USE OF MICROLYSIMETERS TO MEASURE EVAPORATION FROM SANDY SOILS

Evaporation from soil can be a major component of crop water balance a nd land surface energy balance. A number of different applications of the microlysimeter method to measure evaporation from soil have been u sed in recent studies. Microlysimeters were used extensively in three sandy soils for this study. Measurement of evaporation from microlysim eters with different dimensions and of different ages allows discussio n of the sources of error inherent in the method. The evaporation reco rded from microlysimeters of diameters 214 mm, 152 mm and 51 mm was no t significantly different. A comparison of 100 mm and 200 mm deep micr olysimeters showed that depth had no significant influence during the first 2 days after extraction from the soil profile. For periods begin ning 2 or more days after rain, significant differences in evaporation owing to depth may not occur for up to 7 days. Soil cores extracted a t different times showed significant differences in evaporation immedi ately following a rain event, and no significant differences 2 or more days thereafter. This period of significant difference was extended t o about 4 days when the method was used within a crop (i.e. root extra ction of water in the field significant). A protocol for use of microl ysimeters is developed from these results.