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Improving soils for human nutrition

Soils are key for human nutrition (c) James Hutton Institute
"It is hoped that, one day, soil improvements will help eliminate mineral malnutrition of humans both at home and abroad.

Professor Philip J. White, Ecological Sciences, James Hutton Institute

Minerals are the inorganic elements required by a healthy body. Humans need sufficient quantities of about two dozen mineral elements for their wellbeing. They obtain these largely from the foods they eat. Regrettably, it is thought that the diets of up to two-thirds of the world’s population lack one more essential mineral. In many instances, this is because the crops they eat do not acquire enough minerals from the soil. Researchers are addressing this issue by surveying the availability of mineral elements in soils, supplying crops with appropriate fertilisers, and breeding crops with greater ability to acquire and accumulate mineral elements in their edible portions.

The mineral elements most commonly lacking in human diets include iron, zinc, calcium, magnesium, iodine and selenium. Inadequate intakes of any one of these can lead to serious nutritional diseases, such as anaemia (iron deficiency), rickets (calcium deficiency) and goitre (iodine or selenium deficiency). Even marginal deficiencies can lead to a “hidden hunger”, which has no visible symptoms yet can ultimately cause abnormal development, mental impairment, and poor health. The occurrence of mineral deficiencies in humans can be diagnosed with appropriate medical screening and prevented through dietary diversification (eating a balanced diet), food fortification programmes, or the provision of mineral supplements. In the UK, for example, iron and calcium are routinely added to all wheat flour, iodine is supplied as iodinated salt, and many processed foods and drinks are fortified with a variety of mineral elements, particularly iron and zinc. Mineral supplements are readily available.

Plants also require many of the mineral elements needed by humans. Their roots obtain these from the soil. Plants require iron, zinc, calcium and magnesium, but not iodine or selenium. The properties of the soil affect the ability of roots to acquire mineral elements and, therefore, the mineral nutrition of the plant, crop yields, and the nutritional quality of edible produce. Many of the soils of the world lack sufficient nitrogen, potassium and phosphorus (NPK) to support the demands of a rapidly growing crop, and these elements are commonly added as soil fertilisers to increase crop production. Similarly, many soils lack sufficient available iron and zinc for maximal crop production, despite there being large amounts of these elements in most agricultural soils. Since zinc and iron deficiencies in humans occur predominantly in regions where crop production is limited by the availability of these elements in soils, fertilisers containing these elements are used not only to increase crop production but also to improve human nutrition. Deficiency diseases caused by inadequate intakes of iodine or selenium in human diets, such as goitre, also occur where crops are grown on soils that lack these elements. However, since these elements are not required to achieve maximal crop yields, they are applied as fertilisers solely to improve human and animal nutrition. Plants can take up iodine and selenium because they are chemically similar to the essential elements chlorine and sulphur.

The “biofortification” of edible crops is an agricultural strategy to increase the delivery of essential minerals to people susceptible to mineral deficiencies. It is particularly effective in regions where resources or infrastructures are not available for traditional interventions. It combines agronomic techniques that increase the availability of mineral elements to plants, such as soil husbandry and precision fertiliser applications, with the development of new crop varieties that acquire minerals better from the soil and accumulate more minerals in their edible tissues.

The simplest way to increase concentrations of minerals in produce growing on soils with low availability of mineral elements is to apply them in fertilisers, either to the soil or to the leaves. This strategy has improved the health of people in various countries. For example, incorporating selenium into mineral fertilisers successfully raised the selenium status of people in Finland, adding zinc to NPK fertilisers used in cereal production successfully improved the zinc status of people living in Anatolia, and the iodination of irrigation water successfully raised the iodine status of rural Chinese populations. Similar experiences have been reported in other regions of the world.

These agronomic practices can be combined with crop varieties bred for greater potential for biofortification. This breeding effort is led by the international HarvestPlus Programme, which has developed many new bean and cereal varieties that accumulate greater concentrations of zinc and iron in their seeds. These seeds provide better mineral nutrition and are being widely promoted for a healthier future. At home, the Scottish Government funds work to increase the concentrations of essential mineral elements in Scottish crops. This work focuses on biofortifying our staple crops, wheat and potatoes, and common vegetables, such as brassicas, with mineral elements essential for human nutrition. It is hoped that, one day, this work will help eliminate mineral malnutrition of humans both at home and abroad.

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The James Hutton Research Institute is the result of the merger in April 2011 of MLURI and SCRI. This merger formed a new powerhouse for research into food, land use, and climate change.