Water Management in Horticultural Crops

4.2.Sunken screen pan evaporimeter

• Sharma and Dastane (1968) developed the sunken screen pan evaporimeter that provides evaporation values more close to crop ET values than the USWB Class-A pan evaporimeter. The crop coefficient values in a sunken screen pan evaporimeter was found to be 0.95 to 1.05 in New Delhi, while that in a USWB Class-A pan evaporimeter varied from 0.5 to 1.3 for different crops in different locations. However, this device requires extensive evaluation under varying climatic and crop conditions.
• The evaporimeter consists of a 60 cm diameter and 45 cm deep pan made of 20 gauge galvanized iron sheet and stilling well of 15 cm diameter and 45 cm depth attached to the pan with a tube. The pan and the well are painted white and screened at the top with 6/20-mesh wire net. The stilling well has a pointer inside at the centre. The pan with the well is buried in the soil with 10 cm edge over the soil surface. The fall of water level in the well during 24-hour period is taken as the measure of the evaporation rate per day. Further, evaporation rate may be computed from the measured quantity of water added daily to bring the water level to the pointer tip level after each measurement. Tip of the pointer should be at level with the soil surface while installing the evaporimeter. The pan is located in the field with no obstruction to wind movement over the pan.