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Manipulating the nitrogen cycle to maximise production
Answers
| Technique | Outline | Advantages | Disadvantages | Judgement |
|---|---|---|---|---|
| Green manuring | Growing a legume crop and ploughing it back into the ground. | The growing legume increases N through the symbiotic relationship with rhizobia bacteria fixing atmospheric N into a useable for plants. N rich OM increases when the crop is ploughed into the soil. |
Farmer forgoes the financial return of the crop not harvested but ploughed in instead. N is not immediately available from the OM incorporated as it must first undergo decomposition. |
This technique is highly beneficial as it has the double action of increasing N through legume growing and incorporation of N rich OM that releases N in a less leachable form than chemical fertilisers. Short term costs are more than offset by reduced expenditure on fertilisers and long term soil sustainability. |
| Crop rotation | Growing a different crop in the same paddock over successive years, e.g. wheat, chick peas, canola. | By incorporating a legume into the rotation, particularly if the legume crop is for green manuring, the advantages are as above. Each crop uses different quantities of different nutrients, therefore not exhausting the same soil nutrients year after year. |
If a legume crop is incorporated and green manured and not harvested, the disadvantages are as above. Different machinery may be required for sowing and harvesting of each crop. Farm manager must have knowledge and expertise with the production of a variety of crops. |
This technique is highly beneficial, particularly when a legume is incorporated into the rotation. It has the double action of increasing N through legume growing and incorporation of N rich OM that releases N in a less leachable form than chemical fertilisers. In addition there is a reduced drain on the same nutrient balance each year and a break in the pest and disease cycle as different crops are grown. This reduces the need for chemical usage with long term sustainable outcomes. |
| Adding N fertilizer | Addition of nitrogenous fertilisers, e.g. urea, nitram at the time of sowing or during the growth cycle. | N is added in the form that is able to be used by the plant immediately. A measured amount suitable to the crop needs and soil nutrient deficiency can be supplied. |
Synthetic N fertilisers are expensive to buy. Toxicity and pH problems can arise from long term use indiscriminate use of synthetic fertilisers. |
A viable option if used appropriately, after analysing soil nutrient status and soil pH and in line with crop demands. If a particular crop has high nutrient demands this method is useful in avoiding depletions. |
| Legume inoculation | When high numbers of the appropriate rhizobia bacteria are not present in the soil they must be added to the seed at sowing time in a process called inoculation. Inoculated seed may be pelleted by adding a protective layer of fine lime to improve the survival of the rhizobia, particularly when sowing into acidic soils or if inoculated seed is in direct contact with acidic fertilisers such as superphosphate. | Increases the chance of legume crop growing and producing to its potential. Lime pelleting helps to reduce increase acidity problems. |
Additional cost and time involved. | If there is any doubt about the presence of appropriate rhizobia bacteria in the area to be sown then the small increase in cost and labour input is well justified. The alternative risks the chance of legume crop failure or severely decreased production. |
| Liming/pH | Applications of lime help reduce the problem of soil acidification. Soil acidification can lead to reduced production as some plant species become intolerant to the rising acidity and soil nutrients may become unavailable for plant growth. | Helps reduce the increase in acidity so a broad range of plant species can be grown successfully and soil nutrients are available for plant growth. | Extra cost for lime and its application. | If soil acidification is a problem then it is advisable to apply agricultural lime. This will have both short and long term sustainability advantages. In the short term crop production will be improved and in the long term sustainability of the environment will be enhanced. |
| Planting deep-rooted plant species | Deep rooted plant species help to open up the soil, aerating and allowing water infiltration. This encourages populations and activities of microbes and invertebrates, resulting in a healthier soil that breaks down OM releasing ammonium and nitrates for plant growth. | Increased breakdown of OM and hence release of available N into the soil. Increased aeration and water infiltration for microbes/invertebrates and plants. Increased water infiltration reduces waterlogging and hence denitrification. |
High costs involved in planting trees and other deep rooted species plus costs involved in establishment, e.g. fencing, weed control. | An essential management practice for the long term sustainability of the environment. Not only is the soil a healthier environment but vertebrate biodiversity is increased with shelter belts created for both native and farm animals. |
Please note: You may have included some other techniques, e.g. pasture mixes, improved structure in your answers. The techniques included in this table are not exhaustive and are only provided to give you some good examples.
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