Food production: crops

Advantages of using pesticides

- Easily accessible and relatively cheap

- Have an immediate effect

- Kills the entire population of pests

What are factors farmers can control to maximise crop yield?

- Soil ions

- Soil strcuture

- Soil pH

- Carbon dioxide, light and heat

How can we increase rate of photosynthesis?

More light, CO2 and temperature (not too much or denature)

Water is not a limiting factor (not in ms) because even though it is necessary for photosynthesis, the amount needed is relatively small compared to the amount of water transpired from a plant so there is hardly ever a situation where there is not enough of it.

Also too much water in soil means it becomes waterlogged. - This reduces oxygen in soil so less respiration for plants.

- Anaerobic conditions perfect for denitrifying bacteria to convert nitrates into nitrogen gas, reducing mineral ions in soil for plants

- Also oxygen is needed for nitrification (oxidising nitrogen from proteins in dead material into nitrates)

How can the amount/concentration of soil ions be controlled? Why would they want to control this factor?

Adding fertilisers to the soil or growing in a hydroponic culture (a method of growing plants without soil, using a water-based nutrient solution instead, in glasshouses/polytunnels)

Extra mineral ions

- Nitrates can be taken up and used to make amino acids and DNA for more growth

- Magnesium to make chlorophyll (which traps light)

- Phosphates for DNA/ATP (en el ms lo pone)

Why is growing in hydroponic culture good?

It provides exactly the right balance of mineral ions for the particular crop

Not in textbook: uses less water

How can the soil structure be controlled? Why would they want to control this factor?

Ploughing fields to break up compacted soil, adding manure to improve drainage and aeration of heavy, clay soils

Good aeration and drainage allow better uptake of mineral ions (by active transport) and water

How can the soil pH be controlled? Why would they want to control this factor?

Adding lime (calcium salts) to acidic soils; few soils are too alkaline to require treatment.

soil pH can affect crop growth as an unsuitable pH reduces uptake of mineral ions.

How can the amount of carbon dioxide be controlled? Why would they want to control this factor?

These cannot be controlled for field crops but in a glasshouse or polytunnels yes. Burning fuels produces carbon dioxide (and heat and water vapour)

CO2 is a raw material for photosynthesis. More CO2 = more photosynthesis = more glucose so more growth

How can the amount of light be controlled? Why would they want to control this factor?

Cannot be controlled for field crops but in greenhouses and polytunels yes. Transparent walls allow enough natural light for photosynthesis during summer months, while additional lighting during winter gives a 'longer day'

More light = more photosynthesis = more glucose so more growth

How can the amount of heat be controlled? Why would they want to control this factor?

Cannot be controlled for field crops but in greenhouses and polytunels yes. Artificial heating (only used in temperate countries like the UK) increases temperature. If heaters use fossil fuels like gas, this produces CO2 and water vapour as well as heat.

Warmer temp (optimum) means more 'kinetic energy' so more 'enzyme' substrate collisions. This means more 'photosynthesis so more glucose' for respiration (and then energy for growth)

Heating in glasshouses provides optimum temperature for photosynthesis and a farmer can maximise crop yield. What would happen if we heat it above this temperature? What does it mean to the farmer?

- Enzymes denature (less photosynthesis = less glucose for respiration = less energy released so less growth)

- For farmer it is more expensive and a waste of money as there is no further increase in yield (might even mean less crop yield)

What is the benefit of burning fossil fuels?

- Release heat = optimum temp for enzymes, more photosynthesis, more glucose for respiration, more energy for growth

- Produces CO2 = more photosynthesis as CO2 is a reactant (raw material for photosynthesis), more glucose for respiration, more energy for growth

- Produces water vapour = mantains moist atmosphere and reduces water loss by transpiration

How is the use of glasshouses and polytunels advantageous for crop growth?

They can provide very controlled conditions for plants to grow (light, heat, CO2 only can be controlled in these structures. Rest: mineral ions, soil structre, soil pH).

Also provides shelter.

- Less crops are eaten by consumers

- Less damage from weather like wind, rain (water) and other extreme temperatures

- Prevent entry of pests that might damage plants or diseases that can kill plants

What are the two types of fertilisers and examples

Organic (farmyard manure and compost) are made from faeces of farm animals mixed with straw

Inorganic fertilisers are inorganic compounds like potassium nitrate or ammonium nitrate and can be applied to soil as dry granules or can be sprayed in liquid form.

Suggest two advantages of using animal waste as a fertiliser rather than using a chemical fertiliser

1. cheaper / readily available / less transport needed / renewable / sustainable / recycles / eq;

2. less eutrophication / leaching / run off / pollution / slow release of ions / less soluble / eq;

- It may return some nitrogen lost but just a portion since it is made from indigestible fodder

3. improves soil structure / holds water / stops erosion / eq;

- It contains decaying matter which is essential for soil

Suggest an advantage of using inorganic fertilisers.

Suggest 2 disadvantages

It can replace all nitrates and other mineral ions lost (lost as in plants absorb them so you need more in soil to grow more)

- Leads to eutrophication

- Do not improve soil structure the way organic fertilisers can because they do not conain any decaying matter essential to soil.

What is another way of replacing lost nitrates that is not using inorganic fertilisers?

Grow a legume crop (like clover) ievery 4 years

- They have nitrogen fixing bacteria in nodules converting nitrogen gas into ammonium ions

- Some of this is absorbed by the plants (some ammonium ions is quickly converted into nitrates before uptake if soil is well aereated) to make proteins

- At the end of season, the crop is ploughed back into soil

- Decomposers break down plant material and convert the nitrogen in proteins into ammonia

- Nitrifying bacteria in soil convert ammmonia into nitrite ions and then into nitrate ions (they oxidise the nitrates in proteins)

- These are then available in soil for other crops

What are pests? Organims that can be pests? How can pests harm crop yield?

Pests are organisms that reduce crop yield of crop plants or stock animals.

Any type of organism can be a pest (plants, animals, bacteria, fungi, protoctist and virus)

2 ways:

- Lowering the amount by reducing growth (damaging leaves and reducing photosynthesis)

- Affecting the appearance or quality of a crop, making it unsuitable for sale

How can pests be controlled?

Using pesticides or biological control

How are pesticides named? Examples?

They are named after the organism they kill:

- Herbicides (plant pests, weedkillers)

- Insecticides

- Fungicides

- Molluscicides (snails and slugs)

When are pests a problem? What is the decision of the farmer of using pesticides or not dependent on?

When they are present in big enough numbrtd to cause economic damage

The increase in income due to higher yields against cost of pesticides

How are weeds, fungi and insects a problem for crops?

Weeds can outcompete crop plants for space, water and soil nutrients.

Fungi can infect crop plants and spread disease which can affect growth and yield

Insects eat leaves so there is less SA to absorb light so less photosynthesis = less glucose for respiration = less growth

Advantages and disadvantages of using pesticides

- Easily accessible and relatively cheap

- Have an immediate effect

- Kills the entire population of pests

- Organisms they are meant to kill can develop resistance to the chemical (natural selection)

- They are non specific chemicals and can often kill other instects that are harmless or are helpfull like bees (pollinators for crops)

- They can be persistent chemicals (slow to decompose) so they can accumulate in organisms' tissues (bioaccumulation). This builds up and become more concentrated along food chains and harm top predators (biomagnification)

- Need to be repeatedly applied

An ideal pesticide would

-Kill only the target species

-Control the pest effectively

-Be biodegradable so that no toxic products are left in the soil or on crops

-Not accumulate in organisms (no bioaccumulation)

-Be safe to transport, store and apply

-Be easy to apply

Not in textbook

-Avoid the development of resistance

What is the method of using a biological control?

Using an organisms to reduce the numbers of a pest

What are examples of methods of biological control?

- Introducing natural predator

- Introducing a herbivore

- Introducing a parasite

- Introducing a pathogen (disease casuing) microorganism

- Introducing sterile males -- these mate with females but result in no offspring so numbers fall

- Using pheromones -- these are natural chemicals produced by insects to attarct mates. They attarct pests to traps and are then destroyed, reducing reproductive potential of the population.

Advantages of using biological controls

- Avoids bioccumulation (ignore pollution/environmentally friendly)

- No development of resistance (ignore immune)

- Lasts longer

- No need for reapplication (ignore cheaper)

- Specific (ignore no allergy/harm to people/contamination of products)

Disadvantages of using biological controls

- May eat other organisms instead of pest

- Takes a longer period of time to be effective

- Cannot fully kill entire population of the pest. If the control organism killed all pests, then it would too die out as it would have no food supply

- May not adapt to new environment or may move out of the area

- May become a pest itself

Taking into account the limitations of using biological controls, what is the aim?

To reduce pest numbers to a level where they no longer cause significant economic damage. These controls won't kill the entire pest population