Many attempts have been made to understand the plant response to water using plant growth models. The effects of fertilizer on crop yield are greater than those of water. Therefore, some models that have been developed for the evaluation of water–yield relationships can also be used for fertilizer-yield relationships. | Turkish Journal of Agriculture and Forestry Research Article Turk J Agric For (2014) 38: 732-738 © TÜBİTAK doi: The application for fertilizer–yield relationships of the ET–yield response factor equation Ahmet ERTEK* Department of Irrigation, Faculty of Agriculture, Süleyman Demirel University, Isparta, Turkey Received: Accepted: Published Online: Printed: Abstract: Many attempts have been made to understand the plant response to water using plant growth models. The effects of fertilizer on crop yield are greater than those of water. Therefore, some models that have been developed for the evaluation of water–yield relationships can also be used for fertilizer–yield relationships. The purpose of this study was to develop an equation to use in fertilizer applications similar to one used to evaluate crop production under adequate and deficit water supply regimes. The equation can be rewritten for the fertilizer consumed by plants instead of the evapotranspiration (ET). Sample applications showed that the resulting ET–yield response factor equation can be used successfully in the evaluation of fertilizer–yield relationships. Thus, the yield loss per unit of fertilizer deficiency can be determined more precisely by the equation. Key words: Yield–response factor, fertilization, relative yield decrease, fertilizer uptake 1. Introduction The upper limit of yield is set by soil fertility, climatic conditions, management practices, and genetic potential of the crop. Where all of these are optimal throughout the growing season, yield reaches its maximum value. Any significant decrease in soil water storage has an impact on water availability for a crop and, subsequently, on actual yield and actual evapotranspiration (Moutonnet, 2000). The extent to which this limit can be reached will always depend on how adequately the water supply meets the biological needs of
