While we now know that a spectrum of genetically controlled adaptations to soils low in available micronutrients exists in the germplasm of our major staple crops, these appear insufficient for the high yields demanded of agriculture. Thus, we have a demand for both macronutrient and micronutrient fertilisers that is growing and that must be supplied with increased efficiency via ever improving technologies. Once the macronutrient deficiencies of soils are treated, Sillanpää (1990) estimated that of the important agricultural soils of the world, 49% are deficient in zinc (Zn), 31% deficient in boron (B), 15% deficient in molybdenum (Mo), 14% deficient in copper (Cu), 10% deficient in manganese (Mn) and 3% deficient in iron (Fe). These figures may be compared with corresponding figures for the human population that depends on these same soils. In the same broad terms, it appears that more than half the human population is deficient in Fe, at least half is deficient in Zn, 25% in iodine (I) and 20% in selenium (Se). Selenium and I are not known to be required by plants and the extent of B deficiency in soils does not lead to the same high priority in human nutrition as it does for crop growth. It appears that there is more than enough Fe in food, but its bioavailability is poor. Of the micronutrients, only Zn is directly linked in the food chain such that deficiency is extensive in both humans and their food crops. Zinc deficiency is therefore the highest priority among micronutrients for agriculture to address. An agricultural solution to Zn deficiency in humans is all the more compelling because mild to moderate Zn deficiency in humans is very difficult to diagnose, so the blanket approach, justified by production gains derived through greater tolerance to a broad spectrum of stresses on the crop itself, is the surest and safest way to proceed, and is likely to yield important advances in human welfare globally.
In ‘Micronutrient Deficiencies in Global Crop Production.’ B. J. Alloway (editor). ISBN 978-1-4020-6859-1 (Print) 978-1-4020-6860-7 (Online). Chapter 2, pp. 41-61 [doi: 10.1007/978-1-4020-6860-7_2]