Keywords: Rhizosphere, water stress, root growth, proton pumping, root secretions, nutrient uptake.

Summary:
This paper addresses the importance of using fertilizers in a sustainable, non-polluting manner while maintaining crop yields. Several approaches which may help achieve this goal are considered. The first approach is to improve the efficiency of fertilizer nutrient uptake and metabolism by plant roots. Such improvements will be dependent on plant genetics and the soil environment. Breeding and genetic engineering can be used to increase plant capacity to take up and metabolise soil-nutrients. Another approach is to understand and, where possible, try to reduce environmental changes which limit nutrient uptake by plants. Chemical, physical and biological interactions which occur naturally between plant roots and the surrounding soil are reviewed, together with potentially adverse effects of environmental stresses, particularly water stress. A recently discovered inhibitory effect of water stress on rhizosphere acidification by plant roots and its association with root growth and nutrient uptake capacity is described. Two suggestions are made for managing the adverse effects of water stress on root growth and nutrient uptake:
1. The provision of supplementary irrigation.
2. Development of plants with increased capacity to maintain proton pumping and root growth under water stress.

Peter M Neumann, Department of Environmental, Water and Agricultural Engineering, Faculty of Civil and Environmental Engineering, Technion Israel Institute of Technology, Haifa 32000, Israel.

16 pages, 5 figures, 2 tables, 26 references.