Halfway through the 20thcentury, a curious shift took place in theconcept and definition of the agronomic term“crop water requirements.” Where these cropneeds were originally seen as the amount ofwater required for obtaining a certain yieldlevel, in the second half of the 20thcentury, the term came to mean the water neededto reach the potential or maximum yield in acertain season and locality. Some of themultiple academic, economic, social, andgeopolitical aspects of this conceptual shiftare addressed here. The crucial role of theproduction ecologist (...) Cees de Wit in formulatingthis paradigmatic shift in the 1950s isdiscussed. It is seen how the incipient concernfor an expected global scarcity of waterresources has contributed to a trend back tothe conservative view of crop water control ofde Wit. The development over the years ofengineering and agricultural science conceptsconcerning irrigation and crop water control ispresented as an evolution from practicalhusbandry to specialized applied science;from an empirical, ecological approach to amainly physical/mathematical discipline. Inthe section ``The scientific heritage of Occamand Bacon,'' it is argued that this developmentregarding irrigation is part of a general trendin agricultural (and other) sciences andtechnologies over the last 150 years, althoughtendencies to return to a more holisticapproach have, at times, occurred. The current mainstream concepts and methodsin the art and science of crop water control,far from being objective and value-free, oftenact as ``a siren song'' for decision-makersresponsible for daily irrigation practice andregional or global water resource management.The seductive ``tune'' of maximum yields,concurrently the highest crop water use, drownsout the more modest aim of making anefficient use of the available waterresources. The latter's allure might,however, become the morecompelling as a greater scarcity ofphysical water resources becomes moreimportant than scarcity of land and labor. (shrink)