The purpose of this study was to develop a procedure to determine seed moisture content from intact pelleted seeds. Samples of `Sentinel' onion and `Salinas' lettuce were pelleted by the following companies; Asgrow, Germains (Seed Systems), Harris Moran, Incotec, Peto and Seed Dynamics. Physical characteristics of the various pellets were quantified including weight, volume and density. Measurements were made on intact pellets and densities ranged from 0.84 to 1.67 g/cc. Seed drying curves were obtained on the different pellets under controlled environmental conditions. Pellets were first equilibrated at 85% RH, and then dried at 25C and 18% RH. In general drying rates were similar among pellet types within crops. With regards to seed moisture content determination, neither the electronic moisture meter, based on measuring capacitance, nor oven methods were able to accurately measure seed moisture from intact pellets. Measurement of the head space RH from pre-equilibrated intact pellets (water activity) resulted in an accurate method to assess seed water status for all samples. The actual seed moisture content could be determined by using the moisture isotherms for each seed lot at a given temperature.
A. G. Taylor, D. H. Paine, and D. F. Grabe
Said A. Hamido, Kelly T. Morgan, Robert C. Ebel, and Davie M. Kadyampakeni
Because of the decline in production and negative economic effects, there is an urgent need for strategies to reduce the impact of Huanglongbing (HLB) on citrus [Citrus ×sinensis (L.) Osbeck]. The objective of this study was to evaluate the impact of different irrigation schedules on total available soil water (TAW) and water uptake characteristics of citrus trees affected by HLB in central and southwest Florida. The study was initiated in Jan. 2014 for 2 years on 5-year-old sweet orange trees located in three commercial groves at Arcadia, Avon Park, and Immokalee, FL. Each grove had three irrigation scheduling treatments including the University of Florida, Institute of Food and Agricultural Sciences (UF/IFAS) recommendations, Daily irrigation, and an Intermediate treatment. All groves received similar volumes of water per week based on evapotranspiration (ETo) reported by the Florida Automated Weather Network. Sap flow (SF) measurements were taken for two trees per treatment for at least 10 days per site (twice/year). During those periods, leaf area, leaf area index (LAI), and stem water potential (Ψ) were determined. Also, TAW was determined using drainage curve and capacitance soil moisture sensors installed at incremental soil depths of 0–15, 15–30, and 30–45 cm. Results showed significant differences in average SF, LAI, Ψ, and TAW measurements among treatments. Diurnal SF value under daily irrigation treatment increased by 91%, 51%, and 105% compared with UF/IFAS irrigation in Arcadia, Avon Park, and Immokalee, respectively. Soil water contents (WCs) under daily treatment increased by 59%, 59%, and 70% compared with UF/IFAS irrigation treatment in Arcadia, Avon Park, and Immokalee, respectively. Our results indicated that daily irrigation improved tree water dynamics compared with IFAS or Intermediate irrigation scheduling treatments and reduced tree stress with the same volume of water.
Rashid Al-Yahyai*, Bruce Schaffer, and Frederick S. Davies
The effect of soil water depletion on plant water potential and leaf gas exchange of carambola (Averrhoa carambola L. cv. Arkin) in Krome very gravelly loam soil was studied in an orchard and in containers in the field and in a greenhouse. The rate of soil water depletion was determined by continuously monitoring soil water content with multi-sensor capacitance probes. Stem water potential and leaf gas exchange of carambola in containers were reduced when the soil water depletion level fell below 50% (where field capacity = 100%). Although there was a decrease in the rate of soil water depletion in the orchard as the soil dried, soil water depletion did not go below an average of 70%. This was presumably due to sufficient rainfall and capillary movement of water in the soil. Therefore, soil water content did not decline sufficiently to affect leaf gas exchange and leaf and stem water potential of orchard trees. A decline in soil water depletion below 40% resulted in a concomitant decline in stem water potential of the container trees in the field and greenhouse to below -1.0 MPa. Stomatal conductance, net CO2 assimilation, and transpiration declined significantly when stem water potential was below -1.0 MPa. The reduction of net CO2 assimilation and transpiration was proportional to the decline in stomatal conductance of container trees in the field and greenhouse. Thus, soil water depletion in Krome very gravelly loam soil must be less than 50% before water potential or leaf gas exchange of carambola is affected. Based on these results, irrigation scheduling should be based on physiological variables such as stem water potential and stomatal conductance or the amount rather than the rate of soil water depletion.
George Kargas, Nikolaos Ntoulas, and Panayiotis A. Nektarios
)], electrical capacitance ( Fares and Polyakov, 2006 ), and others ( Bittelli, 2011 ). Time domain reflectometry is generally regarded as the most accurate electronic technique for determining substrate moisture content ( Noborio et al., 1994 ; Robinson et al
Yong Ha Rhie, Seonghwan Kang, and Jongyun Kim
(DLI) and vapor pressure deficit (VPD) have been developed. However, they are not easy to adapt for ornamental plant production owing to varying environmental conditions across production areas ( Kim et al., 2011 ). Capacitance soil moisture sensors
using four capacitance soil moisture sensors, a low-cost open-source microcontroller, and solenoid valves. The technology effectively monitored and controlled volumetric water content over a range of thresholds (0.2, 0.3, 0.4, and 0.5 m 3 ·m −3 ) to
Amanda Bayer, Imran Mahbub, Matthew Chappell, John Ruter, and Marc W. van Iersel
irrigation event ( Wells et al., 2011 ). Capacitance soil moisture sensors can accurately measure θ in peat- and bark-based substrates ( van Iersel et al., 2009 , 2010 ) indicating potential for use in container nurseries and greenhouses ( Majsztrik et al
Jonathan Foster, Stephanie Burnett, and Lois Stack
ensure proper fog containment. The tops and bottoms of all systems were left open for ventilation and drainage. Irrigation was provided using a capacitance sensor-automated fog system that was a variation of the sensor-automated drip irrigation system
on the probe, such as time-domain reflectometry (TDR; Robinson et al., 2003 ), or by measuring the capacitance of the bulk soil. Other sensors measure the dielectric properties of the reflected electromagnetic wave in the frequency domain, to obtain
Thomas A. Obreza and Arnold Schumann
) . Continuously measuring soil moisture with modern technology (e.g., time-domain reflectometry sensors or capacitance probes) is the most accurate irrigation scheduling method. For example, a multilevel capacitance probe can be used to irrigate such that nutrient