Large and/or aged seeds are prone to hypoxic conditions during germination. Germination of selected vegetable seeds including corn (Zea mays L.), squash (Cucurbita pepo L.), and tomato (Solanum lycopersicum L.) was studied in water with different concentrations of hydrogen peroxide (H2O2) solution ranging from 0, 0.06% to 3.0% (v/v) or in aeroponics, all with 0.5 mm CaSO4. Imbibition, oxygen consumption, proton extrusion, and alcohol dehydrogenase (ADHase) activity of corn seeds were measured gravimetrically, electrochemically, and colorimetrically as appropriate. The results showed that 0.15% H2O2 provided the optimum oxygen concentration for seed germination. The germination percentage of aged corn seeds treated with H2O2 was significantly greater than those without H2O2 treatment. Corn embryo orientation in relation to a moist substrate also significantly impacted oxygen bioavailability to the embryo and hence ADHase activity. Corn seeds without H2O2 imbibed significantly more slowly than those with oxygen fortification by 0.15% H2O2. Increased oxygen bioavailability improved the metabolism of the seeds, which extruded 5-fold more protons from the embryos. Each treated embryo consumed twice the amount of oxygen as compared with the untreated one and likewise for treated and untreated endosperms. Increased oxygen bioavailability may be used to improve production of the tested crops. The results from this research imply that consideration should be given to including oxygen fortification in seed coatings for aged seeds and for large seeds regardless of age. The artificial provision of bioavailable oxygen might be effective in rescuing the germplasm in aged seeds in plant breeding and in crop production.
Guodong Liu, D. Marshall Porterfield, Yuncong Li, and Waldemar Klassen
Yang Fang, Jeffrey Williamson, Rebecca Darnell, Yuncong Li, and Guodong Liu
Southern highbush blueberry (SHB, Vaccinium corymbosum L. interspecific hybrid) is the major species planted in Florida because of the low-chilling requirement and early ripening. The growth pattern and nitrogen (N) demand of SHB may differ from those of northern highbush blueberry (NHB, V. corymbosum L.). Thus, the effect of plant growth stage on N uptake and allocation was studied with containerized 1-year-old SHB grown in pine-bark amended soil. Five ‘Emerald’ plants were each treated with 6 g 10% 15N labeled (NH4)2SO4 at each of 12 dates over 2 years. In the first year, plants were treated once in late winter, four times during the growing season, and once in the fall. In the second year, treatment dates were based on phenological stages. After a 14-day chase period following each 15N treatment, plants were destructively harvested for dry weight (DW) measurements, atom% of 15N, and N content of each of the plant tissues. Total DW increased continuously from mid-May 2015 to Oct. 2015 and from Mar. 2016 to late Sept. 2016. From August to October of both years, external N demand was the greatest and plants absorbed more N during the 2-week chase period, about 0.53 g/plant in year 1 and 0.67 g/plant in year 2, than in chase periods earlier in the season. During March and April, N uptake was as low as 0.03 g/plant/2 weeks in year 1 and 0.21 g/plant/2 weeks in year 2. Nitrogen allocation to each of the tissues varied throughout the season. About half of the N derived from the applied fertilizer was allocated to leaves at all labeling times except the early bloom stage in 2016. These results suggest that young SHB plants absorb greater amounts of N during summer and early fall than in spring.
Qiang Zhu, Monica Ozores-Hampton, Yuncong Li, Kelly Morgan, Guodong Liu, and Rao S. Mylavarapu
Florida produces the most vegetables in the United States during the winter season with favorable weather conditions. However, vegetables grown on calcareous soils in Florida have no potassium (K) fertilizer recommendation. The objective of this study was to evaluate the effects of K rates on leaf tissue K concentration (LTKC), plant biomass, fruit yield, and postharvest quality of tomatoes (Solanum lycopersicum L.) grown on a calcareous soil. The experiment was conducted during the winter seasons of 2014 and 2015 in Homestead, FL. Potassium fertilizers were applied at rates of 0, 56, 93, 149, 186, and 223 kg·ha−1 of K and divided into preplant dry fertilizer and fertigation during the season. No deficiency of LTKC was found at 30 days after transplanting (DAT) in both years. Potassium rates lower than 149 kg·ha−1 resulted in deficient LTKC at 95 DAT in 2014. No significant responses to K rates were observed in plant (leaf, stem, and root combined) dry weight biomass at all the sampling dates in both years. However, at 95 DAT, fruit dry weight biomass increased with increasing K rates to 130 and 147 kg·ha−1, reaching a plateau thereafter indicated by the linear-plateau models in 2014 and 2015, respectively. Predicted from quadratic and linear-plateau models, K rates of 173 and 178 kg·ha−1 were considered as the optimum rates for total season marketable yields in 2014 and 2015, respectively. Postharvest qualities, including fruit firmness, pH, and total soluble solids (TSS) content, were not significantly affected by K rates in both years. Overall, K rate of 178 kg·ha−1 was sufficient to grow tomato during the winter season in calcareous soils with 78 to 82 mg·kg−1 of ammonium bicarbonate-diethylenetriaminepentaacetic acid (AB-DTPA)-extracted K in Florida.
Qiang Zhu, Monica Ozores-Hampton, Yuncong Li, Kelly Morgan, Guodong Liu, and Rao S. Mylavarapu
Phosphorous (P) has a significant role in root growth, fruit and seed development, and plant disease resistance. Currently, no P fertilizer recommendations are available for vegetables grown on calcareous soils in Florida. The objective of this study was to evaluate the impact of different P rates on leaf tissue P concentration (LTPC), plant growth, biomass accumulation, fruit yield, and postharvest quality of tomato (Solanum lycopersicum L.) grown on a calcareous soil. The experiment was conducted with soils containing 13 to 15 mg·kg−1 of P extracted by ammonium bicarbonate-diethylenetriaminepentaacetic acid (AB-DTPA). Phosphorus fertilizers were applied at rates of 0, 29, 49, 78, 98, and 118 kg·ha−1 of P before laying polyethylene mulch. Tomatoes were grown using drip irrigation during the winter seasons of 2014 and 2015. No significant responses to P rates were found in LTPC during both growing seasons. Plant height, stem diameter, and leaf chlorophyll content at 30 days after transplanting (DAT) were significantly affected by P rates in 2015, but not in 2014. The responses of plant biomass were predicted by linear models at 60 DAT in 2014 and at 30 DAT in 2015. There were no significant differences in plant biomass at 95 DAT in both years. At the first and second combined harvest, the extralarge fruit yield was unaffected in 2014, but predicted by a quadratic-plateau model with a critical rate of 75 kg·ha−1 in 2015. The total season marketable yields (TSMY) and postharvest qualities were not significantly affected by P rates in either year. Phosphorous rate of 75 kg·ha−1 was sufficient to grow a tomato crop during the winter season in calcareous soils with 13–15 mg·kg−1 of AB-DTPA-extractable P.
Ibukun T. Ayankojo, Kelly T. Morgan, Davie M. Kadyampakeni, and Guodong D. Liu
Effective nutrient and irrigation management practices are critical for optimum growth and yield in open-field fresh-market tomato production. Although nutrient and irrigation management practices have been well-studied for tomato production in Florida, more studies of the current highly efficient production systems would be considered essential. Therefore, a two-season (Fall 2016 and Spring 2017) study was conducted in Immokalee, FL, to evaluate the effects of the nitrogen (N) rates under different irrigation regimes and to determine the optimum N requirement for open-field fresh-market tomato production. To evaluate productivity, the study investigated the effects of N rates and irrigation regimes on plant and root growth, yield, and production efficiency of fresh-market tomato. The study demonstrated that deficit irrigation (DI) targeting 66% daily evapotranspiration (ET) replacement significantly increased tomato root growth compared with full irrigation (FI) at 100% ET. Similarly, DI application increased tomato growth early in the season compared with FI. Therefore, irrigation applications may be adjusted downward from FI, especially early during a wet season, thereby potentially improving irrigation water use efficiency (iWUE) and reducing leaching potential of Florida sandy soils. However, total marketable yield significantly increased under FI compared with DI. This suggests that although DI may increase early plant growth, the application of DI throughout the season may result in yield reduction. Although N application rates had no significant effects on biomass production, tomato marketable yield with an application rate of 134 kg·ha−1 N was significantly lower compared with other N application rates (179, 224, and 269 kg·ha−1). It was also observed that there were no significant yield benefits with N application rates higher than 179 kg·ha−1. During the fall, iWUE was higher under DI (33.57 kg·m−3) than under FI (25.57 kg·m−3); however, iWUE was similar for both irrigation treatments during spring (FI = 14.04 kg·m−3; DI = 15.29 kg·m−3). The N recovery (REC-N) rate was highest with 134 kg·ha−1 N; however, REC-N was similar with 179, 224, and 269 kg·ha−1 N rates during both fall and spring. Therefore, these study results could suggest that DI could be beneficial to tomato production only when applied during early growth stages, but not throughout the growing season. Both yield and efficiency results indicated that the optimum N requirement for open-field fresh-market tomato production in Florida may not exceed 179 kg·ha−1 N.