冬小麦拔节抽穗期作物系数的研究

在2000～2004年4个冬小麦生长季节研究了冬小麦拔节抽穗期农田蒸散量和参考作物腾发量（FAO56 PM方法计算）的关系，以及作物系数和叶面积指数及作物株高的关系。研究发现在冬小麦拔节抽穗前期，参考作物腾发量要大于或者接近于农田蒸散量，而在后期则要明显小于农田蒸散量。作物系数随着叶面积指数的增加和株高的增加而增加。用2003和2004年的数据回归建立了叶面积指数和株高与作物系数的数学表达式，并计算了2001和2002年的农田蒸散量。结果显示用叶面积和株高两种方法都能够很好的估算农田蒸散量。但是当农田蒸散量小于3 mm/d时，计算值要小于观测值。用叶面积指数和株高两种方法计算的农田蒸散量没有明显差别，说明用株高计算农田蒸散量是可行的。

Calculation of crop coefficient of winter wheat at elongation-heading stages

An experiment was conducted to investigate the relationship between reference crop evapotranspiration(ET_0) and actual crop evapotanspiration(ET),and relationship among crop coefficient(Kc),leaf area index(LAI) and plant height(H) at winter wheat elongation-heading stages during 2000~2002 winter wheat(season) at Yucheng Comprehensive Experimental Station and 2002~2004 season at Tongzhou Experimental Base.Results show that ET measured using lysimeters was lower than or near to ET_0 computed using FAO 56 PM method at the beginning of wheat elongation-heading stages and then increased higher than ET_0 at the end of the stage.Crop coefficient,the ratio of ET to ET_0,increased with LAI and H.The mathematical relationships(between) Kc and LAI and H were developed using datasets in 2003 and 2004.ET values in 2001 and 2002 were estimated using above relationship incorporated with ET_0.The estimated ET values computed using both LAI and H methods agreed well with the measured except when ET was less than 3 mm/d,which might be because of higher soil evaporation at the beginning of the stage under small LAI level.The estimated ET computed using both methods showed that there was no significant difference between LAI method and H method,and therefore H method could be used to estimate crop evapotranspiration at wheat elongation-heading stages in the North China Plain.