On environmental issues, I think there are three possible issues. The first is how the tractor is used - i.e. is it being used in a way that protects and enhances the natural environment (eco-forestry, organic farming) or in a way that damages it (e.g. clear felling). This is related to the tractor market only indirectly because even with other machines (or none at all), the same farm practices, good or bad, could well be carried out. Arguably though, with a tractor well intended butchers, bakers and candlestickmakers can do more damage inadvertently than their use of traditional gardening machinery permitted. So I guess that the growth in tractor use increases the potential for its environmental misuse.
Second issue is how the construction of the machine impacts on the environment. A simple example of this is how the growth in imported machines increases consumption of fuel used to transport them and so is causing increased depletion of a non-renewable resource and also increased pollution. Making them at home is definitely more environmentally friendly from this point of view. In addition, third world countries are unlikely to have the same degree of legislation to protect the natural environment and so might cause more pollution, resource depletion, etc. than would be the case were the tractors built at home.
Third issue is the use of fuels. My Kubota is incredibly fuel efficient but I was a little disappointed that Kubota didn't extend their warranty automatically to cover use of licensed biodiesel. When I asked the question, they said that damage that could be specifically identified as being caused by biodiesel would not be covered by the warranty. Nonetheless, biodiesel use is increasing in proportion to its availability and cost although here, in Saltspring, it's still more expensive than the other stuff.