Soils and Food Security: Challenges and Opportunities

PETER J. GREGORY

East Malling Research, New Road, East Malling, Kent, ME19 6BJ, UK, and Centre for Food Security, School of Agriculture, Policy and Development, University of Reading, Reading, RG6 6AR, UK

E-mail: peter.gregory@emr.ac.uk

ABSTRACT

Soils most obviously contribute to food security in their essential role in crop and fodder production, so affecting the local availability of particular foods. They also have a direct influence on the ability to distribute food, the nutritional value of some foods and, in some societies, the access to certain foods through local processes of allocation and preferences. The inherent fertility of some soils is greater than that of others, so that crop yields vary greatly under semi-natural conditions. Husbandry practices, including the use of manures and fertilisers, have evolved to improve biological, chemical and physical components of soil fertility and thereby increase crop production.

The challenge for the future is to sustain soil fertility in ways that increase the yield per unit area while simultaneously avoiding other detrimental environmental consequences. This will require increased effort to develop practices that use inputs such as nutrients, water and energy more efficiently. Opportunities to achieve this include adopting more effective ways to apply water and nutrients, adopting tillage practices that promote water infiltration and increase of organic matter, and breeding to improve the effectiveness of root systems in utilising soil-based resources.

1 The Role of Soils in Food Security

There are many definitions of food security, but one that is most commonly employed is that food security is the state when "all people, at all times, have physical and economic access to sufficient, safe, and nutritious food to meet their dietary needs and food preferences for an active and healthy life". Food security is, then, a social construct in which availability, accessibility and utilisation all contribute to its achievement (Figure 1). Food security is underpinned by effective food systems, which constitute a set of dynamic interactions between and within biogeophysical and human environments. Food systems comprise a number of activities (producing food; processing, packaging and distributing food; and retailing and consuming food) that lead to a number of associated outcomes, some of which contribute to food security (i.e. food availability, access to food and food utilisation), and others which relate to environmental and other social welfare concerns. Because food security is diminished when food systems are disrupted or stressed, food security policy must address the whole food system.

Soils most obviously contribute to food security in their essential role in crop and fodder production, thereby markedly influencing the availability of food. The inherent properties of different soils have marked effects on crop productivity (see, for example, the writings of Cato and Pliny the Elder) and, while interventions to improve fertility can over-ride these properties, some soils are inherently more fertile and productive than others. However, soils also have a direct influence on the ability to distribute food, the nutritional value of some foods and, in some societies, the access to certain foods through local processes of allocation and preferences. An obvious, if slightly extreme, example of the influence of soils on the ability to distribute food is seen in the behaviour of soils containing large amounts of swelling and shrinking clays (vertisols). These soils are frequently inherently fertile but are often very wet or waterlogged in one season making it impossible to harvest crops or to move easily across their surface, while in the dry season the shrinking of the soil induces large cracks so that engineered structures such as houses and irrigation ditches fail. The combination of shrinkage in the dry season followed by considerable swelling in the wet season means that roads are also difficult to sustain and the distribution of food can be affected.

The nutritional value of many foods is markedly influenced by the soils on which they are grown, although processed foods are often supplemented with essential minerals and vitamins to make good any deficiencies. Crop production depends on the availability of sufficient quantities of the 14 essential mineral elements required for plant growth and reproduction. These essential nutrients include the macronutrients required in large amounts by plants (nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg) and sulfur (S)) and the micronutrients (boron (B), chlorine (Cl), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), nickel (Ni), and zinc (Zn)) which are required in smaller amounts. Deficiency in any one of these elements restricts plant growth and reduces crop yields, so that they are often applied to crops as inorganic or organic fertilisers to increase crop production. Humans require many more mineral elements for their wellbeing than plants. In addition to the 14 elements essential for plants, humans also require significant amounts of cobalt (Co), iodine (I), selenium (Se) and sodium (Na) in their diet and, possibly, small amounts of arsenic (As), chromium (Cr), fluorine (F), lead (Pb), lithium (Li), silicon (Si) and vanadium (V). The majority of these mineral elements are supplied to humans by plants.

Unfortunately, the diets of over two-thirds of the world's population lack one or more of these essential mineral elements, with over 60% being Fe-deficient, over 30% Zn-deficient, almost 30% I-deficient, and about 15% Se-deficient. Dietary deficiencies of Ca, Cu and Mg are also prevalent in many countries. This mineral malnutrition is attributable to either crop production on soils with low phytoavailability of the mineral elements essential to human nutrition, or consumption of staple crops, such as cereals, or phloem-fed tissues, such as fruit, seeds and tubers, that have inherently low tissue concentrations of certain mineral elements,...