Int Plant Nut Man - Chap 20

Nutrients are transported all over the world through fertilizer imports, exports of agricultural commodities, massive erosion in some places and gross volatilization and leaching in high-input/high-output agricultural systems. In other words, more or less balanced natural ecosystems have turned into highly unbalanced agricultural systems. Figure 20.1 shows the inputs and outputs that make up the nutrient balance of a farming system. In many managed ecosystems, the sum of inputs minus the sum of outputs is far from zero, putting the sustainability of such systems at risk. The figure at the same time shows that only IN 1 and 2, and OUT 1 and 2 are normally valued in economic terms. The other INs and OUTs certainly have an economic value, but this is less apparent to mainstream economists. In general terms, one can say that large parts of the ‘developed’ world have a large surplus of inputs (Oenema et al., 1998; Goh and Williams, 1999). Availability of cheap fertilizers (IN 1) stimulated their liberal use, and contributed to substantial crop yield increases. Moreover, import of cheap animal feeds from developing countries (IN