ضرورت انتخاب زمان کاشت متفاوت برای پرورش گیاهچه‌های علف‌های‌هرز یکسان در پژوهش‌های علوم‌علف‌های‌هرز از طریق تحلیل سرعت جوانه‌زنی

The preparation of similar experimental units is essential for conducting agricultural experiments. This is particularly important in evaluating the efficacy of herbicides under various conditions, especially considering the significance of herbicide application timing relative to the different phenological stages and growth of various weed species. Consequently, many researchers simultaneously sow seeds of different weed species, unaware that due to the potentially varying germination rates and growth speeds of different weed species, the timing of herbicide application for the tested species will inevitably differ. To address this issue, some researchers apply herbicides to different weed species on different dates to ensure uniform growth stages of weed species. However, this practice contradicts the fundamental principles of agricultural experimental design, as treatments should not only be applied at the appropriate growth stage but also simultaneously on a specific date and time. In this study, the germination speed of three weed species, barnyardgrass (Echinochloa crus-galli), sorrel (Rumex spp.), and jimsonweed (Datura stramonium), was investigated to test this hypothesis. A total of 100 seeds from each species were placed in 9 cm Petri dishes on two layers of filter paper, and 7 mL of distilled water was added to each Petri dish. There were four Petri dishes (replications) per weed species. Seed germination was counted daily over 25 days. Germinated seeds were removed from the Petri dishes after counting. To determine germination parameters, including maximum germination (Gmax) and time to reach 50% of maximum germination (G50), a three-parameter logistic model with a time-to-event approach was fitted to the germination data. The Gmax values were estimated as 89±1.57% for barnyardgrass, 99±0.51% for sorrel, and 71±4.1% for jimsonweed. The G50 values were estimated as 3.1±0.089 days for barnyardgrass, 6.2±0.084 days for sorrel, and 16.8±0.54 days for jimsonweed. The t-test showed significant differences between the three weed species for both parameters at the 0.001 level. The results of this experiment confirmed the hypothesis, indicating that to achieve uniform weed seedlings with the same growth stage for applying various experimental treatments (e.g., herbicide application), it is essential to sow seeds of different species on different dates. Additionally, it should be noted that the growth speed of different species may also vary. Therefore, further investigation into the growth speed of different weed species is recommended to substantiate this hypothesis and to ensure having weed seedlings with uniform growth stages.