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  • Author or Editor: Earl E. Albregts x
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The phosphorus content is usually high in soils on which strawberry production occurs in west central Florida because of moderate P levels in the virgin soil and yearly applications of P by the growers. A P rate study was conducted to test the calibration of P for strawberry nursery production, and a randomized complete block design with four replicates was used. Rates of 0, 11, 22, and 33 kg/ha P were applied to a Seffner sand which had an initial soil P level of 86 mg/kg using the Mehlich II soil extractant. Soil tests routinely show P soil concentrations up to 250 mg/kg or greater with 86 mg/kg rated in the high range. In this study the P applied to the beds was cultivated into the soil and six plants of two strawberry clones (Fl 87-210 and Fl 85-4925) were set in each plot on 28 May 1991. All nutrients except P were applied as needed during the season. Leaf P content of daughter plants on 20 Aug 1991 varied from 0.23 to 0.25% among P treatments and were not different because of P rates. All marketable size daughter plants were harvested on 8 Oct 1991. The number, total wt, and average wt of daughter plants were not different because of applied P rates.

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Eight colors of polyethylene mulch were evaluated in the strawberry (Fragaria × ananassa, Duch.) production field. Fruit production by March 1 was increased during 3 seasons by yellow and 2 seasons by white colored mulches compared to the black mulch. Average fruit weight, number of fruit per plant, and percent marketable fruit affected fruit yield depending on the season. Total fruit yield was reduced with some of the colored mulches during two seasons. The soil temperature of the plant beds was warmest throughout the season with the black mulched beds and coldest with the white and yellow mulched beds.

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During the 1992-93 fruiting season, strawberries were fertigated weekly with 0.28, 0.56, 0.84, 1.12, or 1.40 kg N/ha/day from ammonium nitrate. K was applied uniformly at 0.84 kg/ha/day by fertigation. Irrigation maintained soil moisture tension in the beds between -10 and -15 kPa. Fruit yields responded positively to N fertilization with yields maximized at 0.56 kg N/ha/day. Leaf N and petiole sap nitrate N concentrations increased with N rate with leaf-N for the plants receiving 0.28 kg N/ha/day remaining below 25 g·kg-1 most of the season. Sufficiency ranges for petiole sap nitrate-N quick testing were developed.

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During the 1992-93 fruiting season, straw berry plants were fertigated weekly with either 0.28, 0.56, 0.84, 1.12, or 1.40 kg/ha/day of K derived from KCl. Other nutrients were applied in the plant bed before fumigation except for N which was applied at 0.84 kg/ha/day by fertigation. Soil moisture in the plant beds was maintained between 10 and 15 cbs. Initial soil K tested medium with the Mehlich I soil test. Seasonal average fruit weight and percent marketable fruit decreased with increasing K rate. Seasonal fruit yields did not increase with K rates above 0.56 kg/ha/day. Leaf K concentrations increased with increasing K rates throughout the harvest season. The leaf K concentrations in the 0.28 K treatment were below 1% during the last month of harvest. K rates did not affect fruit firmness.

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Abstract

‘Douglas’, ‘Tufts’, and ‘Pajaro’ strawberry (Fragaria × ananassa Duch.) plants were sampled for 3 consecutive years (1982–1984), and ‘Chandler’ plants were sampled for one year (1984) from September through October from a North Carolina nursery. Plants were subjected to short days (12-hr photoperiod) at day/night temperatures of 15.5°/4.4°C in 1982–1983 and to short days (9-hr photoperiod) and long days (9-hr photoperiod with a 3-hr night interruption) with or without chilling [15.5°/4.4° (day/night) or 22.0718.0° (day/night), respectively] in 1984 for 0, 1, 6, or 12 days in the NCSU phytotron. After treatment, plants were shipped to Florida for planting in the winter planting system for evaluation of early season yield (1 Dec. -15 Jan.). Optimum digging dates for all cultivars were observed to be a photoperiod response. Chilling enhanced early yield for ‘Douglas’ and ‘Pajaro’ when plants were dug prior to or at the optimum date. Plants dug later than the optimum date had much lower yields, even with substantial chilling. In ‘Chandler’, slight chilling (<125 hr from 1 Sept. until digging date) suppressed early yield, while increased chilling (>125 hr) enhanced early yield when plants were dug at or prior to the optimum date. Chilling decreased early yield in ‘Tufts’ regardless of digging date. Significant yield increases were only obtained with chilling much greater than that which naturally occurs in North Carolina.

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Cold-stored (frigo) plants of `Irvine' and `Seascape' and non-chilled plug plants of `Sweet Charlie' and FL 87-123 were planted on August 31 on raised beds covered with white-on-black polyethylene mulch. Very little water was needed for establishment of these plants (compared to that which is normally needed for the establishment of foliated bareroot plants). `Irvine' and `Seascape' produced more runners and were later to initiate fruit production than `Sweet Charlie' and FL 87-123. `Sweet Charlie' and FL 87-123 started producing a small amount of marketable fruit in late October, while `Irvine' and `Seascape' did not produce any marketable fruit until mid and late January respectively.

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Plants of `Selva', `Pajaro', and three Univ. of Florida strawberry (Fragaria × ananassa Duch.) selections were grown near Dover, Fla., for five seasons using the annual hill cultural system. Genotype × environment interactions were significant for both marketable yield and fruit weight; therefore, stability analyses were performed. None of the genotypes had consistently high marketable yield, but one of the selections, FL M-1350, had relatively large and stable average fruit size. A genotype was desirable if it had a mean yield (or fruit weight) above the grand mean of all five genotypes, a regression coefficient 1, and a nonsignificant deviation from regression.

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Strawberries (Fragaria ×ananassa Duch.) were grown in two seasons at Dover, Fla., with polyethylene mulch and drip irrigation. Nitrogen was injected weekly at 0.28 (50), 0.56 (100), 0.84 (150), 1.12 (200), and 1.40 (250) kg N/ha per day (kg·ha-1 for season) for `Oso Grande' and `Sweet Charlie' in 1991-92 season and for `Oso Grande' and `Seascape' in 1992-1993 season. Nitrogen fertilization in 1991-1992, over the range of 0.28 to 1.40 kg N/ha per day, had no significant effect on early (November to January) strawberry yields. March (the largest production month) yield and total-season yield increased with increasing N fertilization to 0.76 and 0.54 kg N/ha per day, respectively. Nitrogen fertilization did not affect yields of strawberry in 1992-93. Fruit firmness and average fruit weight were not affected by N fertilization from 0.28 to 1.40 kg N/ha per day. Nitrogen fertilization increased whole leaf N, leaf blade N, and petiole sap nitrate-N concentrations linearly for most sampling dates in both years. Early yields were greater for `Sweet Charlie' than `Oso Grande'. Yields were greater for `Oso Grande' during March, and total-season yields were similar for both cultivars in 1991-92. `Oso Grande' had greater early, March, and total yields than `Seascape' in 1992-93.

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`Oso Grande' and `Sweet Charlie' strawberries (Fragaria × ananassa Duch.) in 1991-92 and `Oso Grande' and `Seascape' in 1992-93 were grown in a K fertilization study using polyethylene-mulched and fumigated beds. Potassium was injected weekly into the drip irrigation system at 0.28,0.56,0.84, 1.12, and 1.40 kg K/ha per day. Early, March, and total-season marketable fruit yields were not affected by K rate during either season. The average fruit weight of `Oso Grande' for the early, March, and total-season harvest periods in the 1992-93 season decreased with increased K rate. For the same harvest periods, `Seascape' average fruit weight increased, decreased, and did not change, respectively, with increased K rate. Cull fruit yield during both seasons and fruit firmness during the 1992-93 season were not affected by K rate. Petiole sap, whole leaf, and leaf blade K concentrations increased with increasing K rates on most sampling dates during both seasons. `Oso Grande' and `Sweet Charlie' produced similar total marketable fruit yields the first season, but `Oso Grande' produced higher total yields than `Seascape' during all harvest periods of the second season.

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