High-volume top irrigation (Chapin) was compared to subirrigation (ebb and flow) using 15-cm-diameter (1.56 liter) pot-grown chrysanthemums [Dendranthema ×grandiflorum (Ramat.) Kitamura] with peatwool (50 peatmoss: 50 granulated rockwool) as the growing substrate. Preplant moisture contents (25%, 125%, and 250%, gravimetric) and compaction (0, 20, and 50 g·cm-2) of the peatwool were also studied. Shrinkage of growing substrate was large (>309'6 of pot volume) when peatwool in the pots was not compacted. Compaction reduced shrinkage and produced plants with larger leaves, more fresh weight, and longer stems than without preplant compaction. Drainable pore space, container capacity, and total porosity was not affected by compaction. The higher preplant moisture contents increased drainable pore space but had no effect on plant growth. Chapin-irrigated plants had significantly more fresh weight (+ 24%) at the pea-size bud stage than plants grown in the ebb-and-flow system. The difference in growth was similar at flowering but significant only at P = 0.08. Soluble salts concentration in the peatwool and foliar nutrient contents differed at flowering for the two irrigation systems.
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