Background information - land management
- Current scientific conceptions
- Student's prior understandings
- School authority principles
Current scientific conceptions
Sustainable agriculture means striking a balance between meeting our present needs, maintaining productivity and conserving natural resources, protecting the environment for the benefit of future generations. Science has an important role to play in working towards this goal. Some of these roles are listed below.
- Science can help in the development of new agricultural techniques that are environmentally friendly.
- Science is involved in the development of higher-yield, pest-resistant agricultural products.
- Science can help find remedies for environmental degradation attributed to agricultural practice (e.g. soil erosion, decline in soil fertility, loss of soil structure, salinity, pollution).
- Science has, however, been involved in the development of agricultural practices that have had negative effects on humans and the environment.
In agricultural practice scientific theories and techniques must be applied with care to ensure the sustainable production of high-standard primary products.
Australia is known for its vast natural resources, which have made this country one of the world’s largest primary producers. As a result of human settlement (first by Aboriginal peoples and more recently by Europeans) and the consequent patterns of land use, Australia’s environment has changed markedly. Among other things, land use practices have led to the development of a number of problems including the following:
- soil degradation, including erosion and salinisation, as a result of agricultural practices
- eutrophication as a result of agricultural run-off depositing plant nutrients in water catchments
- effects on the environment by pesticides and herbicides
- a decrease in the biodiversity essential for the survival of our planet’s ecosystems.
Soil erosion is the removal of soil by water or by wind. Splash, sheet, rill and gully erosion are some of the different types. Of the 2 percent of land in Queensland that is cultivated, 80 percent of this land is affected by water erosion. Due to the medium to heavy texture of most soils cultivated in Queensland, wind erosion is not a major factor in soil losses. However, wind erosion does occur in lighter-textured soils on inland grazing areas, especially during droughts. Queensland’s high-intensity rainfall, when coupled with poor agricultural practices, is a contributing factor in soil erosion.
Erosion affects crop yields and grazing lands by reducing the ability of the soil to store water and nutrients and by exposing subsoil with poor physical properties. Erosion also results in silting of water catchments, which has effects on aquatic life.
Measures to control erosion include the use of conservation cropping practices to provide protective plant cover and measures to control run-off. These include use of contour banks on upland areas and strip cropping on floodplains.
The general health of the soil is important in preventing soil erosion problems, because soil cover is affected by soil condition. The following outlines some of the issues involved with the general health of soil.
- Over-fertilisation with both organic and inorganic fertilisers can lead to soil acidification (due to excess nitrogen in the soil).
- Soil structure is degraded through compaction of the soil by farm machinery such as tractors and ploughs. A solution to this is ‘tramlining’ or ‘controlled traffic’, where vehicles travel over the same paths so as to minimise the compacted area. The benefits and best methods of controlled traffic are still being investigated. (Search on these topics for more information)
- Soil fertility will naturally be reduced through even the most sustainable of farming practices, because removing crops takes nutrients from the soil. Soil fertility must be maintained through the selective application of fertilisers or through crop rotation, or by a combination of both.
High levels of soluble salts in a soil result in a reduction in the productive capacity of the affected land and water, degradation of wildlife habitats, loss of water quality for household supplies and damage to household equipment.
Salts are natural components of all landscapes. They result from the weathering of rocks and other sediments and are moved by water. Thus the flow of water in a landscape determines the movement and final distribution of salt. Salt accumulates in the soil when water is removed by evaporation and the salt is left.
Australia’s present salinity problems have resulted largely from human activities, which, in the brief period since European settlement, have modified the natural distribution of salt in the landscape. The reason for most salinity problems of soil and water has been a rise in the water tables, bringing salt to the surface.
European farming methods (and, to a lesser extent, Aboriginal use of fire) led to the clearing of native vegetation. Removal of deep-rooted native trees and grasses, and the development of irrigation projects, have allowed more water to soak into the soil and raised the level of groundwater. The effects of clearing in an area may not necessarily cause local salinisation but may cause salinity problems further down the catchment.
Salinity problems occur in Queensland and other States, particularly Victoria, South Australia and Western Australia. However salinity problems in Queensland are less common than in southern States due to the different climate we experience. Because Queensland receives the majority of its rainfall in summer (as opposed to winter in southern States,) excess water evaporates readily from the soil and the watertable does not rise significantly. In the southern States water does not evaporate as readily, due to the decreased solar intensity during the winter months.
Techniques to reduce dryland salinisation in affected areas may include tree planting (salt-resistant species), reduced summer fallowing and the replacement of shallow-rooted plants with deep-rooted species. In irrigation regions, control techniques include various methods of water management, groundwater pumping and proper layout of land to facilitate surface drainage and efficient water application.
A few things need to be considered concerning the use of fertiliser, pesticide and herbicide use in agriculture:
Many soils are naturally infertile and require additional nutrients to make them productive. Once crops are harvested the nutrients they have removed from the soil are removed from the farming system, and these nutrients need to be replaced, even in fertile soils.
- Chemicals used wisely can contribute to the health of the soil. For example, a reduction in the use of tillage (as a means of controlling weeds) by the strategic use of suitable herbicides greatly minimises soil erosion and associated pollution of downstream areas and minimises the use of tractors, which have an adverse effect on soil structure.
- It is important that fertiliser use is managed to minimise off-site effects. Examples of management include: matching fertiliser inputs to crop demand; controlling erosion to ensure fertilisers are not removed with soil; and careful use of irrigation, especially where permeable soils may allow leaching of nutrients into groundwater. (However, most cultivated soils in Queensland have a heavy-textured soil and leaching rates are very slow. Phosphorus is firmly attached to soil and is not leached. Some leaching of nitrogen can occur under irrigation in permeable soils in coastal areas.)
Even with these points in mind, however, use of fertilisers to combat increasingly low soil nutrient levels may result in plant nutrients leaching and/or running off into water catchments. This excess nutrient level may cause varying degrees of eutrophication (other causes of excess nutrient levels in waterways include: sewage; phosphates from detergents; waste from abattoirs or feedlots; manure and dead animals and plants).
Eutrophication occurs when algal blooms (caused by increased nutrient levels) reduce water movement and light penetration, and slow the rate of replenishment of dissolved oxygen in the water. Dead plant material starts to accumulate and bacterial activity increases. The bacteria deplete the dissolved oxygen level through respiration. Some aquatic fauna cannot tolerate even small reductions in dissolved oxygen content, therefore a change in fauna species composition may occur. In severe cases oxygen is totally depleted. Conditions are then termed anaerobic and most living things in the water at that point will die.
Use of some pesticides and herbicides may cause pollution of the environment, causing a decline in the natural flora and fauna. In some cases this may also result in the contamination of agricultural products (e.g. beef contamination by Endosulphan, a pesticide used in the cotton industry to kill Heliothis grubs).
A few things must be considered before spraying crops with pesticides and/or herbicides:
- Integrated pest management strategies are important, and farmers must carefully evaluate their options before they elect to spray. Questions to be asked are:
a) What is the balance between pests and predators in the management area?
b) Is it possible to do nothing? That is, will the problem solve itself or cause an acceptable level of damage?
c) What alternative measures are at the farmer’s disposal?
d) How can the chemical be applied so that any adverse impact will be minimised?
- Spraying with a single type of herbicide/pesticide may lead to herbicide/pesticide resistance.
- Manufacturers’ instructions should be carefully followed when using pesticides or herbicides.
There is a strong interdependent link between degraded habitats and loss of flora and fauna. Degradation of habitats as a result of agricultural practices leads to a decrease in biological diversity. Failure to maintain biodiversity upsets the ecological balance and may lead to other problems such as weed and pest infestation. Farming practices may impact on biodiversity in a variety of ways, including:
- clearing land of native flora and fauna, which may also lead to weed invasion
- removal of natural competitors/ predators from an ecosystem by spraying crops with pesticides, which may lead to plagues of pest and weed species
- addition of plant fertilisers leading, through subsequent run-off, to eutrophication.
To conserve biodiversity, both species and habitat diversity need to be maintained. Farm planning and good management practices are important for maintaining species diversity.
Poor resource management reduces the productive capacity of agricultural and pastoral land, pollutes water catchments and marine ecosystems, and decreases the biodiversity of our native species. Science has made significant contributions to understanding of the effects of different types of land use and provision of alternatives for a more sustainable future.
Student's prior understandings
Students’ prior understandings may differ from current scientific conceptions in a range of ways:
Students may think that:
- sustainable agriculture refers only to long-term economic factors, in contrast to the definition given in this module. In working towards sustainable agriculture, environmental, social and economic factors all influence decision-making.
The teacher can question the students on the necessary criteria for a farm to make a profit. The next step is to relate the health of the land to profit, thus showing that profit and land management are interrelated. Teachers can help build and expand students’ concept of sustainability by comparing two farms, one using sustainable land management practices and the other not. The comparison can be made in the short term and the long term, with the teacher asking students which farmer will still be making a profit in 5, 10, 15 or 20 years.
- not value agriculture, because they may not consider the source of food beyond the supermarket.
Teachers can remind students of the importance of agriculture and the people who produce agricultural products (i.e. farmers and graziers). Students can discuss food and other products they rely on, and trace them back to the source that produced them. This will show how much we rely upon the agricultural practices that we often take for granted.
Students may think that:
- farmers are destroying the land through their land-use practices.
- cropping and grazing do not affect the environment, as they are processes that occur in nature.
Teachers can help students build and expand their knowledge of cropping and grazing by asking them how farming differs from natural growth of plants and grazing of animals. Teachers can highlight how these differences, although slight, may have dramatic effects on the land (e.g. cropping replaces a number of different flora species with one species and so reduces biodiversity). Teachers can enhance students’ understanding of the potential of poor farming practices to contribute to pollution, by discussing the effects of run-off carrying soil or fertilisers into waterways. It is important to remember that it is possible to farm with minimal impact on the environment, and that many farmers and graziers are already doing this. Teachers can also discuss with students some of the economic and social issues that influence farm management decisions.
Terms associated with sustainable agricultural practices are essential to the activities in this module. Some examples are:
- soil degradation
- soil salinisation
- biological diversity
- conservation cropping
- contour banking
- strip cropping
- compliment cropping
- El Niño
- La Niña
- Southern Oscillation Index (SOI)
- splash erosion
- sheet erosion
- rill erosion
- gully erosion
- controlled traffic
School authority principles
Teachers need to be aware of school policies that may be relevant to this module. Safety policies are of particular relevance to the activities that follow. It is essential that demonstrations and student activities are conducted according to procedures developed through appropriate risk assessments at the school.
In this module teachers need to consider safety issues relating to:
- handling scientific equipment
- field work
- working with chemicals.
Last updated 6 August 2010