In winter strawberry (Fragaria × ananassa Duch.) production, early-season nitrogen (N) fertilization greatly affects fruit earliness and yields, especially when pre-plant N is not applied. The ...objective of this study was to characterize the dose-responses of canopy growth, yield, and fruit quality to early-season N fertilization in ‘Florida Radiance’ and ‘Florida127’ strawberry. Field experiments were conducted in west-central Florida, United States. Treatments included four (0.56, 0.84, 1.12 and 1.40 kg ha−1 d−1) and five (0.22, 0.67, 1.12, 1.57, and 2.02 kg ha−1 d−1) early-season N rates in the first and second growing seasons, respectively. Increasing the early-season N rate increased early and total season yields by up to 62% to 65% and 56% to 58%, respectively, in the two cultivars. The total season yield had high positive correlations with leaf area and shoot DW. Model fitting analysis revealed cultivar-dependent dose-responses. Yield and berry size responses in ‘Florida Radiance’ were linear increases, whereas those in ‘Florida127’ were quadratic with peaks occurring at N rates of 1.21 or 1.57 kg ha−1 d−1. In ‘Florida Radiance’, soluble solids concentration showed a linear dose-response with a slope of –0.91 (0.91 °Brix decrease per 1 kg ha−1 d−1 N increase) during the early season. These results suggest that optimization of early-season N fertilization is an important production strategy to improve the profitability of winter strawberry production. Furthermore, fertilizer management that takes into account cultivar-dependent dose-responses can improve fertilizer use efficiency while minimizing fruit quality loss and environmental pollution risks.
Under inadequate chilling conditions, hydrogen cyanamide (HC) is often used to promote budbreak and improve earliness of Southern highbush blueberry (Vaccinium corymbosum L. interspecific hybrids). ...However, HC is strictly regulated or even banned in some countries because of its high hazardous properties. Development of safer and effective alternatives to HC is critical to sustainable subtropical blueberry production. In this study, we examined the efficacy of HC and defoliants as bud dormancy-breaking agents for 'Emerald' blueberry. First, we compared water control, 1.0% HC (9.35 L ha.sup.-1 ), and three defoliants potassium thiosulfate (KTS), urea, and zinc sulfate (ZS) applied at 6.0% (28 kg ha.sup.-1). Model fitting analysis revealed that only HC and ZS advanced both defoliation and budbreak compared with the water control. HC-induced budbreak showed an exponential plateau function with a rapid phase occurring from 0 to 22 days after treatment (DAT), whereas ZS-induced budbreak showed a sigmoidal function with a rapid phase occurring from 15 to 44 DAT. The final budbreak percentage was similar in all treatments (71.7%-83.7%). Compared with the water control, HC and ZS increased yield by up to 171% and 41%, respectively, but the yield increase was statistically significant only for HC. Phytohormone profiling was performed for water-, HC- and ZS-treated flower buds. Both chemicals did not increase gibberellin 4 and indole-3-acetic acid production, but they caused a steady increase in jasmonic acid (JA) during budbreak. Compared with ZS, HC increased JA production to a greater extent and was the only chemical that reduced abscisic acid (ABA) concentrations during budbreak. A follow-up experiment tested ZS at six different rates (0-187 kg ha.sup.-1) but detected no significant dose-response on budbreak. These results collectively suggest that defoliants are not effective alternatives to HC, and that HC and ZS have different modes of action in budbreak induction. The high efficacy of HC as a dormancy-breaking agent could be due to its ability to reduce ABA concentrations in buds. Our results also suggest that JA accumulation is involved in budbreak induction in blueberry.
Quantification of plant phenotypic traits, such as height, width, stem diameter, and leaf area, is often performed manually in the field; however, these measurements can be performed more quickly and ...precisely through simple imaging techniques using an image processing program. This new 5-page publication of the UF/IFAS Horticultural Sciences Department, written by Shinsuke Agehara, describes simple imaging techniques for plant growth assessment using the public domain program ImageJ.https://edis.ifas.ufl.edu/hs1353
Tryptophan is a precursor of indole-3-acetic acid (IAA), which is the major auxin involved in the regulation of lateral root formation. In this study, we used a scanner-based rhizotron system to ...examine root growth and morphological responses of soybean (Glycine max, ‘Golden Harvest’) seedlings to exogenous tryptophan. Seeds were sown directly in the rhizotron filled with field soil. Tryptophan was applied at 1.9 and 3.8 mg plant−1 by soil drenching or foliar spray. Canopy and root projected area were monitored by analyzing canopy and rhizotron images using ImageJ software. Seedlings were sampled at the first trifoliate stage, 18 days after sowing (DAS), and root morphology was determined by analyzing washed root images using WinRHIZO software. According to contrast analysis, when all tryptophan treatments were pooled, tryptophan application increased canopy and root projected area by 13% to 14% compared with the control at 18 DAS. Tryptophan application also increased root dry matter accumulation by 26%, root:shoot ratio by 24%, and secondary root number by 13%. Tryptophan applied by soil drenching also increased root length and surface area of fine roots (<0.2 mm diameter) by 25% and 21%, respectively, whereas it slightly inhibited primary root elongation. The efficacy of tryptophan soil drenching in stimulating root formation became greater with increasing the application rate. These results suggest that exogenous tryptophan induces auxin-like activities in root development. Soil drenching of tryptophan appears to be an effective strategy in improving the establishment of soybean. Importantly, this strategy is easily implementable by commercial growers with no negative side effect.
Strawberry is an important crop in Florida, produced as an annual crop on plastic-mulched beds with drip irrigation. The main production area is in west-central Florida, including Hillsborough, Polk, ...and Manatee counties. Fertilizer is becoming a more significant portion of strawberry production costs, hence, proper fertilizer management is important for minimizing production costs and maximizing yield and fruit quality, while minimizing potential negative impacts on the environment caused by leaching or runoff of excess fertilizer nutrients. This guide summarizes the recent history of strawberry fertilization research and presents the updated research-based fertilizer management recommendations for strawberry production in Florida.
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•White-striped plastic mulch reduces root-zone temperatures during establishment.•White-striped mulch allows winter strawberry growers to advance transplanting.•Entirely black mulch ...and white-striped mulch exhibit comparable winter soil warming.•White-striped mulch increased early yield up to 46% and total yield up to 11%.•The magnitude of yield increase by white-striped mulch is cultivar-dependent.
Early-season yields are critical to winter strawberry (Fragaria ×ananassa Duch.) production in Florida and other winter and spring production regions around the world. Although advancing planting dates is a common practice to improve earliness, it can increase heat stress during establishment, especially on black plastic mulch. This problem could be addressed by adding a white center stripe to black plastic mulch. The white center stripe should cool the root zone during establishment while the black bed shoulders remain exposed to the sun to warm the soil during the winter. We conducted three field trials across two seasons to compare black plastic mulch (black mulch) to black plastic mulch with a white center stripe (white-striped mulch) using three cultivars (Florida Radiance, Florida Beauty, and Florida Brilliance). Bare-root transplants were planted on 26 Sept. in 2015 and 29 Sept. and 17 Oct. in 2016. Compared to black mulch, white-striped mulch reduced root-zone temperatures (10-cm depth) under the white stripe by up to 4.5 °C in November, while maintaining the same soil warming capacity on the bed shoulders throughout the growing season. White-striped mulch treatments resulted in increased growth, earliness, and yields, although the magnitude of improvement depended on cultivars and seasonal weather conditions. Early-season ambient temperatures were unusually high in the 2015–16 trial and the 2016–17 later-planted trial. In these two trials, white-striped mulch increased early yields by 20%–31% across cultivars. In the 2015–16 trial, white-striped mulch also increased canopy area by 11% during the early harvest period and root biomass by 26% at the end of the trial. Because late-season yields were unaffected in all trials, white-striped mulch only improved total yields for the second planting of 2016–17. By contrast, cultivar-specific effects were only observed for the first planting of 2016–17, in which white-striped mulch improved early and total yields of ‘Florida Radiance’ by 46% and 28%, respectively, compared to black mulch. Our results suggest that white-striped mulch is an easily implementable strategy for improving earliness of winter strawberry production in warm climates.
Inadequate winter chill causes poor budbreak in blackberry (
Rubus
L. subgenus
Rubus
Watson), limiting the commercial production in the subtropics. In ‘Natchez’ blackberry, our previous study found ...that, under inadequate chilling conditions, urea and lime sulfur (LS) applied as defoliants before chill accumulation advanced budbreak but did not improve final budbreak. In this study, we applied the two defoliants at the end of chill accumulation and examined their effectiveness in breaking dormancy, with a hypothesis that it can be enhanced with increased exposure to chilling. Field experiments were conducted over two growing seasons under subtropical climatic conditions. ‘Natchez’ blackberry was sprayed with urea or LS at 10%. Both defoliants were effective in both advancing and maximizing budbreak. Final budbreak reached 42.6% to 76.8% in the defoliant treatments, compared with 27.1% to 31.6% in the control. Advanced budbreak by defoliants increased early season yield by 35% to 88%. Although not statistically significant, defoliants increased total-season yield by 19% to 56%, compared with the control. Phytohormone profiling revealed no changes in abscisic acid and gibberellic acid 4, but increasing trends in jasmonic acid and indole-3-acetic acid (IAA) during budbreak. The LS treatment increased IAA accumulation by up to 377% compared with the control. These results suggest that urea and LS are highly effective dormancy-breaking agents for blackberry when applied after winter chill accumulation. These defoliants could be an important adaptation tool for subtropical blackberry production. Furthermore, increased IAA accumulation appears to be, at least in part, the mode of action for LS-induced budbreak.
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