ISHS Acta Horticulturae 458: International Symposium on Water Quality & Quantity-Greenhouse
RESPONSE OF LETTUCE PLANTS GROWN ON DIFFERENT SUBSTRATES TO PHOSPHORUS FERTIGATION |
| Authors: | P. Imas, B. Bar-Yosef |
| Abstract:
Apart from its direct role in plant development, P nutrition affects plant growth and yield indirectly by influencing the uptake rate of other nutrients and by modifying the ionic environment in the rhizosphere. The objective of this work was to study the response of greenhouse lettuce to P concentration in irrigation water (Cp) and to substrate chemical properties. Four levels of P (0, 10, 25 and 60 mg P/l) were tested in three growth media: inert rockwool, mildly P absorbing sand and strongly P retaining yellow tuff. The response in canopy fresh weight (CFW) to P concentration in irrigation solution (Cp) followed an optimum type relationship. At any Cp, CFW decreased in the order tuff>sand>rockwool. The Cp which gave maximum CFW in all substrates was 25 mg/l. At Cp=25 mg/l, the P content in the canopy was ≈ 0.8%, coinciding with maximum CFW. The flux of P uptake (Fp) vs. the average P concentration in the inflowing and outflowing substrate solutions (CpA), for the three substrates fitted the Michaelis Menten equation. The threshold CpA corresponding to saturation in Fp was ≈ 25 mg/l. Concentrations of P, K, Ca, Mg and pH of leachates with and without plants were differently affected by Cp in the three substrates. A probable mechanism behind this interaction between plant, substrate and P supply involves the exudation of H+ and organic anions by the roots, followed by the reaction of these exudates with the substrates and added nutrients. | |
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