S Parveen
Bangladesh Rice Research Institute, Gazipur, Bangladesh
E Humphreys
International Rice Research Institute, Los Banos, Philippines
M Ahmed
Bangladesh Agricultural University, Mymensingh, Bangladesh
Water productivity, Soil water tension, Wet season, Physiological maturity
Bangladesh Rice Research Institute, Gazipur, Bangladesh
Crop-Soil-Water Management
Water productivity
The research was carried out in the greenhouse at the International Rice Research Institute (IRRI), Los Baños, Philippines (14°11’N, 121°15’E), from July to November 2011. Rice was grown on a silty clay loam soil (28% sand, 34% silt, 39% clay) in 20 cm diameter, 25 cm high polyvinyl chloride pots. Bulk soil was obtained from the IRRI experimental station, homogenized well with water and added to the pots to a depth of 20 cm. The soil was re-puddled using an electrical stirrer before wet seeding. The soil was slightly acidic, with medium levels of organic C, available P, exchangeable Ca and K, and total N The experiment was designed to evaluate the effects of different levels of water stress at different growth stages. There were three levels of water stress (10, 20 and 40 kPa soil water tension) applied at one of three growth stages: 3 leaf (3L) to panicle initiation (PI), PI to flowering (FL), and FL to physiological maturity (PM). In addition there was a control treatment, which was continuously flooded (CF), and three treatments, which had stresses of 10, 20 or 40 kPa during all the three stages. Thus, there were 13 water management treatments in a randomized complete block design. Implementation of CF involved topping the pots up daily to a pond water depth of 2 to 3 cm. For the stress treatments, irrigation was applied whenever soil water tension increased to the threshold value (10, 20 or 40 kPa), with water added in two doses, topping up to a depth of 2 cm each time, to ensure that the soil was fully saturated to depth. Soil tension was measured using 30-cm long tensiometers installed in 4 replicate pots of each treatment. The tensiometers were installed 4 cm to the side of the centre of the plant rows, and the middle of the ceramic cup was 10 cm below the soil surface. All pots of a given treatment were irrigated when the average of the four monitored pots reached the threshold value. All pots were kept continuously flooded at all stages other than during the stage when the 10, 20 or 40 kPa stresses were being applied. After the final puddling, the soil was allowed to settle for 1 d. A solution of 27 ml of fertilizer containing muriate of potash, diammonium phosphate and zinc sulphate was poured onto the soil surface 24 h before seeding, giving a basal fertilizer application rate of 40 kg K2O ha-1, 41 kg P2O5 ha-1, 30 kg N ha-1 and 5 kg Zn ha-1. Urea was top-dressed at maximum tillering, PI and heading at 50, 50 and 30 kg N ha-1, respectively, and muriate of potash (40 kg ha-1) was also applied at PI. The top dressing was done immediately prior to irrigation. The rice variety NSIC Rc222 was pre- germinated by soaking the seeds for 24 h, draining, then incubating for 24 h prior to sowing. NSICRc222 was selected for its high yield potential under non-continuously flooded conditions. The seeds were placed on the saturated soil surface on 20 July 2011. Twelve pre-germinated seeds were sown in a single 20 cm long row along the diameter of each pot. The plants were thinned to eight plants per pot after establishment. The pots were kept weed free by hand weeding as needed. Insects were well-controlled by applying insecticides as needed against whorl maggot, leaf and plant hoppers, stem borer, and rice bugs. Air temperature, relative humidity and solar radiation were measured hourly using an automatic weather station in the greenhouse near the middle of the experiment. The same parameters were also measured outdoors at the IRRI lowland farm weather station, located among rice fields about 1 km from the greenhouse. All data were analyzed by analysis of variance (ANOVA) using GenStat V.14.1. The interaction between water stress treatment and growth stage was also analyzed using a factorial design with three levels of water stress (10, 20 and 40 kPa) and three stages of stress application (3L - PI, PI - FL, FL - PM). The comparison of treatment means was made by the least significant difference (LSD) at the 5% level of probability (p=0.05).
Bangladesh Rice J. 21 (1) : 1-12, 2017
Journal