Kelly T. Morgan

Comparison of laboratory- and field-derived soil water retention curves for a fine sand soil using tensiometric, resistance and capacitance methods

The approximate range from 100 to 50% of plant-available water in Apopka fine sand (loamy, siliceous, hyperthermic Grossarenic Paleudult) is 0.08–0.04 cm3 cm−3 soil water content (θ) or −5 to −15 kPa of soil water matric potential (φ). This narrow range of plant-available soil water is extremely dry for most soil water sensors. Knowledge of the soil water retention curves for these soils is important for effective irrigation of crops in fine sand soils of subtropical and tropical regions of the world. The primary objective of this study was to compare sandy soil water retention curves in the field as measured by tensiometer and resistance block φ values and capacitance sensor θ. The second objective was to compare these curves to one developed on a Florida fine sand soil using a pressure plate apparatus. Tensiometer and resistance block φ values were compared to θ values from capacitance sensors calibrated gravimetrically. The effective range of both tensiometers and resistance sensors in fine sand soils is between −5 and −20 kPa φ. Soil water potential values for both sensors were within 2 kPa of the mean for each sensor. Change in φ was similar over the range of 0.04–0.08 cm3 cm−3 θ. Curves for the two sensors were different by 4 kPa at 0.04 cm3 cm−3. The relationship between φ and θ were similar at 10–20, 20–30 and 40–50 cm depths. This was not true for a laboratory determined soil water retention curve for the same soil type. These differences are significant in soils with very low water holding capacities. Differences between laboratory- and field-determined retention curves could be due to a combination of entrapped air in the field soil and/or alteration in bulk density in the laboratory samples.

Comparison of Evapotranspiration Rates for Flatwoods and Ridge Citrus

Florida citrus groves are typically grown in two regions of the state: flatwoods and ridge. The southern flatwoods citrus area has poorly drained fine textured sands with low organic matter in the shallow root zone. Ridge citrus is located in the northern ridge citrus zone and has fine to coarse textured sands with low water-holding capacity. Two commercial citrus groves, selected from each region, were studied from 15 July 2004 to 14 July 2005. The flatwoods citrus (FC) grove had a grass cover and used drainage ditches to remove excess water from the root zone. The ridge citrus (RC) grove had a bare soil surface with weeds periodically eliminated by tillage. Citrus crop evapotranspiration (ETc) rates at the two citrus groves were measured by the eddy correlation method, and components in the energy balance were also examined and compared. The study period had higher than average rainfall, and as a result, the two locations had similar annual ETc rates (1069 and 1044 mm for RC and FC, respectively). The ETc rates were 59% (RC) and 47% (FC) of the rainfall amounts during the study period. The annual reference crop evapotranspiration (ETo) rates were 1180 mm for RC and 1419 mm for FC, estimated using the standardized reference evapotranspiration equation. The citrus crop coefficients (Kc, ratio of ETc to ETo) were different between the two locations because of differences in latitude, ground cover, and rainfall amounts. The Kc values ranged from 0.70 between December and March to 1.05 between July and November for RC, and from 0.65 between November and May to 0.85 between June and October for FC. The results are consistent with other Kc values reported from field studies on citrus in both Florida and elsewhere using these and alternate methods.

Nitrogen Recovery and Transformation from a Surface or Sub-Surface Application of Controlled-Release Fertilizer on a Sandy Soil

ABSTRACT Controlled-release fertilizers (CRF) are used to reduce leaching of nutrients, especially nitrate-nitrogen (NO3 −-N) to groundwater, caused mainly by application of soluble N fertilizers to sandy soils in Florida. A leaching column study was conducted to evaluate N release and transformation from a CRF (CitriBlen) over a 16-week period when it was applied on the soil surface or incorporated into the soil. When one pore volume of water was applied to column weekly or biweekly, the CRF released urea-N slowly over time with three peaks of release on 3–4, 8, and 12 week after application. Both ammonium-nitrogen (NH4 +-N) and NO3 −-N were leached in large amounts on week 2, likely from soluble forms of N. Cumulatively, the most leached N at the end of study was in the NH4 + form, followed by the NO3 − form. The sum of all N forms leached and volatilized accounted for 53–69% of total N applied. Total N recovery was 70% and 93% of total N applied for surface and sub-surface application of the fertilizer, respectively. It was indicated that the better recovery rate found with sub-surface application may have been due to minimized N loss by volatilization. Sub-surface application of fertilizer resulted in more than three times NH4 +-N remained in soil, compared with surface application. On average for both application treatments throughout 16-week period, 5.8 h was required for ammonification and 4.7 d for nitrification to occur after N release from the fertilizer. Characterization of CRFs for specific soil type, leaching volume and cycle, and application manner as well as knowledge of N requirement of the crop will allow for the Best Management Practices of these fertilizers, thus obtaining optimum yields and minimizing nutrient losses from CRFs.

Imidacloprid sorption kinetics, equilibria, and degradation in sandy soils of Florida.

Imidacloprid (IMD) is a neonicotinoid insecticide soil-drenched on sandy soils of southwest Florida for the control of Diaphorina citri Kuwayama or Asian citrus psyllid (ACP). The ACP vectors causal pathogens of a devastating citrus disease called citrus greening. Understanding the behavior of IMD in these soils and plants is critical to its performance against target pests. Samples from Immokalee fine sand (IFS) were used for sorption kinetics and equilibria experiments. IMD kinetics data were described by the one-site mass transfer (OSMT) model and reached equilibrium between 6 and 12 h. Batch equilibrium and degradation studies revealed that IMD was weakly sorbed (K(OC) = 163-230) and persistent, with a half-life of 1.0-2.6 years. Consequently, IMD has the potential to leach below the citrus root zone after the soil-drench applications.

Performance evaluation of urban turf irrigation smartphone app

A new smartphone turf app was field tested in South Florida.Results showed water savings with the app comparable to evapotranspiration controllers.A water conservation option in the app offers additional seasonal water savings when rainfall exceeds evapotranspiration. Data and technology are available to support a real-time irrigation smartphone app for turf that would result in more efficient irrigation scheduling which is needed to reduce water volumes applied and increase irrigation water conservation. Objectives were to (1) develop a turf irrigation smartphone app for warm season turf that would generate real-time irrigation schedules for users to program automatic timers and (2) evaluate app performance in regards to turf quality and water volumes applied with a field plot study. A smartphone app was developed and tested in a plot study in Homestead, Florida, USA, from December 2013 to November 2014. Study treatments included different irrigation scheduling methods: time-based schedule, smartphone app, and two on-site evapotranspiration (ET) controllers. Results indicated that the app and ET controllers resulted in significantly lower irrigation depths compared to the time-based treatment, ranging in water savings from 42% to 57%. The difference among the app and ET controllers was how rainfall was integrated into the schedule. Use of the seasonal water conservation model in the smartphone app is recommended to compensate for the lack of on-site rainfall measurements in the generated irrigation schedule.

Open Field Hydroponics: Concept and Application

Advanced citrus production systems that combine grove design, size limiting rootstocks, irrigation and nutrient management, and mechanical harvesting have the potential to make citrus more efficient and economically competitive. Recently, the open hydroponic system (OHS) of citrus production has been combined with orchard design to achieve these efficiencies. Open hydroponics are defined as a system of management practices aimed at increased productivity of citrus orchards by continuously applying a balanced nutrient mixture through the irrigation system, limiting the root zone by restricting the number of drippers per tree and maintaining the soil moisture in the rooted zone near field capacity. Concepts of OHS are to maximize water and nutrient use efficiency through improved nutrient availability to concentrate roots in the irrigated zone. These concepts are accomplished through intensive water and nutrient management and results in increased early growth, sustained yields, and reduced nutrient leaching. Additional horticultural principles employed include higher tree density with size-controlling rootstocks grown on soil ridges, if needed, for improved drainage. Limited published information is available for citrus grown under OHS conditions. However, one study reported that orchards on OHS have outgrown trees on conventional production systems and appear to be more productive. Canopy volumes increased by approximately three times and fruit volume by more than five times per unit of N after 4 years of intensive management compared with conventionally grown trees in replicated trials. Yield increases approaching 30% have been reported from several studies in many citrus-producing regions of the world. Use of this advanced production system may maintain higher levels of productivity through improved water and nutrient use efficiencies resulting in improved short- and long-term economic returns, particularly in citrus industries infected with diseases such as Citrus Greening.

Development and assessment of a smartphone application for irrigation scheduling in cotton

Easy-to-use and engaging smartphone application.Interactive ET-based soil water balance model.Uses meteorological data from weather station networks.Estimates root zone soil water deficits (RZSWD).Has mostly outperformed other irrigation scheduling tools. The goal of this work was to develop an easy-to-use and engaging irrigation scheduling tool for cotton which operates on a smartphone platform. The model which drives the Cotton SmartIrrigation App (Cotton App) is an interactive ET-based soil water balance model. The Cotton App uses meteorological data from weather station networks, soil parameters, crop phenology, crop coefficients, and irrigation applications to estimate root zone soil water deficits (RZSWD) in terms of percent as well as of inches of water. The Cotton App sends notifications to the user when the RZSWD exceeds 40%, when phenological changes occur, and when rain is recorded at the nearest weather station. It operates on both iOS and Android operating systems and was released during March 2014. The soil water balance model was calibrated and validated during 2012 and 2013 using data from replicated plot experiments and commercial fields. The Cotton App was evaluated in field trials for three years and performed well when compared to other irrigation scheduling tools. Its geographical footprint is currently limited to the states of Georgia and Florida, United States, because it is enabled to use meteorological data only from weather station networks in these states. A new version is currently under development which will use national gridded meteorological data sets and allow the Cotton App to be used in most cotton growing areas of the United States.

Effect of inoculum density, nitrogen source and saprophytic fungi on Fusarium wilt of Mexican lime

SummaryMexican lime seedlings were inoculated with 0, 500, 1000, 2000, 4000 and 8000 microconidia ofFusarium oxysporum f. sp.citri per gram of potting media. The percent infection and mean disease severity rating increased with increasing inoculum density of the pathogen. In potting mix infested withAspergillus ochraceus, Penicillium funiculosum andTrichoderma harzianum at 5000 conidia per gram 2 weeks prior to infestation withF. oxysporum f. sp.citri at 0, 1000, 4000, and 8000 microconidia per gram,A. ochraceus reduced,P. funiculosum increased andT. harzianum had no effect on disease severity or pathogen population. OnlyP. funiculosum showed antagonistic activityin vitro against the pathogen. Disease severity and pathogen propagule densitites were greater and pH was lower in potting media fertilized with NH4−N than in media fertilized with NO3−N.

Nutrient Mobility and Availability with Selected Irrigation and Drainage Systems for Vegetable Crops on Sandy Soils

A wide variety of vegetable crops is produced on varying types of soils including sandy soils where the production can be maximized as long as proper fertilization, irrigation and drainage systems are implemented. However, most sandy soils have low waterand nutrient-holding capacities, hence appropriate irrigation scheduling is critical for proper plant health as well as for minimizing water requirement. Healthy crops are better able to withstand pest and disease pressures, as well as produce a high quality commercial product. Irrigation management should be geared towards maintaining optimum moisture and nutrient concentrations within the plant root zone. If this goal is achieved, crops will take up their maximum amounts of water and nutrients with minimum wastage. Equally important, excessive irrigation will reduce water use efficiency, as well as require more water and contribute to potentially negative environmental impacts. It is crucial to recognize how nutrients move and transform in soils after the application for improved application efficiencies and reduced environmental losses. However, different irrigation and drainage systems practiced on sandy soils for vegetable production can complicate the dynamics of mobility and availability of nutrients and water. Yet, the number of researches on this matter has not been as many as needed. Therefore, this review attempts to summarize characteristics of sandy soils for vegetable production (Section 2), clarify pros and cons of different irrigation and drainage systems practiced on sandy soils (Section 3), and elucidate the nutrient mobility and availability for vegetable production under different irrigation systems specifically on sandy soils (Section 4), in which the soil environment can greatly differ from other soil types in terms of nutrient dynamics in soil.

In-Season Irrigation And Nutrient Decision Support System For Citrus Production

The sandy soils of central and southern Florida have low water and nutrient retention capacities. Excessive irrigation may greatly increase nutrients leaching thereby contribute to contamination of the aquifer under-lying citrus production system. These systems can be managed in such a manner that the excessive downward drainage through the soil is minimized via use of improved irrigation management and/or scheduling strategies which are also critical to maximize water use efficiency. To aid growers in water management decision making, a computer-based decision support system was developed to facilitate more efficient use of water by making use of specific site characteristics and local weather data. System requirements include information on tree age, spacing, soil water holding characteristics, and monthly irrigation set-points for specific production blocks. The user inputs irrigation duration, and/or rainfall depths by block on a daily basis. The soil profile is divided into 40 five cm layers and both irrigated and non-irrigated zones are identified. Horizontal water movement is assumed to be confined within each vertical zone due to lack of lateral movement in the sandy Entisols that prevail in the citrus production region of central Florida. To estimate crop evapotranspiration (ET), daily reference ET values from the Florida Automated Weather Network station nearest the production area are downloaded automatically. Monthly and yearly water use reports are also provided by the decision support system. Appropriate use of this system should not only reduce statewide agricultural water requirements but also nitrogen-loading of groundwater resources associated with citrus production thereby enhancing the profitability and sustainability of Florida citrus production systems.