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As seen in the previous topic on energy transfer, plants produce a great deal of energy which is used up increasingly at every trophic level. This is the basis on which decisions are made in agriculture and rearing of domestic livestock.
In the wild, both plants and animals are subject to a lot of energy loss due to pests, physical activity or insufficient nutrients. This results in a relatively inefficient flow of energy between trophic levels. We think of this in terms of net productivity.
Net productivity is equal to gross productivity minus respiratory loss.
In both terms, productivity refers to the amount of leftover useful tissue such as cereals or animal flesh.
As opposed to the wild, in human-made growth environments this respiratory loss is kept as low as possible. Extreme measures are taken to achieve this, which include:
1. The use of chemical pesticides and biological agents to kill all or certain organisms which may infect or feed on plants e.g. insects, fungi, small animals
2. Intensive rearing of animals which includes keeping them indoors and in confined spaces to prevent their energy being lost on movement; and administering antibiotics to prevent mass spread of infection
To enhance plant growth fertilisers are used, whether natural (manure) or artificial.
A strategy to maximise net productivity is an integrated system. Put simply, this is a self-contained nutrient recycling approach which involves using manure as plant fertiliser, and leftover plant “waste” as additional feed for animals.
There are many issues (economical, social, ethical) surrounding intensive farming across the globe. Here are a few:
1. Prioritising land – since so much energy is inherently wasted every time plants are used for anything else apart from direct eating by us, it is both an economical and social issue to decide whether so much land should be used for plants grown simply to feed animals which then pass on a tiny fraction of energy onto us; for plants grown to produce biofuel rather than food for us; or for plants grown to end up straight onto our plates so that the energy they pass on is maximised.
2. Controlling the effects of chemicals – artificial compounds used en masse such as antibiotics and pesticides can have far-reaching impacts. For example, if fertilisers leak underground and are transported to a distant lake, they will result in an algal bloom which will cover the entire surface of the lake. All organisms living below will eventually be starved of oxygen and nutrients and die, while other species may colonise the lake and shift the flora and fauna of the area, causing a cascade of events that will radiate outwards.
3. Drawing ethical boundaries – intensive rearing of livestock comes with an array of ethical issues. The range includes forced growth using hormones, captivity in crowded conditions, mass murder for meat, mass torture for cutting off the beads of chicks, and enhancing bacterial resistance by the mass use of antibiotics preventively.