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Renuka Rao and Yuncong Li

The review of effects of excessive soil water on performance of various vegetable crops and selected field crops indicates that in areas where temporary flooding hazards are expected during the growing season, crops can be selected on their relative ability to tolerate excessive moisture. Field crops are generally less sensitive than vegetable crops in terms of yield. In addition to the choice of crop species, planting dates could be shifted when possible by delaying dates of sowing or planting to avoid probable periods of flooding during the sensitive growth stages. In most instances, crops are more sensitive at their early developmental phase than at the later stages in terms of yield. Soil management practices like ridging and furrowing or making raised beds before planting is recommended. In addition, amelioration with foliar application of chemicals like nutrients, growth hormones and fungicides is also recommended to overcome nutritional deficiencies, hormonal imbalances and disease infections. Every effort of amelioration should be exerted at the earliest opportunity, since water damage to crops becomes more severe with longer flooding duration.

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Yuncong Li and Min Zhang

Excessive bicarbonate concentrations and high irrigation water pH affect the growth and appearance of nursery plants in southern Florida. A greenhouse experiment consisting of five nitrogen (N) rates of urea or nitric acid was conducted to evaluate the influence of N sources and rates in irrigation water on bicarbonate concentrations, medium pH, and growth and appearance of anthurium (Anthurium andraeanum Lind.) plants. Pot medium pH, dry weight, plant appearance and N uptake by plants were significantly affected by N rates in irrigation water amended with either liquid urea or nitric acid, but the differences between the two N sources were not significant. The optimum growth and the best appearance of anthurium were achieved when N was added to irrigation well water as either urea or nitric acid at a rate of 20 mg·L-1 (ppm) and an electrical conductivity in a range of 0.36 to 0.42 dS·m-1 Nitrogen rates at 80 and 120 mg·L-1 induced adverse plant growth because of the greater salinity of the solutions and the lower pH of the medium.

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Herbert H. Bryan and Yuncong Li

Cover crops have become an integral part of vegetable production practices in south Florida for weed control and retaining nutrients during the heavy summer rains. A wide variety of plants are used as cover crops in south Florida. Obviously, legumes contribute more nitrogen by fixing N compared to nonlegumes such as sorghum sudan grass, which is a common cover crop in this area. We have evaluated 10 cover crops, where six were legumes in 1997. In 1998, four cover crops (sunnhemp, sorghum sudan, sesbania, and aeschynomene) were evaluated. The sunnhemp (Crotalaria juncea L.) stands out from other tested cover crops for 2 years. Sunnhemp produced 8960 to 11,400 kg dry weight/ha and fixed up to 285 kg N/ha. The evaluation of effects of sunnhemp and other cover crops on the following tomato growth and yield are still in progress and will be discussed.

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Qingren Wang, Yuncong Li and Waldemar Klassen

A pot experiment with summer cover crops and soil amendments was conducted in two consecutive years to elucidate the effects of these cover crops and soil amendments on `Clemson Spineless 80' okra (Abelmoschus esculentus) yields and biomass production, and the uptake and distribution of soil nutrients and trace elements. The cover crops were sunn hemp (Crotalaria juncea), cowpea (Vigna unguiculata), velvetbean (Mucuna deeringiana), and sorghum sudangrass (Sorghum bicolor × S. bicolor var. sudanense) with fallow as the control. The organic soil amendments were biosolids (sediment from wastewater plants), N-Viro Soil (a mixture of biosolids and coal ash, coal ash (a combustion by-product from power plants), co-compost (a mixture of 3 biosolids: 7 yard waste), and yard waste compost (mainly from leaves and branches of trees and shrubs, and grass clippings) with a soil-incorporated cover crop as the control. As a subsequent vegetable crop, okra was grown after the cover crops, alone or together with the organic soil amendments, had been incorporated. All of the cover crops, except sorghum sudangrass in 2002-03, significantly improved okra fruit yields and the total biomass production (i.e., fruit yields were enhanced by 53% to 62% in 2002-03 and by 28% to 70% in 2003-04). Soil amendments enhanced okra fruit yields from 38.3 to 81.0 g/pot vs. 27.4 g/pot in the control in 2002-03, and from 59.9 to 124.3 g/pot vs. 52.3 g/pot in the control in 2003-04. Both cover crops and soil amendments can substantially improve nutrient uptake and distribution. Among cover crop treatments, sunn hemp showed promising improvement in concentrations of calcium (Ca), zinc (Zn), copper (Cu), iron (Fe), boron (B), and molybdenum (Mo) in fruit; magnesium (Mg), Zn, Cu, and Mo in shoots; and Mo in roots of okra. Among soil amendments, biosolids had a significant influence on most nutrients by increasing the concentrations of Zn, Cu, Fe, and Mo in the fruit; Mg, Zn, Cu, and Mo in the shoot; and Mg, Zn, and Mo in the root. Concentrations of the trace metal cadmium (Cd) were not increased significantly in either okra fruit, shoot, or root by application of these cover crops or soil amendments, but the lead (Pb) concentration was increased in the fruit by application of a high rate (205 g/pot) of biosolids. These results suggest that cover crops and appropriate amounts of soil amendments can be used to improve soil fertility and okra yield without adverse environmental effects or risk of contamination of the fruit. Further field studies will be required to confirm these findings.

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Teresa Olczyk, Yuncong Li, Waldemar Klassen and Qingren Wang

Summer cover crops can improve soil fertility by adding organic matter, supplying nutrients through mineralization, reducing nutrient leaching, and improving soil water and nutrient holding capacity. Other benefits include weed suppression and reduction of soil parasitic nematodes. A series of field experiments have been conducted at the UF IFAS Tropical Research and Education Center in Homestead, Florida to evaluate several summer cover crops for use in vegetable production in South Florida followed by field demonstrations conducted in the growers' fields. Best performing cover crops were legumes: velvet bean (Macuna deeringiana) and sunn hemp (Crotalaria juncea L. `Tropic Sun') providing 13 and 11 Mt of dry matter/ha, respectively. Sunn hemp supplied 330 kg N/ha followed by velvet been with 310 kg N/ha. Traditional summer cover crop sorghum-Sudan produced 4 Mt of dry matter/ha and retained only 36 kg N/ha. In addition Sunn hemp significantly reduced soil parasitic nematodes for successive crops. Limitations in use of Sunn hemp by more vegetable growers in South Florida include cost and availability of seeds.

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Teresa Olczyk, Yuncong Li, Xing Wang and Eric Simonne

Sweet corn (Zea mays) is a major cash crop produced on calcareous soils in Miami–Dade County. Applications of large amounts of phosphorus (P) fertilizer for many years resulted in the accumulation of high levels of P in these soils. Accumulated P is slowly released into the soil solution to become available for plant roots. Previous studies conducted in this area showed little or no yield and crop quality response to P fertilizer applications. Large-scale field trials with reduced P applications were conducted in a grower's field. The treatments were: 1) no P; 2) 50% grower's rate; and 3) 100% grower's rate with six repilications. The data collected included: plant stand, height, nutrient concentrations in leaf tissue, leaf chlorophyll, tip fill, number, and weight of marketable ears/acre. Reduced rates of P fertilizer did not significantly reduce yield and quality of sweet corn.

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Guodong Liu, D. Marshall Porterfield, Yuncong Li and Waldemar Klassen

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.

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Gladis M. Zinati, Herbert H. Bryan and Yuncong Li

Using herbs for medicinal purposes, ornamentals, and landscape plantings has increased significantly. Propagating from seeds is considered the most-efficient method of producing medicinal plants for commercial production. Among the herb seeds the purple coneflower (Echinacea angustifolia) was found difficult to germinate. Laboratory studies were conducted to: 1) determine optimum temperature from a temperature range 15 to 30 °C for seed germination; 2) determine effects of 5 10, 20, and 30 days of stratification at 5 and 10 °C in darkness on germination; and 3) determine effects of priming in the dark for 1, 3, 6, and 9 days with 0.1 M KNO3 and biostimulants at optimum temperature to enhance early emergence and final germination. Germination was enhanced from 45% in untreated seeds to 81% in seeds treated with either 50 ppm GA4/7 or 100 ppm ethephon at 24 °C. Final germination was 81% under daylight conditions when seeds were stratified in dark at 10 °C for 30 days over nonstratified seeds (13%). Priming seeds in 0.1 M KNO3 for 3 days significantly enhanced early germination to 70% with 100 and 150 ppm ethephon and final percent germination of 88% with either 100 ppm ethephon or 150 ppm GA4/7, while untreated control seeds resulted in 31% for same period of priming.

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Yuncong Li, Tom Davenport, Renuka Rao and Qi Zheng

Despite the increasing popularity in American markets of the fruit of the illustrious lychee (Litchi chinensis Sonn.), unreliable flowering and yield has had serious impacts on lychee growers in southern Florida. Lychee flowering is normally induced by chilling temperatures. Unpredictable weather, high rainfall, and excessive nutrients cause unreliable flowering in southern Florida. Although growers have no control over the weather, they need to be able to manage the growth, vigor, and reproduction of trees through practices that optimize flowering. When excessively watered and fertilized, lychee trees grow vigorously with frequent vegetative flushes every 2 to 3 months. The lack of maturity of these late vegetative flushes prevents flower stimulation from mild temperatures in January and February, when flowering typically occurs on trees that have not experienced vegetative flushes in the late fall or early winter. Thus, by adopting nitrogen fertilizer management practice, growers should be able to induce abundant flowering even in mild winters. Our preliminary results demonstrated that timing and rates of applications of nitrogen fertilizer significantly affected concentrations of soil and leaf N. High nitrogen levels in the leaves induced more vegetative flushes and less flowering, and consequently less fruit yield.

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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.