Irrigation, fertilization and non-chemical plant growth regulation in greenhouse production
Alem, Peter Otieno
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Rising concerns over environmental impacts of excessive water and fertilizer use in the horticultural industry necessitate more efficient use of water and nutrients. Both substrate volumetric water content (θ) and fertilizer affect plant growth, but their interactive effect is poorly understood. The objective of this study was to determine the optimal fertilizer rates for petunia (Petunia ×hybrida) ‘Dreams White’ grown at different θ levels. Petunias seedlings were grown at four levels of θ (0.10, 0.20, 0.30, and 0.40 m3•m-3) with eight different rates of controlled release fertilizer (Osmocote 14-14-14; 14N-6.1P-11.6K; rates of 0 to 2.5 g/plant, equivalent to 0 to 6.25 kg•m-3 substrate). Shoot dry weight increased as the fertilizer rate increased from 0 to 1.67 g/plant but decreased at even higher fertilizer rates. The effect of fertilizer rate on growth was more pronounced at higher θ. Leaf size doubled as the θ thresholds increased from 0.10 to 0.40 m3•m-3. Flowering was reduced by a combination of high fertilizer rates (> 0.63 g/plant) and high θ (0.30 and 0.40 m3•m-3), indicating that optimal conditions for vegetative growth are different from those for maximal flowering. These results suggest that without leaching, high quality petunias (sufficient biomass and flowers) can be grown with lower fertilizer rates than commercially recommended rates.