Graduate Thesis Or Dissertation
 

Paclobutrazol and nutrient treatment effects on ovation perennial ryegrass

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  • Rapid tiller and root production can improve seedling survival and benefit stand establishment of perennial ryegrass (Lolium perenne L.) in commercial seed fields. Environmental conditions after establishment and inherent morphological factors combine to reduce the commercially harvested yield below the theoretical potential yield. These studies were conducted to determine if the growth retardant paclobutrazol and KCl could favor maximum seed yields of the cultivar Ovation under field conditions. In addition, effects of paclobutrazol and P on seedling development were examined in a growth chamber. Paclobutrazol increased seed yields in both first- and second-year stands in each of three climatically different years. Yield increases were primarily due to increased numbers of spikes per unit area during the wet year of 1984 and to increaseed numbers of seeds per spike in the dry years of 1985 and 1986. Seeds per unit area and harvest indices increased and thousand seed weights (TSW) decreased in all three years. KC1 applications were intended to offset the anticipated paclobutrazol-induced TSW reductions. Positive fertilizer effects were due to Cl rather than K. Chloride fertilizer salts tended to increase seed yields, seeds per unit area, and TSW in 1984 and significantly increased yields, seeds per unit area and TSW in 1985. Severe drought masked possible Cl effects in 1986. The effects of Cl were thought to be due to its influence on N form taken up by the plant. Paclobutrazol reduced shoot and root weights but did not affect the shoot:root ratios of 90-day old growth chamber grown seedlings. Plant growth in height was reduced within two days of application, which suggested the dependence of seedlings on continual gibberellin production. Phosphorus increased the shoot weights of 90-day old seedlings, but did not affect root weights. Significant interactions were observed on the numbers of leaves and tillers per plant within 9 and 16 days of treatment applications, respectively. Paclobutrazol increased numbers of leaves and tillers per plant, but only at the high P rate. The reduced root growth caused by paclobutrazol and the immobile nature of P in the soil may account for the interaction effects.
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