The experiment was conducted in a micro-lysimeter at the research farm of Bangladesh Agricultural Research Institute, Gazipur, during kharif season of 2016. It was a warm-dry climate, with the average temperature of 30.73°C. The average relative humidity, wind speed, and sunshine hour were 80%, 380 km/day, and 5.37. The highest rainfall was recorded during the month of July which was 42.11% of total rainfall during the growing season. The soil characteristic of experimental field was silty clay loam, with field capacity and bulk density were 29.5% and 1.5 g/cc.
Jute (variety O9897) was sown in a 1m×1m micro-lysimeter at a spacing of 0.30 m × 0.10 m on 18 April. Also, the same crop was sowing adjacent to the lysimeter tank with the objective of creating favorable atmospheric condition. Recommended fertilizer was applied at the rate of N75, P12, K39, S15, Zn3. kg/ha and cowdung of 5 t/ha (FRG-2012). Half of N and total amount of other fertilizers will be applied at the time of final land preparation and the rest of N will be top dressed at 40-45 days after sowing under moist soil condition. Intercultural operation and pesticide application were applied according to necessity. Irrigation was started 25 days after sowing. The crop was harvested at 10 August 2016. The following treatments were used in this experiment.
T1 = Irrigation at 7 days interval allowing drainage
T2 = Irrigation at 14 days interval allowing drainage
T3 = Irrigation at 21 days interval allowing drainage
T4 = Irrigation at 28 days interval allowing drainage
The micro–lysimeter contains 4-tanks, with the area of 1 sq. meter. In this system, crop is grown in a completely controlled environment which was shown in the design done by Khan et al. (1993) so no need to further replicate. This system was also used by Mila et al. (2016) by estimating crop coefficient values of sunflower at Gazipur. The crop was irrigated according to the design of the experiment. Measured quantity of water was applied to the tank for assurance of drainage as well as adjacent plot outside of the tank was irrigated. Drainage water from lysimeter was measured by graduated cylinder and ETc was calculated by following water balance equation (Eq. 1). Prior to irrigation, soil moisture was measured to determine the depleted soil water. The part of rainfall and or excess irrigation water was collected as drainage and the stored soil moisture during the period under consideration were subtracted from the total water applied to obtain crop evapotranspiration (ETc). The following formula was used to calculate the crop evapotranspiration for the specific period.
ETc = Wa – (Dw ± ΔSs) -------------------------- (1)
Where, ETc = Crop evapotranspiration in mm for time t
Wa = Applied water + rainfall (mm) for time t
Dw = Drainage water (mm) for time t
ΔSs = Stored soil moisture (mm) for time t
Reference evapotranspiration (ETo) was estimated by using CROPWAT software only by inserting location information (like, latitude, longitude, and elevation), and climatic data (such as, maximum, and minimum temperature, air humidity, sunshine hour, and wind speed).
Finally crop coefficient (Kc) was estimated by using the following formula.
ETc = Kc × ETo ------------------ (2)
After 112 DAS, plant population, plant height, and base diameter were collected. After harvest, data on green weight with leaves/m2 was collected. After collecting green weight, treatments were staked in a shady place to remove the leaves. The green stem was rotten into water. It was taken 12 days to completely rotten. Then fiber was detached from the rotten stem and dried on sun. After drying, the data on dry fiber and stick/m2 were recorded.