冬小麦能量平衡及蒸散分配的季节变化分析

SEASONAL VARIATION OF ENERGY BUDGET AND EVAPOTRANSPIRATION PARTITIONING IN WHEAT FIELD

本文分析了华北平原冬小麦生态系统辐射收支、热量平衡以及蒸散在冠层蒸腾和土壤蒸发之间的分配特征。结果发现，在冬小麦生长过程中，系统截获的太阳短波辐射随小麦的生长而变，它占太阳总辐射的比例，初期为０．８左右，尔后随叶面积的增加而逐渐下降，在孕穗期最小，约为０．７５，之后，随叶片枯黄、麦穗的成长又上升，最后可达０．８６。净辐射占太阳总辐射的比例，可分成如下３个阶段：拔节期比值较低，约为０．４５；孕穗抽穗期约为０．５；灌浆期比值最大，约０．５７。随着叶面积指数（ＬＡＩ）的增加，土壤热通量与净辐射之比，由返青初期的０．１３迅速下降，直至较为稳定的０．０６。潜热通量消耗净辐射的大部分，且随ＬＡＩ的增加而增大。从返青到乳熟的５８天内（４月１日～５月２８日），麦田总蒸散量约为２５０ｍｍ，其中土壤蒸发量约为５０ｍｍ，冠层蒸腾约为２００ｍｍ，分别占总蒸散量的２０％和８０％。

Based on the experiments conducting in Luancheng Agro ecological Experimental Station, Chinese Academy of Sciences, from March to June, 1995, the characteristics of radiation budget, energy balance, as well as evapotranspiration partitioning into canopy transpiration and soil evaporation in wheat field are analyzed. The results show that the ratio of the absorbed to the incoming short radiation in canopy soil system is varying with wheat growth stages. The value is 0 8 in the jointing, decreasing with the increase of leaf area index ( LAI ), and reaches the minimum of 0 75 in the booting. It then increases again and finally reaches the maximum of 0 86 with the appearance of ears and wilting leaves. The ratio of net radiation to incoming radiation enhancing with the growth stage can be distinguished by three periods. The value is 0 45 in the jointing, becomes 0 5 in the booting and finally increases to 0 57 in the milking. The experiments identify that with the increasing of LAI , the ratio of soil heat flux to net radiation decreases from 0 13 in the jointing to 0 06 in the milking. However the ratios of latent heat flux and sensible heat flux to net radiation all increase, sometimes the former is larger than 1 and the latter turns to negative. LE is shown the main component of energy balance in the system. From jointing to maturing, i.e., from April 1st to May 28th, total evapotranspiration ( E t ) in field is 250 mm with 50 mm from underneath soil evaporation and 200 mm from canopy transpiration. The relative evaporation (E t/E p) tends to increase with the season, the average of which is 0 70. The value of evapotranspiration, 4 3 mm/d, based on aerodynamic energy balance method, is agreeable with that based on water balance method. The similar results of E t/E p and daily evapotranspiration are also found in Yucheng Experimental Station, CAS, locating in North China Plain.