Agriculture and Yields

Introduction

While there is no universal meaning for the term, agriculture is often referred to as "the cultivation of animals, plants and fungi for food and other goods used to sustain human life". The food items are fairly straightforward to recognise, but the "other products" can include growing timber on a plantation for house construction or fuel, growing plants to make medications, breeding fish to make fish oils, or growing roses to make table decorations for upscale restaurants.

This means that the definition of agriculture is far broader than you might think and that it need not even involve soil. The sort of agriculture practiced in various regions of the world is influenced by a variety of factors, such as: climate culture technology economics. Types of Agriculture

It is helpful to group different agricultural practices using different classifications because there are so many distinct products that are grown in different ways.

1.1 Subsistence versus commercial

The cultivation and production of food for the farmers' and their families needs is known as subsistence farming. There is very little extra food, and what there is is frequently exchanged (bartered) for other necessities for the family and sometimes a little amount of money. The goal of subsistence farmers is to grow nearly everything they need.

Commercial farming is the production of goods with the main objective of cash sales. Even though the farmers (and their families) may consume some of the food, this is a relatively small part of the total amount of food produced. Technology is frequently used by commercial farms to increase yields and lower production costs. Commercial farmers aim to grow crops in order to make money to spend on necessities.

While both farming systems have the potential to provide a farmer a living, the crucial factor is how much food is used for which purpose.

1.2 Arable versus pastoral

Another way of describing the type of farming is by the type of product.

Arable farming is the practice of growing crops for human consumption. Growing rice, maize, wheat, and soybeans are a few examples. There are both commercial and subsistence arable farmers, and the area and quantity of fields used for cultivation might vary substantially.

The production of animals or animal-related goods is known as pastoral farming. Grazing or livestock farming are other names for this practice. On the farm, crops like grass or grain may be cultivated, but they will only be utilised to feed the animals. Meat and other animal byproducts, such as milk, wool, and eggs, can be produced on pastoral farms.

Farms that raise animals and grow food crops are a third type of farming. Mixed farming is the term used to describe this.

1.3 Extensive versus intensive

Farm production can also be described by comparing the relative yield to the amount of space required.

When a lot of land is used to produce a relatively little amount (either of crops or animals), this is referred to as extensive production.

Intensive production is the process of producing a lot from a little quantity of land. This kind of production typically requires substantial 'inputs', like a lot of labour, fertiliser or equipment.

Why isn't intensive production used more frequently since it is frequently thought to be very efficient? This question has a complicated answer. Although yields are high, the associated costs can often be expensive, which is a challenge for many farmers. Similarly to this, some people opt to disregard intensive production due to moral or environmental concerns. This is because it can have a negative impact on the neighborhood's ecosystem and, in the case of livestock, there are welfare concerns related to confining animals in such small areas.

These categories can be combined, so you could have a large, pastoral farm for subsistence or an extensive, commercial, arable farm.

Increasing Agricultural Yields Introduction As the world's population grows, so do the demands for food. By 2050, there will be 9 billion people on the planet – an increase of 20% from 2015.

Additionally, the need for housing has led to the growth of cities and towns and the clearing of vast tracts of forest for the production of fuel and building materials. Local farming has frequently suffered as a result of the growth of built-up areas. There are many pressures on food production, such as: an increasing world population needing more resources climate change affecting the availability of fertile land increasing settlement sizes reducing available farmland increases in the standard of living creating a demand for more food variety larger populations impacting on the availability of water for irrigation.

1. Solutions to World Hunger

Some people are not surprised by the issues the world is currently facing because scientists, economists, and politicians have been discussing this topic for years. Here are some ideas for fixing the issue.

• Limiting the growth of the population, as this will lower the anticipated need for food. Initiatives like China's one-child policy are an attempt to control population growth.

• Growing more high-yielding staple crops as opposed to as many inefficient luxury goods. If people consumed more staple foods (such as rice, wheat, maize and soy) and fewer luxuries, current resources may be used to cultivate a larger amount of food. However, as countries develop, people in those countries desire to explore a larger variety of things.

• Ensuring greater food equality. Some people do not have access to enough food, while others have more than they need. Should there be laws (rationing) to guarantee that all people have equal access to food?

• Eating less meat. It wastes a lot of resources to eat meat. A significant amount of energy is lost when an animal transforms plant matter into meat for us to eat, according to research on food webs and energy pyramids (see Section 9.1 for more information). The amount of land required to grow food would decrease if we consumed only plant matter (become vegetarians).

All of these are intriguing concepts, but because they call for legislation controlling what people can do or consume, they would be quite unpopular in most countries. International agreements to further these ideas are quite unlikely.

Therefore, scientists have been putting a lot of effort into creating methods that would boost production from the currently accessible land while maintaining the freedom of choice for the global population. Farmers are already able to meet the demand for increasing food production to feed a growing population thanks to a number of effective approaches.

Since the middle of the 20th century, a number of techniques and improved varieties have been developed—often referred to as the "Green Revolution"—to increase, for instance, the production of wheat in Mexico and the production of rice in Asia, most notably with the introduction of a high-yielding rice variety called IR8. As a result, these staple crops have witnessed a huge rise in production, eliminating serious food shortages in rapidly growing populations. The Green Revolution is not just one thing; rather, it refers to a number of changes made to various sectors of agricultural production that together result in a rise in crop yield.

2. Techniques for Improving Crop Yield

2.1 Crop rotation

The idea of crop rotation is to grow various plant species on various plots every year. During one growing season, related plant groups are cultivated together before being relocated at the beginning of the following season to a new plot of land that has just been used for a different plant group. The rotation follows a predetermined pattern. Research over many years has shown that many plants grow better using this system than if continually grown on the same plot.

Farmers noticed that yields frequently declined over time when the same kind of plant was grown in the same plot year after year. Further research has revealed that cultivating the same plants repeatedly in the same location results in:

• a build-up of diseases in the soil that affect plant growth

• an increase in the pests that attack the plants

• a depletion in soil nutrients, because the same crop uses the same ratio of nutrients each year.

Moving a crop to a different piece of land each year means that:

• diseases in the soil affecting that plant are left behind and have nothing to infect

• pests need to find the new site so their numbers are reduced

• the soil in the new plot is more likely to have the nutrients the crop needs.

Additionally, the ability of some plants to make their own fertiliser (nitrates) has long been known. The nitrogen-fixing bacteria found in the root nodules of these plants, sometimes referred to as legumes, capture nitrogen from the atmosphere and transform it into a form that the plant can utilise. Any nitrogen that the legumes didn't consume during a growing season is left in the soil when the crop is harvested, where it can be used by the following plants in the cycle.

The image below shows an example of a simple crop rotation and how each crop benefits another. In this example, a large plot of land has been divided into four smaller areas, each to contain a particular type of plant.

An example of a four-part crop rotation

• Legumes: plants in the pea and bean family, which are able to fix nitrogen from the air using bacteria in nodules on their roots.

• Leafy crops: a range of vegetables grown for their leaves, which require a lot of nitrogen fertiliser (left in the soil by the legume roots). These plants are grown in a plot the season after legumes.

• Root crops: plants that have deep root systems, which help to break up the soil. A lot of soil cultivation is needed to harvest the roots. Legumes like well-cultivated soil and so benefit from being grown in a plot the season after root crops.

• Fallow: the land is left to rest, so no crops are grown.

Although there were originally intended to be four plots in the rotation, it is extremely typical to see a three-part rotation with no fallow plot due to the quantity of land that a farmer has access to. (Leaving land fallow is when the ground is given a chance to replenish its resources naturally).

Depending on the crops farmed and the local seasons, this procedure will appear slightly different in various climates. Nevertheless, rotation in some form has been adapted to a variety of conditions and is often very advantageous to plant output. For instance, some mixed farms will rotate grazing instead of the fallow area, and the animals naturally fertilise the plot as they eat.

Crop rotation reduces pest and disease populations and requires less fertiliser (if legumes are included); however, it is less beneficial if one of the crops to be grown has little market value (in the case of commercial production) or little nutritional value (in the case of subsistence farming), as this would have a significant negative impact on the efficiency of the land under cultivation.

The fact that crops can be ready for harvest at various periods implies that generally, the farmer needs less labour and less equipment and has less potential waste at harvest time because there is more time for the process. This is another less visible benefit of this method.

2.2 Fertilisers

Minerals like nitrogen, potassium and phosphorus, which are crucial for a healthy plant's growth, are found in fertilisers. Fertilisers boost crop yield when applied properly because they enhance the mineral nutrients already present in the soil. They are washed into rivers and lakes by rain, and when utilised improperly, they can harm the ecosystem.

The crop rotation strategy is well-liked because not all plants consume the same proportion of mineral nutrients, and the subsequent crop might utilise some of the surplus minerals that the preceding crop left behind. Because different plants require various amounts of mineral nutrients, producers create customised blends (or 'formulations') of substances to create fertilisers that are better suited for certain crops and minimise the loss of mineral nutrients.

Organic versus inorganic The wide range of fertilisers available is often classified into two groups: organic and inorganic fertilisers.

Organic fertilisers are products that come from natural sources (typically living sources). Most commonly this includes animal manures, but also includes composted plant materials. Bone meal (ground-up animal bones), hoof and horn (also ground-up animal parts), and dried blood are additional examples of organic fertilisers. Because they are relatively bulky and include a lot of organic matter, manure and compost are excellent soil improvers because they expand the air gaps in compacted clay soils and increase the ability of sandy soils to hold water.

Inorganic fertilisers are made in a factory. They can be made to provide a specific amount of each nutrient and are often more consistent from batch to batch. In comparison to composts and manures, they are frequently cleaner, less unpleasant to handle, and less bulky, making them easier to store and transport.

A farmer with a mixed farm may have an abundant supply of organic fertiliser (in the form of manure). Inorganic fertilisers are used by many large-scale commercial farms because they are more affordable, simpler to procure, and easier to apply with machines to the crops.

The ions of the chemicals in the fertiliser are absorbed by plant roots, which are unable to tell where they came from.

The effect of fertilisers A variety of necessary nutrients are required by plants for healthy growth. The three major nutrients (nitrogen, phosphorus and potassium) are required in relatively large amounts, while a variety of minor nutrients (including calcium, magnesium and sulfur) are required in smaller amounts, and a wider range of trace elements (including zinc, iron and boron) are required in relatively trace amounts. A lack of any one of these nutrients may prevent the plant from growing as quickly as it should; a severe lack of any one can cause a deficiency illness, which will affect the crop's yield and look.

Fertilisers provide an additional supply of essential nutrients that help plants build protein (in the case of nitrogen) and help the effective development of cells (in the case of trace elements).

Applying fertiliser safely To increase the soil's natural availability of essential mineral nutrients, fertilisers should be used. They will be wasted and carried away in rains if they are given at an inappropriate time or in an incorrect amount, which could potentially harm the environment.

It is best practice for a farmer to determine which crops require more fertiliser by either visually inspecting plants for symptoms of insufficiency or by analysing the soil to determine the amounts of naturally available nutrients. If the plant cannot absorb nutrients through its roots, which require moisture, fertilisers will be wasted. If there is a drought, applying fertiliser won't do much good unless the farmer can also provide for irrigation.

A fertiliser that dissolves quickly should not be administered until heavy rains have stopped since the mineral nutrients will be leached (washed) away. Fertilisers will also be wasted if there is too much rain. The farmer should use a slow-release fertiliser (one that dissolves gradually over time) if fertiliser needs to be added during a rainy season so that the roots can absorb little amounts over a longer period of time. However, this strategy results in a minimal immediate impact.

The table below compares the different types of fertiliser.

Fertiliser type Advantages Disadvantages Organic - Uses natural resources

• Bulky types also supply organic matter to improve the soil
• Can be unpleasant to handle
• Bulky types are harder to transport
• May be variable in composition Inorganic - Can be manufactured to meet a particular need
• Can be easier to store
• Cost of manufacture
• Transportation costs Quick acting - Fast acting: deficiency problems are dealt with swiftly
• Can easily leach out in heavy rain Slow acting - Long lasting: no need to reapply - Little immediate impact if plants may already have a deficiency problem 2.3 Irrigation

The availability of water in the soil is frequently a significant barrier to crop growth. Water is also needed for cattle, industry and human consumption, therefore using water for crops may not be as important as other uses. Making sure water is used effectively in these circumstances is crucial. According to estimates, farming uses close to 70% of the water that is used globally today.

Why is irrigation important? Water makes up a major portion of plants. Water is used in photosynthesis and is necessary for cell function. Water in the soil is necessary for the roots to absorb mineral nutrients.

A plant lacking water will show signs of it by withering its leaves. As a result, photosynthesis stops, which slows down the growth of the plant. The plant might eventually die if there isn't enough water available.

Using water wisely Water is scarce in a lot of places. The water must be free of pollution and sufficiently low in salt so that it does not harm crop plants, even though it may be possible to utilise water that is not appropriate for drinking. When water is plentiful, many farmers look for ways to capture it or store it for later use when it is scarce. Rainwater can be gathered from field run-off or from the roofs of buildings.

In warmer areas, wide expanses of water give a large surface area for evaporation, yet reservoirs do not need to be sophisticated. Although they cost more to establish, underground or covered sources lose less water.

Some farmers might have access to subsurface resources like boreholes or the equipment needed to draw water from lakes or rivers. As the sources of water become increasingly under pressure for drinking water, water for human use becomes more scarce.

Three steps make up the process of providing water to plants: storing the water, moving it to the necessary location, and applying it to the plants. For each of these phases, water conservation techniques can be used.

Transporting water to the crop through soil channels (rills) is the cheapest approach, but it is also the most wasteful because the dry soil will absorb most of the water before it reaches the plants. Nonetheless, this method is appealing to many farmers because it is simple to set up and new channels may be cut flexibly.

Solid pipes are far more expensive, and more difficult to build, but less likely to leak. Also, this distribution system calls for additional abilities and construction expertise.

Once the water has reached the crop field, there can be a significant difference in the efficiency of using the water depending on how it is applied.

Common water application methods The spray nozzle used in overhead sprinkler systems is a particular one with a tiny opening that pushes the water out under pressure. Due to this pressure, the water jet breaks up into droplets that will fall like rain on top of the crop. Large droplets will cover a broader area, whereas small ones are finer on plant leaves and will do less harm. The average size of the droplets can be changed.

The advantages and disadvantages of overhead irrigation Advantages Disadvantages Relatively easy to set up Can cover a large area from one sprinkler No need to attach pipes or equipment to each individual plant Large droplets may 'cap' the soil (damage the structure to form a hard crust), reducing the ability of rain to enter Small droplets are easily blown by wind so not all plants may be irrigated Water lands on leaves and the surface of the soil, which may evaporate before roots can use the water Not very precise With clay pot systems, porous clay pots are buried next to the plant roots in the soil. Water is poured into each pot, slowly permeating the earth around the roots. This is shown in the image below.

Source: IGCSE Environmental Management coursebook

An example of a clay pot irrigation system. As water seeps out of the pot it can be taken up by the plant's roots.

The advantages and disadvantages of clay pot irrigation Advantages Disadvantages Simple technology, little can go wrong Easy to check the amount of water provided to the soil Little surface evaporation because the water is released into the soil Only suitable for larger (more permanent) plants Large labour costs (burying pots, checking on water levels, topping up manually) 'Leaky pipes', or trickle drip systems, use a number of flat polythene hoses laid on the soil's surface between the rows of crops. Water is delivered to these hoses through pipes and released gradually at the soil's surface through tiny holes in the hoses when further irrigation is required. Some systems contain tiny tubes (emitters) that let water drip right onto the target plant. The image below is an example of the layout.

An example of a trickle drip irrigation system. Plants are watered directly through either microtubes (emitters) or a porous hose.

The advantages and disadvantages of a drip irrigation system Advantages Disadvantages Water placed directly at the base of the plant The system can be automated and controlled via a computer Water is used very efficiently Expensive to install and complex to maintain Small particles such as grit can block tubes Inflexible: cannot be moved The oldest type of agricultural irrigation is likely flood irrigation. A dirt channel or pipe transports water to the field, where it is then allowed to run freely throughout the crop. The fields must be somewhat flat for this method to work, and barriers must be put in place to stop water from just rushing off the edges of the fields.

The advantages and disadvantages of flood irrigation Advantages Disadvantages Inexpensive Can cover large areas quickly Very inefficient use of water (run-off, evaporation, etc.) Damages soil structure Non-targeted plants (such as weeds) also benefit Modern water conservation methods use information like weather predictions and the soil's current water content to determine when and how much irrigation is needed. It is being studied at what points in a crop's development it is most crucial to make sure there is enough water (such as the point of flowering or when fruit are swelling). Then, farmers may choose when it is best to use their limited water supply.

By giving their crops shelter – either by sheltering them from the sun's strong heat or by employing a windbreak to slow down the wind's movement over the crop, which lowers the rate of transpiration from the leaves – farmers can limit the rate of water loss from their crops. Other steps, such as adding a layer of natural compost or a polythene sheet to the ground, will mulch the plant's base, preventing water from evaporating from the soil and chilling the root zone.

2.4 Control of competing organisms

Even though a crop can be given enough irrigation and nutrients to grow at a maximum rate, the crops might not be able to absorb all of the water and nutrients. The growth of a crop plant can also be reduced by attacks from other organisms that can feed on it, weaken it, and in extreme cases kill it.

Weeds, pests and illnesses have cost farmers a significant amount of their potential crops for ages. It is believed that the level of loss may have reached 70% before the development of chemical controls.

A plant that is growing in an inappropriate location is considered a weed. Examples include 'jungle rice' (Echinchloa colona), a plant that competes with rice crops. This grassy plant is widespread throughout Asia and prefers environmental factors comparable to those of rice cultivation. As a result, it uses space and nutrients that the food crop could use.

A previous food crop growing among the next crop in a crop rotation is also a weed. If some were missed during harvesting, potato tubers can survive in the soil and grow and shade the next crop (such as peas or beans), reducing that crop’s yield.

Weeds need to be controlled because they:

• compete with crops for water, light and nutrients

• reduce the quality of a seed or grain crop (the weed seeds affect the purity of the crop for sale)

• might be poisonous, either to livestock or to humans (and so might result in a tainted crop)

• make cultivation difficult, tangling up tools and clogging up machines

• can block drainage systems with excessive growth

• can be a source of pests and diseases that also attack the crop

• can look untidy, which might have an impact in tourism areas.

The most effective method for controlling weeds over a wide area is probably chemical control. Herbicides are chemicals that eradicate weeds. Before sowing or planting a crop, they can be used to fully remove all prior vegetation from uncultivated areas. They can also be used to destroy weeds that are developing among a crop.

Since a plant growing in an improper location is considered a weed, the success of a herbicide depends on how precisely the farmer applies it. Carelessly using a herbicide can harm a crop or other significant local plants, which will have an adverse effect on the environment.

The majority of herbicides are administered as liquids using a sprayer that divides the liquid into incredibly little droplets. They coat the weeds in a fine layer that allows the pesticide to work. Fine droplets are likely to travel a long way when it is windy.

Herbicide granules are a different approach since they are administered with sufficient weight to fall to the ground and do not stick to the leaves of most plants. As the granules dissolve in the water of the soil, the herbicide begins to work.

The impact of weather A farmer must be aware of the forecast and current weather before applying herbicides. The spray pattern from the sprayer is influenced by wind, which may have an impact on nearby plants. Soon after application, heavy rain will wash the herbicide off the weeds' leaves or cause the granules' chemicals to leak into the surrounding area. With the lens-like effects of herbicide droplets, intense sunlight can scorch the foliage. Certain herbicides can only be used during the growing season in temperate areas because they are most effective on plants that are actively growing.

2.5 Controlling pests and diseases

Chemicals can be used to control weeds, pests, and illnesses. An animal that attacks or feeds on the crop plant is referred to as a pest. A pesticide is a substance that is used to eradicate pests. Insects are the most frequent plant pests. An insecticide is a substance that kills insects.

Fungi, bacteria or viruses can cause crop diseases. Pathogens are the name given to all of these. The most prevalent of these three kinds of crop illnesses is fungus. Fungicides are substances that stop the spread of fungal infections.

Sadly, there is no one word that describes all compounds used to manage pests and diseases, hence the phrase "pesticide" is occasionally used to refer to all of these substances. While reading about pesticides, be sure you understand the meaning being used.

Similar to herbicides, there are different ways to apply insecticides and fungicides, and the method to use will frequently depend on which portion of the plant is impacted. Once more, if they are administered improperly, there is a risk to the ecosystem because they will have an impact on nearby organisms and perhaps disrupt food chains. Farmers may be required to use PPE (personal protective equipment) while using the chemicals because they can be hazardous to humans. If pesticide residues are left in the crops, too high a concentration could be dangerous.

Alternatives to chemical control There is no denying that farmers' yields have increased significantly as a result of using synthetic pesticides to manage weeds, diseases and pests, therefore chemical use is very common, however, scientists, amongst others, are worried about their widespread usage. Biologists first highlighted the impact pesticides were having on food webs in the 1960s. For instance, fewer insects mean fewer foods for their predators (small birds and reptiles). As a result, there will be less food available for top consumers such as birds of prey.

Also, it was shown that the pesticides do not degrade in the bodies of predators that consume treated insects even though they may not immediately kill them. The concentration of hazardous chemicals increases when top predators consume a creature (biomagnification). Higher quantities may be hazardous to top predators. The most obvious example of this in many areas is the sharp decline in raptor populations that have occurred since pesticides were first used. These findings have led many people to advocate for lessening the application of chemical controls and promoting the use of alternative techniques to address insect, disease and weed issues.

Biological control One alternative way to control pests and diseases is to find natural predators that can solve the problem. If the natural predators can be bred in large enough quantities and introduced to a crop, they can feed off the pest and therefore control the infestation.

The advantages of biological control methods are:

• no chemical residues are left in the crop

• there is no impact of sprays on the surrounding ecosystem

• once introduced, the population of the control agent should increase and breed, so there is no need for reapplication

• when the pest has been controlled, the lack of food will mean the predator will naturally reduce numbers

• there is no need to wear protective clothing when applying the predator.

The disadvantages of using biological control are:

• the control is not as instant as chemical control

• climatic conditions might mean the pest breeds faster than the predator, so the problem is not controlled

• the predator might not stay on the crop and move elsewhere, instead of feeding on the intended pest

• the predator might escape into the local countryside and impact the natural ecosystems and food web.

Why not leave it all to nature? While an ecological balance is achieved naturally in a natural environment, growing crops creates an unnatural environment: it is rare to find large numbers of the same plants naturally growing together in one place with few other species present. Crop plants are also grown in areas where they do not grow naturally in the wild, away from their natural predators. In a natural environment, crop plants may yield less or suffer high levels of damage, which farmers do not want.

Alternative to herbicides Herbicide use is controversial, and some people, including some experts, are worried about the potential effects it may have on the soil environment. There are different approaches to weed control.

• Cultural controls: hand weeding and hoeing are useful methods for removing individual weeds but require a lot of labour.

• Weed barriers: using black plastic sheeting over the ground or a deep layer of composted organic matter (mulches) helps smother weeds. Mulches help to stop the growth of weeds by stopping light from reaching germinated weed seeds, as well as preventing evaporation of water from soils, which leads to waterlogged soils.

• Flame guns: paraffin (kerosene) is a highly flammable liquid that can be used in a flame gun to scorch off the tops of weeds and kill weed seeds at the soil surface. This process has risks and is only really suitable for use in areas before crops are planted.

Farmers may prefer to use herbicides rather than a nonchemical control because:

• herbicides are easier to manage and the weed control can be applied over a longer season

• alternatives may be less effective and more variable

• the use of herbicides can be cheaper

• the results are more predictable, with less risk of failure

• less labour is needed compared with cultural controls

• the effect of herbicides can be more rapid.

2.6 Efficiency gains through mechanisation

There is no denying that farming practices have significantly changed in a big section of the world. The amount of land that could be used for cultivation was traditionally restricted by the amount of labour required to grow many crops. One person can cultivate bigger regions with ease by using tools like tractors. This reduces the labour costs for the farmer and also means they are cropping from a larger area. Because of the machine's powerful engine, operations like plowing may be done while the soil is heavier (i.e., when there is more water in it), extending the growing season for soils.

A tractor's auxiliary attachments can be used for basic cultivation operations as well as the effective application of fertilisers and pesticides. Large loads can be transported by tractors as well, which is advantageous during harvest.

Modern farming methods have altered the landscape for some crops; large machines work best in large fields because time is lost when they need to change direction. As a result, natural vegetation has been removed in order to remove obstacles to the machines' efficient operation.

2.7 Selective breeding

Selective breeding has been used traditionally for centuries by farmers all over the world to enhance the performance of crops and livestock.

The process of selective breeding is as follows:

• identify which characteristics of the species are important

• choose parents that exhibit these characteristics

• raise the offspring from these parents

• select the best offspring that show the desired characteristics

• repeat the process.

This can be applied to both plants and animals. Examples of desirable characteristics in certain organisms include:

• dairy cattle: an increase in milk yield

• beef cattle: an increase in muscle size

• wheat: increased disease resistance and higher yields

• rice: an increase in yield, for example, IR8.

Source: https://www.bbc.com/news/world-asia-india-38156350

How big an impact has selective breeding had? The milk yield per cow in the USA has doubled thanks to the selective breeding of dairy cattle since 40 years ago. The Belgian Blue breed of beef cattle was created through selective breeding because it has remarkable muscular growth and produces more meat per animal. When wheat was introduced in India in the middle of the 1960s, improvements to wheat varieties helped quadruple production; similar effects have been observed in Pakistan, where production has doubled in just five years. A strain of rice known as IR8 was created through the selective breeding of rice, and it has significantly impacted rice production in many parts of the world. For instance, the annual rice yield in the Philippines has doubled from 3.7 tonnes to 7.7 tonnes in 20 years thanks to the introduction of IR8 (and other innovative cultural practices).

It is important to keep in mind that selective breeding is a continual process that involves integrating the current traits of the parents and choosing the finest offspring for further crosses. It takes a long time and has a low success rate. Only 1 new plant seedling in 20,000 is thought to develop into a viable commercial species. For many animals, testing and evaluation will take longer than selective breeding because it will take some time until the offspring are old enough to reproduce, which can take up to 20 years.

Genetic modification Genetic modification can lead to quicker results. Scientists can now map the genetic material (DNA) of many plant and animal species to comprehend their genetic code thanks to technological advancements. The relationship between the characteristics of a live organism and the tiny segments of DNA called genes has become better understood as a result of genetic mapping.

Scientists have inserted DNA from one organism into the genetic code of another by deciphering this code. The result is called a genetically modified organism (GMO). The procedure is controversial; there are supporters and opponents of the technology.

There are many different reasons for genetically modifying plant species.

• Disease and pest resistance: genes can be cut from a resistant plant and added to a crop plant

• Nutritional value: plants can be developed that are more nourishing

• Growth of plants in inhospitable areas

• Higher yields

• Herbicide resistance, which would allow farmers to spray the whole crop and its weeds and only affect the weeds

• Less use of pesticides, if the GMO plant is pest resistant

• Crops with longer storage lives, leading to less food wastage.

Concerns about the development of GMOs include:

• the unknown impact of the new characteristics on human health

• the products are not natural

• the genes might get into wild plants if they interbreed with GMOs

• issues for other insects caused by insect-resistant varieties.

It is possible to transfer genetic material between species of plants or even between animals, not just between breeds of the same species. Transgenic creatures are what result. This method offers scientists even more opportunities to control how a plant or animal grows. Unexpected applications of this technology are being developed by scientists, such as the production of a human-useable medication within the cells of genetically altered carrots. If successful, the development of these GMO carrots could offer farmers a new commercial crop.

2.8 Controlling the crop environment

The growing environment, both for raising livestock and growing crops, is one of the most variable aspects that affect agricultural productivity. Attempting to regulate the environment over very large areas can be challenging or expensive, yet there are certain crucial strategies:

• providing shade for cattle so that they do not get too hot

• using windbreaks at the edges of crops to reduce wind speed and prevent damage to the crops

• removing trees that shade a crop in order to maximise the light the plants receive.

While these methods can alter the environment and avert extreme situations, they are difficult to reverse or adapt if the local weather conditions change.

It is possible to spend more money on environmental control over fewer areas, producing an end product that can be sold for a high price and generate a profit. The use of greenhouses is one example of this.

A greenhouse is a structure used for growing plants in a controlled environment. While some greenhouses are made of glass, many are made of stronger and more insulating materials like transparent plastic. Greenhouses provide a warm environment for plants to grow and are often used to extend the growing season or grow plants that wouldn't normally survive in a particular climate.

Source: IGCSE Environmental Management coursebook

A modern greenhouse

The word 'greenhouse' also refers to constructions like polytunnels, which are made of the plastic film stretched over big metal hoops. This is much less expensive to install than a more durable greenhouse, but it does not last as long and is less effective at controlling the atmosphere.

Glass vs polycarbonate: which is more efficient at converting sunlight to heat?

Glass and polycarbonate have different properties when it comes to converting sunlight to heat. Glass is generally more efficient at converting sunlight to heat compared to polycarbonate. This is because glass has a higher solar heat gain coefficient (SHGC), which measures its ability to transmit solar radiation into heat. Glass typically has a higher SHGC value, meaning it allows more solar energy to pass through and convert into heat inside a space.

On the other hand, although polycarbonate has a lower SHGC than glass, it has a higher ability to reflect or block a portion of the solar radiation, reducing the amount of heat transmitted into a space. This can be beneficial in certain applications where minimising heat gain is desired, such as in greenhouses or buildings in hot climates.

It's important to consider the specific requirements and goals of the application when choosing between glass and polycarbonate. If the aim is to maximise heat gain from sunlight, glass would be the more efficient option. However, if heat reduction or energy conservation is a priority, polycarbonate may be a better choice due to its lower SHGC and ability to block a portion of solar radiation.

Source: IGCSE Environmental Management coursebook

A polythene tunnel (polytunnel) is a relatively cheap structure that is commonly used for growing food crops.

When plants are grown in an enclosed location, the grower has a better chance of controlling the environment. Many different environmental conditions can be controlled in a greenhouse.

Managing factors that affect plant growth Growth factor How it might be increased How it might be decreased Temperature Operate greenhouse heating system Open roof ventilators Light level Use supplementary lighting Use shading materials in the roof Humidity Use misting units to add moisture to the air Open roof ventilators or use extractor fans Day length Use supplementary lighting at the end of the day Use shading material in the roof and curtains at the side Water Use a sprinkler or irrigation system Install drainage material underneath the pots or beds A costly crop is the only one where it makes sense to invest in additional greenhouse equipment. There may be a lot of labour involved in maintaining all the extra systems. Nonetheless, a variety of sensors are used by the majority of contemporary greenhouses to keep an eye on the weather. These sensors may operate the machinery autonomously when connected to a computer, negating the requirement for a worker to be present at all times.

A growing blueprint, or the optimal environmental conditions needed for a plant for maximum growth, has been discovered through research on numerous greenhouse crops. This may be programmed into a computer to allow for remote control of the greenhouse. In order to predict future climatic conditions and modify the greenhouse's environment accordingly, the computer system is also connected to sensors outside the greenhouse and to precise weather forecasts. For instance, if clouds are on their way, there will be less sunlight, necessitating more heating. This will be anticipated by the computer, which will then increase the greenhouse heating system so that it can compensate when the temperature begins to fall.

The greenhouse effect Greenhouses work by trapping heat from the sun's rays, which helps to create a warm environment for plants to grow. Sunlight passes through the glass or other transparent material and is converted into heat energy, which is then trapped inside the greenhouse. This causes the temperature inside the greenhouse to become warmer than outside. Glass is the most effective material for this process because it converts the most amount of sunlight into heat. This effect is similar to the global warming effect we see happening to the Earth, where heat is trapped in the Earth's atmosphere, causing the temperature to increase.

Controlling the whole environment Farmers can regulate the majority of environmental factors and boost crop yields in a greenhouse. Potential crop yields can also be significantly increased by advances in selective breeding or genetic manipulation. The actual material the plants are growing in is another aspect a grower can try to optimise.

As was previously mentioned, the soil is quite varied, thus farmers may need to make significant adjustments to make it an optimal growing environment. This is not economically viable on a wide scale, but it might be beneficial in a greenhouse. In order to eliminate the requirement for soil, scientists have created a variety of different composts and growing media. For each crop, the plants are grown in a substance that is homogenous and has the proper structure. This is a fairly effective method, but the idea has been expanded upon: plants can now be grown using only water and dissolved nutrients. Hydroponics is the term for this.

While there are several hydroponic systems, one popular one involves floating plants on polystyrene rafts in a body of circulating water. Water circulates through plant roots where it is recycled. Key mineral nutrients are measured by sensors in the water, and more are added as necessary. To make sure the plant roots have adequate oxygen to breathe, air bubbles are added to the mineral fertiliser solution.

An example of a hydroponic growing system. Sensors within the system allow the process to be automated once it is set up.

Advantages of hydroponics include:

• no need for soil

• can be used anywhere (there are experiments being carried out in space)

• an intensive system that can provide high yields

• easy to harvest

• plants are given exactly the nutrients they need in the irrigation water

• water is recycled, so used efficiently

• no weeds or pests and diseases in the 'soil'

• pollutants are not released into the environment.

Disadvantages of hydroponics include:

• it is expensive to set up

• only suitable for small production areas

• requires a lot of technical knowledge

• disease, if present, is rapidly spread through the water supply to all plants

• plants can die quickly if conditions are not maintained at optimum levels.