The experiment was conducted during the rabi (winter) season of 2016-2017 at the experimental field of Agricultural Research Station (ARS), Bangladesh Agricultural Research Institute (BARI), Benarpota, Satkhira. The annual average maximum temperature of the study location is 35.5 °C and the minimum temperature is 12.5 °C, where April-May is the warmest period and December-January is the coolest period of the year. The average annual precipitation in Satkhira is around 1700 mm, which is comparatively lower than that of the country’s average. The weather data was recorded at Benarpota, Satkhira during the experimental period. The experimental site lies within AEZ 13. The soil of this area is generally clay with higher field capacity and bulk density, but the field capacity of the experimental plot was found extremely high (38.5-40.88%). The basic chemical properties of the experimented soil profile.
Wheat variety BARI Gom–25 was used for the study. For wheat, there were four irrigation treatments, such as
T1= Two Irrigation: at CRI (17-21 DAS), booting (50-60 DAS) with fresh water
T2= Two Irrigation: at CRI (17-21 DAS) stage with freshwater + irrigation at booting (50-60 DAS) stage with saline canal water
T3= Three Irrigation: at CRI (17-21 DAS) stage with freshwater + irrigation at booting (50-60 DAS) and grain filling (75-85 DAS) stages with saline canal water
T4= Three Irrigation: at CRI (17-21 DAS), booting (50-60 DAS) and grain filling (75-85 DAS) stages with saline canal water
The experiment was laid out in a Randomized Complete Block Design (RCBD) with all four treatments replicated thrice. The unit plot size was 5 m X 4 m. The experimental blocks were separated by 2 m and the plots in each block were separated by a buffer of 1 m. Fertilizers were applied in the form of urea, TSP, MP, gypsum, borax, and zinc sulphate according to the Fertilizer Recommendation Guide (FRG) 2012 (N120P30K60S20Zn3B1 kg/ha). Decomposed cowdung was used as a source of organic matter at a rate of 5.0t/ha. Two-thirds of the total urea along with all other fertilizers were applied at the time of final land preparation while the remaining one-third of the total urea was applied at the time of first irrigation as a top dress. Seeds of wheat were sown in line on 04 December 2016 with row to row spacing of 20 cm. Intercultural operations were done according to the guidelines recommended for BARI Gom–25. Moreover, recommended doses of pesticides were sprayed timely to prevent disease and pest infestation. On 21 March 2017, when wheat grain was fully matured, harvesting was done.
Maize
BARI Hybrid Maize–9 was used as a second crop for the study, where there were four irrigation treatments:
T1= Two Irrigation: at vegetative (40-50 DAS), tasseling (75-80 DAS) stages with fresh water
T2= Two Irrigation: at vegetative (40-50 DAS) stage with freshwater + irrigation at tasseling (75-80 DAS) stage with saline canal water
T3= Three Irrigation: at vegetative (40-50 DAS) stage with freshwater + irrigation at tasseling (75-80 DAS) and grain filling (100-110 DAS) stages with saline canal water
T4= Three Irrigation: at vegetative (40-50 DAS), tasseling (75-80 DAS) and grain filling (100-110 DAS) stages with saline canal water
Like the previous crop, the experimental plots for maize were also laid out in RCBD, where all four treatments were replicated three times. Here, unit plot size was 5 m X 3.75 m. Distance between two consecutive blocks was kept at 1.5 m, and within each block, a buffer of 1 m was kept between the successive plots. Fertilizers were applied in the form of urea, TSP, MP, gypsum, borax, and zinc sulphate @ N250P55K100S40Zn4B1.4 kg/ha (FRG 2012). Decomposed cowdung was also applied at a rate of 6 t/ha. All the fertilizers were applied following standard procedures. Seeds of Maize were sown on 05 December 2016 with row to row spacing of 75 cm and plant to plant distance of 25 cm. Intercultural operations were done according to the guidelines recommended for BARI Hybrid Maize–9. Moreover, recommended doses of pesticides were sprayed timely to prevent disease and pest infestation. Maize was harvested on 18 April 2017.
Data collection and processing
Soil moisture was monitored prior to each irrigation event and a measured amount of water was applied according to the treatments. Data on growth and yield parameters of both wheat and maize were collected at different growth stages. Soil salinity (soil solution) was monitored at 15 days intervals throughout the entire crop season with the help of a digital EC meter. The water salinity of both sources (groundwater and canal water) was also measured before each irrigation event. Finally, analysis of variance of the growth and yield parameters of both crops was done for the RCBD design using Statistix 10 software.
Estimation of irrigation water
Two different sources of water were used for irrigation: (i) relatively fresh groundwater, (ii) moderately saline canal water. Irrigation water was applied to bring the soil moisture content at the root zone to field capacity considering the effective root zone depth. Irrigation water was calculated using the following equation (Michael, 1985):
Where,
d = Depth of water applied (cm)
Fc = Moisture content (%) at the field capacity of soil
Mci = Moisture content of the soil at the time of irrigation (%)
As = Apparent specific gravity of the soil
D = Depth of root zone (cm)