The experiment was conducted at the Soil Science research field of Bangladesh Agricultural Research Institute (BARI), Gazipur, Dhaka, Bangladesh during the period from 22 November 2017 to 07 April 2018. The experimental field situated at 24° 05’ N latitude and 90° 25’ E longitudes having an elevation of 8.2 m from sea level.
The micro-lysimeter were constructed recently by Soil Science Division, Bangladesh Agricultural Research Institute (BARI) and established at Soil Science research field, Gazipur. It has 12 tanks spaced at equal distance (4 m). The tanks were installed in 3 lines taking 4 in each line for the 3 replicate measurements. The lysimeter tank has 1 meter square area with effective soil depth of 100 cm followed by a perforated Stainless Steel (SS) sheet. Below the SS sheet, 2 meshes of no. 20 and 40 are placed. Below the mesh, a 15 cm thick coarse gravel packs are sandwiched. Then water receiving reservoir was provisioned where the excess water from the upper parts are discharged. Then the discharged water goes through the drainage piping to the reservoir.
Each lysimeter tank is provided with a stainless steel pipe of 1.75 cm diameter which serves as an air vent. The vent is inserted up to the gravel layer and is provided with a cap at the top end. Below the lysimeter tank, a 7.5 cm thick concrete layer is provided followed by a 7.5 m thick stone soling. A 13 cm thick brick wall was constructed around the lysimeter tank leaving 5 cm sand pack between the tank and the wall. The brick wall is constructed at a depth of 30 cm from the soil surface. For more details, please refer to Khan et al. (1992).
Twenty seven days old chilli (cv. BARI morich 3) seedlings were transplanted in lysimeter tanks, each having 1 m2 area on 30 November, 2017. Planting was done in the afternoon maintaining the spacing of 30×30cm. Also, to maintain a similar environment, the same crop was grown in the lands surrounding the tanks. The soil was clay loam with field capacity and bulk density, 28.53% and 1.48 g cc-1, respectively. There were four treatments as follows:
T1 = Irrigation up to FC at 5 days interval
T2 = Irrigation up to FC at 10 days interval
T3 = Irrigation up to FC at 15 days interval
T4 = Irrigation up to FC at 20 days interval
As lysimeter has 12 tanks in operation, therefore the experiment was set up in a completely randomized design with 3 replications. The crop was fertilized with N100P55K90S15Zn2B1 kg ha-1 and cow dung @ 10 t ha-1. Entire amount of cow dung, TSP, gypsum, boric acid and 2/3rd of Mop were applied during the final land preparation. Urea as a source of nitrogen was applied in 4 equal splits at 5, 25, 50 and 75 days after transplanting (DAT). The rest of MoP was applied with third dose of urea at 50 DAT. The crop was irrigated up to field capacity for 30 cm depth rooting zone as per treatment schedule. Measured quantity of water depending on the FC value was applied. Soil moisture was measured before irrigation. As per treatment, 12, 8, 6 and 4 irrigations were required for T1, T2, T3 and T4, respectively. Vertimec @ 1 ml L-1 and Succexx @ 2 ml L-1 were sprayed for controlling mite and chilling injury, respectively. Percolate was collated whenever it deposited in the buckets placed underneath of the drainage outlets coming from each lysimeter tank. In this way 3 collections after 2nd, 3rd and 4th irrigation were possible during the growing period of chilli. The collected water samples were analysed for NO3-N, P, K, Ca, Mg, S, Zn and B content in them. The crop showed luxuriant growth especially for the treatment T1 and T2. Harvesting of green chilli was started on 18 March 2018 and ended on 7 April having 4 pickings altogether. Climatic data, such as maximum and minimum temperatures, air humidity, sunshine hours/day and wind speed were collected from the nearest meteorological station. The location information like elevation, latitude, and longitude were also collected. All these data were then used to estimate the potential evapotranspiration (ET0). Crop data like plant height, number of fruits per plant, fruit length, fruit breadth and green chilli yield were recorded and statistically analyzed. The part of rainfall collected as drainage and the change in stored soil moisture during the period under consideration were subtracted from the applied water to obtain crop evapotranspiration (ETc). The crop evapotranspiration for the specified period was estimated using the following equation:
ETct= Wa – (Dw ±ΔSs)
Where,
ETct = crop evapotranspiration in mm for time, t
Wa = applied water, mm + rainfall, mm for time, t
Dw= drainage water, mm for time, t
ΔSS= stored soil moisture, mm for time, t
Then from the potential evapotranspiration (ET0) estimated for the specified period, the value of Kc for the period was determined from the ratio, ETc / ET0.