Grade 7 - Plants for Food and Fibre

Section 1: People and Plants

Plants are an essential part of the ecosystem; they utilize carbon dioxide from the atmosphere, which helps to reduce pollution. Plants then produce oxygen, which is utilized by several organisms (including humans) to survive. Plants are also the basis of most food webs as producers of food for herbivores and ultimately carnivores. Plants also provide shelter for animals, clean and filter water and help prevent soil erosion.

Plants For Food: Over 70% of the the world's food supply is based on seven major crops: wheat, rice, maize (corn), potatoes, barley, cassava and sorghum. The following are examples of everyday common foods and the plants they are made from.

Chocolate: Chocolate is made from the fruit of the cocoa tree. Cocoa beans are roasted, shelled and then crushed. Cocoa butter and cocoa powder are separated. Cocoa powder is then mixed with milk to make chocolate.
Sugar: About 50% of the world's sugar is obtained from the roots of sugar beets. The rest of the sugar is obtained mostly from sugarcane.
Vegetable oil: In Canada, over 78% of vegetable oil production is from canola. Canola is pressed from the canola seeds and used as salad oil and frying oil. The oil is used to make margarine, shortening, baked goods, potato chips and french fries

People use plants for other purposes other than food. Plants also provide fibre, which is obtained from the tissue of plants including the stem, leaves, seeds or roots.

Plants for Fibre
Plants provide fibres, which are raw materials for making clothing, paper and shelter. Plants were used by the aboriginal people from the west coast to weave cloth from the bark of the western red cedar tree. Much of modern clothing comes from synthetic material, such as polyester and nylon.

Cotton - The cotton fibres come from the plant's seeds. The silky fibres are strong, flexible and have a gradual spiral that causes the strans to intelock when twisted, making them ideal for spinning into thread. The second layer of fibers are shorter and are 'fuzzy' - they are used to make cotton batting, rayon and various types of plastic and paper. Materials made from cotton absorb moisture and then allow it to evaporate easily, making it the world's most important non-edible plant.

Hemp - hemp is the oldest cultivated fibre plant in the world. Early models of jeans were made using hemp. Hemp was also used for other products such as sails and ropes. Hemp has a less negative effect on the environment, because it uses less land area than trees, can be harvested in a year, lasts longer than paper, can be recycled up to seven times, chokes out weeds naturally and is not prone to insect pests.

Flax - is used as a food and a fibre crop. The flax fibres, which are smooth and straight, are taken from the stem of the plant and are 2-3 times stronger than cotton fibres. Flax fibre is used for making linen paper, linseed oil - which is used as a drying oil in paints and varnish.

Plants for Medicine

Several medicines contain ingredients made from plants. Herbal remedies are also common examples of how plants are used to prevent illness. Examples of medicines that contain ingredients from plants include:

Ginger root (such as that added in tea) - is used to soothe an upset stomach
Opium poppy's seed pod - the milky fluid obtained from the seeds provides a powerful pain medication. Used to produce morphine
Codeine is also found in the poppy - it is used in cough medications.
Quinine - which comes from the cinchona tree - is used to prevent malaria.

Plants for Transportation and Construction

Rubber is one of the most important plant products that people use. Natural rubber comes from the Brazilian rubber tree. Synthetic rubber is made from coal and oil by-products - but natural rubber is also an important ingredient.

Canoes were carved from trees by Aboriginal people.

Lubricants are provided from coconut and castor bean oils.

The construction industry all over the world uses wood as a building materialto varying extent, on walls, windows, doors, floors etc.

Plants for Fuel

Wood (firewood) and coal are used to heat homes or cook food. Sugar can be turned into ethanol and wood can provide methanol (wood alcohol). Fuel from plants is economical, but not energy efficient, because a large amount of energy is need to grow the plants and a lot of the energy is lost when it is converted to fuel.

Section 2: Plant Structures and Adaptations

Different plant species live in specific habitats with different conditions including light, temperature, water and soil conditions. The structure of a plant helps it to adapt and survive in these conditions.

Roots

There is much more to a plant than what you are able to see above the surface of the soil. In fact, up to one third of the plant can be beneath the soil.

Roots perform several functions such as water absorption, transport of minerals from the soil, and they also anchor the plant to the soil. Roots store food to help the plant survive during times of scarcity.

Many plants have a single, prominent taproot with numerous small roots coming out of it. These smaller roots are covered in tiny root hairs. The smaller roots and root hairs increase the ability of the plant to absorb water and nutrients from the soil. Most trees and large desert plants grow taproots that reach deep into the ground, as do dandelions. Other plants have fibrous roots. This is a shallow system of similar-sized roots that can quickly soak up moisture.

Roots are adapted to the plant's habitat.

The duckweed on the other hand has tiny roots on the underside of the leaf and are surrounded entirely by water.

Root crops grow in a short period of time, they can survive when there is little moisture and can be stored for long periods of time.

The movement of water and minerals occurs through diffusion and/or osmosis.

Diffusion is the tendency of particles in a gas or liquid to become evenly distributed by moving from areas of greater concentration to areas of lesser concentration. The particles continue to spread out until they are evenly distributed within the enclosed area. Osmosis is a particular type of diffusion in which only some of the particles are allowed to pass through a barrier. This barrier is called a differentially permeable membrane. Osmosis is the diffusion of water through a differentially permeable membrane.

Selective permeability: root cells are differentially/selectively permeable. This means that they allow some materials to pass through, such as water and specific nutrients, and keep out other materials.

Stem

The stem of a plant has several functions. Most importantly, the stem enables the transport of water, minerals and other nutrients from the soil to the leaves, and then transport food from the leaves to other parts of the plant including the roots.
The stem also supports the plant to ensure that the leaves receive adequate light. To achieve this most stems grow above the ground.
In some plant species, the stem functions as food storage. Potatoes are actually swollen underground stems called tubers. They store starch which is used by the plant to grow. Some plants store food as sugar as well - the sugar cane is a good example.

Types of Stems

The stem of the common strawberry plant grows horizontally on the ground and is called a runner. At various spots along the stem, roots begin to grow and can form a new plant. These plants, as expected, are clones.

Cattails have fleshy horizontal stems called rhizomes, which allow the plant to spread underground.

Several cacti, like the prickly pear, have flattened stems. This adaptation ensures that part of the plant always faces away from the Sun, helping the cactus to preserve water.

Leaves

Leaves are the part of the plant that use the energy of sunlight and change it to a kind of chemical energy. They do this by combining two simple materials, carbon dioxide (from the air) and water. These combine to make the material that we know as sugar. Sugar is a kind of energy-storing chemical made by plants. This process is called photosynthesis.

A pigment called chlorophyll makes the leaves green and absorbs energy from the sun and changes it into chemical energy. Plants also need oxygen - at night when photosynthesis does not happen, respiration does. Respiration is a process by which plants release carbon dioxide and let oxygen into their cells.

Water enters and leaves the cells in the leaves through the guard cells. When they absorb water they swell, opening the stoma (many-stomata). The loss of water through evaporation is called transpiration. The pushing and pulling action of osmosis (pushing water up from the roots) and transpiration (pulling the water up the xylem tissue from the roots) moves water up to the very top of the plant.

Section 3: Plant Reproduction and Breeding

Plant reproduction is the production of new offspring in plants. This may be accomplished by sexual or asexual reproduction. Sexual reproduction produces offspring by the fusion of gametes, resulting in offspring genetically different from either parent. Asexual reproduction produces new individuals without the fusion of gametes, resulting in clones, i.e. offspring that are genetically identical to the parent plant and each other.

Types of plant reproduction

We have already learnt that plants can reproduce in two very different ways. Sexual reproduction and Asexual, or vegetative reproduction. Traditional types of vegetative reproduction include:

Cuttings
Layering (runners)
Grafting
Fragmentation (buds and root systems)

Seed Plant Reproduction

Unlike asexual reproduction, when plants reproduce using seeds — the resulting plants are all slightly different from their parents. These differences help plants to adapt to changes in their environment.

Seeds: A seed is a structure that contains a young developing plantand stored food. Under suitable environmental conditions, the seed will grow into a new plant. Seed plants reproduce by sexual reproduction. The male sex cell is called a sperm, and it must unite with the femaile sex cell called the egg. Sperm cells are located within pollen grains, which are produced in the anther of the flower. Eggs are located in the flower's ovary. The ovary is located at the bottom of the stigma. The transfer of pollen from the anther to the stigma is called pollination. The transfer results in the union of male and female sex cells. This union is called fertilization and results in the formation of a viable seed.

Parts of a flower

Petal - brightly colored parts of the flower to attact pollinators such as insects and birds.
Sepal - green, protect the flower before it opens.
Anther - where pollen is produced and stored.
Pollen grains - particles containing the male reproductive cells (male gametes).
Filament - stalk that supports the anther.
Stigma - sticky 'lip' of the pistil that captures pollen grains.
Style - stalk that supports the stigma.
Ovary - swollen base of the pistil containing ovules.
Ovules - sacs containing female reproductive cells.

Self pollination occurs when pollen is transferred from the anthers to the stigma on the same flower. Cross pollination is when the pollen is transferred to the stigma of a different flower. Pollinators are organisms that transfer pollen from flower to flower, such as bees, butterflies, birds etc.

Seeds need to be transferred from the parent plant/tree so that they can grow in a different area not too close from the parent. This process is called Seed dispersal. Some seeds are light and can be blown away by wind. Other seeds stick on animal fur and are carried by the animals to distant locations. Some other seeds are eaten by animals but not digested so the animal poops the undigested seed at a different location.

Some plants use spores instead of seeds. Spores are cells that can develop into new organisms. Spores do not contain stored food. Mosses and ferns use spores to reproduce.

Cones: The cone is the part of the tree that has a series of woody scales, and come in various shapes and sizes. Both male and female cones are produced by cone-bearing trees. Female cones contain ovules (eggs) - the small bumps at the end of a scale in a cone. Pollen grains (containing sperm) develop on the smaller male cone. Wind carries the pollen grains to the female cones. Although most of the pollen grains never reach the female cones, those that do get caught in the sticky fluid near the ovule. A pollen tube grows to the ovule and sperm is able to ferilize the egg. The process of pollination is complete. Female cones of pine trees matrure, open, and release their seeds during the fall or winter months. (This whole process takes at least two years) The seeds can then be dispersed by various methods and when they get covered they can eventually sprout and become new pine trees.

Plant Breeding

Selective breeding refers to people choosing specific plants with desirable characteristics and encourage or utilize these plants to reproduce. This way, the desirable characteristics increase in the population.

Frequently, plants are selected to produce more yield, larger fruits. However, other characteristics that maybe desirable include: ability to withstand certain environmental conditions (hardiness), resistance to disease, their appearance etc.

Canola was developed using selective breeding and originated from a plant called rapeseed. It was developed to produce seeds that created a good-tasting oil. Through successive selective breeding and genetic modification, canola crops are now more resistant to diseases, drought and even certain chemicals.

In addition to selective breeding, scientists can also change plants by going inside an individual plant cell and modify some of its genetic material, by removing the parts (genes) that control particular characteristics, or adding parts (genes) that introduce new traits. This genetic material can then be combined with genetic material from another plant to create a new plant - having characteristics from both plants. This process (biotechnology) is called genetic modification, or genetic engineering.

Planting and Harvesting Seeds on Farms

Farmers (may) use machines/tools to disperse seeds. Once they have grown into the crop, they are harvested in two steps. A swather cuts the plants and lays them in rows (the stubble - what is left of the plant after being cut - prevents the plant from touching the soil, so the seeds can ripen). A combine then separates the grain from the rest of the plant. (The grain seeds are collected and the straw is baled, or spread evenly over the field).

Germination: When the seed is able to come in contact and get covered by the soil, it remains inactive until the right conditions are present for it to germinate. Germination is the development of a seed into a new plant.

Section 4: Meeting the Need for Food and Fibre

An Alberta, Canada Case Study

Canada exports the excess agricultural products to other countries around the world. Canada is also a leader in forestry and agricultural research science. Scientists, farmers and foresters are working together, developing practices that will reduce the negative effects that could occur when we harvest plants for food and fibre. Sustainability is essential to keep natural resources healthy in the long term.

Agriculture in Alberta

Agriculture is important, but relatively new as an industry in Alberta. The vast natural resources in Alberta attracted many settlers who cultivated the grasslands to grow crops and harvested trees for construction, manufacturing and fuel. Nearly all of the grassland in the prairie provinces was converted to cropland, thus destroying the natural vegetation and native plant species that had been around for a thousand years.

Alberta agriculture is worth over $20 Billion (in 2021). The food industry is second only to oil and gas in terms of earnings. Alberta's Agricultural exports totalled more than $12.4 billion in 2020, including $5.8 billion in primary agricultural products and $6.7 billion in value-added products. Alberta’s top five agri-food exports in 2020 were beef, wheat, canola seed, crude canola oil and live cattle.

Uses of various crops

Wheat: Wheat is used to make several food. The seeds are ground to make bread, pasta and many other processed foods.
Oats: Oats are mostly grown to feed livestock. Oats can also be used to produce processed products such as oat milk, oat cereal/oat meal, granola bars, bread, muffins etc.
Canola: used to extract canola oil. Oil is pressed out of the canola seeds and is used to make margarine, cooking oil and salad dressing. Leftover 'canola meal' is used to feed poultry and livestock, because it is high in protein. Recently, some of the canola meal is being used in the pharmaceutical industry.
Barley: Is fed to livestock and is used for making malt flavouring (used in many foods).
Legume crops such as field peas, faba (or fava) beans and lentils are high in protein and are consumed directly bu humans and animals. They are also useful to increase fertility in soils and reduce the reliance on chemical fertilizers.
Potatoes: The cool climate is ideal for growing potatoes. Most potatoes are grown in the irrigation districts in Southern Alberta. About half of the potatoes grown in Alberta are processed into frozen french fries and potato chips. Many potatoes are sold to other farmers as seed potatoes.
Alfalfa (also called Lucerne): Alfalfa is grown for its leaves and stems. It is used as hay crop or forage crop and are fed to livestock. Its high protein level makes it good to improve the nutritional quality of livestock feed.
Specialty crops such as sunflowers, beans, field corn, sugar beets, lentils, safflower and spices are mostly grown in the irrigation district in Southern Alberta.

Farming Practices

To be economically sustainable, farmers need to make more money with their crops than they spend to grow their crops. They are able to do this by using very large machinery that can cover large parcels of land as they seed and harvest their crops. They also need to add fertilizer to the soil to increase the yield and irrigate to provide the need moisture for growth of the crop. Most farmers only grow one type of crop in one particular area - this is known as monoculture.

Farming practices have changed significantly over time as farmers reliy more heavily of mechanization and chemical amendments to increase yield. Smart farming is the most recent innovation with computerized equipment such as modern combine harvesters that can collect several types of data (crop yeild, nutrient percentages, yield mapping, soil mapping, etc) during harvest time.

Irrigation

Irrigation is a technique that farmers use to make sure that moisture gets into the soil for crop growth. It is often a problem in grassland areas, where the moisture evaporates quickly. Irrigation systems (using natural waterways and irrigation canals) can often be the life or death of a crop and must be maintained to ensure an adequate supply of water is available when it is needed.

Fibre and the Forestry Industry

Canada has about 10% of the world's forests. From these forests come lumber and pulp and paper products. Natural forests have many different kinds of trees, shrubs, and smaller plants. There are many animals that make their homes in, around and under these plants. A natural ecosystem has a higher diversity, or variety, of plants and animals than a field of wheat or a stand of trees. The species within this ecosystem are all interdependent. Forestry practices can increase the diversity of forest species by careful cutting to let in more light and air.

In Alberta, the tree species most valued for lumber and paper include: Lodgepole Pine, White Spruce, Black Spruce, Aspen, White Birch and Tamarack (Larch).

Foresters explore a potential tree cutting area thoroughly before any work begins. They map the area indicating which trees to be cut and what special features should be noted. They also decide how to cut the trees, either clear cut (removing all the trees)- or, selective harvesting (removing only selected trees).

In Canada, foresters attempt to improve the conditions within the forest. Leftover branches are cleared and disposed of. Replanting is always done by hand. When the trees begin to grow again, if too many of a particular kind compete, they must be removed by thinning or pruning. Fertilizer may be dropped from a helicopter to improve the level of nutrients for the young trees. Forest fires are a natural development of forests, but foresters try to ensure that they burn in a controlled fashion.

Global Challenges

The most common challenges affecting agriculture globally include drought, floods and soil erosion.

Section 5: Sustaining the Soil

Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support the life of plants and soil organisms.

Soil consists of minerals and organic matter (the soil matrix), as well as a porous phase that holds gases (the soil atmosphere) and water (the soil solution). Therefore, soil is a three-state system of solids, liquids, and gases. The interaction between biotic and abiotic factors in soil means we can view soil as an ecosystem.

A typical soil is about 50% solids (45% mineral and 5% organic matter), and 50% pores of which half is occupied by water and half by gas. The proportion of soil mineral and organic content can be treated as a constant in the short term because it takes a long time to change its components, while the proportion of soil water and gas content is highly variable. An increase in one is simultaneously balanced by a reduction in the other.

Several factors determine how soils develop:

Parent material-is the mineral (non-organic) matter (rock, soil, clay) from which the soil developed.
Climate - determines the kinds of plants, how fast they grow and decompose. Warmth and moisture are required for soil organisms to break down plant and animal matter and change it to a rich, dark soil called humus. Humus holds nutrients and water for plants.
Vegetation - determines the amount and type of organic matter in the soil. Vegetation can also contribute to weathering and soil erosion.
Landscape: the landscape may promote or limit weathering and erosion and as a result influence soil formation.
Water brings new soil and nutrients. In healthy soil, spaces between the particles hold water and air for roots. If soil is saturated with water, less oxygen is available.
Time: Most of these process happen over long periods of time.

Soil Organisms

Healthy soil contains several rodents and other small animals, bacteria, fungi, small bugs, worms, and other decomposers. The decomposers break down plant and animal tissue, forming humus, which helps roots grow by trapping water and air. The four main types of decomposers are:

Bacteria are the most diverse and numerous of all soil organisms. In healthy grasslands, billions of bacteria live in every kilogram of soil. A hectare could have up to 4 t of live bacteria, all actively breaking down dead plant and animal tissues.
Fungi include moulds and mushrooms. These organisms are especially important in forest soils and where soils are cooler and more acidic. The fungi make nutrients available to the plants and receive carbohydrates in return.
Actinomycetes are a special type of bacteria that also play a vital role in decomposing organic matter and forming humus.
Earthworms play an essential role in healthy soils. Earthworms eat the soil, they grind, digest, and mix it. They produce casts that are richer in nutrients and bacteria than the soil they took in! Earthworm tunnels help air and water move through the soil. The mucus that worms add helps stick soil particles together. Earthworms also bring up nutrients from lower levels of the soil as they tunnel through it.

Soil Nutrients

Plants require 6 basic nutrients from the soil in order to grow healthy, these include nitrogen (N), phosphorus (P), potassium (K), sulphur (S), calcium (Ca), and magnesium (Mg).

As we grow plants, they extract these nutrients from the soil leaving the soil with less and less of them over time. Fertilizers are designed to supplement these nutrients in soils. Soils can also be amended using compost, manure, mulch, bioactives, introduction of microbial cultures etc.

Soil Health Challenges

1. Soil salinization (Salty Soil)

High levels of salt in the soil have the same effect as dry conditions. As more salt collects in soil, the soil becomes less and less able to grow crops. There are two factors that lead to salinization: too little vegetation and too much water (excess irrigation). When farmers cultivate land to grow field crops, they remove vegetation. Water enters the soil since there are no plants to absorb water. Irrigation brings even more water into the soil, adding to the ground water. The excess ground water dissolves minerals (salts) from the soil. Eventually, when the water evaporates the salts are left behind. Soil salinization can be solved by replanting the areas so that plants use up the water that falls before it has a chance to seep away.

2. Loss of organic matter and soil erosion

The most serious problem in soils is the loss of organic matter. This in turn leads to soil erosion. Soil then is less able to hold nutrients, water, and air. This makes the soil poor for growing plants. Loss of organic matter begins with removal of natural vegetation so as to prepare farms for commercial agriculture. This exposes the soil to the Sun and wind. In additon, due to the need to control weeds and prepare perfect seedbeds, producers ploughed and cultivated the soil too much. Ssummer fallow was also a common practice. (Summer fallow is the practice of cultivating land to control weeds but planting no crops.) This exposed the soil to sunlight and higher temperatures and encouraged bacteria to decompose the organic matter at a rapid rate and cause soil nutrient depletion.

Ways to Improve Soil Sustainability

As more research and observations are made around soil sustainability, several practices are recommended to improve soil health and limit the negative effects of commercial agriculture on soil health.
Soil erosion can be solved by planting a cover crops, these are vegetation on the surface of the ground to slow the flow of water. This also gives the soil more time to absorb the water. When more water soaks in, less will flow along the surface and cause erosion. Vegetation covers also protect soil from the wind. Farmers, particularly those in drier areas, have realized how important it is to “keep the covers on” their fields. They need ways to keep protective vegetation on the field, while still being able to remove weeds. Cover crops also feed the soil microbial organisms which improves the soil organic matter and general soil health metrics. Cover crops protect the soil from direct heat from the sun which would otherwise dry the soil to fast. uncovered soil develops a dry crust, which prevents vegetation from growing.

Zero-tillage and minimal tillage are techniques that enable farmers to use specialized equipment that push seed right through the stubble of the previous crop therefore not requiring to plough the land before planting. This protects the soil from wind and water erosion. In addition, it lower tillage costs, improves soil structure, and preserves more soil moisture for the next crop. Its disadvantages are that herbicides and pesticides may be needed to control the weeds and disease- causing organisms previously killed by cultivation.

Crop rotation is the practice of planting a different crop species on the land in different years. There are several types of crop rotations allowing 3, 4 or more crops to be planted in alternating years. It is important to incorporate a legume into the rotation for nitrogen fixation. Planting the same crop over and over again results in excessive depletion of specific nutrients from the soil. It also results in an increase in specific pests, weeds and diseases.

Shelterbelts: Shelterbelts reduce wind damage to crops, trap snow to increase soil moisture, and provide wildlife with habitat.

Forestry can also have an impact on soils. When trees are cut and removed from an area, wind and water can erode the soil. To minimize damage, some trees and debris such as logs and stumps are left on cut areas. As the debris decays, it adds organic matter to the soil. Forests are also replanted with new trees shortly after they are harvested.

Section 6: Pests and Pest Control

From the point of view of a farmer or forester, a pest is any organism that is causing plants to die or produce less than they otherwise would. . Insects are not the only types of pests, however. Fungi, weeds, and other animals such as slugs or birds can also be pests in certain situations.

The pests that cause most damage are insects, fungi, and weedy plants. Weeds steal moisture, nutrients, space, or light from the crop. Insects usually eat some part of the plant, and fungi and bacteria can cause infections, destroying parts or all of the plant.

Pests that Affect Canola

Canada thistle: This is a perennial weed that regrows from roots or fluffy seeds spread by wind.
Fusarium fungus: It lives in the soil and attacks canola shortly after it starts to grow.
Blackleg fungus: This fungus attacks seedlings at night, shortly after seeds germinate.
Wild oats: Thiis is an annual weed that sprouts any time, grows rapidly, and produces seeds before the crop is cut. Seeds will live many years in soil, then grow into very competitive weeds.
Sclerotina: It lives in or on the soil surface until the next crop of canola grows. It infects leaf axils and causes severe crop damage. It lives in or on the soil surface until the next crop of canola grows.
Lygus bugs sucks the juice out of buds, flowers, and seeds.
Bertha army worm: generally eats everything in sight. Adult moths lay eggs in blooming canola. After hatching, the larvae grow rapidly by eating huge amounts of leaves and pods, resulting in tremendous crop losses.

Many of the worst weed and insect pests are organisms introduced from other countries. They are called introduced, or exotic species. Most of the weeds that cause crop losses such as Quack grass, thistles, and chickweed were accidentally introduced from Europe. Some of the foreign weed species came by accident, but others were introduced intentionally. Dandelions, for example, were brought from Europe to be used as a salad vegetable. The tiny European bark-boring beetle arrived in North America in 1940 with a shipment of elm logs from the Netherlands (see Figure 2.69). Unfortunately, it brought a fungus called Dutch elm disease that has since wiped out nearly all the native elm trees of North America.

Controlling Pests

In the past farmers grew different crops each year as a way of controlling some weeds and crop diseases. Crop rotation is a practice where a field might grow wheat in the first year, barley in the second, peas in the third, and hay crops in the fourth, fifth, and sixth years. This system gave pests no opportunity to establish themselves since a new crop was grown each year. Regular summer fallow helped control a variety of weeds and crop diseases, but it led to soil damage. Due to commercial and convenience, chemical control seemed to be effective and relatively inexpensive. Herbicides, insecticides, and fungicides were used to control weeds, insects, and fungi. These chemicals were effective but after several years of use, there were indications that these chemicals were causing major problems such as:

Bioacummulation: Bioaccumulation occurs when chemicals move from one level of the food chain to the next level and get stored in organisms in the same way that food energy is stored. Animals at the top of the food chain are particularly affected by bioaccumulation.
oil residue: Some of the chemicals wash off the plants and leave residues in the soil and water where they can stay in the environment and remain poisonous.
Harming Non-Target Organisms: Pesticides are often toxic to more than one organism, in most cases, beneficial organisms. For example, earthworms are often non-target organisms that are affected by chemical controls.
Development of Resistant Species: Resistance describes a situation where a chemical is no longer effective in controling an organism because the organisms has developed ways to withstand the chemical. In such cases, the organisms require higher doses of the chemical for it to be effective. Using higher doses comes with more negative effects.

Organic Food Production

Organic food is food that has been grown without the use of chemical fertilizers and chemical pesticides. Organic food growers use manure and compost to add nutrients to the soil. They control weeds and other pests using practices such as tilling, crop rotations, mulching, polycultures, and by removing insects by hand. Soaps can also be used to control many insect pests. The increased biodiversity helps reduce weeds, insects, fungal diseases, and the excessive drain on some soil nutrients. Consumers of organic food enjoy reduced exposure to chemicals, but usually pay more for the organic food.

Biological Control

Biological control means using a pest’s natural enemies to control it. It’s like using one living organism to control another. For example, the soil bacterium Bacillus thuringiensis (Bt) produces a toxin that is deadly to certain insects but is not known to be harmful to humans and other animals. Some growers use ladybugs or predatory wasps to control insect pests such as aphids or white flies.