What do we mean by sustainable agriculture? In its simplest form a sustainable system is one where output is equal to input, the system is in balance, and can continue in this manner indefinitely. In agriculture this means that you need to put back into the land what you take out, without any detrimental effect to the rest of the planet, so that the land can continue to be productive without causing any unwanted side effects.
Nutrients that are taken out of the soil by crops need to be replaced, and to do this sustainably the nutrients need to be from a source that does not deplete any other system, so chemical fertilisers that are produced at a cost to the atmosphere or waterways are not considered sustainable. Soil can be fertilised sustainably with animal manure, when the animals have been fed on sustainably grown crops, and with green manures such as clover or other leguminous crops which can be dug back into the soil.
These principles are utilised in organic farming and permaculture, and have been used throughout the history of humankind by generations of farmers. It is only in the last century or so, due to population growth and industrialisation that things have change to more intensive and potentially detrimental farming methods.
Land use is a major issue of sustainability. With an ever increasing world population, the pressure is on to produce more and more food, and large areas of previously undeveloped land is cleared for farming. This situation is not sustainable, for several reasons. Firstly land is not finite, so growth cannot continue unchecked. Destroying the rain-forests is reducing the Earth’s ability to produce atmospheric oxygen and absorb carbon-dioxide. Another reason is that the felling of large areas of trees causes soil erosion, and the rich topsoil that has accumulated on the forest floor can be washed away by rain or floods in a relatively short period of time, making the ground nearly useless for crops.
Intensive use of land for crops also strips the soil of nutrients, increasing the need for more and more artificial fertilisers. The trouble with these are that they leach out of the soil and into the waterways. leading to eutrophication (or over-nutrification) of rivers, increasing algal growth that reduces the oxygen content of the water, and kills the fish in the rivers. Use of pesticides also needs to be considered, long term use can result in not just the harmful pests being destroyed, but also useful bacteria, soil organisms and whole swathes of other insect life, that form an integral part of the food chain, having the knock-on effect of reducing the biodiversity of the local ecosystem.
Sustainable farming should mean respecting the environment, maximising the productivity of the land, and ensuring the future of farming.