Three field experiments were conducted in farmers’ fields at Sikandorkhali village (latitude and longitude of 22007/45.82//N and 90013/44.04//E), Amtali upazila in Barguna and Tildanga village, Dacope upazila ((latitude and longitude of 22034/19.92//N and 89030/39.96//E) in Khulna districts during rabi season of 2018-2019. The land situation is medium low land and the soil texture is silty clay loam. Field experiments on wheat, barley and mustard were carried out in two locations. The soils were clay loam and silty-clay loam with an average field capacity of 37.2% (gravimetric water content) and a mean bulk density of 1.40 g/cc over the 60 cm soil profile (15 cm soil layers).
Experimental design and treatments
Three field experiments were laid out in a randomized complete block design with four irrigation treatments for wheat, barley and mustard, and replicated thrice. Each experiment was conducted in a farmers’ field. The unit plot size was 30 square meters which depended on the existing farmers’ plot. The irrigation treatments were as follows: Wheat; T1 = One IR at CRI stage (17 - 21 DAS) with FW; T2 = Two IR at CRI with FW and booting stages (55 - 60 DAS) with SW; T3 = Two IR at CRI and grain filling stages (75 - 80 DAS) with SW; T4 = Three IR at CRI with FW, booting and grain filling stages (75 - 80 DAS). Barley
T1 = One IR at 17 - 21 DAS with FW
T2 = Two IR at 17-21 DAS with FW and booting stages (55 - 60 DAS) with SW
T3 = Two IR at 17-21 DAS with FW and grain development stages (75 - 80 DAS) with SW
T4 = Three IR at 17-21 DAS with FW, booting and grain development stages with SW
Mustard
T1 = No irrigation
T2 = One irrigation at pre-flowering stage (30-35 DAS) with FW
T3 = One irrigation at siliqua filling stage (45-50 DAS) with SW
T4 = Two irrigations at pre-flowering with FW and siliqua filling stages with SW
Crop management
Standard crop management practices and irrigation scheduling of different crops were followed. Different crops with duration under different cropping patterns were considered over two locations. Wheat (BARI Gom-25), a medium salt-tolerant variety (optimum yield up to 6-7 dS/m of soil salinity) was sown at 120 kg seed/ha on 8 December 2018 with a row spacing of 60 cm at Amtali and continuous seed sowing 150 kg/ha on 17 December 2018 at Tildanga. Barley (BARI Barley-7), a salt-tolerant variety was sown on 9 December 2018 at 120 kg seed/ha with a row spacing of 60 cm at Amtali and continuous seed sowing (broadcasting) on 17 December 2018 at Tildanga. Mustard (BARI Sarisha-14), a low salt-tolerant variety (optimum yield up to 3.5 - 4.5 dS/m of soil salinity) was sown on 7 December 2018 at Amtali and 17 December 2018 at Tildanga. Seeds were planted in continuous (Broadcasting) at the rate of 7 kg/ha in both locations. Fertilizer was applied in the forms of urea, triple super phosphate, muriate of potash, gypsum, borax, and zinc sulphate, respectively. Fertilizers were applied for wheat and barley @ N120 P30 K90 S15 Mg6 Zn2.6 B1, with two-thirds of N and all the P, K, S, Mg, Zn and B applied basally. The remaining one-third of N was applied at 17-21 DAS after the first irrigation. Fertilizers were applied for mustard @ N75, P20, K45, S15, Zn1.25, and B0.5in the form of urea, triple supper phosphate, muriate of potash, gypsum, zinc sulphate and borax, respectively. Two-thirds of N and the total amount of other fertilizers were applied at the time of final land preparation and the remaining N was applied as a top dressing after the first irrigation. Adequate plant protection measures were undertaken at vegetative stages. The crops were sprayed with Rovral-50wp at 0.2% at 30 DAS for prevention against diseases. Wheat, barley and mustard were harvested on 20 March 2019, 10 March 2019 and 28 February 2019, respectively at Amtali and 24 March 2019 (wheat / Barley) at Tildanga. There was no significant pest or disease infestation in the experimental plots except the mustard experiment at Tildanga village in Dacope After germination, the mustard experiment has been damaged.
Monitoring
Crops yield
Crop yields were determined at harvest. The mean yields of each crop were taken from each plot within one square meter. Plants were harvested manually at the ground level from the corner avoiding the border effect. After manual threshing, the cleaned dried filled grain yields were recorded at desired moisture (12%) content. The number of spikes, the number of grains per spike, 1000 grain weight, and grain yield of wheat and barley were determined at harvest. The sample size of the harvested area was one square meter for determining grain yield. Sub-samples (30 plants) from each plot were randomly selected to determine yield contributing characters. Plant population, the number of siliqua per plant, seed per siliqua, 1000 seed weight, and grain yield of mustard were determined at harvest. The size of the harvested area was one square meter for determining grain yield. Sub-samples (10 plants) from each of the plots were randomly selected to determine yield contributing characters. All the treatment mean values were compared following a randomized complete block design with three replications.
Soil sampling for soil water content, salinityand osmotic potential
Soil was collected from each treatment to monitor soil moisture and soil salinity, osmotic potential and pH dynamics at different growth stages and soil profiles. Soils were sampled from 0-15, 15-30, 30-45 and 45-60 cm soil depths at the time of sowing to harvest. The Electrical conductivity of EC1:5 was determined and converted to actual salinity ECw of soil water content (dS/m) while using the formula derived from Richards, 1954 and Rengasamy, 2010). Field soil gravimetric moisture content was determined. The soil samples were taken from each plot in 15 cm increments, well-mixed together, subsampled, weighed, dried at 105oC, and reweighed to determine gravimetric moisture content. EC1:5 was also converted to osmotic potential (kPa) of field soil solution using the formula derived from Rengasamy, 2010. EC1:5 was determined using a portable instrument.
Application of irrigation water
Irrigation water was applied based on the pan evaporation method at different crop growth stages. The calculated amount of irrigation water was supplied to the experimental plots using a polyethylene hose pipe. Each experiment plot were separated by a distance of 1.5 m to prevent the lateral movement of water from one to another. Effective rainfall was considered by using the USDA Soil Conservation Method (Smith, 1992).
Statistical analysis
Data on yield attributes, crop yield and water productivity were statistically analyzed to test the effects of irrigation using R software version 3.5.0. All the treatment means were analyzed and compared for any significant differences using R-statistical models at a 5% (P≤0.05) probability level of significance.