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May / June 2003

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Founder : Len Abrams
Water Policy International

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Food Security

Content

Human Nutrition
Plant Nutrition

 

Human Nutrition

Food security is commonly defined as sustained access for all individuals to an adequate and safe supply of food for an active, healthy and productive life. Depending on how food security is measured as many as one in three children and one in six adults are malnourished. The WHO estimates that half of the 10.4 million child deaths which occurred in 1995 in developing countries were due to malnutrition. Roughly 80 percent of these deaths were due to mild or moderate forms of malnutrition. This is because many mildly malnourished people have serious deficits of micronutrients, such as iodine, vitamin A, iron and zinc. The most vulnerable groups likely to suffer from malnutrition are children and women, but men may also be affected and suffer from decreased work capacity.   Source: Esrey et al, 2001

As ecological sanitation not only seeks to sanitise faeces, but also to provide nutrients for plants and thus food, it is a very powerful method of improving the overall health of people (see figure alongside).

 

There are three basic approaches to correcting nutritional deficiencies and malnutrition:

1. Food supplementation - the provision of nutrients in some form, e.g. vitamin A capsules.
2. Control of public health diseases which lead to specific nutritional problems, e.g. through deworming or improved sanitation.
3. Food-based approaches, which seek to promote dietary diversity in the foods locally available to people.

Ecological sanitation can play a major role in both of the last two points. By closing nutrient loops and improving soil fertility and structure, yield will be higher per unit space, plants will be healthier and more nutritious and lower levels of external inputs and less water will be required. Growing food closer to consumers also strengthens local communities. Even in urban areas sole reliance on food produced in the rural areas will not achieve food security amongst the poor. It is necessary for cities and communities to practise urban and peri-urban food production. This is especially important for poorer households as they spend over 60 percent of their disposable income on food. Urban food production can also be a generator of income as people begin to sell surplus produce. For instance, in La Paz, Bolivia, urban food production supplies women producers with 25 percent of their income.

In Kampala, Uganda, a study was conducted which investigated levels of malnutrition amongst children from families who practised urban agriculture and compared them to levels of malnutrition of children from families who did not farm. Several crops were grown, cassava, plantains, potatoes, cocoyams and maize being the most popular. Urban agriculture was found to have a positive and significant association with the height of children. There was a difference of nearly 1.5 cm between farming and non-farming children. Eighty percent of those who farmed were women, and it was found that mothers of farming families spent an average of two to four hours more time in child care per week did than non-farming mothers.


 

Plant Nutrition

All plants require oxygen, carbon and hydrogen to grow. These they receive from air, sunlight and water. But to promote optimum growth plants also need a variety of elements in the soil. The major ones are:

  • nitrogen
  • phosphorous
  • potassium
  • magnesium
  • calcium
  • sulphur

A variety of trace elements are also required:

  • iron
  • zinc
  • copper
  • manganese
  • boron
  • molybdenum

Ninety-six percent of what plants need for healthy growth is provided by oxygen (45%), carbon (45%) and hydrogen (6%). Although elements are required in smaller amounts, such as nitrogen (1.5%), phosphorous (0.15%), potassium (0.15%) and others (0.2%), they are equally important. In general, green, leafy, non-legumous vegetables need more nitrogen than other types of plants. Flowering and fruiting vegetables need more phosphorous, and root vegetables need more potassium. Each of these nutrients performs complementary functions and an imbalance in nutrients may lead to an increase in the incidence of pests.

Nitrogen is needed for leaf and stem growth, and also affects a plant's ability to access other nutrients. Nitrogen is also important from the point of view of nutrition as it increases the protein content of some foods and feed crops. Phosphorous helps make plants more drought resistant and hardy. It also hastens maturity, helps seed and fruit formation and stimulates root growth. Potassium increases resistance of plants to disease, creates winter hardiness and drought resistance and produces strong stalks and stems to reduce water logging.

Element (g/person/day)
Urine
Faeces
Nitrogen
11.0
1.5
Phosphorous
1.0
0.5
Potassium
2.5
1.0
Organic carbon
6.6
21.4
Wet weight
1 200
70 - 140
Dry weight
60
35

 

The table alongside attempts to give the quantities of various nutrients excreted per person per day. This will obviously vary according to diet, sex of person and lifestyle, but the proportion of nutrients and water excreted remains roughly the same regardless of total output. As can be seen, about eighty percent of total nitrogen and potassium is excreted in the urine as is two-thirds of the phosphorous. These are the three major components of commercial fertiliser. In total a human being annually produces enough nutrients to grow that persons annual food requirements.

Once faeces have been converted into compost it can be used to improve the general quality of the soil. It keeps particles of air in the soil as well as trapping moisture. Fifty kg of silt holds about 12 litres of water, while 50 kg of compost holds 100 litres of water, resulting in overall reduced water use by the plants in the soil as the runoff is lower. Compost also assists with the regulating of soil temperatures, preventing excessive heating up or cooling down.

Thus, a an ecological sanitation system can assist both urbanites and rural people in improving food security and nutritional status. The by products from excreta can increase yield, reduce fertiliser costs and conserve water and soil.

 

   

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