Soil fertility
Soil fertility refers to the ability of soil to sustain agricultural plant growth, i.e. to provide plant habitat and result in sustained and consistent yields of high quality.[3] It also refers to the soil's ability to supply plant/crop nutrients in the right quantities and qualities over a sustained period of time. A fertile soil has the following properties:[4]
The following properties contribute to soil fertility in most situations:
In lands used for agriculture and other human activities, maintenance of soil fertility typically requires the use of soil conservation practices. This is because soil erosion and other forms of soil degradation generally result in a decline in quality with respect to one or more of the aspects indicated above.
Soil fertility and quality of land have been impacted by the effects of colonialism and slavery both in the U.S. and globally. The introduction of harmful land practices such as intensive and non-prescribed burnings and deforestation by colonists create long-lasting negative results to the environment. The institution of slavery reproduced distress to the natural world and crop production.
Soil fertility and depletion have different origins and consequences in various parts of the world. The intentional creation of dark earth in the Amazon promotes the important relationship between indigenous communities and their land. In African and Middle Eastern regions, humans and the environment are also altered due to soil depletion.
Light and CO2 limitations[edit]
Photosynthesis is the process whereby plants use light energy to drive chemical reactions which convert CO2 into sugars. As such, all plants require access to both light and carbon dioxide to produce energy, grow and reproduce.
While typically limited by nitrogen, phosphorus and potassium, low levels of carbon dioxide can also act as a limiting factor on plant growth. Peer-reviewed and published scientific studies have shown that increasing CO2 is highly effective at promoting plant growth up to levels over 300 ppm. Further increases in CO2 can, to a very small degree, continue to increase net photosynthetic output.[14]
Humans and Soil[edit]
Human Health[edit]
Albert Howard is credited as the first Westerner to publish Native techniques of sustainable agriculture. As noted by Howard in 1944, “In all future studies of disease we must, therefore, always begin with the soil. This must be gotten into good condition first of all and then the reaction of the soil, the plant, animal, and man observed. Many diseases will then automatically disappear...Soil fertility is the basis of the public health system of the future...”. Howard connects the health crises of crops to the impacts of livestock and human health, ultimately spreading the message that humans must respect and restore the soil for the benefit of the human and non-human world. He continues that industrial agriculture disrupts the delicate balance of nature and irrevocably robs the soil of its fertility.[28]
Soil has been known to have positive mental health effects as well. The exposure to microbiomes in quality soil aids human depression. Specifically, a study by scientist Christopher Lowry treated mice with the bacteria, Mycobacterium vaccae, which is found in the soil on the shores of Lake Kyoga in Uganda. Lowry has studied this bacteria’s impact on the brain since 2001. The brains of these mice produced more serotonin, known as the mood-regulating hormone, and increased levels are known to help with depression.[29]
Reconnecting Communities with the Soil[edit]
Many community organizations work to reconnect humans with the soil, bring people together based on a shared passion, and strengthen autonomy and power for individuals. For example, one community-based organization in Portland, Oregon, Black Futures Farm, strives to rebuild the relationship between humans and the soil. Community programs and outreach coordinator for Black Futures Farm, Nia Harris, describes the goal to be “to heal the connection between Black people and the land…We achieve this by cultivating a healthy place for the Black community to gather in joy…In a state where we’re so beaten down by so many factors that have to do with identity and politics and just pure hatred and greed, to have a space that’s literally a sanctuary for so many people — not just those of us who work here, but our community — that’s what makes it so special”. The farm has programming for people to engage in healing, meditative, and artistic wellness practices. All of the produce grown on the farm is distributed to Black individuals who do not have healthy food readily accessible to them. The Black Food Sovereignty Coalition which the Black Futures Farm is part of, has a similar mission to create events and spaces in which Black and brown communities are liberated through community-building practices and food sovereignty. According to the co-founders Malcolm Hoover and Mirabai Collins, farming is an act of resistance against the disconnection between Black people and the land.[30]
Irrigation effects[edit]
Irrigation is a process by which crops are watered by man-made means, such as bringing in water from pipes, canals, or sprinklers. Irrigation is used when the natural rainfall patterns of a region are not sustainable enough to maintain crops. Ancient civilizations heavily relied on irrigation and today about 18% of the world's cropland is irrigated, mainly in Asia, Africa, and South America.[31] The quality of irrigation water is very important to maintain soil fertility and tilth, and for using more soil depth by the plants.[32] When soil is irrigated with high alkaline water, unwanted sodium salts build up in the soil which would make soil draining capacity very poor. So plant roots can not penetrate deep into the soil for optimum growth in Alkali soils. When soil is irrigated with low pH / acidic water, the useful salts (Ca, Mg, K, P, S, etc.) are removed by draining water from the acidic soil and in addition unwanted aluminium and manganese salts to the plants are dissolved from the soil impeding plant growth.[33] When soil is irrigated with high salinity water or sufficient water is not draining out from the irrigated soil, the soil would convert into saline soil or lose its fertility. Saline water enhance the turgor pressure or osmotic pressure requirement which impedes the off take of water and nutrients by the plant roots.
Top soil loss takes place in alkali soils due to erosion by rain water surface flows or drainage as they form colloids (fine mud) in contact with water. Plants absorb water-soluble inorganic salts only from the soil for their growth. Soil as such does not lose fertility just by growing crops but it lose its fertility due to accumulation of unwanted and depletion of wanted inorganic salts from the soil by improper irrigation and acid rain water (quantity and quality of water). The fertility of many soils which are not suitable for plant growth can be enhanced many times gradually by providing adequate irrigation water of suitable quality and good drainage from the soil.