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Michael T. Martin Jr., Geoffrey M. Weaver, Matthew R. Chappell and Jerry Davis

A study was conducted to observe changes in mineral element concentrations within different sections of leafy stem cuttings of Hibiscus acetosella ‘Panama Red’ (PP20121) during a 21-day propagation period under standard industry propagation conditions. Concentrations of 13 mineral elements were analyzed in leaves, lower stems (below substrate), upper stems (above substrate), and roots at 3-day intervals. Before root emergence (day 0–6), P, K, Zn, Ca, and Mg concentrations decreased in the shoots (including upper stems and leaves), whereas Zn, Ca, and B concentrations decreased in the lower stems. Sulfur increase occurred in lower stems before root emergence. After rooting (day 9–21), N, P, Zn, Fe, Cu, and Ni concentrations decreased in the roots; K, S, B, and Mg concentrations increased. In the lower stems, N, P, K, S, and Zn concentrations decreased, whereas B increased. Potassium concentration decreased in the leaves; P, K, S, and Zn decreased in the upper stems. Calcium and Mg increased in leaves. This study indicates specific nutrients are important in adventitious rooting, and that it is important to analyze rooting as a function of fine-scale temporal measurements and fine-scale sectional measurements.

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Rhuanito Soranz Ferrarezi, Geoffrey Matthew Weaver, Marc W. van Iersel and Roberto Testezlaf

Subirrigation is a greenhouse irrigation method that relies on capillary action to provide plants with water and nutrients from below their containers. The first documented subirrigation system was described in 1895, and several variations on the basic design were used for research purposes before the modern ebb-and-flow type systems emerged in 1974. Most subirrigation systems apply the fertilizer solution to a waterproof bench or greenhouse section, allowing the substrate to absorb the water through holes in the bottom of the containers. Because there is little or no leaching, subirrigation typically allows for the use of lower fertilizer solution concentrations. Although excess fertilizer salts typically accumulate in the top layer of the substrate, this does not seem to have a negative impact on plants. Subirrigation can conserve nutrients and water, reduce labor costs, and help growers meet environmental regulations. A challenge with subirrigation is the potential spread of pathogens via the fertilizer solution. When this is a concern, effective disinfection methods such as ultraviolet radiation, chlorine, or ozone should be used. Sensor-based irrigation control has recently been applied to subirrigation to further improve nutrient and water use efficiencies. Better control of irrigation may help reduce the spread of pathogens, while at the same time improving crop quality. The primary economic benefit of subirrigation is the reduction in labor costs, which is the greatest expenditure for many growers.