Agriculture

The contol of terrestrial ecosystems to divert energy and nutrients into the human food chain

• Length of thermal growing season: important for growth, not survival • Frost-free period: effects crops that are easily damaged, e.g. maize • Impact on evaporation • Biochemical reactions • Thermoregulation: keeping livestock warm reduces heat losses, increasing energy efficiency

• Avoid cultivation in low-lying areas where cold air collects • Utililisation of south-facing slopes (in nothern hemisphere) as they recieve more solar insolation. • Construction of greenhouses, that can be heated with fuel or ventilated with windows. • Utilisation of fans or combustion to disperse cold air and prevent frosts from destroying crops, e.g. in orchards. • Application of transparent woven plastic cloth over fields to retain warm air and protect crop seedlings • Provision of heated or ventilated shelter for livestock

Light intensity affects photosynthesis. Photoperiodism affects the growth and development of crops as well as the reproductive function of some livestock species. • Long day length increases milk production • Poultry grow bests with short day lengths while egg production is greatest when days are long • Some livestock, such as sheep, mate when days are shorter in the autumn, with the lambs being born in spring

Artficial lighting can extend the growing season and can instigate a second mating season for sheep.

• Support of physiological functions as a solvent. • Nutrient absorption often requires being dissolved in water. • Provision of cell turgidity which supports plants. • Transportation of materials • Replacement of water lost in transpiration • Control of gaseous exhange in plants (stomata open less in arid contions to prevent unnecessary water loss)

• Some crops have a high requirement, such as maize • Some cereal crops have a low requirement such as wheat • Irregular water supplies can cause some crops to expand and split, e.g. tomatoes • Humid conditions increase the risk of fungal disease

• Higher risk of fungal diseases • Soils become anaerobic, which provides ideal conditions for denitrifying bacteria. This reduces soil fertility as nitrates are lost from the soil.

• Excavation of drainage ditches or installation of drainage pipes • Deep ploughing • Avoidance of soil compaction by machinery or livestock • Provision of conditions to encourage worms, for example, soil organic matter

Crops: - death due to cell dehydration - reduced gas exchange, which stops the absorbtion of CO2 and therefore inhibits photosynthesis. Livestock: - Death in semi-arid areas. - Shortages can increase trampling damage if animals have to reguarly walk longer distances to reach water. - May also increase risk of soil erosion and desertification

• Quantity: the amount of water available to plants is affected by precipitation rates and soil properties. • Reliability: it is difficult for farmers to plan activities if they do not know how much water will be available. • Quality: substances dissolved in irrigation water can cause problems, especially if groundwater or polluted river water is used.

• Crop irrigation • Soil mulching (to reduce evaporation losses from soil surface) • Provision of suitable conditions for worms (to increase infiltration and reduce runoff losses) • Reducing soil compaction (to increase infiltration and reduce runoff losses) • Adding soil organic matter (to increase water retention)

A measure of the ability of the soil to support good plant growth

Nutrients that are needed in large amounts to support growth and good health

Nutrients that are needed in smaller amounts to support growth and good health

• Nitrogen - protein manufacture • Phosphorus - root growth and ATP manufacture • Potassium - ion transport and seed development

• Calcium - cell walls • Magnesium - chlorophyll synthesis • Sulfur - protein synthesis

• Iron - chlorophyll manufacture • Zinc - enzyme activation • Copper - enzyme activation

• Nitrogen fixation in the root nodules of legumes, utilising rhizobium • Nitrogen fixation by some free-living soil bacteria, such as azobacter • Crop rotation gives time for weathering to release more nutrients and to even out the demands for particular nutrients by different crops

• Many are waste products and may be locally available • They increase soil humus content • They increase soil biota populations

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

• The nutrient composition can be controlled to meet specific crop requirements • The nutrients are released rapidly

• Some require large amounts of energy during manufacture by the chemical industry • They do not add organic matter to the soil, so humus levels and soil biota populations may decline • Some are toxic to worms • Some have high solubility and may he leached after application • Raw material supplies for manufacture may be limited, for example, phophate rocks

• Cultural, which utilise natural processes and may feature a rotation cycle • Mechanical