Biological Resources (A2); Agriculture (Complete)

About 10% being cultivated & further 25% used as permanent pasture

Due to a growing human population

Affects large areas of natural habitats & many important natural processes

The control of terrestrial ecosystems to divert energy & nutrients into the human food chain

-Market demand & access -Whether environmental conditions are within the range of tolerance of the food species -Whether environmental conditions/species adaptations can be controlled to improve productivity

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

-It’s not just necessary for temperatures to be warm enough for survival, it must be warm enough for growth -For example, grass can survive very low temperatures but doesn’t grow at temperatures below 5°C

-Some crops are damaged by frost, eg maize, so it can’t be grown in areas where late frosts are likely -The blossom of many fruit crops is damaged by frosts

High temperatures increase the rate of evapotranspiration which increases crop water requirements

Rate of biochemical reactions, incl those involved in photosynthesis & plant growth, are generally increased by higher temperatures

-Mammals & birds use food energy to maintain a constant internal body temperature -Keeping the animals warm reduces heat losses & increases the amount of food energy put into growth

-Low lying areas eg valley bottoms are more likely to have frosts as cold dense air collects there -South-facing slopes in northern hemisphere (& north-facing slopes in southern hemisphere) receive more solar insolation, tend to be warmer. Where crop is sufficiently valuable, temps may be raised w/ more intensive methods; greenhouses achieve higher temps from solar heating, may be heated in cold weather by burning fuel eg gas/paraffin & their overheating can be prevented by ventilation -Frosts in orchards during flowering period can destroy flowers & prevent any crop from being produced. Can be prevented by burning gas, oil, candles in orchards/by dispersing cold air w/ large fans -Transparent woven plastic cloth over fields helps to retain warm air close to ground & protect crop seedlings -Livestock can be kept warm by providing shelter/buildings that may be heated. In hot weather, buildings may need to be ventilated to prevent overheating

-Intensity of light affects rate of photosynthesis; brighter light producing more rapid photosynthesis -Photoperiodism (daylength) affects growth & development of crops. Some plants require longer periods of light each day for flowering, eg oats, while others require shorter days, eg maize -Day length can affect reproductive function of some livestock species; long day length increases milk production, poultry grow best w/ short days while egg production is greatest when days are long & some livestock like sheep mate when days are getting shorter in autumn, w/ lambs being born in spring

-Artificial lighting can be used to extend growing season, eg for salad crops in greenhouse -Artificial production of autumn lighting conditions in spring will produce another mating season for sheep, w/ second lambing season in autumn

-Physiological functions; water= general physiological solvent in all living cells -Nutrient absorption from soil as ions dissolved in water; nitrogen is absorbed as nitrate ions, phosphorus is absorbed as phosphate ions & potassium is absorbed as potassium ions -Cell water produces cell turgidity which provides support, esp in seedlings -Is used to transport materials eg glucose, oxygen & mineral nutrients -Is needed to replace water that’s lost during transpiration, which causes water to be drawn upwards to leaves, carrying nutrients from roots w/ it -Gaseous exchange; stomata= pores in leaves where CO² dissolves & is absorbed, so can be used in photosynthesis. Water’s lost during this process by evaporation from cells in stomata. If there’s a shortage of water, stomata close to prevent dehydration + death. Plant may survive, but gaseous exchange & growth will stop

-Some crops have a high water requirement eg most rice varieties must be flooded during early growth -Some cereal crops have a low water requirement, eg wheat -Irregular water supplies can cause some crops to expand & split, eg tomatoes -Humid conditions can increase risk of fungal diseases

-Precipitation rates & soil properties like permeability & water retention -The ‘hydrological growing season’ is the time during the year that there’s sufficient water to sustain growth

-It’s difficult for farmers to plan activities if they don’t know how much water will be available -This is a particular problem in areas w/ unreliable seasonal rainfall/where there’s no alternative water supplies for irrigation

-Substances dissolved in irrigation water can cause issues, esp if groundwater/polluted river water is used -A high salt content can cause salinisation, leading to osmotic dehydration of the crop -Heavy metals may bioaccumulate in crops & be a threat to health of people who eat harvested crop

-Higher risk of fungal diseases -Soils become anaerobic & create ideal conditions for denitrifying bacteria, but not nitrifying bacteria—> reduces soil fertility as nitrates are lost from soil more rapidly & replaced more slowly

-Excavation of drainage ditches/installation of drainage pipes -Deep ploughing -Avoidance of soil compaction by machinery/livestock -Provision of conditions to encourage worms, eg soil organic matter

-Plants lose water by transpiration during dry weather but this is reduced by closure of stomata in their leaves -This also stops absorption of CO² so photosynthesis & growth stop. Even a moderate water shortage reduces crop productivity -A severe water shortage will kill plants as cell dehydration inhibits cellular biochemical reactions

-Livestock in semi-arid areas may die if there’s a water shortage -Shortages can increase trampling damage if animals have to regularly walk longer distances to reach water; can increase risk of erosion & desertification

-Crop irrigation -Soil mulching to reduce evaporation losses from soil surface -Provision of suitable conditions for worms to increase infiltration & reduce runoff losses; -Reducing soil compaction by machinery & livestock to increase infiltration & reduce runoff loses -Adding soil organic matter to increase water retention