From Food Production to Food Security - Global Environmental ...

These advances have resulted from a fortuitous combination of factors including scientificadvances in irrigation practices, fertiliser formulation and application technologies, weedcontrol including herbicides, disease and pathogen control using pesticides, andimprovements in crop phenotype from breeding especially the widespread adoption of semidwarfinggenes in cereals (Evans, 1998). Globally, these advances have increased averageglobal cereal productivity (yield per unit area) from 1.2 Mg ha —1 in 1951 to about 3.4 Mg ha —1currently with projected increases to 4.2 Mg ha —1 by 2020 (Dyson, 1996). This increasedproduction per unit area, coupled with small increases in the area cropped, hascompensated for the decrease in cropped area per caput (Figure 3).However, while crop yields have increased throughout North America, Europe, Australia andAsia, this has not occurred in much of Africa. For example, Sanchez et al. (1997) show thatper capita food production in Africa decreased by about 5–10% between 1980 and 1995,and FAO data analysed by Greenland et al. (1998) demonstrate significant decreases in cropyields in several African countries; the number of countries in Southern Africa classifiedas ‘food surplus’ has actually declined over the last decade (Drimie et al., 2011). The reasons forthe comparatively poor performance of African agriculture are many and complexbut include social instability, poor governance, weathered soils deficient in nutrients, andclimatic variability making reliable irrigation problematic. Greenland et al. (1998) concluded thatin many parts of Africa the yield decreases were a consequence of declining soil fertility—aprocess that could be reversed with inputs of fertilisers if money were available to purchaseinputs. It is noteworthy that globally about 40% of crop production comes from the 25% ofland that is irrigated. Restricted or irregular water supply is a major factor constrainingcrop productivity and this is evident in many data sets. Figure 2, for example, shows yieldsrising more slowly in the Mediterranean countries compared with those in northern Europedue to less favourable agroecological conditions related to less rainfall (but also highertemperatures leading to shortened growing period). Similarly, yields of wheat (grown mainlyin rainfed conditions) in the USA (data given above) have increased more slowly than those ofmaize and rice which are often irrigated.Figure 3 World cereal yield and area harvested per capita. Based on Dyson (1996) and updatedfrom FAOSTAT-Agriculture (2006).26