Search Results

Florida's citrus (Citrus spp.), vegetable, and turfgrass industries must improve nitrogen (N) and phosphorus (P) fertilizer use efficiency to remain sustainable in an era of emerging environmental policies designed to protect water quality. Producers have traditionally used water-soluble N and P fertilizers because they are plentiful and economical. Improving nutrient use efficiency (NUE) is being addressed through implementation of best management practices (BMPs) such as nutrient management planning, proper fertilizer material selection, better application timing and placement, and improved irrigation scheduling. Emerging technology that will aid in this effort includes increased use of enhanced efficiency fertilizers (EEFs), organic soil amendments, fertigation, and foliar fertilization. However, any new technology shown to improve NUE must be economically feasible before it can be considered a BMP. Future research in this area will aim to improve the economics of EEFs and precision fertilizer application.

Best management practices (BMPs) for Florida's green industries have been established since 2002. BMPs for nonagricultural industries such as commercial lawn care were developed in 2002 by the Florida Department of Environmental Protection (FDEP), the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS), and other parties. The BMP educational program, delivered primarily by UF/IFAS extension in partnership with the FDEP, began in 2003 as a voluntary program. As a result of increasing concerns regarding lawn fertilization and potential harmful effects on ground and surface waters, several local governments throughout the state require commercial fertilizer applicators to have a certificate of completion in a BMP educational program. The BMP program emphasizes appropriate fertilization practices to reduce nonpoint source pollution, including proper rates, timings, and application of fertilizers. Research done on fate of fertilizer applied to turfgrass demonstrates that a properly maintained lawn provides an effective means for uptake of nutrients. Some of the factors that have been shown through research to increase the opportunity for nutrient leaching include nitrogen (N) application at higher than recommended rates, excess rainfall after fertilization, and fertilization at a time when turf is not actively growing. Research results vary regarding N source and the difference in nitrate leaching resulting from N source. To provide concise research-based information for lawmakers and elected officials in Florida, there is currently a large research project underway to further quantify nutrient leaching under a variety of circumstances. Results of this research should form the basis for future regulations regarding fertilizer applications.

Abstract

Juniperus horizontalis ‘Andorra Compacta’ and Rhododendron simsii ‘Redwing’ were grown for 6 months in 3 media to evaluate selected nutrient sources at 2 lime levels. Sulfur-coated urea (SCU) induced the lowest final medium pH, and isobutylidene diurea (IBDU) induced the highest. Lime application to the 2 Canadian peat : 1 calcined clay medium (v/v) was detrimental to ‘Redwing’ azalea shoot growth. Nutrient source did not affect shoot or root growth of azaleas growing in the 2 pine bark : 1 sand medium (v/v). In general, SCU produced more azalea shoot and root growth than the other nutrient sources. Liming decreased juniper shoot growth in the 1 pine bark : 1 Canadian peat : 1 sand medium (by volume). Oxamide and Osmocote produced significantly more juniper shoot growth in the pine bark : sand and pine bark : Canadian peat : sand media than other nutrient sources. After 6 months, plants fertilized with either IBDU or SCU had a higher concentration of leaf N than did those fertilized with Osmocote (18N–2.6P–10K).

The effects of potassium (K) on stress tolerance of turfgrass have been documented for some environmental stresses but not for shade tolerance. ‘Captiva’ st. augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze] was evaluated in this research project to determine the effects of K and shade on turf performance. The study was conducted at the University of Florida Envirotron Turfgrass Research Laboratory in Gainesville, FL. Grasses were planted in 15.2-cm plastic pots in a climate-controlled glass house. Two consecutive studies were conducted, the first from 20 May to 24 Oct. 2009 and the second from 18 Jan. to 20 June 2010. Grasses were placed in either full sun or under shade structures covered with woven black shadecloth to provide 30%, 50%, or 70% shade. Potassium was applied as potassium chloride (KCl) (0–0–62) at four rates (0, 0.6, 1.2, or 2.4 g·m⁻²) every 30 days. In both trials, turf visual quality and color scores and dry weight (DW) of shoot and root were lowest at 70% shade and highest at 30% shade. Turf visual quality score increased as K rate increased. Leaf length increased and leaf width decreased as shade level increased. Leaf tissue total Kjedahl nitrogen (TKN) and K concentration increased as shade level increased from 0% to 70%. Thatch DW was greatest at 70% shade and lowest at 30% shade. In the first trial, turf treated with a higher K rate had longer leaf length and greater root DW. Results from this study showed that ‘Captiva’ could maintain acceptable visual quality at up to 50% shade and that K at 2.4 g·m⁻² may help turfgrass grow in a shaded environment by improving turf visual quality score, root growth, and leaf tissue K concentration. Additional field plot research should be conducted to verify these responses.

Slow-release fertilizers marketed to the public usually include a claim that nutrient release will last for a specific time period (e.g., 6, 9, or 12 months). However, no official laboratory method exists that can verify these claims. A long-term (180 days) incubation method has been developed that produces constants for an exponential model that characterizes nutrient release as a function of time. In addition, a relatively short-term (74 h) extraction method has been developed to assess nutrient release under accelerated laboratory conditions. Through regression techniques, release constants established for individual slow-release nutrient sources by the incubation method are used in conjunction with the laboratory extraction data to verify the release claims of slow-release fertilizers. Nutrient release for selected single materials has been predicted with greater than 90% accuracy in previous studies. Nutrient release from mixtures of slow-release products has been more variable. It is typical for water-soluble and slow-release fertilizers to be mixed in commercial products. Ultimately, it is intended that these methodologies will be accepted as an official method to verify nutrient release claims placed on slow-release fertilizers.

Determination of nutrient release duration from controlled-release fertilizers (CRFs) or soluble fertilizers encapsulated in polymer, resin, or sulfur covered fertilizer coated with a polymer differs among manufacturers, but may be determined as 75% to 80% nitrogen (N) release at a constant temperature (e.g., 20 to 25 °C). Increases or decreases in temperature compared with the manufacturer release determination temperature increase or decrease CRF N release; thus, coated fertilizer may release more rapidly than stated during the fall season when soil temperatures in seepage-irrigated tomato (Solanum lycopersicum) production can reach 40.1 °C. The objectives of this study were to evaluate N release duration of CRFs by measuring N release from CRFs incubated in pouches under polyethylene mulch-covered raised beds and to determine the CRF duration suitable for incorporation into a fall tomato fertility program. In 2011 and 2013, 12 and 14 CRFs from Agrium Advanced Technologies, Everris, Florikan, and Chisso-Asahi Fertilizer were sealed in fiberglass mesh pouches (12.7 × 14 cm) that were buried 10 cm below the bed surface in a tomato crop grown using commercial production practices. A data logger collected soil temperature 10 cm below the bed surface. Pouches were collected and N content was measured eight times through two fall seasons. A nonlinear regression model was fit to the data to determine N release rate. During the 2011 and 2013 seasons, minimum, average, and maximum soil temperatures were 21.2 and 19.2, 25.7 and 23.5, and 32.2 and 27.7 °C, respectively. Seasonal total CRF N release was between 77.6% and 93.8% during 2011 and 58.3% and 94.3% in 2013. In 2011, PCU90 and in 2013, PCU90 and PCNPK120 had the highest seasonal total percentage N release (PNR) and FL180 had the lowest in both years. A nonlinear regression fit N release from CRF with R ² = 0.85 to 0.99 during 2011 and 0.49 to 0.99 during 2013. Nitrogen release from all CRFs was faster than the manufacturer’s stated release, probably as a result of high fall bed temperatures. A CRF or CRF mixture containing CRFs of 120- to 180-day release duration may be recommended, but the CRFs must release greater than 75% N during the season.

Controlled-release fertilizers (CRFs), a vegetable production best management practice in Florida, are soluble fertilizers (SFs) coated with a polymer, resin, or a hybrid of polymer coating sulfur-coated urea. In 1994, a Controlled Release Fertilizer Taskforce developed an accelerated temperature-controlled incubation method (ATCIM) to predict column-incubated CRF nitrogen (N) release for regulatory purposes. Determination of CRF field N release uses a field method such as a pouch field study, which requires multiple samples and high costs for laboratory N analysis. If the ATCIM may be used to predict CRF N release in the field, then vegetables growers will have a faster and lower-cost method to determine N release compared with the pouch field method. Therefore, the objective of this study was to evaluate the correlation of the ATCIM and the pouch field method as a predictor of N release from CRFs in tomato production in Florida. In 2011 and 2013, 12 and 14 CRFs, respectively, were incubated in pouches placed in polyethylene mulched raised beds in Immokalee, FL, and extracted in the ATCIM during 2013. The ATCIM CRF results were used individually and grouped by release duration to create predicted N release curves in a two-step correlation process. The two-step processes predicted the percentage N release of individual CRF with R ² of 0.95 to 0.99 and 0.61 to 0.99 and CRFs grouped by release duration with R ² of –0.64 to 0.99 and –0.38 to 0.95 in 2011 and 2013, respectively. Modeling CRF N release grouped by release duration would not be recommended for CRF 180-d release (DR), because coating technologies behaviors differ in response to high fall soil temperature in polyethylene mulched beds. However, with further model calibration, grouping CRFs of 90 to 140 DR to simulate the CRF N release profile may allow the ATCIM to predict CRF N release without performing the pouch field method, which currently negated the usefulness of the ATCIM in a tomato production system.

Applying water-soluble nitrogen (N) fertilizer to Florida citrus (Citrus spp.) trees on deep sandy soils may lead to poor nutrient use efficiency and possible nitrate contamination of groundwater if rainfall or irrigation is excessive. Controlled-release fertilizer (CRF) is a possible alternative to increase N uptake efficiency and minimize losses to the environment, but current grower acceptance is limited as a result of lack of experience with CRF performance and its high relative cost. The objective of this study was to measure the N release characteristics of a CRF blend (CitriBlen^®) designed for mature Florida citrus trees and its three CRF components [Agrocote^® Type A, Agrocote^® Type C(D), and Agrocote^® Poly-S^®] under laboratory and field conditions. We first characterized N release from these CRF materials using a 270-day laboratory soil incubation. The quantity of N released was influenced by CRF material used; after 270 days, cumulative leached N recoveries were 90%, 82%, 85%, and 69% of the total N applied as CitriBlen^®, Agrocote^® Type A, Agrocote^® Type C(D), and Agrocote^® Poly-S^®, respectively. We then measured the N release patterns of the fertilizers in a 1-year field evaluation and developed their N release curves. Studies were simultaneously conducted in central and southwestern Florida. Mesh bags containing 3.5 g of elemental N from each source were placed on the soil surface within the irrigated zone under a citrus tree canopy to estimate N release rates from the fertilizers. Despite differential N release rates between locations, at 1 year, the rank of N release was Type A > CitriBlen^® > Poly-S^® > Type C(D). CitriBlen^® N release patterns matched well with the current University of Florida, Institute of Food and Agricultural Sciences citrus fertilization strategy recommended as a best management practice.

Citrus production in Florida is commonly affected by a high degree of spatial variability of soils. Therefore, this study developed rapid indicator crop bioassays to evaluate the relationships between indicator crops and citrus production at various soil depths. A citrus grove was divided into five productivity zones based on existing tree canopy volume using GIS software (“very poor,” “poor,” “medium,” “good,” and “very good”). Visual ratings of percentage cover were collected from each zone using a 1-m² quadrant. Six random soil samples were collected between the tree rows from each productivity zone at four depths (0 to 15, 15 to 30, 30 to 45, and 45 to 60 cm). Greenhouse bioassay experiments used sorghum and radish crops grown in soil sampled from four depths. Overhead photographs of potted radish plants were captured periodically with a SLR digital camera to calculate leaf area by image processing. Shoot weights, shoot length, root weights, and leaf nutrient concentrations were measured at harvest (56 and 21 days after germination for sorghum and radish, respectively). Germination, shoot length, and shoot weight of sorghum and radish were significantly affected by the productivity zone. Sorghum (0 to 30 cm), radish (0 to 45 and 0 to 60 cm) and weed cover were strongly correlated (r ≈0.50 to 0.60***) with citrus yield and canopy volume at the lower two depths. The strong relationships (r > 0.50***) of sorghum and radish shoot weights and weed cover with soil properties at greater depths demonstrated the important role of cumulative root zone depth of 60 cm in differentiating citrus productivity. These results revealed that citrus production in poor areas of the grove was limited by the shallow depth of productive soil, and citrus productivity could be successfully mapped using indicator crop bioassays with soil samples taken at multiple depths.

Urban watersheds include extensive turfgrass plantings that are associated with anthropocentric attitudes toward landscapes. Native and construction-disturbed urban soils often cannot supply adequate amounts of nitrogen (N) and phosphorus (P) for the growth and beauty of landscape plants. Hence, fertilization of landscape plants is practiced. Mismanaged fertilization and irrigation practices represent a potential source of nutrients that may contribute to water quality impairment. This review focuses on turfgrass fertilization practices and their impacts on urban water quality. Research results show that fertilization during active growth periods enhances turfgrass nutrient uptake efficiencies. The major concern regarding the fertilization of turfgrass and landscape plants in urban watersheds, therefore, is selecting the proper combination of fertilizer rate, timing, and placement that maximizes nutrient utilization efficiency and reduces the risk for nutrient loss to water bodies. Encouraging individuals to adopt best management practices (BMPs) is a priority for watershed managers. Research has found that educational programs are an important part of changing fertilization habits and that education needs to be thorough and comprehensive, which is beyond the scope of many seminars and fact sheets currently in use.