Comparison of Crop Evapotranspiration by FAO, BREB and Pristley- Taylor methods in mustard Crop in Central Bihar Region

Untimely sowing, poor crop stands and absence of lack of high yielding varieties and lack of zone specific crop production technology, moisture stress and uncertain and extreme weather conditions are the major factor which govern the productivity of rapeseed-mustard in eastern India particularly in Bihar. This study was conducted in the experimental farm of ICAR Research Complex for Eastern Region, Patna, Bihar during 2011-12 and 2012-13. Bowen ratio energy balance (BREB) method is a micrometeorological method by combining Bowen ratio with energy balance equation of earth surface. The climate of the experimental site is semi-arid with dry hot summer and mild winters. Summers are long (early April–August) with monsoon setting in between July and September. May and June are the hottest months with mean daily maximum temperature ranging from 30 to 40°C. At 11.00 to 12.00 hours, the Rn reaches the maxima and its value reduces drastically after 15.00 hours. ET0 calculate by established empirical equation was compared with the pan evapotranspiration (ETpan) data and it was observed that PT method can be safely used to calculate ET0 in the study zone. The crop evapotranspiration (ETc) using Bowen Ratio Energy Balance method was also observed and compared with output from PT method. The ratio between LE/Rn attained the higher value at siliqua emergence (SE) and pod formation (PF) stages indicating higher water demand during the same crop growth period.