Molecular Soil Biology 2024, Vol.15, No.5, 227-235 http://bioscipublisher.com/index.php/msb 229 0.34 mg/100 g Na, 0.23 mg/100 K, 0.20 mg/100 g H, and 8.86 mg/100 g CEC. It had 1.12 mg/cm3 bulk density, 36.13% field capacity, and 19.08% permanent wilting point. 3.2 Effect of water stress on growth Water stress (waterlogging and drought) had significant negative impact on growth of onion (Table 1). Plant height and number of leaves were reduced from (38.00±1.21) cm and (13.40±0.68) under daily watering (W0) to (11.96±0.15) cm and (4.00±0.32) under waterlogging (68.53% and 70.15% reduction) respectively. Likewise, waterlogging reduced shoot fresh weight, root fresh weight, shoot dry weight and root dry weight from (38.42±3.72) g to (19.41±1.51) g, (14.00±1.95) g to (2.60±0.68) g, (6.01±0.28) g to (1.31±0.27) g, and (3.56±0.56) g to (0.73±0.09) g respectively relative to daily watering. Table 1 Effect of watering regime on growth and vegetative biomass of Allium cepa Growth parameter Watering regime W0 W1 W2 W3 W4 W5 LSD(0.05) Plant height (cm) 38.00±1.21cd 40.28±0.41d 35.02±0.56bc 32.94±0.93b 31.12±0.92d 11.96±0.15a 0.80 Number of leaves 13.40±0.68b 13.20±0.58b 13.40±0.24b 11.60±0.68b 10.20±0.97b 4.00±0.32a 0.12 Shoot fresh weight (g) 38.42±3.72bc 43.21±4.21bc 40.3±3.11bc 32.11±2.61bc 25.32±2.01a 19.41±1.51b 1.50 Root fresh weight (g) 14.00±1.95b 17.20±3.93bc 13.40±2.79b 10.40±0.75b 9.20±1.16b 2.60±0.68a 0.03 Shoot dry weight (g) 6.01±0.28ab 7.28±0.12ab 7.02±0.09ab 3.21±0.15ab 3.32±0.22ab 1.31±0.27b Ns Root dry weight (g) 3.56±0.56b 4.72±1.01a 2.01±0.21b 1.76±0.30a 1.55±0.21ab 0.73±0.09b 0.02 Note: Values are mean + standard error of 5 replicates. Means with the same letter(s) in superscript on the same row are not significantly different at p=0.05 (LSD Test). W0= watered 4 times/week, W1= watered 3 times/week, W2= watered 2 times/week, W3= watered once/week, W4= watered once/2 weeks, W5= permanently waterlogged, Ns = non-significant, LSD =Least Significant Difference Drought conditions also significantly reduced plant height and number of leaves but with less intensity than waterlogging. Reduction increased with increasing severity of drought with the highest reduction obtained under watering once per 2 weeks (W4). This brought about 18.11% and 23.88% reduction in plant height and number of leaves respectively. W1 resulted in higher values of growth parameters than other treatments. 3.3 Effect of water stress on biomass Drought had negative effect on biomass parameters leading to 34.11%, 35.71%, 44.76% and 56.46 % for shoot fresh weight, root fresh weight, shoot dry weight and root dry weight respectively (Table 1). W1 resulted in higher values for root fresh weight and dry weight than W0. Higher values were recorded both at W1 andW2 for shoot fresh and dry weight than at W0. Meanwhile, the highest values were obtained at W1 in the dry and fresh weight parameters. 3.4 Effect of water stress on yield There was increase in number of fruits from 2.60 at W0 to a range of 2.80~3.82 at W1-W4 (Table 2). However, size of bulbs was highest at W1 andW2 relative to other treatments. For example, bulb length increased from 3.54 cm at W0 to 4.82 cm and 4.01 cm at W1 andW2 respectively. Bulb diameter likewise increased from 8.46 cm to 9.02 cm and 9.00 cm at W1 andW2 respectively. Bulb circumference likewise increased from 9.46 cm at W0 to 11.02 cm at W1. Higher values of fresh and dry weight of bulbs were also recorded at W1 andW2 than other treatments. Fresh weight increased from 134.60 g at W0 to 149.00 g and 148.80 g under W1 andW2 respectively. Dry weight also increased from 16.80 g to 31.10 g and 26.50 g at W1 andW2 respectively. 3.5 Effect of water stress on bulb nutritional and proximate compositions Watering regime had significant impacts on nutritional and proximate composition of onion bulbs (Table 3; Table 4). Except Ca and Mg, bulb nutrients were reduced by drought, with the highest values of 2.44, 20.26 and 1.84 (mg/100 g) for N, P and K respectively (Table 3). W5 on the other hand reduced all the bulb nutrients: N (48.06%), P (12.61%), K (50.66%), Ca (28.00%) and Mg (47.69%). Except nitrogen free extract (NFE), all bulb proximate
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