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CONTRIBUTIONS OF CHEMISTRY TO REMOVING SOILCONSTRAINTS TO CROP PRODUCTIONR. Scott Russell(formerly Director, Letcombe Laboratory)East Hanney, Wantage, Oxfordshire, OX12 0HQ, EnglandandG.W. CookeRothamsted Experimental StationHarpenden, Hertfordshire, AL5 2JQ, EnglandABSTRACTChemistry provided the background for the scientific control of soilfertility by providing fertilizers and other agrochemicals. It is closelyinvolved also in multidisciplinary studies of the soil—plant system which havecreated our understanding of how the growth and function of root systems isregulated. New opportunities have thus been provided for identifying constraintsto crop production and for devising methods to overcome them. Fertilizers make itpossible to remove all nutrient constraints, but information is needed on theirinteraction with other production factors, such as the supply of available water,before recommendations for applying them can have a sound scientific basis.Fertilizers are rarely used with the maximum efficiency and more research isneeded to specify fertilizers to meet local needs in developing countries, toprovide nitrogen fertilizers by methods which consume less energy, and to determinethe amounts and methods of application which fit local conditions of soil,climate and cropping system. Considerable increases in crop yields should bepossible with adequate research, development and advisory services.KEYWORDS: Crop yields, Cultivation, Fertilizers, Nitrogen, Plant nutrients,Rhizosphere, Roots, Soil, Yield gap.INTRODUCTIONThe major part of the food which man eats has its origin in plants which growin the soil. Thus, the topic of this paper is basic to any discussion of worldfood supplies, especially when emphasis is given to the contribution of chemistry.This began with the identification of the elements which are essential plantnutrients and was followed by the development of industrial chemical processes toprovide additional supplies of them as fertilizers, as well as other agrochemicalswhich benefit crop production. These pioneer contributions of chemistspaved the way for modern studies of the plant/soil system, which requires inputsalso from plant physiologists and pathologists, microbiologists and physicists.This interdisciplinary approach has in the past 30 years, much increased ourunderstanding of the basic principles which govern crop growth in the soil,and enlarged the opportunities to manage crops and use inputs, includingfertilizers, more efficiently and economically. Some of the backgroundinformation is reviewed in the first part of this paper, attention being given1