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Qingren Wang, Waldemar Klassen, Yuncong Li, Merlyn Codallo, and Aref A. Abdul-Baki

Intensive rainfall during summer causes substantial nutrient leaching in a subtropical region, where most vegetable lands lay fallow during this period. Also, an excessive amount of irrigation water supplied during the winter vegetable growing season leads to soil nutrient loss, which greatly impacts vegetable yields, especially in soils that possess a low capacity to retain soil water and nutrients. A 2-year field experiment was carried out to evaluate the effects of various summer cover crops and irrigation rates on tomato yields and quality, and on soil fertility in a subtropical region of Florida. The cover crops were sunn hemp [Crotalaria juncea (L.) `Tropic Sun'], cowpea [Vigna unguiculata (L.) Walp, `Iron Clay'], velvetbean [Mucuna deeringiana (Bort.) Merr.], and sorghum sudangrass [Sorghum bicolor × S. bicolor var. sudanense (Piper) Stapf.], with a weed-free fallow as a control. The cover crops were planted during late Spring 2001 and 2002, incorporated into the soil in the fall, and tomatoes [Lycopersicon esculentum (Mill.) `Sanibel'] were grown on raised beds during Winter 2001–02 and 2002–03, respectively. Irrigation in various treatments was controlled when tensiometer readings reached –5, –10, –20, or –30 kPa. The cover crops produced from 5.2 to 12.5 Mg·ha–1 of above ground dry biomass and 48 to 356 Mg·ha–1 of N during 2001–02 and from 3.6 to 9.7 Mg·ha–1 of dry biomass and 35 to 277 kg·ha–1 of N during 2002–03. The highest N contribution was made by sunn hemp and the lowest by sorghum sudangrass. Based on 2-year data, tomato marketable yields were increased from 14% to 27% (p ≤ 0.05) by growing cover crops, and the greatest increase occurred in the sunn hemp treatment followed by the cowpea treatment. Irrigation at –10, –20, and –30 kPa significantly improved marketable yields by 14%, 12%, and 25% (p ≤ 0.05) for 2001–02, and 18%, 31%, and 34% (p ≤ 0.05) for 2002–03, respectively, compared to yields at the commonly applied rate, –5 kPa (control). Irrigation at –30 kPa used about 85% less water than at –5 kPa. Yields of extra-large fruit in the sunn hemp and cowpea treatments from the first harvest in both years averaged 12.6 to 15.2 Mg·ha–1, and they were significantly higher than yields in the fallow treatment (10.2 to 11.3 Mg·ha–1). Likewise at –30 kPa yields of extra-large fruit from the first harvest for both years were 13.0 to 15.3 Mg·ha–1 compared to 9.8 to 10.7 Mg·ha–1 at –5 kPa. Soil NO3-N and total N contents in sunn hemp and cowpea treatments were significantly higher than those in fallow. The results indicate that growing legume summer cover crops in a subtropical region, especially sunn hemp and cowpea, and reducing irrigation rates are valuable approaches to conserve soil nutrients and water, and to improve soil fertility and tomato yields and quality.

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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.

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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.

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Rafael Muñoz-Carpena, Yuncong C. Li, Waldemar Klassen, and Michael D. Dukes

A low-volume/high frequency (LVHF) soil moisture-based drip irrigation system was tested on a shallow sandy soil at a commercial tomato (Lycopersicon esculentum) farm in southern Florida. Six LVHF irrigation treatments were compared with the standard commercial practice on the farm (control), where a portable pump was used for manual drip irrigation twice each week. In the six LVHF treatments the system was continuously pressurized by means of an electrical pump and a pressure tank, and controlled by an irrigation timer set to irrigate a maximum of five times per day with the irrigation time (i.e., volume) set according to historical evapotranspiration (ET) demands in the area. Two treatments were based on timer schedules, one to supply 100% of the maximum recommended crop water needs in the area based on historical ET (ET-100%), and the other to supply 150% of those needs (ET-150%). The other four treatments were created by interfacing two types of soil moisture sensors (switching tensiometers and granular matrix sensors with control modules) set at two moisture points (wet = 10 kPa, optimal = 15 kPa) in a closed control loop with the irrigation timer programmed at the ET-100% schedule. Results showed that the six LVHF treatments reduced water use while not significantly affecting tomato yields. Switching tensiometers at the 15 kPa set point performed the best (up to 73% reduction in water use when compared to the control, 50% with respect to ET-100%). The results show that water use below historical ET levels can be obtained without sacrificing yield by keeping the root zone moisture at controlled levels with the soil-moisture based system. Routine maintenance was critical for reliable operation of the switching tensiometers. Granular matrix sensor based irrigation behaved erratically, and did not improve water savings compared to ET-100%, indicating that this system was not effective under the conditions of the area due to the sensor's slow response to frequent wetting-rewetting cycles and characteristics of the interface.

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Yuncong Li, Edward Hanlon, George O'Connor, Jianjun Chen, and Maria Silveira

Compost is the product resulting from the controlled biological decomposition of organic material that has been sanitized through the generation of heat and processed to further reduce pathogens as defined by the U.S. Environmental Protection Agency and stabilized to the point that the compost is beneficial to plant growth. Organic materials used for composting in Florida are mainly yard wastes (trash) and food wastes. More than 5.7 million tons of composts could be produced from yard trash and food waste in the state. Animal manure and biosolids (treated sludge) can also be composted, but are not discussed in this article. “Other wastes” as discussed herein [food processing wastes, coal ash, wood ash, drinking water treatment residuals (WTRs), and phosphogypsum] are by-products of leading Florida industries and are available in large quantities for reuse. About 5 million tons of food processing waste [citrus (Citrus spp.) and vegetables alone], 1.85 million tons of coal ash (from 28 coal-burning power plants), 0.05 million tons of wood ash, 1000 million tons of phosphogypsum (from the state's phosphate fertilizer industry), and significant, but unknown, amounts of WTRs are available. Due to the growing interest in sustainable agriculture practices, this article is intended to discuss the current regulations and guidelines for composting and the use of composts and other wastes in Florida, the characteristics, benefits, and concerns of Florida compost and other wastes, and current research and needs of research and extension for incorporating compost and other waste materials in Florida's sustainable agriculture. Our literature search was largely limited to studies conducted in Florida.

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Qiang Zhu, Yuncong C. Li, Rao S. Mylavarapu, Kelly Morgan, and Mingjian Geng

Preplant soil testing is essential for optimizing phosphorus (P) fertilization and minimizing the potential for soil P losses. Currently, there is no effective soil P extractant for calcareous soils in Florida. This study was conducted to compare Mehlich-3, ammonium bicarbonate–diethylenetriaminepentaacetic acid (AB-DTPA), and Olsen for evaluating P availability, estimating soil-test P (STP) critical levels, and calibrating P application rates for fresh-market tomato (Solanum lycopersicum L.) production in a calcareous soil. Tomatoes were grown during Winter 2014 and 2015 with P application rates of 0, 29, 49, 78, 98, and 118 kg·ha‒1 P. Water-extractable P (water-P) and dissolved reactive P (DRP) in leachate were used to determine the STP change point of leaching potential. Results showed the greatest correlation occurred between Mehlich-3 and Olsen of the three STP extractants. For Mehlich-3-P, the medium STP level (producing 75% to 90% relative yield) was predicted from 76 to 89 mg·kg‒1 and the change point was predicted at 88 or 104 mg·kg‒1 by split-line models. The P requirement was calculated from 52 to 112 kg·ha‒1 when Mehlich-3-P was rated as low level (producing 50% to 75% relative yield), which was from 42 to 76 mg·kg‒1. The multiple regression models using AB-DTPA-P and Olsen-P could not predict either the medium STP level or the practical P application rates for the low level. Consequently, based on 2 years of data, Mehlich-3 was the most effective extractant for estimating soil P availability and calibrating P rates in calcareous soils with an extremely high calcium carbonate (CaCO3) content.

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Sueyde Fernandes de Oliveira Braghin, Simone C. Mello, Jéssika Angelotti-Mendonça, Keigo Minami, and Yuncong C. Li

Fertilizer management is an essential step in the production process, as it allows the plant to use its productive capacity to the fullest extent possible. Researchers have tested maximum nutrient use with reduced losses to the environment aiming to increase productivity with fewer environmental impacts. This study compared the effects of controlled-release fertilizers (CRFs) with water-soluble fertilizer (WSF) and clear water (control) on the growth and nutrient uptake of croton (Codiaeum variegatum L.) and nitrogen leaching. The experiment was conducted with three replications and six treatments: two rates (1.5 g and 3.0 g per liter of substrate) of two CRFs [Osmocote Plus (15% N, 3.93% P, and 9.96% K) and Basacote (15% N, 3.49% P, and 9.96% K)], WSF, and clean water as control. All CRFs were applied before planting and WSF was supplied as nutrient solution through automated moisture sensor activated irrigation system. Plant growth (number of leaves, leaf area, stem height, root volume, and shoot and root dry weights) and total nutrient contents in the leaf tissue were evaluated every 30 days. Electrical conductivity (EC), pH, nitrate, ammonium, and total nitrogen contents were measured in the leached solution. Indeed, results showed that CRFs at a low rate provided similar development and quality of croton plants compared with WSF. Plant growth indicators were similar until 90 days after transplanting (DAT). After that, at 150 DAT, the highest values to number of leaves and leaf area occurred with WSF and with the lowest CRF rate as compared with the other treatments and control. The highest root volume was found with the WSF, which resulted in larger roots compared with the other treatments. These results showed WSF can be replaced by CRFs at low rates on croton growth. Moreover, according to the visual scale, the best treatments were WSF and Basacote at the low rate, where plants were bright, with multicolored leaves with prominent orange shades. However, CRFs maintained pH and EC within the recommended range for the growth of croton and reduced the nitrogen leaching from the pots.

Open access

Wenjing Li, Zihang Zhang, Ji Tian, Jie Zhang, Yanfen Lu, Xiaoxiao Qin, Yujing Hu, and Yuncong Yao

Free access

Ji Tian, Zhen-yun Han, Li-ru Zhang, Ting-Ting Song, Jie Zhang, Jin-Yan Li, and Yuncong Yao

Anthocyanins are protective pigments that accumulate in plant organs such as fruits and leaves, and are nutritionally valuable components of the human diet. There is thus considerable interest in the factors that regulate synthesis. Malus crabapple leaves are rich sources of these compounds, and in this study we analyzed leaf coloration, anthocyanin levels, and the expression levels of anthocyanin biosynthetic and regulatory genes in three crabapple cultivars (Royalty, Prairifire, and Flame) following various temperature treatments. We found that low temperatures (LTs) promoted anthocyanin accumulation in ‘Royalty’ and ‘Prairifire’, leading to red leaves, but not in ‘Flame’, which accumulated abundant colorless flavonols and retained green colored leaves. Quantitative reverse transcript PCR (RT-PCR) analyses indicated that the expression of several anthocyanin biosynthetic genes was induced by LTs, as were members of the R2R3-MYB, basic helix–loop–helix (bHLH) and WD40 transcription factor families that are thought to act in a complex. We propose that anthocyanin biosynthesis is differentially regulated in the three cultivars by LTs via the expression of members of this anthocyanin regulatory complex.

Free access

Mary Lamberts, Teresa Olczyk, Phyllis Gilreath, Gene McAvoy, Alicia Whidden, Darrin Parmenter, Ed Skvarch, Yuncong Li, Christine Coffin, and Donald Pybas

Florida, like other states, is developing BMPs for specific commodities. Vegetables are in a statewide document that includes field crops. Vegetable advisory committee members from the counties in southern Florida were concerned that the existing document was too broad in its scope and that many practices did not apply to production on sandy or calcareous soils. Based on grower comments, extension agents organized grower meetings to address these issues. The first meeting was a presentation by the Florida Department of Agriculture and Consumer Services (FDACS) Office of Agricultural Water Policy. The second meeting in Miami–Dade was a hands-on session, where growers and industry were divided into three areas—nutrition, pesticides, and water quality. Each group was facilitated by a faculty member or the NRCS conservationist. Other counties used newsletters and other methods to receive grower feedback. Participant comments were compiled and forwarded to FDACS, where they are being incorporated into a greatly revised document. Concerns will be presented.