detailed article about understanding and managing soils

Here's another article about soils and climate, it's part of an online book for people new to farming. Unfortunately I can't find the link anymore but it came from a Victorian government site http://www.nre.vic.gov.au
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Natural resource management deals with the physical management, retention and enhancement of resources such as soil, water, vegetation and wildlife. As a small property owner, you need a clear understanding of the natural resources on your property and the importance of conserving and managing them. In addition, the small property owner needs an appreciation of the natural resources in the catchment in which he or she resides. Any action that will affect the natural resources on the small farm is likely to effect other aspects of the catchment in either a positive or negative way. For example, soil erosion on your property may create turbidity in a local stream affecting the aquatic values of that stream.

Assessment of your resources will help determine such things as the most appropriate place to site your house and dam, and the selection and management of a suitable agricultural enterprise. In other words, understanding your natural resources will allow you to assess what your land is capable of achieving without risking the natural assets on your property. This will also help maintain the value of the property.

The components in this chapter will provide an introduction to natural resource management but to enable effective natural resource management, a Whole Farm Plan should be completed. A Whole Farm Plan will provide you with a physical plan of what your property should look like to provide for long-term natural resource management. The Plan will also provide you with goals to work towards in developing the property.

Land classes and land capability

Land everywhere is not the same but varies due to a number of factors including soil type and slope. How the land is managed will depend on the type or class of land therefore, the classes of land on a property need to be determined. Your property is likely to have several different land classes. These are determined by the physical features of an area, such as:

Climate - average annual rainfall and the spread of the rainfall, average maximum temperature in summer, average minimum temperature in winter, frost frequency & wind

Topography - angle of slope, aspect, local drainage

Soil type - including soil texture, chemical fertility, physical structure and depth of the soil.

Land capability is an assessment of the ability of an area of land to continually and sustainably support a particular land-use, at a given level of management and production. The capability of the land varies according to and within a land class.

Climate, topography and soil type can combine to cause wide differences in land classes over short distances. The number of different uses possible on a land class decreases with decreasing land capability. For example, an area with poor soil, short growing season, and steep slope would have low land capability and few possible uses. An area with fertile soils, plentiful rainfall, and flat topography, would have a high land capability, provided it did not flood, and could support a wide range of uses.

To obtain further information about land classes and land capability, contact your local office of Department of Primary Industries, or Landcare group. Climate, topography and soil, the main components of land classes and land capability will be discussed in more detail below.

Climate

Temperature, rainfall, wind, humidity are aspects of climate that are crucial to any farming enterprise. Climate in Victoria varies greatly across the State and is predominantly determined by altitude and distance from the ocean.

Rainfall reliability - Just looking at the Average Annual Rainfall can be deceiving as it gives the impression that the average rainfall is what can be expected. However, rainfall is very variable in Victoria causing both drought and floods. For example, in the Parwan Valley near Bacchus Marsh the lowest rainfall on record is 230 mm in 1967 whilst the highest rainfall on record is 800 mm (1970), and the average 500 mm. A general rule of thumb for rainfall variability is that once in every five years rainfall will not be as expected. This may be either wetter or drier. Droughts can be expected on average every 10-15 years.

Drought - Drought is very much part of the Australian environment. Your home and agricultural enterprises need to be managed for the advent of drought. Recent significant droughts have occurred every 10 or 15 years (1967, 1983, 1995, 2002). Chapters 4 & 5 discuss management against the risk of drought in more detail.

Flooding - Flooding in Victoria occurs at irregular intervals and may result in stock losses and damage to other assets such as fencing and sheds. Your local Shire and neighbours should be able to give you information on how flood prone your property is.

Temperature - Temperatures tend to be more extreme away from the coast ie colder overnight temperatures in winter and hotter day temperatures in summer. South of the Divide, temperatures are generally more moderate and evaporation rates are lower due to higher humidity as compared to north of the Divide. Central and northern Victoria by contrast has hot summers with an evaporation rate that exceeds rainfall, while winters are much colder. Frosts are more common as you move further inland. This is an important consideration when choosing your agricultural enterprise as frosts can effect stock, pastures and crops. Some areas of your farm may also be more frost prone than others. Cold air sinks to the bottom of valleys and depressions resulting in a frost hollow.

Wind - Cold winds prevail from the south and southwest in winter while in summer strong hot winds come from the north and northwest. This should be a major consideration when planting windbreaks. (Discussed further in Chapter 5.)


Topography

Slope and aspect are components of topography that effect the capability of land.

Slope - Steeper slopes cannot be cultivated and therefore are unsuitable for cropping and make pasture renovation more difficult. The greater the slope the greater the velocity of water that can run off hills which increases the likelihood of erosion if slopes are unprotected. Soil depth varies with slope. Soil at the top of a hill is generally shallower than in the valley. Hills are generally more suited to grazing and tree planting whereas valleys are more suited to crops except in flood prone areas.

Aspect - The direction which the slope of a hill faces (aspect) influences the soil. Shallow, stony, weakly structured soil is found on dry exposed northern slopes, in contrast to deeper well structured soil on the southern aspect. Northern slopes generally provide better winter growth due to direct exposure to the sun while southern slopes produce better summer growth due to less exposure to the sun which extends the growing season.

Soil

Soil, the thin layer of weathered material on the outer crust of the earth, is one of our most valuable assets. Physically it provides support, water and air for plants, while chemically providing the nutrients essential for growth. Soil needs to be managed appropriately and utilised within its capability otherwise degradation that will effect productivity and other natural resource components will result.

Soil is a mixture of 5 components: Mineral particles, Organic material, Living organisms, Water and Air.

The mineral components of soil result from the weathering of rocks over tens of thousands of years. Mineral particles are described based on their diameter; Gravel -particles larger than 2 mm in diameter, Sand - particles between 0.02 and 2 mm in diameter Silt particles between 0.002 and 0.02 mm in diameter, and Clay - particles less than 0.002 mm in diameter.

The texture of a soil is the proportion of sand, silt, clay and organic matter and is a way of describing a soil. Approximately 20 texture classes can be described but the most common include, sandy loam, loam, silt loam, clay loam, sandy clay and clay. The texture of the soil can vary between the topsoil and the subsoil, eg a sandy loam topsoil over a clay subsoil. Large changes in texture between the topsoil and the subsoil can lead to water drainage problems. The texture of the soil is an inherent property of the soil that cannot be changed and therefore management strategies for particular soil types need to be developed.

The physical structure of soil is as important as the chemical status of the soil. Sand, silt, clay and organic matter are able to cement together to form aggregates. Soil structure is the number, size and arrangement of soil particles and aggregates. A good soil structure consists of many stable aggregates with spaces in between.The space (in between known as macropores) allows for rapid movement of air and water into and through the soil (drainage) and allows for good plant root growth. Water is held for plant growth in smaller spaces within the soil aggregates (micropores). Well-structured soils allow for good water infiltration into the soil and therefore minimises the risk of soil erosion.

Poorly structured soil on the other hand has few aggregates and fewer macropores. Without sufficient macropores between the aggregates, rapid water and air movement does not occur. Water therefore does not move easily into the soil, resulting in waterlogging on flat country or water run-off on sloping country. Water run-off increases the risk of soil erosion. Root penetration into these soils is very difficult resulting in poor plant growth.

The structure of the soil can be adversely affected by management practices such as excessive tillage, tillage when soils are too wet, as well as compaction from vehicles and stock.

There is a suite of good information on assessing soils for their structure, ranging from developing your general understanding of soils, to a detailed examination of soils found on the property. Ultimately you could pay someone else to do the testing, however you can do the same tests yourself at a greatly reduced cost and all the while further enhancing your understanding of the land that you have invested in.

Agriculture Notes and Landcare Notes (http://www.dpi.vic.gov.au/notes) are a series of free information sheets that provide brief information on a wide range of land use issues. These free information sheets are available from the Department of Primary Industries website or any office. Alternatively, you may be interested in carrying out some of the simple tests yourself. A step by step guide is detailed in the Centre for Land Protection publication 'Know Your Soils'. This is a no fuss, common sense approach to explaining and carrying out common soil tests. For those who are keen there is the 'Land Classing Kit for Farmers' that build on the simple soil assessments with the aim of developing a Whole Farm Plan. Both the 'Know Your Soils' and the 'Land Classing Kit for Farmers' may be purchased from;

The Manager,
Land Evaluation Unit
Centre for Land Protection Research
Phone: 5430 4444

Organic matter

Organic matter is an essential component of good soil health. Organic material consists of dead and decaying plant material, animals and animal products. It contains most of the nitrogen (N), phosphorus (P) and many other nutrients in the soil. It also provides food for soil organisms and helps to bind the soil together. Water holding capacity, airflow, nutrient availability, infiltration and soil organisms are influenced by the amount of organic matter. Management, such as excessive tillage, can decrease the amount of organic matter in the soil, which can have detrimental effects on the structure, and the nutrient status of the soil.

Soil life is a good indicator of the health of the soil. Soil provides a home for a great variety of organisms including bacteria, fungi, algae, nematodes, slugs, earthworms, termites, ants and millipedes. Management can effect the number and type of organisms living in the soil.

Soil Chemistry

Plant nutrients
Nutrients are essential for plant growth and are provided by chemicals that are held in the soil. Some soil textures such as clays and loams hold plant nutrients better than other soils such as sands, therefore the nutrient holding capacity is dependent upon the texture of the soil.

Table 4. Nutrients found in each of the groups.

Macronutrients (required in large quantities)
Nitrogen (N)
Phosphorus (P)
Potassium (K)
Calcium (Ca)
Magnesium (Mg)
Sulphur (S)

Micronutrients (required in small quantities)
Iron (Fe)
Manganese (Mn)
Copper (Cu)
Zinc (Zn)
Boron (B)
Molybdenum (Mo)
Cobalt (Co)

The quantity of nutrients required by plants varies and is divided into macronutrients (those required in the highest quantity) and micronutrients (those required in the least quantities).

Macronutrients are required in large quantities while micronutrients, essential for plant growth, are required in smaller quantities. Imbalances in any of the nutrients will result in reduced plant growth.

Removal of produce from a paddock takes with it nutrients that were once in the soil. To be sustainable, nutrients exported through produce need to be replaced. Exported plant nutrients can be replaced through fertiliser. Generally the nutrients most often required to be added by fertiliser include phosphorous (P), potassium (K), sulphur (S), molybdenum (Mo) and zinc (Zn).

Nitrogen is the soil nutrient required in the largest quantities by growing plants and can be supplied by growing legumes which are able to biologically transform nitrogen from the atmosphere into a form that is available to plants in the soil. Legumes include clovers, medic, wattles and the bean and pea plants. By combining legumes in pastures or in crop rotations, nitrogen can be added to the soil without the need for nitrogen fertiliser in most circumstances.

The majority of Australian soils are relatively infertile with nitrogen and phosphate deficiency being very common. Indigenous vegetation, having evolved with these soils, has adapted to these deficient soils, however, introduced pastures and crops will need the addition of fertilisers.

Soil pH

The pH of the soil will also have a strong influence on nutrient availability to plants. Soil pH is a measure of the acidity or alkalinity of the soil and is measured on a scale of 1 to 14. A pH of 7 is neutral, less than 7 acid and greater than 7 alkaline.

The pH expected to be found in soils ranges from 4 to 9. As soil pH changes, certain nutrients are less available to plants while other elements become toxic. For example, in soils with low pH (acid), nitrogen (N), phosphorous (P), potassium (K), calcium (Ca) and molybdenum (Mo) are likely to be less available while aluminium (Al) becomes more available to such an extent that it can be toxic to some plants.

The pH of the soil is an inherent property of soil but can be affected by management. Agricultural production has an acidifying effect on soils and therefore soil acidification is becoming a major problem particularly in the higher rainfall areas of southern and eastern Victoria. Lime will increase the pH of soil (make it more alkaline) and will be required on soils when the pH becomes too acid if productive agriculture is to continue. Generally speaking an application of approximately 3-3.6 tonnes/hectare will be needed to raise the pH measurement by 1 unit. Plants have different tolerances to soil pH and should be selected to suit the pH of your soil.

Soil depth

The depth of a soil is a major determining factor (along with soil texture and structure) as to the quantity of water and nutrients that can be stored for plant growth. Plant growth on shallow soils is limited by sufficient water storage and therefore shallow soils are often not viable for agriculture.

The best way to observe soil horizons and therefore the depth of soils is by excavating soil pits. Whilst a sufficient pit can be dug by hand, soils that are more difficult to work with may require the help of a backhoe etc.

Soil types

Parent rock material (geology) is a strong determinant of soil types, however, climate, topography, biological activity and time have all contributed to the types of soils found in Victoria. Victorian soil can be divided into 6 broad groups.

Deep Sands - these sandy soils are usually located along the coast and in the Mallee. They are relatively infertile. Mallee sands are alkaline whilst coastal sands are generally neutral to acid.

Alluvial Sediments - these are associated with the flood plains of streams and have a high degree of clay deposited during floods making them generally fertile. Many of the red clay soils north of the Divide fall into this category. They vary in pH depending partly upon their age and rainfall.

Sedimentary and metamorphic soils - clays, silts and sands depending upon the parent rock. These are often shallow and stony soils found along the Great Dividing Range. If derived from mudstone, soil will be silty clays or loams. They are often low to moderately, acid.

Wimmera plains soils - Deep well-structured cracking clay soils deposited when parts of Victoria were influenced by an inland sea. These soils are alkaline and show good fertility.

Basalt soils - Can be red or black in colour showing neutral pH. Black soils are often stony and display seasonal cracking, which can cause problems with buildings and drainage during wet periods. Red basalt soils have good structure and moderate to high fertility and are prime agricultural soils.

Granite soils - Range from deep coarse sands to sandy loams over medium clay soils. They are generally low fertility with steep areas being very prone to erosion. Waterlogging can be a major problem on granite soils. These soils generally are acid to strongly acid.

Victorian Resources Online (VRO) is your gateway to a wide range of natural resource maps and associated information. You can access this information at both Statewide and Regional levels across Victoria. The VRO also provides access to the Victorian Soil and Land Surveys database. This Directory comprises over 100 bibliographic records of Victorian soil and land surveys, dating from early this century to the present day. The Victorian Land and Soil Survey database can be accessed at http://www.dpi.vic.gov.au/vro. You are able to search the database by either keyword, shire or Catchment Management Authority area. This will result in a list of soil survey publications, including maps being generated. Publications can either be ordered from the DPI bookshop or viewed at DPI libraries.

Assessing Your Own Soils

Even though soil tests cost you money initially, they may save you money in the long run. A failed dam wall, which may cost thousands of dollars to repair, could have been avoided with appropriate soil testing. Equally unwarranted use of fertiliser is costly and may damage the environment. Soil scientists and engineers use different ways to test soils for different purposes. The type of activity you want to carry out on your property will determine the type of soil test you require.

Engineering Tests

Engineering tests are essential if you are planning any engineering works such as building a house or dam construction. Your local shire will tell what types of tests are required for particular works. Remember you may require a planning permit for many works around the property such as dam construction. Tests are done through geo-technical consultants listed in the Yellow Pages telephone directory under consultants. Dispersion testing, linear shrinkage, ribbon tests, liquid limits and test for fine and coarse sands are all available. Costs vary depending on the type of test required.

Soil tests for engineering purposes:
DAM - dispersion test, linear shrinkage, ribbon test
HOUSE - liquid limit
SEPTIC TANK - coarse sand


Agricultural Tests

Soil tests can be carried out for different agricultural activities. A soil test kit can include an assessment of soil type, structure, nutrition, electrical conductivity and pH as well as including interpretation of the results and a set of recommendations. This usually costs between $60-$110 depending on the number of tests included.

Soil augers for sampling for agricultural tests are available for loan from your local DPI office. Soil sampling kits with instructions are also available from DPI. If you are not near a DPI office check with your local fertiliser supplier to see if they have test kits and soil augers.

If you cannot locate a soil auger you will need to improvise when sampling. Using a shovel is possible provided that sampling is done very carefully. All samples need to be taken to the same depth, usually 0-10 cm and sample the same volume of soil from each depth. Sampling should cover at least 30 different sites across the whole paddock in a zigzag pattern. Instructions are available in test kits. Many firms offer a soil analysis service. Check your local Yellow Pages telephone directory or DPI Office for soil testing companies.

Do it yourself!

Laboratory testing will tell you a lot about your soil but may not give you all the answers for successful management. Topsoil depth, compaction, porosity, soil life, texture and crusting may vary across your property. So why not get a shovel and dig a few holes around your property and assess your own property.