AGR2303 Exam Flashcards
Module 1 Question 1 (10 Marks)
Describe the geographic distribution of canola, maize and mungbean crops in Australia and what influences this distribution.
The main factors of distribution are soils, climate, topography, pest prevalence, disease prevalence and economic status of the region. Mungbeans are best suited to subtropical and drier tropical regions of about 300-400mm of rainfall within a growing season. Much of their distribution and production areas is within regions used to grow cowpeas, including the coastal central region of Queensland and down to the irrigated regions of northern and central NSW. Favouring the warm/hot environments of these regions, they compete with cotton, sorghum and rice. They may be grown as a rotation crop with winter cereals such as wheat. They grow best on sandy loam soils with good drainage and a pH of between approximately 6 and 7.2
Canola has a wider distribution than mungbeans, growing from higher rainfall wheat regions of south east Queensland, all the way down through high-rainfall regions in the Tablelands, and through central and southern NSW, into the north of Victoria, as well as throughout south-western WA. This region of distribution is largely defined by higher-rainfall, but irrigation along western rivers of NSW is becoming more common and expanding its distribution. Canola also grows best on fertile soils with pH levels between 5.0 and 8.0
A minor summer crop, maizes distribution is primarily restricted to Queensland and northern NSW, as well as the Riverina region. As maize is quite adaptive to a large range of climatic conditions, inland irrigation systems now provide the most production. Rainfed maize is still widely grown however, in the higher rainfall regions listed above. Soils with neutral pH, and good water holding capacity and organic matter content produce the best yields and also affect distribution significantly.
Module 1 Question 2 (5 Marks)
What are the adaptations that pasture must have that field crops and horticultural crops don’t?
Pasture crops must be adapted to high levels of inter-species competition, as a result of being grown in mixed species. This is different to field and horticultural crops that are primarily grown in single species. Adaptation to livestock grazing of the above ground or upper component of the plant involves protecting growing points of the plant. They must grow quickly also, for both of the aforementioned reasons, in order to be successful.
Module 2 Question 3 (5 Marks)
Define conservation farming. How does conservation farming lead to improvements in crop production?
Conservation farming primarily aims to minimise the negative impacts of tillage upon agricultural landscapes. This is achieved through practices such as minimum or no-till practices and stubble retention. These practices may help minimise losses of soil biological and organic matter, and maximise soil nutrient and water retention, thus improving crop production through significantly improving soil health.
Module 2 Question 4 (5 marks)
How does crop architecture and sowing depth impact crop production
Crop architecture is the population of plants and the row spacing, whilst sowing depth is the depth into the soil that the seed is planted. Both of these vary for different crop types. Effective crop architecture maximises the capture of resources. Ensuring competition for the growth factors of nutrients and water are not limited by over-population of a crop ensures that crops have the best chance to produce maximum yield.
Sowing depth balance is crucial in both protecting the seed, whilst allowing it to be shallow enough for rapid and easy emergence. If a seed is too shallow, dessication may occur which significantly impacts emergence and growth. A seed planted too deep may receive adequate moisture and nutrients, but uses much of its stored energy just on emergence, making its photosynthetic abilities upon emergence greatly reduced.
Module 3 Question 5 (5 marks)
Outline Liebig’s law of the minimum and describe how it impacts on fertiliser practices.
Liebigs Law of the Minimum is essentially where crop growth is limited by the least available resource, commonly water or nitrogen (N). An example might be a plant that has adequate water and nutrient availability, with the exception of N. The plant will therefore only grow to the level determined by N availability, regardless of the supply of other resources. In this instance, there is no purpose or benefit obtained by adding Potassium or Phosphorus fertilisers, as the plant has adequate amounts of those already, but is lacking in N. Therefore, an N fertiliser would be the necessary fertilisation application. A lack of understanding of this important concept may result in costly and ineffective inputs for farmers.
Module 3 Question 6 (5 marks)
How does nutrient budgeting help farmers to increase productivity while reducing environmental impacts?
Nutrient budgeting is used to identify whether an application system produces nutrient deficits, surplus or balance. It examines the number of nutrients inputted and outputted from a system. By correctly identifying what a system needs (in terms of nutrients), crops can be provided with an optimal and balanced nutrient application to maximise yield. A key component of nutrient budgeting is limiting nutrient losses to the environment. An example of this is the loss of N, which may result in acidification or eutrophication as well as the release of NO2 and NO.
Module 4 Question 7 (5 marks)
List two preparatory steps that may be taken prior to the harvesting of crops. What is the purpose of each of these steps?
i) Weed control - This should be undertaken late in the crop growth cycle, as weeds have the potential to interfere with the harvesting process. Another crucial element of weed control is to limit the weed seed that may lead to a product being downgraded.
ii) Irrigation - The timing of the final irrigation before harvest is important. If it is performed just prior to harvest, running heavy harvesting equipment over the wet soils may heavily compact the soil, or even potentially bog the equipment. It should be planned well and timed so that there is sufficient plant-available water to complete its life cycle, but be appropriately dried by the time of harvest.
Module 4 Question 8 (5 Marks)
How does crop maturity impact on the harvest timing of forage crops?
[Page 21 of module;
https://www.publish.csiro.au/an/pdf/EA08244;
Page 219 of textbook pdf]
Each crop is harvested at different stages of maturity. The maturity of forage crops and the subsequent timing of their harvest has significant impacts on the nutritive characteristics of the crops. Forage crops generally produce the best yields when the crop is in the reproductive growth stage. Going beyond this stage has been shown to reduce crude protein
Module 4 Question 8 (5 Marks)
Outline the concept of harvest maturity for field crops and how it is different to crop physiological maturity?
Harvest maturity is the stage whereby the best possible quality and yield balance is met by harvesting. Too early may result in unripe or small grains, thus limiting yield, whilst too late may lead to a downgrade in quality. Harvest maturity is literally the stage a crop is harvested at.
Physiological maturity however, is when the dry weight of a seed is maximised. Field crops will generally reach harvest maturity after physiological maturity. Doing so before this point will often lower the quality and yield of the seed and grain.
Module 5 Question 10 (5 Marks)
Describe two non chemical weed control methods?
Weed prevention is the best first measure. This involves preventing weeds from establishing themselves on the property. This can be achieved through preventing their introduction through seed contamination, quarantining livestock moved onto the property, and thorough / optimal cleaning of equipment, particularly during harvest. Two control methods include:
i) Cultivation - The primarily effective component of this mechanism is the disturbance of weed seedlings through their uprooting and subsequent death. Weed ecology is important to understand when undertaking cultivation as a primary weed control measure. Weeds have variable dormancy periods and adaptive mechanisms to cultivation that may mean that this control measure actually enhances or promotes weed growth and germination.
ii) Using a break crop / diverse crop rotation - The use of a break crop such as canola has been shown to be an effective weed control method. Rotating crops with varied characteristics prevents weeds from becoming accustomed to and adapting to the system.
These measures should be used in accordance with the weed ecology on the landscape, and usually as part of a multifaceted approach to control.
Module 6 Question 11 (10 marks)
Describe what a ley farming system is and outline the benefits of this farming system
Ley farming is a soil conservation measure that involves phases of pasture within the cropping sequence, primarily to increase soil N. Used as an alternative to crop fallow, rotation legume species such as lucerne are used in N fixation and thus increase N levels in the soil for the grain or tilled crop. It is also particularly effective at improving soil fertility, increasing soil organic matter, and reversing declining soil structure and soil health. Weed management, primarily through livestock grazing and competition may assist in reducing weed seed set. The improved ground cover of pastures assist in the prevention of runoff and soil erosion. This is especially the case in perennial pastures that often have deep root systems, accessing moisture and nutrients from below the water zone and subsequently resulting in a drier profile. This limits the loss of water and nutrients to drainage. By possibly providing a direct and high quality food source for livestock, farmers are also able to increase the carrying capacity and productivity (weight gain) of livestock, through the consumption of feed such as legumes that increase animal growth.
These listed benefits of growing legumes (or other pastures) with tilled crops or grain will result in either improved soil conservation and health and thus indirect yield increases, or directly improve livestock productivity.
Module 6 Question 12 (5 marks)
Define two different methods of calculating water use efficiency and identify when each of these methods would be used
i) Crop Water Use Efficiency (WUE): This is the seemingly simple concept of dividing the crop yield by the water used. A more accurate system of calculating is: water used = (soil water content at sowing - soil water content at harvest) + rain + irrigation – run-off – sub-root-zone drainage. This is a commonly used calculation and is often useful in comparing management practices and different crops.
ii) Farm production WUE: The gross production for a farm divided by the gross water inputs (both irrigated and rainfall). This can be useful in comparing entire farm systems. On broader, regional scales, it can also be used to assist in the implementation or introduction of policy.
Module 6 Question 13 (5 marks)
What are two benefits to crop production from fallowing?
i) The increased storage of soil organic matter, increased mineral N and moisture retention are the most common reasons that fallowing is used. This benefits the coming crop (often, but not always, wheat) and generally improves the yield. Just one season of fallow may be sufficient to reduce the leaching of soil nutrients required for optimum plant growth.
ii) Fallowing is also a very useful mechanism in breaking crop disease and pest cycles. Many pathogens and weeds require a host to suvive and / or reproduce, and as such, an effective fallow will deprive them of this and break the cycle prior to the coming crops sowing period.
Module 6 Question 14 (10 marks)
Why are crop rotations important for ensuring the continued productivity of crop production systems?
Repeated cropping of cereals can lead to a progressive building up of weeds and diseases. A viable alternative to ley farming is through crop rotations. Crops such as chickpeas as a break crop help raise soil N, whilst Canola acts as an effective disease break. Break crops can achieve benefits similar to ley farming, but with the added bonus of increased returns and a diversification of income sources and market reaching. Where water limitations are negated by irrigation, the storage of soil water for the next crop is of less importance than in dryland systems where soil moisture retention is of the utmost importance. In irrigated systems particularly, continued productivity may be more limited by mineral (particularly N or SOC) deficiencies. Complex rotation systems of crops also ensures that pathogens and pests don’t have a ready access to a host. These systems are biologically resilient and provide a number of potential non-chemical options to manage weeds, insect pests and disease. By increasing the soil health and mineralisation, diversifying income streams, and breaking cycles of pests, pathogens and weeds, crop rotations enhance the productivity of cropping systems, as well as increasing their sustainability.
Module 7 Question 15 (5 marks)
Outline two potential mechanisms by which crop production impacts on the broader environment.
i) Freshwater eutrophication - Nutrients, provided to the crops as fertiliser, may run off into waterways (especially after heavy rainfall events or when excessively applied), causing an enrichment of nutrients, leading to events such as algal blooms and a decline in marine / fish species. This is particularly common in sandy soils that have rapid drainage, and as such should be a consideration of farmers when applying synthetic fertilisers to their crops.
ii) Greenhouse gas emissions - Nitrous Oxide (N2O) is a greenhouse gas almost 300x as potent as Carbon Dioxide (CO2). This gas is released from crops and pastures of which nitrogen fertilisers have been readily applied. This occurs as a result of biochemical processes that use inorganic N compounds such as nitrate and ammonium. Agriculture is responsible for approximately 80% of Australia’s N2O emissions.
