In order to better make use of pan evaporation for guiding crop irrigation,a simple,cheap and easy for use evaporation pan with a device of water automatic replenishing was designed based on the working principle of the Markov′s bottle.In fact,such a pan was an updated version of the 20 cm standard evaporating pan by attaching a device that can replenish water automatically,so that water keeps a constant level in the updated pan.According to the standard evaporation in the 20 cm standard evaporation pan,the water evaporation process in the designed pan was verified.The relationship between the water evaporation and water consumption by winter wheat during the same growing period was established by field experiment.The results showed that the designed pan has a good stability,the average relative error between two different measurement groups was less than 5%,and the average relative error in more than 5 day was less than 2%.In addition,there was such a significant correlation between the water surface evaporation of the designed pan and 20 cm standard evaporation pan that the correlation coefficient was as high as 0.99.In North China,the ratios of the water consumption by winter wheat over that accumulated water evaporation of the designed pan device were 1.09,1.31 and 1.16 at jointing,headingflowering and grainfilling maturity stage,respectively.Therefore,the water evaporation of the designed pan device can guide farmland irrigation to realize excellent quality,high efficient and high yield of crop.
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