Molecular Soil Biology 2024, Vol.15, No.5, 227-235 http://bioscipublisher.com/index.php/msb 228 There are several research reports on watering regime of onions worldwide including African nations such as Ethiopia (Temesgen et al 2018; Tolossa, 2021), Ghana (Shu-aib et al., 2023) and Nigeria (Gwandu and Idris, 2016). This research has some departures from existing literature as most works on onions in relation to irrigation have centered majorly on field studies. Interestingly, field experiments are characterized by limitations to test waterlogging as a stress factor, and this research was meant to fill this knowledge gap. Besides, cultivation of vegetables in screen houses using pots is gaining popularity in recent times. Crops like pepper, tomatoes, and cucumber etc. are grown as potted plants with huge yield for income generation. We hypothesized that onion should not be an exception, premised on the fact that Shah (2020, https://greenhouseplanter.com/how-to-grow-onions) postulated that onion is one of the crops that can be successfully grown in a greenhouse; and a comprehensive guide was provided by him. Therefore, this study serves in determination of suitable watering treatment for optimal growth and yield of the crop. The objective was to investigate the watering regime for its optimal yield and determine bulb nutritional composition of the plant under different watering regimes. 2 Materials and Methods 2.1 Experimental site The experiment was conducted in the screenhouse of Plant Science and Biotechnology Department, Adekunle Ajasin University, Akungba-Akoko, Ondo State, Nigeria. 2.2 Experimental set up Onion bulbs were planted in polyethylene bags filled with 9 kg top soil (0~15 cm depth). At 2 weeks after planting, they were subjected to wet conditions: watering daily (W0), 3 times/week (W1) and once/week (W2); drought conditions: watering once/1½ weeks (W3) and once/2 weeks (W4); and waterlogged condition: planted in water-saturated soil (W5). Except waterlogging, each pot was perforated and plants received 250 ml of water (volume enough to keep the soil at field capacity) at every watering time. The volume was based on 36.13% field capacity, equivalent to 250 ml in 9 kg of the soil. Soil bulk density was determined using a procedure described by Stanley and Bernard (1992) with undisturbed soil samples at 4 cm height and 4.6 cm internal diameter of core sampler. Field capacity and permanent wilting point were analyzed through pressure plate apparatus: pressure of 1/3 bar (for field capacity) and 15 bars (for permanent wilting point).There was 5 replicates per treatment in completely randomized experimental design. 2.3 Data collection Plant height was measured from the base of the stem to apical bud using meter rule and leaves were counted manually. At harvest, plants were separated into shoot and root, weighed fresh and after drying in oven to constant weight at 80 ℃. Bulbs were counted with length, diameter and circumference measured. Bulbs were also weighed fresh and after drying in oven maintained at 80 ℃. 2.4 Laboratory analyses Samples of the soil used for planting were taken, shade-dried, passed through a 2 mm sieve, and analyzed for the physico-chemical parameters using standard methods of the Association of Official Analytical Chemists (AOAC, 1990). Dried onion bulbs were milled into fine powder and analysed for nutrients and proximate compositions using standard methods of AOAC (1990). 2.5 Data analysis Data were statistically analyzed using the statistical package for Social Sciences (SPSS version 24.0). Statistical means were separated using Least Significant Difference Test at 95% level of significance. 3Results 3.1 Soil used for planting The soil used for planting was topsoil (0~15 cm depth) collected from the experimental field of Plant Science and Biotechnology Department, Adekule Ajasin University, Akungba-Akoko. It was a sandy soil with 5.60 pH, 6.19% clay, 4.29% silt, 89.7% sand, 2.89% C, 0.14% N, 9.02 mg/100 g P, 6.24 mg/100 g Ca, 1.84 mg/100 g Mg,
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