| Penman-Monteith formulae recommended by the FAO of the united nation were adopted to calculate the daily water requirements of the major crops (spring wheat, winter wheat, maize and potato) so as to statistically analyze their temporal and spatial changes and thus set up their patterns in different crops. The research showed that the water requirements rose with increased latitude and the higher water requirements matched with the arid and semi-arid regions of Gansu province; the water requirements had tended to decrease in the last forty years and the tendency appeared more strongly in the western part of Gansu corridor than the eastern part of the corridor. the analysis of the water daily requirements of several crops indicated that the crop water requirements increased from seedling emerging to flowering, peaked between flowering and milky maturity with the crops growing luxuriantly, and declined quickly after milky maturity. |