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  • Author or Editor: D.D. Warncke x
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Growth media used for growing containerized plants in greenhouses have changed greatly since the initiation of the Spurway test procedure (8). Well-aggregated field soils gradually gave way to mixtures of soil and manufactured coarse amendments and eventually to soilless growth media. Along with these changes in growth media composition came changes in physical and chemical properties—some desirable, some not so desirable. Field soils generally have a high-nutrient capacity value and a low-intensity factor. The level of the capacity factor has decreased as the change in growth media composition has taken place. Geraldson (1-3) developed an “intensity and balance” analysis system for the unique, sandy soils of Florida; soils that provide little buffering capacity. He found the concentration (intensity) and balance of nutrients in the soil solution to be important when the capacity factor was small. Similarly, the concentration and balance of nutrients in the solution phase of greenhouse growth media today have become important to plant growth and quality.

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Single-plant microplots of `Russet Norkotah' potatoes (Solanum tuberosum L.) were grown outdoors in a 5 × 5 factorial RCBD of indigenous phosphorous level (200, 325, 450, 575, 700 kg·ha-1 Bray-Kurtz Pl extractable; McBride sandy loam) and banded triple super phosphate (0, 50, 100, 150, 200 kg P2O5/ha). Disease in the low P soil that was used to create the four lower P soil blends completely confounds response of the plants across indigenous P levels and might have accentuated responses within levels. Plants responded to fertilizer P with tuber yield increases of 100, 70, 40, and 10 percent within the 200, 325, 450, and 575 indigenous P levels, respectively. Fertilizer P also increased marketable yield and tuber P concentration. Neither indigenous nor fertilizer P altered tuber specific gravity.

Companion studies compare the responses of corn (Zea mays L.) and potato to indigenous soil P levels and quantify P uptake among potato cultivars in solution culture.

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Six potato cultivars (Atlantic, Sebago, Onaway, Russet Burbank, Lemhi Russet,and Norland) were evaluated for phosphorus uptake efficiency in solution culture. Individual rooted cuttings of each cultivar were transferred from a standard 1/5 Hoagland's solution into solutions containing one of six P concentrations (0.05,0.1,0.22,0.5,1.1 and 2.3mg/l). After a 24h adjustment period P uptake was followed over a 6h period by collecting solution aliquots every two hours. All cultivars depleted the two lowest initial P concentrations to similar stable P concentration. The P uptake rate per unit length of root showed a sigmoidal relationship to the initial P solution concentration. The general nature of the P uptake relation to solution P concentration was similar among the cultivars, although the actual values varied. In general, P uptake rate increased from 5.0 × 10-4 at the lowest concentration to 7.0 × 10-2μg·cm-1·h-1 at the highest P solution concentration.

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Phosphorus applications can increase potato yields in Michigan soils with over 400 kg·ha-1 Bray-Kurtz P1 extractable P. Four potato cultivars (Onaway (On), Kennebec (Ke), Russet Norkotah (RN), and Snowden (Sn)) were planted on 7 May 1993 to study P fertilizer effects on root growth and development. Each plot received adequate N & K, and either 0 or 50 kg·ha-1 P. Two minirhizotrons (5 cm i.d.) were set 1.1 m deep at 45° to the soil surface into each plot. P treatment did not influence tuber yield. At 65 days after planting, root counts for On, RN and Sn averaged 72, 44 and 58%. respectively, of those in Ke plots. The P treatment did not significantly influence total root counts within or across cultivars on any of five sampling dates. More visible roots were produced in the first 0.4 m of soil by plants receiving P than by plants not receiving P. Below the first 0.4 m, plants not fertilized with P produced more visible roots than those receiving P.

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