Agriculture+as+a+Managed+Ecosystem

//A managed system is where some of the endogenous variables are determined by purposeful human decision making. For example, a farmer makes management.//


 * Sustainable Agriculture**

http://en.wikipedia.org/wiki/Sustainable_agriculture#Farming_and_Natural_Resources
 * Wikipedia**

Sunlight is available everywhere on Earth, which crops need to grow. But they also rely on soil nutrients and the availability of water. When the crops are grown and harvested, some of these nutrients and removed from the soil. Without replenishment, the land suffers from nutrient reduction and becomes either unusable or suffers from reduced yields. Sustainable agriculture depends on replenishing the soil while minimizing the use of non-renewable resources, such as natural gas (used in converting atmospheric nitrogen into synthetic fertilizer), or mineral ores (e.g., phosphate). Possible sources of nitrogen that would, in principle, be available indefinitely, include:
 * 1) crop waste recycling, and livestock or treated human manure.
 * 2) growing legume crops and forages such as peanuts or alfalfa that form collaborations with nitrogen fixing bactera called rhizobia
 * 3) industrial production of nitrogen by the Haber Process (nitrogen fixatoin to produce ammonia) uses hydrogen, which is currently derived from natural gas, (but this hydrogen could instead be made by [|electrolysis] of water using electricity (perhaps from solar cells or windmills)) or
 * 4) genetically engineering (non-legume) crops to form nitrogen-fixing symbioses or fix nitrogen without microbial symbionts.

Crops that require high levels of soil nutrients can be cultivated in a more sustainable manner if certain fertilizer management practices are adhered to.

__ Water __
In some areas, sufficient rainfall is available for crop growth, but many other areas require irrigation (supplying water to dry lands with the help of ditches, etc.). For irrigation systems to be sustainable they require proper management (to avoid salinization (amount of salt in soil)) and must not use more water from their source than is naturally replenished, otherwise the water source becomes, **in effect, a non-renewable resource.** Improvements in water well drilling technology and submersible pumps combined with the development of drip irrigation and low pressure pivots have made it possible to regularly achieve high crop yields where reliance on rainfall alone previously made this level of success unpredictable. However, this progress has come at a price, in that in many areas where this has occurred, such as the Ogallala Aquifer, the water is being used at a greater rate than its rate of recharge.

Several steps should be taken to develop drought-resistant farming systems even in "normal" years, including both policy and management actions: 1) improving water conservation and storage measures 2) providing incentives for selection of drought-tolerant crop species 3) using reduced-volume irrigation systems 4) managing crops to reduce water loss, or 5) not planting at all

__ Soil __ Soil erosion is fast becoming the one of the worlds greatest problems. It is estimated that "more than a thousand million tonnes of southern Africa's soil are eroded every year. Experts predict that crop yields will be halved within thirty to fifty years if erosion continues at present rates." Soil erosion is not unique to Africa but is occurring worldwide. The phenomenon is being called //Peak Soil// as present large scale factory farming techniques are jeopardizing humanity's ability to grow food in the present and in the future. Without efforts to improve soil management practices, the availability of arable soil (land that is fertile and capable of supporting crops for food production) will become increasingly problematic.

Some Soil Management techniques
 * 1) [|No-till farming]
 * 2) [|Keyline design]
 * 3) Growing [|wind breaks] to hold the soil
 * 4) [|Incorporating organic matter] back into fields
 * 5) Stop using [|chemical fertilizers] (which contain salt)

Salt causes the soil to become more acidic. When this happens, the soil can't transfer nutrients from the plants. Salt in the soil makes the plants become nutrient deficient. The soil releases the nutrients into the groundwater, and the nutrients are exported from the ecosystem.