Adapting Agriculture to Climate Change
Adapting Agriculture to Climate Change
Agriculture, Science, Industry and Entrepreneurship. Nova Science Publishers, Inc., New York, 2009
Global warming and climate change is full of academic and political controversy, where fact and conjecture is fiercely debated [11]. Although evidence exists and is sometimes dramatically portrayed as signs of an impending global disaster, there are still scientists who are disputing that the current temperature trends are within the bounds of natural change based on historical data [12]. Conservative US politicians also dispute the issue where the US Government with Australia (until the election of a Labor Government in November 2007) failed to sign the Kyoto Protocol, claiming the economic costs of achieving 1990 CO2 emissions are too high.
At the end of 2006, a film featuring the former Vice President of the United States Mr. Al Gore, An Inconvenient Truth dramatically and graphically showed a string of natural occurrences which were attributed to climate change, caused primary by carbon dioxide emissions [13]. Mr. Gore in his documentary showed that 10 of the hottest years in history had occurred during the last 14 years, the occurrence of much stronger hurricanes/cyclones and typhoons than ever before, more flooding and droughts across the globe, the permafrost in Siberia and Alaska melting, as well as the melting of the polar ice caps. Mr. Gore also showed evidence that the white house had arbitrarily changed some of the conclusions of the EPA climate reports [14]. An Inconvenient Truth was released at a time which spurred on the arguments for action, but was also not without its criticism and found to be flawed in some of its factualism [15]. Ironically just 24 hours after the British court ruling that there were nine factual inaccuracies in An Inconvenient Truth, Mr. Gore was jointly awarded the Nobel Prize for peace jointly with the United Nations Intergovernmental Panel on Climate Control (IPCC).
It is not disputed that methane and carbon dioxide concentrations are continuing to rise in the atmosphere and the Earth is currently undergoing a period of high temperatures. There are many stories in the media about farming regions struggling with their traditional industries like the vineyards in Australia, South Africa and California, while at the same time, new regions are quickly developing new agricultural industries, like the wine industry in Nova Scotia, due to the decline in frosts [16]. Wide evidence exists of loss of soil moisture due to dehydration, rising land salinity levels in many dry land regions, increasing carbolic acid in the rain changing pH levels in the soil, increased growth of algae, and the increasing incidence and threat of bush or wildfires around the world.
An Australian CSIRO report put the above concerns to the Australian Government stating that “…Australia is one of many global regions experiencing significant climate changes as a result of global emissions of greenhouse gases (GHGs) from human activities” [17]. The report confirms that average temperatures have globally risen over the last 100 years and there are marked declines in precipitation in some regional areas, while increases in others. The report concludes that even though initially there are some benefits of longer day period and shorter winters, with increasing crop yields; rising temperatures, droughts and adverse weather conditions will negate these benefits and become a factor threatening the vitality of agriculture in the future. A more recent report released by the IPCC based on actual measurements rather than projections, establishes that greenhouse gases in the atmosphere are increasing much faster than previously estimated and are already over the threshold that could be potentially dangerous to climate change [18].
At the time of writing there are signs that political figures are slowly bringing the issue up more seriously, as is the case of China [19] and the US. However with the global financial crisis taking most attention of World Governments, it is doubtful that any serious international agreements can be made over the next couple of years.
Some of the challenges that climate change may bring to agriculture and should be considered are;
Habitat Change: The habitat is already undergoing some changes [20], which is improving environmental conditions for some species, while at the same time denigrating the environment for others. Some pests will become more evasive to crops, while others will disappear. There will be increased geographical scope for planting some crops, but a narrower the scope for others. The viability of some existing growing areas will be threatened [21]. For example, a 1.0 C. degree rise in average temperatures will chance core conditions for 25% of eucalypts in Australia. The consequences of this, is not currently known as to whether they will adapt new conditions or become threatened with area extinction [22].
Loss of Arable Agricultural Land: Decreasing precipitation, increasing salinity and long droughts in areas adjacent to drylands is leading to a loss of arable farming lands in many continents [23].
Increase in Adverse Weather Conditions: Weather conditions can be expected to be more abnormal in the future bringing floods and droughts to different geographical regions. The decrease of snow in alpine areas will create water management concerns in respect to drought and flood management, and
Increase of External “Natural” Threats: Bush or wild fires will increase bringing threats to farms and crops and require consideration in farm layout planning and management.
At the field level crop stress will become a prime agronomic issue. Atmospheric warming will expose crops to higher temperatures, which will lead to changes in plant physiology at the cellular level. Once optimal temperature ranges pass for specific plants, heat stress will develop, causing various plant metabolism changes that will slow down cell growth dramatically [24]. The effects of climate change on crops will be profound, not at least upon the basic plant processes within the plant metabolism [25]. Plants have metabolite and growth responses to salinity, heat stress, evaluated CO2 and drought (Table 9.2.), which would most likely lead to changes in whole plant carbon and nutrient budgeting, leading to changing growth patterns.
Table 9.2. Summary of Plant Responses to Environmental Change
Project Preparation and Early Work
Project preparation and early work involves the determination of the major factors that influence yield and oil quality. The analysis of the factors that lead to optimum plant productivity is important in the field development stage. It is important to know how each factor interacts. The key to optimum productivity may rest on a single influencing factor. Thus efforts to uplift yield and quality may have little effect until this single factor is addressed. In other cases, two of more factors may be either co-limiting or co-synergists. The first step in this investigation involves matching the climate, weather, moisture needs of the proposed crop to the locality available.
There is a need to understand the basic paths through which aromatic materials develop within the plant metabolism. This will assist in the development of nutrient and moisture regimes and the timing of harvest. Paramount to good yields and quality is the quality of the genetic planting material. The selection of the correct material for cultivation is important.
Climate and Moisture
Temperature and moisture are two of the most important factors regulating plant growth. Plant adaptability to temperature is the parameter that has most influence upon its growth rate in a new location. Moisture is a factor that greatly influences the vigour and vitality of the plant.
Plants originating from various indigenous environments exist with particular sets of growth and behaviour characteristics. The basic plant climatic zones can be describes as;
Tropical Zone where all mean air temperatures are above 18-20°C, where no frosts exist. This area covers the Earth between the Tropic of Capricorn and Tropic of Cancer (23.5°S & 23.5°N).
Tropical Monsoonal Zone where part of the tropical zone which has a distinct dry season of 3-5 months, where the dry seasons usually increase mean temperature two or three degrees above the wet seasons. Dry seasons are usually cloudless or spasmodically clouded days and these zones are coastal along the equatorial region.
Sub-tropical Zone where the coldest month of the year would have a mean temperature above 16°C, where only occasional frosts would occur. This zone occurs between 23.5-30°+ latitudes.
Arid-Dryland Zones where mean temperatures are above 18°C and there is very little precipitation. Arid-dryland zones are sometimes accompanied with soil salinity, which together with high temperatures and salinity make the land marginal for agriculture.
Temperate Zones where temperatures are high enough for around 6-7 months each year for active plant growth. These zones occur above the mid 30°s latitudes and in the mountainous areas of sub-tropical and tropical zones.
Boreal Zones where mean temperatures are around 10°C and may warm up enough only for plants to grow two to three months a year. Boreal zones also exist in high altitude areas of the other zones.
Examples of some types of crops that grow in these zones are indicated in Table 9.3.
Table 9.3. Examples of Crops Grown in Different Climate Zones
Plants introduced into new areas will exhibit different phyto-synthetic responses (the process of bonding CO2 with H2O to make basic sugars and oxygen). This is directly related to biomass yields in the field [26]. Plants that have difficulty adapting will become stressed, so temperature is a major factor in adaptability. Plant adaptation to higher temperatures is related to photosynthesis efficiency. Four basic photosynthesis systems exist in plants [27];
The C3 plants incorporate CO2 into 3-carbon compounds. The stomata (pores in the leaves through which CO2 is consumed and O2 expelled during photosynthesis) is open during daylight hours, the enzyme rubisco directly uptakes CO2. This is the most efficient photosynthesis mechanism within the plant kingdom and works well during cool and moist conditions under normal light as less energy is required. Most plants are C3.
The C4 plants incorporate CO2 into a 4-carbon compound. The stomata are open only during daylight hours. The vehicle for CO2 uptake is PEP carboxylase which transfers it directly to rubisco for processing, which is fast and moisture efficient. There are numerous species with this type of respiratory system, mainly plants with habitats in warmer conditions, including most tropical grasses.
Plants where photosynthesis alternates between the C3/C4 mechanisms, and
Crassulacean Acid Metabolism (CAM) photosynthesis where CO2 is stored as acid before photosynthesis. In this mechanism the stomata opens during darkness where evaporation rates are usually lower. During daylight hours rubisco breaks down the CO2 for photosynthesis. This mechanism is more moisture efficient than C3 plants due to night collection of CO2. When droughts occur the stomata remains closed and the acids are utilised as needed for photosynthesis. Cacti are CAM plants.
The phytosynthesis systems of plants will strongly influence plant adaptation to new environments. Among the C3 species, the herbaceous annuls, evergreens and non-leguminous plants will adapt better than the perennial woody species, deciduous trees and leguminous plants that fix nitrogen [28]. C4 species should adapt to higher temperature conditions better than the other metabolisms. A plant genotype may have a number of phenotype variances which exhibit different tolerances to different climatic conditions [28]. Plants are capable of adapting to different habitats, however the introduction of new crops from cooler regions where the photosynthesis system may be very sensitive to heat, may require breeding to improve tolerance in hot weather [29].
Potential upper temperature limits will depend on the level of plant stress to the temperature range in the new environment. Stress is the key issue to monitor. At the lower temperature levels, below 10°C plant growth becomes severely retarded. Effective growth ceases around 7°C for most plants [30]. Thus the most suitable upper and lower temperature levels for plants needs to be ascertained before introduction. The mean temperatures, sunlight and day length will define the maximum limits of potential productivity, while the low temperatures and moisture levels through precipitations will define the restrictions on plant growth. Table 9.4. shows some temperature and other habitat parameters for a selection of aromatic plants [31].
A basic evaluation of moisture requires the review of effective rainfall. Effective rainfall is the amount of rain necessary to commence and sustain plant growth. However some rainfall is lost in evaporation (evapotranspiration) and run-off. Thus a quick measure of determining the rainfall needed to start and sustain plant growth is to add 50% to necessary moisture required by a particular plant and compare this figure to the mean rainfall figures of the area in question.
Table 9.4. Temperature, Rainfall and General Habitat Parameters for Some Aromatic Plants.
Historical data for a long period is best to determine the mean and droughts must be taken into account for drainage and irrigation planning during the land preparation stage.
However the above analysis can be misleading as it lacks sensitivity, not taking into account the intensity and distribution of rainfall during the year. In arid and monsoonal regions growth after rain can be vigorous, so additional analysis should be undertaken to determine the annual growing season. Issues such as the number of dry days in succession are important for wilting and growth inhibition. Soil moisture absorption ability, infiltration rate, and the topographic features such as slope, ground cover, etc., also influences how much rainfall actually benefits the crop. These factors also bring up issues of potential for root rot, pathogen development, competitive weed growth and their influences upon growth rates.
A process to make an assessment about the suitability of a particular area for a specified crop would involve the following steps:
Obtain weather station and climatic data for the area. Obtain daylight and dark hours for the year. Obtain the number of rain/dry days averages for each year.
Analyse the data to obtain mean and extreme temperatures on a daylight and nightly basis for each year. Calculate the effective rainfall and the effective growing periods.
Compare this data to the plant habitat data available to see if there is a match.
If there is a mismatch, make predictions about the potential adaptability of the plant to the new environment (this may require some garden trials to assist and confirm deductions)
Look around for similar plant species growing in the area and observe their growth behaviour and growth periods.
Make predictions about possible planting, growth and harvest times based on the above information.
Some other issues to consider are;
The effect of dry seasons on flora and ground cover as it may have a tendency to put most plants into a dormant state, where annuls without cover crops may become stressed,
Storm activity may cause high winds and lightening strikes, which can initiate wildfires, and
Excess rainfall can cause heavy erosion and loss of top soils with channel run-offs, leading to loss of organic matter in the soil.
References:
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