Soil Fertility Decline
Introduction
Soil fertility is a major issue in Australia due to the quality of Australia's soil which is already naturally nutrient and moisture deficient. The increase of farming and other activities drawing nutrients from the soil have further degraded the land quality in Australia. This is also what make the fauna and flora in Australia so unique as they have to adapt to the low phosphorus and nitrogen levels while also managing the scare amount of natural rainfall levels throughout most of Australia.
Soil fertility decline is a major issue for the farms across Australia and the world as soil fertility decline limits crops and pasture production. There is also few preventive measures that would not decrease output of production. This has led to many farmers ignoring soil fertility decline until it is too late. |
Causes
Soil fertility decline occurs when the nutrients removed from the soil in the harvest exceeds the sustainable quantities of nutrients being applied and replaced. In Australia, the main reason for soil fertility decline is continuous cropping with removal of stubble and this has been accelerated by frequent tilling. Tilling is working the soil by turning over the soil. Additional loss of nutrients in soil also occurs from leaching (water erosion) and during limited seasonal rainfall, when the crops have to draw nutrients from the topsoil and subsoil to meet their needs. However not all plants can draw nutrients from the deep subsoil, thus some plants cannot survive. Australia's unique and nutrient deficient soil qualities have lead to many unique flora and fauna however the poor soil quality is tough on the farming sector in Australia.
When there is a lack of nutrients, most often there is a lack of nitrogen and phosphate. Nitrogen is important as it allows the plant to photosynthesize and grow. This can be observed by the yellowing leaves and this represents that the plant is trying to relocate nitrogen from old to newer leaves. Phosphate is vital for healthy growth and lack of phosphate would result in stunted growth. Both of these minerals are very important in the growth of many plants and crops. The diagram on the right shows what the leaves on the plants would look like under certain deficiencies. There are several early signs of soil fertility decline in a particular area. Some early signs include: discolouring of the plant (either leaves or the whole plant itself), more weeds and more crops or plants dying before reaching maturity. |
These two images above show the process of tilling the soil. This method is vital to maintain plant growth as it allows the fresher and more nutrient filled soil underneath to be exposed and allowed for use by the crops while making the surface rougher, thus reduced water and wind erosion. Tillage is also vital to reduce unwanted weeds that will growth if the soil is not tilled. However if it is practiced too often, vital nutrients that have been exposed will be flushed away by light winds or rains. The habitats of earthworms and fungal growth that is vital for replenishment of nutrients will also be harmed. The image shows tillage with a shovel manually while the right image shows tilling using farm equipment.
Sources:http://www.colostate.edu/Dept/CoopExt/4DMG/Soil/tilling.htm (left), http://publicgarden.ucdavis.edu/category/pilot-projects/shields-grove-conversion/page/2 (right)
Sources:http://www.colostate.edu/Dept/CoopExt/4DMG/Soil/tilling.htm (left), http://publicgarden.ucdavis.edu/category/pilot-projects/shields-grove-conversion/page/2 (right)
Effects
The reduction of nutrients in the soil have several devastating effects on the ecosystem and economy. The most common effects of soil nutrient decline are:
- Poorer Yield is a result of lack of nutrients in the soil. The reduced amounts of nutrients in the soil prevents the crops or plants from reaching full yield and maturity within the shortest amount of time. This is the primary problem of soil fertility decline currently and will be in the future. With the reduction of nutrients and plant growth within an area, less food is produced in the area. With the population on Earth expected to rise to 11 billion, the reduction of efficiency will be a big problem that has to be faced. Furthermore, soil fertility decline reduces the amount of money that can be earned on a particular field in a certain period of time.
- Nitrification of water is a concerning problem caused by the loss of nitrate ions in soil and is a form of groundwater pollution. It is caused as nitrate does not bind tightly to soil particles thus when agricultural runoff is not properly directed, nitrate ends up in groundwater. This ground water then makes it way to streams and rivers. Animals such as amphibians and freshwater fish are very sensitive to levels of nitrate in the water. When levels of nitrate exceed natural levels, these animals tend to die. Furthermore, increase of nitrate levels in water leads to growth of algal blooms which decrease oxygen levels. Reduction of oxygen levels is lethal to most water-based animals. It is speculated that nitrification is contributed to acid rain and smog.
- Leads to Soil Acidification: When nutrients such as calcium, magnesium, potassium and sodium are leeched from the soil, these base cations are lost, increasing the ratio of hydrogen ions to the other elements. This decreases the pH of the sol thus the soil becoming more acidic. Thus severe lack of nutrients in soil leads to soil acidification.
Effective Solutions
The usual treatment is the application of fertilizer to the nutrient deficient area as it is the most effective and cost-effective in the short-term however other methods that are being used to manage soil fertility decline are:
- Planting leguminous crops with or without normal crops: This step is the most commonly used throughout the world, including Australia. It is commonly planted alongside nutrient hungry crops such corn to alleviate the nutrient stress on the soil. Leguminous crops such as peas, beans, lentils and lupins all have something in common. While they are one of the most consumed foods in the world, leguminous crops also increase nitrogen levels in soil. They do this with the aid of nodules that form with the roots of the crops as the diagram on the lower left shows. These nodules are filled with a bacteria called rhizobium which feed on the starch and glucose that the plant provides. The byproduct of the bacteria inside the nodules is nitrogen which is feed to the plant. However every 4 weeks, the nodules burst open, releasing nitrogen through the nearby soil. This natural process is a win-win situation for most farmers as these leguminous crops provide nutrients for the soil while being able to be harvested later on for more profit.
Close supervision is required to allow a reduced tillage system to work as without careful management, crops will be unable to mature due to lack of nutrients as a result of reduced tilling. As a result, there are not many farmers that employ this method as close management is difficult in larger fields. However as the image on the right shows, if careful planning and management succeeds, there are big rewards. |
This photograph shows the difference between retaining stubble and not. The field in the background which has utilized these methods has significantly less erosion, thus less loss of soil nutrients than the field in the foreground. The dark lines shows the extent of the erosion on the field that has tilled too often.
Source: http://www.environment.nsw.gov
.au/resources/soils/reducedtillage.pdf
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