The Principles of agriculture, Selection of Species and Abiotic Control

What is the definition of sustainability?

Balancing the needs of human society and the environment so that both current and future needs of people and planet are met.

Why is it important to ensure that agriculture is sustainable?

Farmland covers a large proportion of the Earth’s land area, around 10% being cultivated and a further 25% used as permanent pasture. Because of a growing population, it is important to ensure future agriculture is sustainable, particularly as it affects large areas of natural habitats and affects many important natural processes.

Define agriculture

Agriculture involves the control of terrestrial ecosystems to divert energy and nutrients into the human food chain

What are the key principles of agriculture?

• Selection of suitable species

• Control of abiotic and biotic environmental factors to control production

• Manipulation of food species to improve productivity

Suggest some key aims to manage agriculture in a sustainable way

To protect soil health, planting a variety of crop and animal species, reducing chemical inputs, preserving water stores, improving crop yields, minimising carbon footprints, encourage biodiversity, improve food production with less waste

What does the choice of which species and crop varieties are selected for cultivation depend on?

• Market demand and access (ease of transport)

• Whether environmental conditions are within the range of tolerance of the food species (a high range of tolerance would be desirable as it would mean the crop could cope with changing conditions)

• Whether environmetal conditions or the species’ adaptations can be controlled to improve productivity

What is the issue with the preferential use of certain species? Use a statistic to support.

Only 6 individual crops make up 60% of the world’s total crop production. This preferential selection can lead to a decline of genetic diversity and monocultures. Monocultures are large areas where only single species of crops are grown, including palm oil, soy or wheat. These crops are significant drivers of deforestation in Indonesia and South America. Monocultures reduce ecological niches for species and biodiversity, and increase the risk of diseases spreading because if all crops are the same, then all will be vulnerable to the same diseases, with no genetic resistance.

In what kind of climate and topography might corn be grown versus where rice might be grown?

Farms such as that in Iowa or Illinois in the US might grow corn - they are flat and expansive, which is ideal for growing corn. However, rice might be grown in China and India as it is a less water intensive food source than meat for example and so more ideal for India’s hot and humid climate, high humidity and short supply of water.

How might controlling abiotic factors influence agricultural productivity?

For every abiotic factor, each species has its own range of tolerance within which it can survive. Part of that range will be optimum for survival and growth and maintaining conditions within this optimum range will maximise productivity.

Describe the importance of suitable temperatures for optimising production rates in terms of the length of the thermal growing season

Temperatures must be warm enough not only for survival but also for growth, for example, grass can survive at very low temperatures but doesn’t grow below 5 degrees C.

Describe the importance of suitable temperatures for rates of production in terms of a frost-free period

Some crops are damaged by frost, such as maize or the blossom of many soft fruits, so it cannot be grown in areas where late frosts are likely.

Describe the importance of suitable temperatures in production in terms of its impact on evaporation

Higher temperatures increase the rate of evapotranspiration which increases crop water requirements (require more water input)

Describe the importance of suitable temperatures in production in terms of biochemical reactions

Higher temperatures increase rates of biochemical reaction, such as for photosynthesis

Describe the importance of suitable temperatures for production in terms of thermoregulation

Keeping animals warm reduces the need for them to use energy for thermoregulation, increasing the amount of food energy put into growth and reducing heat losses

Management - How might the careful selection of fields manage temperature so that production rates are optimised?

• Avoiding low lying valley bottoms, which are more likely to have frosts as cold dense air collects there

• Utilising south-facing slopes in the northern hemisphere (and north-facing slopes in the southern hemisphere) that receive more solar insolation and tend to be warmer.

In what other ways might temperature be managed to optimise production?

• If a crop is sufficiently valuable, then temperatures may be raised using greenhouses which achieve higher temperatures from solar heating. In cooler months, greenhouses may be heated by burning fuel such as gas or paraffin. Greenhouse overheating may be prevented by ventilation.

• Transparent woven plastic cloth may be layed over fields to help retain warm air close to the ground and protect crop seedlings (to insulate the fields)

• Keeping livestock in shelters or buildings that may be heated during the winter.

• Frosts in orchards during the flowering period (which can destroy the flowers and prevent any crop from being produced) can be prevented by burning gas, oil or candles in the orchards, or by dispersing cold air with large fans.

In what ways is light important for production rates? (In terms of light intensity and day length)

• Brighter light enhances the rate of photosynthesis and plant growth

• Photoperiodism (daylength) affects growth and development of crops - some plants require longer periods of light each day for flowering (e.g. oats), while others require less daylight (e.g. maize).

• Daylength can also affect the reproductive function of some livestock species - long day length increases milk production; poultry grow best with short days while egg production is greatest when days are long; sheep mate when days are getting shorter in the autumn and sheep are born as days get longer in the spring

Describe two methods that might be used to manage light levels

1 - Artificial lighting - Can be used in greenhouses to extend the growing season for crops
2 - Artificial recreation of autumn lighting conditions - can result in an additional mating season for sheep in spring

Describe the importance of suitable water levels for production rates

• Cell water produces turgidity (firmness) which provides support

• Water is needed to replace water lost during transpiration

• Water is needed for gaseous exchange - Water is lost from plants as stomata open to absorb carbon dioxide by evaporation from the cells in the stomata - if there is a shortage of water, the stomata close to prevent dehydration and death - the plant may survive but gaseous exchange and growth will stop

• Needed for physiological functions - water is a key solvent in many cell reactions

• Nutrient absorption from soil often involves ions dissolved in water e.g. nitrate, phosphate, potassium

• Water is needed to transport materials such as glucose, oxygen, nutrients

Describe the problems that may be caused by waterlogged soils

• A higher risk of fungal diseases such as root rot

• Soil becomes anaerobic and creates ideal conditions for denitrifying bacteria, but not nitrifying bacteria, reducing soil fertility as nitrates are lost from soils more rapidly and replaced more slowly due to lack of nitrifying bacteria

What methods may be used to reduce soil water levels?

• The excavation of drainage ditches or installation of drainage pipes

• Avoidance of soil compaction by machinery or livestock

• Provision of conditions to encourage worms such as by adding soil organic matter

• Deep ploughing

How might water shortages impact crops?

Plants lose water by transpiration during dry weather but this is reduced by the closure of the stomata in their leaves - this also stops the absorption of carbon dioxide, however, so photosynthesis and growth stop. Even a moderate water shortages reduces crop productivity. A severe water shortage will kill plants as cell dehydration inhibits cellular biochemical reactions.

How might water shortages impact livestock?

Livestock in semi-arid areas may die if there is a water shortage. Shortages can increase trampling damage if animals have to regularly walk longer distances to reach water, which can increase the risk of erosion and desertification.

What methods may be used to increase water levels?

• Crop irrigation

• Soil mulching to reduce evaporation losses

• Provision of suitable conditions for worms to increase infiltration and reduce runoff losses

• Reducing soil compaction to increase infiltration

• Adding soil organic matter to increase water retention

Which crops have high water requirements and which crops have low water requirements?

Some crops have a high water requirement e.g. most rice varieties must be flooded during early growth. Some cereal crops, however, have a low water requirement, such as wheat.

How might irregular water supplies or humid conditions affect crops?

Irregular water supplies can cause some crops to expand and split, such as tomatoes. Humid conditions can increase the risk of fungal diseases.

What is the amount of water supplied to crops impacted by and how might it affect crops?

The amount of water available to plants is affected by precipitation rates and soil properties such as permeability and water retention. The ‘hydrological growing season’ is the time during the year that there is sufficient water to retain growth.

How might the reliability of water supplies impact crops?

If farmers do not know how much water will be available, it can be difficult for them to plan activities. This is a particular issue in areas with unreliable seasonal rainfall or where there are no alternative water supplies for irrigation.

How might the quality of water supply affect crops?

Substances that are dissolved in irrigation water may cause problems, particularly if groundwater or polluted river water is used - a high salt content can cause salinisation, which leads to osmotic dehydration of the crop; heavy metals can bioaccumulate in crops and be a threat to the health of people who eat the harvested crop.

What is soil fertility?

A measure of the ability of soil to support plant growth. It is the result of availability of nutrients and water, aeration, texture and structure.

Why is soil fertility important for productivity?

• Soil nutrients include macronutrients such as nitrogen (for protein manufacture), phosphorous (for root growth and ATP manufacture, an energy compound), and potassium (for ion transport and seed development).

• Soil nutrients include micronutrients such as iron for chlorophyll manufacture, and zinc and copper for enzyme activation

Which natural processes in the soil might these nutrients be made available by?

• Legumes have symbiotic nitrogen-fixing bacteria in root nodules e.g. Rhizobium

• Some free-living soil bacteria also fix nitrogen

• Crop rotation gives time for weathering to release more nutrients and to even out the demands for particular nutrients by different crops

How might soil fertility be managed to increase productivity through the use of organic fertilisers?

Organic fertilisers are derived from organic waste that release nutrients as they decompose. They include: faecal material such as manure/sewage sludge; animal food production wastes - bone meal/fish meal/dried blood; plant food production wastes - crop harvest wastes/composted plant waste. Applying these organic fertilisers increases soil biota populations.

Suggest some advantages and disadvantages of using organic fertilisers to manage soil fertility to increase productivity?

Advantages - Many are waste products and may be locally available; they increase the soil humus content; they increase soil biota populations

Disadvantages - The nutrient composition cannot be controlled. Nutrients are released slowly as the material decomposes, so they must be used as part of a long-term cultivation plan. Many are bulky with a high water content so transport is expensive. They usually cannot be added to a growing crop.

What are the advantages of using inorganic fertilisers to manage soil fertility to optimise productivity?

Inorganic fertilisers are derived from nitrate and phosphate nutrients and their nutrient composition can be controlled to meet specific crop requirements. Also, the nutrients are released rapidly.

What are the disadvantages of using inorganic fertilisers to manage soil fertility?

They are energy intensive to manufacture; they do not add organic matter to the soil, so humus levels and soil biota populations may decline; some are toxic to worms; some have high solubility and may be leached after application - the leaching of these fertilisers can cause eutrophication, creating ‘dead zones’ in water bodies; raw material supplies for manufacture may be limited e.g. phosphate rocks.

What is the importance of soil aeration for optimising productivity?

Soil that is uncompacted has larger pore spaces between soil particles and this increases aeration. Many soil processes are aerobic and they require oxygen such as root respiration, nitrogen fixation and decomposition.

Which farming practises may reduce aeration by increasing soil compaction?

Soil compaction is increased by the weight of farm machinery or livestock trampling; farming methods like ploughing and crop removal often reduce soil organic matter content and therefore worm populations; natural communities have deep-rooted plants such as forests but most crops have shallow roots; ploughing can kill soil organisms by moving them to depths at which they cannot survive

Describe methods that might be used to increase soil aeration to optimise productivity

• Adding organic matter provides food for the soil biota that increase aeration such as worms

• Ploughing turns over and aerates surface soil layers but not deeper layers

• Low tillage methods (methods that do not require machinery or ploughing of soil) prevent the disturbance to soil and the killing of soil organisms during ploughing

• Removing livestock from fields where the soil is very wet reduces the compaction caused by trampling

What is the importance of soil salinity for productivity - why are dissolved salts necessary and what may be the results of excessive salinity?

Dissolved salts in soil are essential for plant growth as they include soil nutrients but excessive salinity can kill plants by osmotic dehydration of their roots. Soil salinity therefore must be managed to keep it within species’ range of tolerance.

How might soil salinity be managed?

The main method is to avoid farming methods that increase salinity, particularly irrigating with groundwater that has a high salt content. Freshwater irrigation may be used to wash salts out of the soil, though this carries issues such as increasing water consumption and possibly causing ecological problems by increasing the salinity of the local river.

Why is soil pH important for agricultural productivity?

All plant species have a specific range of tolerance for soil acidity, usually between pH 5 and 7. High pH can inhibit nutrient solubility while low pH can cause leaching of nutrients and inhibit nutrient uptake, it can also mobilise toxic ions in the soil, such as lead.

How can soil pH be managed - both increased or decreased?

Soil pH can be increased by adding crushed lime (calcium carbonate or hydroxide) while soil pH can be decreased by spreading powdered sulfur.

Why is carbon dioxide important for agricultural productivity?

Carbon dioxide can be a limiting factor on the rate of photosynthesis

What methods may be used to manage carbon dioxide levels?

Crop growth rates in greenhouses can be increased by burning carbon-based fuel such as gas or paraffin. This can be expensive but is balanced by the higher value of greenhouse grown crops. The Carbon Dioxide is also kept within the greenhouse, rather than lost.

How can topography, specifically the undulations (valleys and hills) of the land affect its suitability for particular crops and the methods that are used?

• Aspect - undulations, such as valleys, produce some areas which are more exposed to sunlight and tend to be warmer

• Frost pockets - cold dense air may collect in low-lying areas, making crop frost damage more likely

• Runoff rate - steeper gradients make soil erosion by surface runoff more likely. Gentle or flat gradients make flooding more likely.

• Use of machinery - it may be difficult to operate large machinery on hillslopes or where gradients are very steep/there are undulations.

How might the topography be managed?

It isn’t practical to alter land topography, but terracing (series of flat fields) can be used to make hillslopes more suitable for cultivation. This is usually done to retain irrigation water and reduce soil erosion. Areas which are nearly flat can be levelled by machinery to reduce runoff and help to produce flooding fields for rice cultivation.

How might relief (altitude) be important for agricultural productivity? Refer to its impact on both crops and livestock.

The altitude of an area (height about sea level) controls other abiotic factors including temperature, meaning certain species may or may not be suited to higher altitudes. Crops rarely grow well at high altitudes due to lower temperatures and higher rates of evaporation due to lower atmospheric pressure. Livestock such as goats, sheep and llamas can survive at higher altitudes while cattle cannot survive the high altitudes as the low atmospheric pressure causes ‘high altitude disease’ where pulmonary arteries thicken, restricting blood flow to their organs.

What is the problem with relief in terms of management?

This is an abiotic factor that cannot be controlled and management involves selecting suitable species for the relief of farmland.

What issues can high wind velocities cause for agricultural productivity?

• Increased soil erosion, particularly in dry areas

• Increased evaporation rates and drying of soils

• Crop damage such as the flattening of cereal crops e.g. wheat

What methods can be used to control wind velocity to optimise agicultural productivity?

Windbreaks can be used such as hedgerows or rows of trees; Mulching can also help to retain soil moisture (increasing water retention) and make it less vulnerable to soil erosion and meaning that leaching will also be reduced.

How can a hydroponic system closely manage abiotic conditions in the cultivation of crops?

Hydroponics involves growing crops in a water-based nutrient solution rather than in soil. Usually, it is carried out in greenhouses as part of an intensive system and it maximises productivity by controlling limiting factors such as temperature or light levels as closely as possible.

What are the main advantages of hydroponics?

• High yield produced

• Nutrient supply is optimal so this is not a limiting factor for growth

• All the roots are in contact with the nutrient medium, so the roots are smaller and more growth is directed into the harvestable crop

• There is no soil to hold pathogens and there are also no weeds

• The harvested crop still has roots so it stays fresh longer

• The harvested crop is attractive for consumers as it has no soil on it

What are the disadvantages of using hydroponics?

It requires high energy and nutrient inputs, and requires technical knowledge of crop cultivation and quite expensive equipment to deliver necessary temperature and light levels.

How do greenhouses and polytunnels also work to closely manage abiotic conditions in the cultivation of crops?

Conditions, soil nutrients and cultivation can be tightly controlled to deliver crops out of season when natural conditions are not suitable.

What are the disadvantages of using greenhouses?

They are very expensive and energy intensive. When fossil fuels are used as the sources of energy e.g. for heating, they are highly greenhouse gas intensive.