Maize (variety: BARI Hybrid maize-1) was sown in four lysimeter tanks, each having 1 m2 area on 29 November 2002. Also, to maintain a favourable atmospheric condition in the lymimeter tanks, the same crop was grown in the fields around the tanks. The soil was silty clay loam with field capacity and bulk density, 28% and 1.5 gm/cc, respectively.
The selected treatments were: T1 = Irrigation at 10 days interval, T2= Irrigation at 15 Days interval, T3 = Irrigation at 20 days interval, T4 = Irrigation at 25 days interval. Since, micro-lysimeter contains 4 tanks, no replication of the treatments was possible. Climate data such as maximum and minimum temperatures, air humidity, sunshine hrs/day, wind sped km/day together with the location information like elevation (m), latitude and longitude were incorporated in the software, CROPWAT, to estimate the potential evapotranspiration, crop data like plants/in2, cob length, cob diameter, grains/cob, 1000 grain weight and grain yields of each treatment were recorded. The crop was irrigated in accordance with the design of the treatments. The part of rainfall collected as drainage and the stored soil moisture during the period under consideration were subtracted from the applied water to obtain crop evapotranspiration (Etc) i.e., the crop evapotranspiration for the specified period is,
ETct = Wa – (Dw – Ss), where, ETct is the crop evapotranspiration in mm for time period, t; Wa applied water + rainfall, mm for time t; Dw is the drainage water, mm for time, t; Ss is the stored soil moisture, mm for time, t. The value of Kc for the period was determined from the ratio, Etc/ETo. The yield was adjusted for 14% moisture content
Annual Research Report 2002-2003,IWM, BARI, Gazipur
The values of crop co-efficient for different stages were obtained as 0.38, 0.87, 1.36 and 0.75 at the stage of initial, development, mid season and late season, respectively. The FAO values are 0.4, 0.80, 1.15 and 0.70 in initial, development, mid season and late season stages, respectively. However, locally determined values are preferred to those for generalized use to estimate location specific crop ET.