Experimental site:
The experiment was conducted during 2015-2016 rabi season 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 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 lower than that of the country’s average value. The weather data recorded at Benarpota, Satkhira during the experimental period is presented.
Mustard:
Mustard variety, BARI Sarisha –14 was used for the study. For mustard, there were four irrigation treatments,
T1= Irrigation at vegetative (25-30 DAS) stage with fresh water
T2= Irrigation at vegetative (25-30 DAS) and pod formation (50-55 DAS) stages with fresh water
T3= Irrigation at vegetative (25-30 DAS) stage with fresh water and irrigation at pod formation (50-55 DAS) stage with saline canal water
T4= Irrigation at vegetative (25-30 DAS) and pod formation (50-55 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 5.5 m X 3.3 m. The experimental blocks were separated by a distance of 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) at the rate of N75P20K45S15Zn1.25B0.5 kg/ha. Decomposed cowdung was used as a source of organic matter at a rate of 10 t/ha. Two-thirds of the total urea along with all other fertilizers were applied at the time of final land preparation, while remaining one-third of the total urea were applied at the time of first irrigation as top dress. Seeds of Mustard were sown on 10 November 2015 with row to row spacing of 30 cm. Intercultural operations were done according to the guidelines recommended for BARI Sarisha –14. Moreover, recommended doses of pesticides were sprayed timely to prevent disease and pest infestation. On 1st of February 2016, when the mustard seeds were fully matured , harvesting was done.
Maize:
BARI Hybrid Maize – 9 was used as a second crop for the study, where there were five irrigation treatments:
T1= Irrigation at vegetative stage (40-50 DAS) and grain filling (110-120 DAS) stages with fresh water
T2= Irrigation at vegetative (40-50 DAS), tasseling (75-80 DAS) and grain filling (110-120 DAS) stages with fresh water
T3= irrigation at vegetative (40-50 DAS) stage with fresh water and irrigation at grain filling (110-120 DAS) stage with saline canal water
T4= Irrigation at vegetative (40-50 DAS) stage with fresh water and irrigation at tasseling (75-80 DAS) and grain filling stages (110-120 DAS) with saline canal water
T5= Irrigation at vegetative (40-50 DAS), tasseling (75-80 DAS) and grain filling (110-120 DAS) stages with saline canal water
Similar to the previous crop, the experimental plots for maize were also laid out in RCBD, where all five treatments were replicated three times. Here, unit plot size was 5 m X 3.75 m. Distance between two consecutive blocks were kept 1.5 m, and within each block a buffer of 1 m were 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 25 November 2015 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 Sarisha-14. Moreover, recommended doses of pesticides were sprayed timely to prevent disease and pest infestation. Finally, on 15 April 2016, maize was harvested.
Data collection and processing:
Soil moisture was monitored prior to each irrigation events and measured amount of water was applied according to the treatments. Data on growth and yield parameters of both mustard and maize were collected at different growth stages. Soil salinity (in soil solution) was monitored with an EC meter at 15 days interval for mustard and 20 days interval for maize, throughout the entire crop season. . Water salinity of both the sources (groundwater and canal water) was also measured before each irrigation events. Finally, analysis of variance of the growth and yield parameters of both the crops were 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 taking into account the effective of root zone depth. Irrigation water was calculated using the following equation (Michael, 1985): d = {(Fc - MIc) / 100} x As x D.
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)