Yield response to water [antikvár]

PREFACE Water is essential for crop production and best use of available water must be made for efficient crop production and high yields. This requires a proper understanding of the effect of water - rainfall and/or irrigation - on crop growth and yield under different growing conditions. A great deal has been published on aspects of water relations in crop growth and attempts to understand crop response to water through crop growth modelling have met with success. However, for practical application, a method is required to measure yield response to water supply, which should be simple, require commonly available climatic, water, soil and crop data, be widely applicable with acceptable accuracy and allow easy verification through adaptive research. With this in mind, the Land and Water Development Division of FAO initiated a study to establish generalized crop yield and water use relationships of twenty-six important irrigated crops. An impressive amount of related research information was generously made available by scientists contacted in the course of the study (Appendix IV) and was further obtained by a review of literature (Appendix 111). Valuable support was also received from the International Institute for Land Reclamation and Improvement (ILRl), Wageningen, The Netherlands, in formulating the presented approach and through their collection and analysis of data and testing of various water/crop yield models. The results of the work Ijy ILRI are herein further simplified and expanded in an effort to present results in an easy-to-use form. This publication presents a methodology to quantify yield response to water through aggregate components which form the 'handles' to assess crop yields under both adequate and limited water supply. The method is presented in Part A and takes into account maximum and actual crop yields as influenced by water deficits using yield response functions relating relative yield decrease and relative évapotranspiration deficits. Part B gives an account of water-related crop yield and quality information for twenty-six crops. Application of the method provides the user with: guidance in selection of irrigated crops under different growing conditions ; assessment of crop yield under different water supply regimes; criteria, in terms of crop production, on which to base priorities for allocation of limited water to crops both between and within projects ; - directives for field water management for optimum crop production and water efficiency. The publication lays down some of the important principles involved in water management in relation to crop production. However, improvement for site-specific conditions will be needed with respect to the accuracy offered by the methodology and verification through adaptive research is required. It should be pointed out that : THE UPPER LIMIT OF CROP PRODUCTION IS SET BY THE CLIMATIC CONDITIONS AND THE GENETIC POTENTIAL OF THE CROP. THE EXTENT TO WHICH THIS LIMIT CAN BE REACHED WILL ALWAYS DEPEND ON HOW FINELY THE ENGINEERING ASPECTS OF WATER SUPPLY ARE IN TUNE WITH THE BIOLOGICAL NEEDS FOR WATER IN CROP PRODUCTION. THEREFORE, EFFICIENT USE OF WATER IN CROP PRODUCTION CAN ONLY BE ATTAINED WHEN THE PLANNING, DESIGN AND OPERATION OF THE WATER SUPPLY AND DISTRIBUTION SYSTEM IS GEARED TOWARD MEETING IN QUANTITY AND TIME, INCLUDING THE PERIODS OF WATER SHORTAGES, Y1E\ WATER NEEDS REQUIRED FOR OPTIMUM GROWTH AISD HIGH