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  • Author or Editor: Brian Weesies x
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Twelve species of flowering potted plants were grown in a peat-based medium with water soluble fertilizer concentrations of 50, 100, or 200 mg·liter-1 N and K2O. Leaf blade or leaf petiole samples were collected six to eight weeks after planting. Sap was expressed using a hydraulic press and levels of nitrate nitrogen and potassium were determined using Cardy flat sensor ion meters. Petiole nitrate level ranged from 520 to 6300 mg·liter-1 and potassium levels ranged from 870 to 3600 mg·liter-1. The petiole nitrate concentration and change in petiole nitrate levels with changes in media nitrate levels was crop dependent. Leaf blade nitrate and potassium concentrations were lower than leaf petiole concentrations. The relationship of petiole nitrate to final plant fresh and dry mass and appearance at flowering will be presented.

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A small suction lysimeter tube (SLT) was used to extract media solution samples for twelve pot plant species in peat-based media subirrigated with 50, 100, or 200 mg · liter-1 N and K2O. Media samples from different pots were also tested using the saturated media extract (SME) procedure. Sample solution pH, EC, NO3 --N and K+ were measured with Cardy flat electrode meters. Averaged over crops, solution pH was similar for SLT and SME (after extraction) at each N concentration. The mean (12 crops × 3 reps at each N level) SME and SLT solution EC and K+ concentrations were similar for samples collected from the 50 and 100 mg · liter-1 N treatments. NO3 --N values were lower with the SLT than SME method at 50 mg·liter-1 N. SLT levels for EC, NO3 --N, and K+ were 27, 39, and 24% higher than SME values for samples collected from the 200 mg·liter-1 N treatments. Sample variation between replicates and between methods for the single pot samples was unacceptable. More testing is needed with SME and SLT samples from the same pot and composite samples from several pots, but SLT sampling is fast, nondestructive, simple, and economical at $6-7 per tube.

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The rhizon soil solution sampler (RSSS) currently is being used for in situ extraction of the soil solution for nutrient analysis of mineral soils used to produce field-grown crops. In this study, laboratory and greenhouse experiments were conducted to test the effectiveness of the RSSS for in situ solution extraction from soilless container root media and to compare an RSSS extraction method for measuring root-medium pH, electrical conductivity (EC), and NO3-N and K concentrations with that measured with the saturated media extract (SME) method. A near 1:1 correlation was found between the pH, EC, and NO3-N and K concentrations measured in the extracted solution of the RSSS and SME method in media without plants and in media from ten species grown using three water-soluble fertilizer concentrations applied by subirrigation. More testing is needed with the RSSS, perhaps using composite samples form several pots for analysis. The RSSS shows promise for nutrient extraction in container-grown crops because it is fast, nondestructive, simple, economical, and has minimal effect on the nutritional status of the medium in the pot.

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