When economic growth is characterised by a slow rise in the demand for food and rapid growth in farm relative to non-farm productivity, it is understandable that agriculture in a closed economy declines in relative terms as that economy develops. But why should agriculture decline in virtually all open growing economies as well, including those able to retain a comparative advantage in agricultural products? A key part of the answer is that the demand for non-tradable goods . tends to be inc.o me elastic, so resources are diverted to their production even m open economies.