Technological change and the economics of agricultural support have encouraged the concentration of production, which in turn has driven increases in farm size. In order to achieve economies of scale, farmers have tended to concentrate their land, labour and capital resources on the production of a smaller range of commodities. Technological changes in dairy farming have been closely related to processes of specialization and the concentration of production. Modern housing systems and milking parlours also use greater volumes of water for cleaning. The advantages for dairy farmers in making silage are twofold: it is less vulnerable to unpredictable weather conditions than is hay-making; and it can also be cut earlier, making several cuts possible in the season. The nature of the pollution problem from dairy farming means that, for the farmer, the problem is not so much one of causing pollution as being detected of doing so.