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Calcium and sulfur are sometimes called secondary nutrients. This term does not mean that these nutrients play a secondary role in citrus plant growth and development. Ca and S are as essential as N, P, K, Mg, and other nutrients for healthy plant growth. An inadequate supply of Ca and/or S can be a major constraint to crop production and quality. This 5-page fact sheet was written by Mongi Zekri and Tom Obreza and published by the UF Department of Soil and Water Science, July 2013. http://edis.ifas.ufl.edu/ss584

Citrus fruits remove large amounts of K compared to other nutrients. Potassium moves from leaves to fruit and seeds as they develop. Potassium is necessary for several basic physiological functions such as the formation of sugars and starch, synthesis of proteins, normal cell division and growth, and neutralization of organic acids. Potassium is important in fruit formation and enhances fruit size, flavor, and color. This nutrient also helps to reduce the influence that adverse weather conditions (such as drought, cold, and flooding) have on citrus trees. This 4-page fact sheet was written by Mongi Zekri and Tom Obreza and published by the UF Department of Soil and Water Science, July 2013. http://edis.ifas.ufl.edu/ss583

Phosphorus deficiency is not common in Florida citrus groves. If it does occur, it is more difficult to diagnose than nitrogen (N) deficiency or other nutrient element deficiencies. Growth is reduced when P supply is too low. Phosphorus is highly mobile in plants, so when it is deficient, it may move from old leaves to young leaves and other actively growing areas where energy is needed to form seeds and fruit. This 4-page fact sheet was written by Mongi Zekri and Tom Obreza and published by the UF Department of Soil and Water Science, July 2013. http://edis.ifas.ufl.edu/ss581

Nitrogen is the key component in mineral fertilizers applied to citrus groves. N has more influence on tree growth, appearance, and fruit production/quality than any other mineral element. Nitrogen affects the absorption and distribution of practically all other elements, and it is particularly important to the tree during flowering and fruit set. This 3-page fact sheet was written by Mongi Zekri and Tom Obreza and published by the UF Department of Soil and Water Science, July 2013. http://edis.ifas.ufl.edu/ss580

Magnesium deficiency has been a major problem in citrus production. In Florida, Mg deficiency is commonly referred to as “bronzing.” Trees with inadequate Mg may have no symptoms in the spring growth flush, but leaf symptoms develop as the leaves age and the fruit expand and mature in the summer and fall. Magnesium deficiency symptoms occur on mature leaves following the removal of Mg to satisfy fruit requirements. This 4-page fact sheet was written by Mongi Zekri and Tom Obreza and published by the UF Department of Soil and Water Science, July 2013. http://edis.ifas.ufl.edu/ss582

The low water-holding capacity of sandy soils, together with spatial and temporal variations of rainfall, require Florida citrus trees to be irrigated for optimal production. Citrus tree root systems are exposed to various hydrologic conditions because of soil temperature and water gradients due to tree canopy shading and under-tree microirrigation. The main goal of this study was to evaluate water balance components in a mature citrus orchard grown on central Florida ridge soils with special interest in quantifying rainfall interception by a citrus canopy and its effect on effective rainfall estimation. Soil water content was monitored every 30 min at 10-, 20-, 40-, and 80-cm depths in the root zone both under and outside of citrus tree canopies. Microirrigation, rainfall, and weather data were used to calculate effective rainfall, plant water uptake, and deep drainage. We found that the tree canopy intercepted 35 and 50% of the incoming high ([greater than or equal to] 5-mm) and low ( Abbreviations: CitWatBal, citrus water balance model; ER, effective rainfall; ETc, crop evapotranspiration; E[T.sub.o], reference evapotranspiration; IRR, irrigation requirement; TR-21, USDA Technical Release 21.

This document is about managing citrus fertilizer on calcareous soils, common in South Florida's flatwoods. Calcareous soils, with high calcium carbonate (CaCO3) content and alkaline pH levels, affect the availability of essential nutrients like nitrogen (N), phosphorus (P), magnesium (Mg), potassium (K), manganese (Mn), zinc (Zn), and iron (Fe). Effective nutrient management involves tailored strategies such as using ammoniacal fertilizers, foliar sprays, water-soluble P applications, and soil acidulents like elemental sulfur. By understanding and addressing the unique challenges of calcareous soils, citrus growers can enhance nutrient uptake and improve crop yields. First published Dec. 1993.

Water is of primary importance to all life on earth. Freshwater is a finite resource, and managing freshwater requires an understanding of watersheds and a watershed approach. Both quantity and quality of water are important for balanced beneficial and efficient agricultural, industrial, rural, and urban uses. This 7-page fact sheet provides information on watersheds and introduces the watershed approach and management concept as practiced in the U.S., with a focus on Florida watersheds in particular. This document also provides information on the basins, basin groups, and hydrologic units of Florida used by the Florida Department of Environmental Protection (FDEP) to implement watershed assessment, monitoring, and restoration programs. Written by Rao Mylavarapu, Kelley Hines, Thomas Obreza, and Greg Means, and published by the UF Department of Soil and Water Science, July 2012. SL367/SS568: Watersheds of Florida: Understanding a Watershed Approach to Water Management (ufl.edu)

Non-uniform tree growth and fruit yield are very common throughout many Florida citrus groves, but variable groves are typically managed as if they were uniform. This 4-page fact sheet provides information about the relationship between soil variability and citrus production, proposes recommendations for soil sampling that account for spatial variability, and suggests site-specific management practices for variable Florida citrus groves. Written by Kirandeep K. Mann, Arnold W. Schumann, Thomas A. Obreza, Willie G. Harris, and Jerry B. Sartain, and published by the UF Department of Soil and Water Science, January 2012. SL556/SS557: How to Characterize Soil Variability in Florida Citrus Groves as It Relates to Tree Growth and Yield (ufl.edu)

Serine proteases have proven to be promising pharmacological targets in contemporary drug discovery for cancer treatment. Since azaphenylalanine-based compounds manifest cytotoxic activity, we have selected serine protease inhibitors designed and synthesized in-house with large hydrophobic naphthalene moiety for screening. The cytotoxic potential of screened molecules was correlated to modifications of R(1) residues. The most cytotoxic were compounds with greater basicity; amidinopiperidines, piperidines and benzamidines. Amidinopiperidine-based compounds exert cytotoxicity in low µM range, with IC(50) 18 µM and 22 µM for inhibitors 15 and 16 respectively. These compounds exhibited selective cytotoxicity towards the Burkitt's lymphoma cells Ramos and Daudi, and proved nontoxic to PMBC, Jurkat and U937. They induce caspase-dependent apoptotic cell death, as demonstrated by the use of a pan-caspase inihibitor, zVADfmk, which was able to rescue Ramos cells from compound(s)-induced apoptosis. We confirm a disruption of the pro-survival pathway in Burkitt's lymphoma through NFκB inhibition. The accumulation of phosphorylated precursor (p105) and inhibitory (IκB) molecules with no subsequent release of active NFκB implicated the involvement of proteasome. Indeed, we show that the amidinopiperidine-based compounds inhibit all three proteolytical activities of the human 20S proteasome, with the most prominent effect being on the trypsin-like activity. Consistently, treatment of Ramos cells with these compounds led to an increase in ubiquitinated proteins. The amidinopiperidine-based serine protease inhibitors presented are, as selective inducers of apoptosis in Burkitt's lymphoma cells, promising leads for the development of novel chemotherapeutics.

A 2-year study was conducted at a seepage-irrigated vegetable farm in south Florida to develop and evaluate an improved, soil moisture-based irrigation management practice that could potentially reduce irrigation water use, prevent water quality impairment, and maintain or improve crop yield. The improved practice reduced irrigation water use by 36% compared to the conventional irrigation management. Moreover, the improved practice also increased rainfall retention and decreased runoff events by lowering the water table 13 cm compared to the conventional practice. Total dissolved phosphorus (P) concentrations in groundwater were higher (p < 0.01) for the improved practice compared with the conventional practice in two of the three fields where ground water quality was monitored. Higher P concentrations for the improved practice were likely due to the dilution effect. Statistically, no differences (p > 0.05) were observed in groundwater nitrogen (N) (N[O.sub.x]-N, N[H.sub.4]-N, and total dissolved N) concentrations between the improved and the conventional practices. Similarly, no statistical difference was observed in crop yield between the improved and the conventional practices, although the average total yield was higher for the improved practice. The improved practice also reduced the incidence of plant disease compared to the conventional practice which resulted in crop failure in some fields. Thus, use of the improved practice reduced irrigation water use without impacting crop yield. CE Database subject headings: Water management; Runoff: Ground-water management; Water use: Irrigation practices: Instrumentation; Nitrogen; Phosphorus; Crops; Water table; Seepage.

Trace organic chemicals are potentially harmful to human and ecosystem health. They frequently occur in wastewater from septic systems and can be found in concentrations orders of magnitude higher than typical concentrations reported in centralized treatment plant wastewater. This 7-page fact sheet identifies common trace organic chemicals of concern in wastewater and their sources, and summarizes current research on the fate and transport of these chemicals in septic systems. Written by Gurpal S. Toor, Mary Lusk, and Tom Obreza, and published by the UF Department of Soil and Water Science, November 2011. (photo CC BY-SA 3.0 Mila) SL352/SS554: Onsite Sewage Treatment and Disposal Systems: Trace Organic Chemicals (ufl.edu)

Keeping disease-causing microorganisms out of groundwater used for drinking water supplies is important to protect human health. This 7-page fact sheet characterizes the behavior of viruses in septic systems and the soil drain field and summarizes what we know about the extent and character of groundwater contamination with viruses emanating from septic systems. Written by Mary Lusk, Gurpal S. Toor, and Tom Obreza, and published by the UF Department of Soil and Water Science, October 2011. SL351/SS553: Onsite Sewage Treatment and Disposal Systems: Viruses (ufl.edu)

Keeping disease-causing microorganisms out of groundwater used for drinking water supplies is important to protect human health. This 7-page fact sheet reports the sources of bacteria and protozoa in wastewater, discusses diseases associated with drinking water contaminated with wastewater, and then details their fate in septic systems. Written by Mary Lusk, Gurpal S. Toor, and Tom Obreza, and published by the UF Department of Soil and Water Science, July 2011. (Photo by Tara Piasio) SL350/SS552: Onsite Sewage Treatment and Disposal Systems: Bacteria and Protozoa (ufl.edu)

Phosphorus (P) in onsite sewage treatment and disposal systems is a concern because P can impair water quality even lower concentrations than nitrogen. This 8-page fact sheet summarizes the sources of P in septic tank effluent and the forms, concentrations, and behavior of P in the septic tank effluent and the drain field. Written by Mary Lusk, Gurpal S. Toor, and Tom Obreza and published by the UF Department of Soil and Water Science, July 2011. (Photo by Milt Putnam) SL349/SS551: Onsite Sewage Treatment and Disposal Systems: Phosphorus (ufl.edu)

In the United States, about 4,800 water bodies are impaired due to excess nitrogen (N), and septic systems are recognized as one source of N pollution. This 6-page fact sheet describes the behavior and transport of N from a conventional septic system and the summarizes the sources of N in sewage, the forms and behavior of N in septic tanks and drain fields, and the fate and transport of N in groundwater. Written by Gurpal Toor, Mary Lusk, and Tom Obreza, and published by the UF Department of Soil and Water Science, June 2011. SL348/SS550: Onsite Sewage Treatment and Disposal Systems: Nitrogen (ufl.edu)

This 7-page fact sheet introduces common types of septic systems and briefly discusses onsite wastewater flow and the contaminants found in wastewater. Written by Gurpal Toor, Mary Lusk, and Tom Obreza, and published by the UF Department of Soil and Water Science, June 2011. SL347/SS549: Onsite Sewage Treatment and Disposal Systems: An Overview (ufl.edu)

In 2005 we conducted a survey in cooperation with Gulf Citrus Growers Association and FDACS to quantify the current level of Best Management Practices (BMP) implementation and to identify BMPs that might be adopted if a cost-share program was available. This publication describes the survey and discusses the findings regarding nutrient BMPs. This 11-page fact sheet was written by S. Shukla, R.E. Rouse, S.S. Shukla, E.A. Hanlon, K. Portier, and T.A. Obreza, and published by the UF Department of Agricultural and Biological Engineering, August 2010. AE474/AE474: Citrus BMP Implementation in Florida's Gulf Citrus Production Area: Nutrients (ufl.edu)

Revised! Water is essential to sustain life. Not only do we all need a certain quantity of water each day, but the quality of the available water is also critical. Water quality protection in the United States evolved from initially ensuring navigability of waterways to protecting our natural ecosystems. This 5-page fact sheet provides a background for understanding water quality and how it is evaluated and regulated in the U.S. with particular focus on the state of Florida. Written by Kati W. Migliaccio, Yuncong Li, and Thomas A. Obreza. Published by the UF Department of Agricultural and Biological Engineering, January 2011. ABE 381/AE431: Evolution of Water Quality Regulations in the United States and Florida (ufl.edu)

Florida citrus trees must be irrigated to reach maximum production due to low soil water-holding capacity. In a highly urbanizing state with limited water resources, improved understanding of soil water uptake dynamics is needed to optimize irrigation volume and timing. The objectives of this study were: (i) estimate mature citrus daily evapotranspiration ([ET.sub.c]) from changes in soil water content ([theta]), (ii) calculate citrus crop coefficients ([K.sub.c]) from [ET.sub.c] and reference evapotranspiration ([ET.sub.o]), (iii) determine the relationship of soil water stress coefficient ([K.sub.s]) to [theta], and (iv) evaluate how [ET.sub.c] was related to root length density. In a 25-mo field study using mature 'Hamlin' orange [Citrus sinensis (L.) Osbeck] trees, [ET.sub.c] averaged 1137 mm [yr.sup.-1] and estimated [K.sub.c] ranged between 0.7 and 1.1. Day of year explained more than 88% of the variation in [K.sub.c] when [theta] was near field capacity. The value of K, decreased steadily from 1.0 at field capacity ([theta] = 0.072 [cm.sup.3] [cm.sup.-3]) to approximately 0.5 at 50% available soil water depletion ([theta] = 0.045 [cm.sup.3] [cm.sup.-3]). Roots were concentrated in the top 15 cm of soil under the tree canopy (0.71 to 1.16 cm roots [cm.sup.-3] soil), where maximum soil water uptake was about 1.3 [mm.sup.3] mm [root.sup.-1] [d.sup.-1] at field capacity, decreasing quadratically as [theta] decreased. Estimating daily plant water uptake and resulting soil water depletion based on root length density distribution would provide a reasonable basis for a citrus soil water balance model.

SL316, a 9-page illustrated guide by Thomas Obreza, Mark Clark, Brian Boman, Tatiana Borisova, Matt Cohen, Michael Dukes, Tom Frazer, Ed Hanlon, Karl Havens, Chris Martinez, Kati Migliaccio, Sanjay Shukla, and Alan Wright, provides a basic, concise, and understandable description of the United States Environmental Protection Agency’s (EPA) proposed numeric nutrient criteria for Florida, the background events that led to its release, some pertinent scientific issues, and implications for the future. Published by the UF Department of Soil and Water Science, February 2010.

SL-299, an 8-page illustrated fact sheet by Sampson Agyin-Birikorang, George A. O’Connor, and Thomas A. Obreza, explores possible effects of land-applying Al-WTR on the environment, and recommends ways to minimize human impacts. Includes further readings. Published by the UF Department of Soil and Water Science, July 2009. SL 299/SS512: Are Alum-Based Drinking Water Treatment Residuals Safe for Land Application? (ufl.edu)

SL-300, a 7-page illustrated fact sheet by Sampson Agyin-Birikorang, George A. O’Connor, and Thomas A. Obreza, describes the phosphorous problem in Florida, and the use of this byproduct of municipal drinking water purification as a soil amendment to reduce nonpoint source pollution by phosphorous. Includes further readings. Published by the UF Department of Soil and Water Sciences, July 2009. SL 300/SS513: Drinking-Water Treatment Residuals to Control Phosphorus in Soils (ufl.edu)

SL286, a 4-page illustrated fact sheet by Kelly T. Morgan, Edward A. Hanlon, and Thomas A. Obreza, describes an easy to use web-based water-balance irrigation scheduling tool that assists growers in determining irrigation schedules that can improve water use efficiency and reduce nutrient leaching. Published by the UF Department of Soil and Water Science, May 2009.

Revised! SL-238, a 4-page fact sheet by Thomas Obreza, Larry Parsons, and Kelly Morgan, discusses the factors influencing the price of nitrogen fertilizer sources and economic considerations for future nitrogen fertilizer availability. Published by the UF Department of Soil and Water Sciences, February 2009. SL238/SS457: Nitrogen Fertilizer Sources: What does the future hold for citrus producers? (ufl.edu)

SL-265, an 8-page illustrated fact sheet by Tom Obreza, Ed Hanlon, and Mongi Zekri, describes problems with emitter plugging and discusses management strategies to overcome and correct causes of plugging in micro-irrigation systems. This publication focuses, in particular, on iron scaling, documenting recent successes in treating this common problem in Florida. Includes sources of further information. Published by the UF Department of Soil and Water Science, August 2008. SL 265/SS487: Dealing with Iron and Other Micro-Irrigation Plugging Problems (ufl.edu)

SL-279, a 6-page fact sheet by Rao Mylavarapu, Kelley Hines, and Thomas Obreza, presents the details of several types of diagnostic tests for nutrient status and management in commercial citrus groves in Florida, as well as sample submission procedures. Includes references and a copy of the sample submission form (in the pdf version). Published by the UF Soil and Water Science Department, December 2008. SL 279/SS492: Diagnostic Nutrient Testing for Commercial Citrus in Florida (ufl.edu)