A field study was carried out with garlic (cv. BARI Rashun-2) under sprinkler irrigation system during the winter season (December–March) of 2013 – 2014 at the research field of Irrigation and Water Management Division, Bangladesh Agricultural Research Institute (BARI) (Latitude 24.000N, Longitude 90.250E and Altitude 8.40 m msl), Gazipur. A total of six irrigation treatments were tried. Five treatments were based on potential evapotranspiration (ETo) and one treatment was kept as farmers practice. The treatments were as follows:
T1 = Surface irrigation (Farmers’ practice)
T2 = Sprinkler irrigation at 40%ETo
T3 = Sprinkler irrigation at 60% ETo
T4 = Sprinkler irrigation at 80% ETo
T5 = Sprinkler irrigation at 100% ETo
T6 = Sprinkler irrigation at 120%ETo
Each treatment was replicated three times and irrigated using a sprinkler irrigation system while farmers practice treatment was irrigated using pipe irrigation at an interval of 15 days. Irrigation interval for sprinkler irrigation system was 10 days. The treatments with the same irrigation regime were arranged in a line covering three replications for better management of irrigation. Since the characteristics of the experimental land were homogeneous, there was little possibility of variation in results for such arrangements of the treatments. Each plot was of 5 m × 3 m size surrounded by 1.5 m wide buffer strip to restrict lateral seepage of water in-between adjoining plots. Cloves of garlic (cv BARI Rashun-2) were planted at 15 cm × 10 cm spacing on 16 November 2013. During land preparation, farm yard manure @ 5 t/ha was properly incorporated with the soil. Fertilizer application rates were 100 kg N, 54 kg P, 167 kg K and 18 kg S per hectare. Half of N and K in the form of urea and muriate of potash, and full dose of P and S in the form of triple super phosphate (TSP) and gypsum, respectively were applied during final land preparation. The remaining half of N and K were top-dressed in two equal splits at 25 and 50 days after planting (DAP). A light irrigation amounting 20 mm was applied after planting for proper germination and crop establishment. The spinkler irrigation scheduling was imposed from the eighth day of transplanting. Irrigation was applied after 10- days interval based on reference evapotranspiration (ETo). Reference evapotranspiration (ETo) was calculated on a daily basis from daily meteorological data by Penman-Monteith’s equation using CROPWAT computer programme. Daily meteorological data required for CROPWAT model including maximum and minimum air temperature, relative humidity, wind speed at 2 m height and sun shine hour were collected from a weather station about 1.0 km away from the study site. The daily irrigation requirement for the crop was calculated by subtracting the effective rainfall from the computed ETo. Time of operation of sprinkler system was calculated for different levels of irrigation dividing water requirement of the crop over 10 days by discharge of a sprinkler nozzle. The duration of operation was controlled with gate valves provided at the inlet of each lateral. Gravimetric soil water content was measured from 0–15, 15–30, 30–45, 45- 60 cm depths during planting and harvest as well as before and after each irrigation and after rainfall. Seasonal evapotranspiration (SET) during the entire cropping period (planting to harvest) from the crop field was calculated by using the field water balance equation as: ET= IW + P+ - D - R ± SWS
Where P is precipitation (mm), IW is irrigation (mm), D is the drainage (mm), R the run-off and SWS is the variation in water content of the soil profile. The change in soil water contents at 30–60 cm soil layer was considered to be deep percolation. Run-off was taken to be zero since it did not occur with the use of micro sprinkler irrigation system.
The recommended plant protection measures were adopted as and when required. Irrigation was stopped 15 days before harvesting in all treatments. Ten plants from each plot were selected randomly and tagged for recording growth parameters viz., plant height, number of leaves and neck girth. Leaf area and above ground dry matter were also recorded on 10 plants at different phenological stages. Yield parameters viz., bulb diameter, bulb length, bulb unit weight were recorded from the plants used for recording observations. The bulbs were harvested at full maturity stage on 18 March 2014. After proper curing and neck cutting, yield and contributing characters were recorded. The bulb yield per hectare was calculated based on the plot yield. The analysis and interpretation of data were done using the DMRT method of analysis of variance technique as described by Gomez and Gomez (1984).