occur. So an imbalance in the pH of a soil can cause significant nutritional problems for plants in that soil. pH tests are easy to perform and can explain many of the problems experienced by some gardeners. The relevant pH scale for general horticultural purposes is as follows:

4-6 very acid
6-6.5 slightly acid
6.5-7.5 neutral
7.5-8 slightly alkaline
8-10 very alkaline

The pH scale is logarithmic, so an increase of 1 point is an actual 10 fold increase in the alkalinity.

WHY IS pH IMPORTANT?

The reason pH is so significant is that it affects the intake of plant nutrients. The growth and general health of plants can be seriously affected by unsuitable pH levels. In a soil with a pH imbalance, many nutritional elements, essential to plant growth, are unavailable to the plant and so signs of deficiency appear. The addition of fertilizers will not correct the problem, only waste time and effort. Poorly nourished plants are naturally prone to disease and pest attack, which leads to further problems. The solution is relatively simple once the pH imbalance is identified. The nutrients present in the soil, will become readily available to the plant, when the pH is modified and the ‘deficiency’ soon disappears.

HOW IS pH MEASURED?

pH test kits are readily available and simple to use. Basically a sample of soil is mixed with a liquid reagent, then a powered indicator is sprinkled on. The resulting colour change is compared with the colour chart to give a reading. From this reading, changes can be made.

WHO LIKES WHAT pH?

Most common garden plants have pH preferences that fall between 5 and 8. The absorption of nutrients from the soil, occurs when the nutrients are dissolved in a solution, however at high or low pH levels, nutrient soluablity varies. Different plants have varying nutritional needs and these needs are best met at specific pH levels. Some plants are very specific, while others are less effected by pH. When designing and planting a garden, or rotating crops, you can either modify the pH to suit the plants, or grow those plants best suited to that pH. Grouping plants with the same pH and nutrient requirements makes soil management and fertilising programs simpler. Naturally plants growing under optimum conditions are healthier than plants that may be struggling to obtain adequate nutrients. The naturally occuring vegetation or weed infestations can be an indication of the pH of a soil. The following lists show the prefered pH of common plants:

QUITE ACID (pH 4-6)

azaleas blackberry blueberry chicory chestnut chrysanthemum coffee conifers cranberry endive fennel lupin lily of the valley marigold oak peanut pecan potato pine radish raspberry rhododendron rhubarb shallot sweet potato tea watermelon

SLIGHTLY ACID (pH 6-6.5)

apple apricot barley bean lima buckwheat cherry collards corn cowpeas eggplant endive gooseberry grape kale millet mustard oats parsley parsnip pea peach pear peppers pumpkin rhubarb rye salsify snap bean soybean squash strawberry tomato turnip wheat

NEUTRAL TO ALKALINE (pH 7-7.5)

alfalfa alyssum asparagus beet broccoli brussels cabbage carnation cantalope carrot cauliflower celery chard clover cucumber grape iris leeks lettuce lucerne okra olives onion oregano parsnip peas/beans quince rosemary spinach zucchini

HOW CAN SOIL pH BE MODIFIED ?

If it is not possible to choose plants that suit the existing soil pH, then modification should be done before planting begins. After making changes to the soil, allow time for the chemical changes to occur and re-test. Correcting pH organically is a slower approach, but healthier plants and soil result. Adding organic matter is an excellent starting point, for any soil problems. The addition of compost acts as a buffer for the plants while the soil pH is stabilising. It isgenerally easy to raise pH, or sweeten the soil, by adding limestone,chalk,magnesite,dolomite or gypsum. The amount added depends on the acidity and the soil type, clay soils need more lime than sandy soils. Over liming can cause further problems, so care must be taken. Liming is a regular process in most vegetable patch rotations. Wood ashes added with a good mulch will also help correct pH. Lowering the pH is not as simple, but can be achieved with time. Many soils in Australia are slightly acidic and will only need to be acidified for real acid loving plants. A gross imbalance was traditionally treated by adding ‘flowers of sulphur’ or sulphate of ammonia. Acidic phosphate and urine for potash, is suggested by Bill Mollison, for correcting alkaline soils. For organic gardeners, the regular use of compost, manures, and blood and bone should keep the soil close to neutral. A mulch of pine needles, composted saw dust or leaf mould, added to acid loving plants is beneficial. Peat moss has a low pH, but being a non-renewable resource, its use should be discouraged. Regular crop rotation takes advantage of the different needs and pH requirements of crops. The beds that are limed this year will be planted with plants favouring higher pH (like onions or brassicas) and as the crops are rotated the beds become more acidic. The final crops are acid lovers (like tomatoes). The following year this bed is re-limed and the cycle continues.

REFERENCES: