Brent E. Clothier, HortResearch, Tennent Drive, Palmerston North, 5301, New Zealand
Soil is the fragile yet productive skin of our planet. Soil occupies a critical position between the atmosphere and the subterranean realm, and lies astride the main thoroughfare along which water and solutes enter our ground and surface water reservoirs. Our soil is the first filter of the world's water. Water and chemical fluxes though the heterogeneous porous medium of the unsaturated soil, in the active presence of plant roots, are necessary for the healthy functioning of soil as the productive base for sustainable agriculture. As well, these fluxes are critical determinants of the quantity and quality of our underground and surface reserves of water. Our understanding of transport and fate processes in the soil of the rootzone has been enhanced thanks to two developments. New measurement devices and monitoring techniques are providing better observations, at the local scale, of the state and fluxes of water and solute into, and through, soil. Here I outline some of the new observations that are improving the acuity of our vision of rootzone processes. In tandem, better theoretical understanding and new modeling techniques are being developed to extend and extrapolate these still-meagre observations to realise improved understanding at larger spatial and temporal scales. In tandem, measurement and modeling are providing scientists with new knowledge about the functioning of soil as a filter. Policy agencies are then in possession of enhanced understanding with which they can develop protocols, both monitoring and regulatory, to manage strategically our landscapes so that primary production is sustained, and our receiving waters protected. Water is now known as ‘blue gold'. ‘Blue gold' will be this century's most urgent environmental issue. We need to use our scientific understanding of the functioning world's largest water filter – our soil – to protect the quantity and quality of our resources of ‘blue gold'.