Irrigation Scheduling and Soil Moisture Dynamics Influence Water Uptake

Scientia Horticulturae 224 (2017) 272–279

Contents lists available at ScienceDirect

Scientia Horticulturae

journal homepage: www.elsevier.com/locate/scihorti

Research paper Irrigation scheduling and soil moisture dynamics inﬂuence water uptake by MARK Huanglongbing aﬀected trees ⁎ Davie M. Kadyampakenia, , Kelly T. Morganb a University of Florida, Citrus Research and Education Center, Soil and Water Sciences, 700 Experiment Station Rd., Lake Alfred, FL33850, United States b University of Florida, Southwest Florida Research and Education Center, Soil and Water Sciences, 2685 SR 29 N, Immokalee, FL34142, United States

ARTICLE INFO ABSTRACT

Keywords: Improved understanding of citrus water use and soil moisture distribution in Huanglongbing (HLB) (Candidatus Candidatus liberibacter asiaticus Liberibacter asiaticus) aﬀected groves is critical for devising appropriate recommendations for optimizing water Citrus sinensis use and sustaining citrus yields. Thus, a study was conducted to investigate soil moisture movement and water Irrigation scheduling use patterns in central, south-central and southwest Florida. Treatments included: 1) daily irrigation (Daily), 2) Microsprinkler irrigation University of Florida Institute of Food and Agricultural Sciences recommended scheduling characterized by Transpiration irrigating every two days to replace water used by crop evapotranspiration (IFAS), and 3) irrigation scheduled half the number of days between irrigation recommended by IFAS and Daily (Intermediate). The total irrigation

was designed to meet estimated crop water use (ETc) for mature citrus equaling 1127 mm, 1138 mm, and 1211 mm, and 1211 mm per year at Avon Park, Arcadia and Ave Maria, respectively. Field capacities (FC) and − − available water capacity (AWC) varied between 0.062 cm3 cm 3 to 0.11 cm3 cm 3, with AWC estimated to be 86% to 91% of FC. Irrigation set points for irrigation scheduling were estimated at 33 and 50% of allowable soil − water depletion (ASWD) and varied between 0.020 and 0.033 cm3 cm 3 while 50% ASWD varied between 0.031 − and 0.050 cm3 cm 3. Daily water use largely varied between 0.02 and 0.18 g/d/cm2 in Summer 2013, 0.01–0.15 g/d/cm2 in Fall 2013 and 0.01 and 0.24 g/d/cm2 in Spring 2014. Water use pattern was largely of the order Daily > IFAS > Intermediate. Moisture contents were similar among irrigation schedules varying between 5–20%, 1–14% and 5–25% at 15-, 30-, and 45-cm soil depths, respectively, increasing with depth possibly as a result of uptake in the top 30 cm. These ﬁndings should help in reﬁning limits for available water contents and estimating irrigation water demand to sustain citrus productivity of HLB infected trees.

1. Introduction increase water and nutrient use efficiency and tree production in HLB affected groves. Currently, there is no information on the water use of Citrus greening (HLB) is the major disease affecting citrus produc- mature trees affected by HLB. More importantly, investigating the re- tion in Florida and has eliminated > 30% trees and reduced yields in sponse of HLB affected trees to varied irrigation schedules would im- citrus groves in the state (Gottwald et al., 2007; Irey et al., 2006, 2008; prove our understanding about the disease dynamics with regard to Manjunath et al., 2008; USDA, 2016). The problem is exacerbated by plant-soil-water-relationships and help commercial citrus growers the fact that HLB-affected trees show excessive fruit drop, resulting in manage water more efficiently. Information generated from such field fruit losses estimated to be around $150 million annually (Gottwald studies is critical for developing appropriate guidelines for growers to et al., 2007; Albrigo and Syvertsen, 2015). The fruit is not suitable for maintain orange tree yields to optimum production levels while con- the fresh market or juice processing due to significant increase in serving water resources. The objectives of the study were to 1) de- acidity and bitter taste resulting in economic losses (Bassanezi et al., termine water retention characteristics and irrigation set points for the 2009; Dagulo et al., 2010). In addition, HLB-infected trees exhibit de- soils at the three sites, 2) determine soil moisture distribution patterns creased root length density that potentially limits water and nutrient in the citrus irrigated zones, and 3) compare water use of mature citrus accumulation (Graham et al., 2013; Kadyampakeni, 2012; using three different irrigation schedules but similar irrigation rates. Kadyampakeni et al., 2014a,b). Improved water management could

Abbreviations: IFAS, Institute of Food and Agricultural Sciences; AWC, available water capacity; AWSD, allowable soil water depletion; ETc, crop evapotranspiration; HLB, Huanglongbing ⁎ Corresponding author. E-mail addresses: [email protected], dkadyampakeni@uﬂ.edu (D.M. Kadyampakeni). http://dx.doi.org/10.1016/j.scienta.2017.06.037 Received 15 February 2017; Received in revised form 8 June 2017; Accepted 14 June 2017 0304-4238/ © 2017 Elsevier B.V. All rights reserved. D.M. Kadyampakeni, K.T. Morgan Scientia Horticulturae 224 (2017) 272–279

Table 1 Average tree characteristics based on stem and leaf areas.

Site Irrigation schedulea Summer 2013 Fall 2013 Spring 2014

Leaf area (cm2) Avon Park IFAS 16517 ± 4271b 8089 ± 2451 11218 ± 6572 Avon Park Intermediate 20737 ± 7318 16023 ± 11913 9747 ± 3655 Avon Park Daily 14459 ± 11500 10021 ± 8238 5865 ± 2708 Ave Maria IFAS 17220 ± 9445 22614 ± 12178 16220 ± 5620 Ave Maria Intermediate 7403 ± 4627 8559 ± 3312 6731 ± 3377 Ave Maria Daily 8919 ± 2087 11269 ± 6003 6307 ± 2288 Arcadia IFAS 16185 ± 5168 12825 ± 10833 9294 ± 8526 Arcadia Intermediate 8803 ± 7270 8206 ± 7306 4466 ± 1362 Arcadia Daily 20736 ± 7318 10854 ± 6611 8299 ± 2800

Stem area cm2) Avon Park IFAS 2.63 ± 1.09 1.95 ± 0.24 1.79 ± 0.45 Avon Park Intermediate 2.17 ± 0.74 2.32 ± 1.10 2.56 ± 1.04 Avon Park Daily 1.86 ± 0.75 2.55 ± 1.39 2.53 ± 1.51 Ave Maria IFAS 3.81 ± 0.82 4.48 ± 1.81 4.63 ± 1.36 Ave Maria Intermediate 2.74 ± 1.50 2.47 ± 1.17 2.59 ± 1.23 Ave Maria Daily 4.73 ± 2.39 2.56 ± 0.95 2.56 ± 0.95 Arcadia IFAS 2.72 ± 0.91 2.25 ± 1.06 2.86 ± 1.91 Arcadia Intermediate 5.53 ± 1.46 5.30 ± 1.20 3.53 ± 1.43 Arcadia Daily 3.80 ± 2.86 4.00 ± 2.25 5.06 ± 2.41

a Irrigation schedule: IFAS = University of Florida Institute of Food and Agricultural Sciences recommended scheduling characterized by irrigating every two days to replace water used by crop evapotranspiration; Daily - daily irrigation; Intermediate - irrigation scheduled half the number of days between irrigation recommended by IFAS and Daily. All the irrigation schedules targeted replacing full crop evapotranspiration each day. b Mean ± standard deviation of 4–6 replications.

Table 2 Soil physical properties that aﬀect water use and soil moisture dynamics.

a b c d e f Site Depth θsat θr FC AWC 33% ASWD 50% ASWD Bulk density Ksat

− − − cm cm3 cm 3 gcm 3 cm h 1

Ave Maria 0–15 0.370 0.010 0.097 0.087 0.029 0.044 1.518 15.82 Ave Maria 15–30 0.352 0.010 0.072 0.062 0.020 0.031 1.526 13.97 Ave Maria 30–45 0.390 0.010 0.093 0.083 0.027 0.042 1.613 13.22 Avon Park 0–15 0.321 0.009 0.109 0.100 0.033 0.050 1.611 20.74 Avon Park 15–30 0.387 0.009 0.083 0.074 0.025 0.037 1.606 19.22 Avon Park 30–45 0.396 0.009 0.093 0.084 0.028 0.042 1.635 18.33 Arcadia 0–15 0.443 0.010 0.109 0.099 0.033 0.050 1.491 16.42 Arcadia 15–30 0.453 0.010 0.105 0.095 0.032 0.048 1.329 12.51 Arcadia 30–45 0.450 0.010 0.110 0.100 0.033 0.050 1.467 10.51

a θsat = moisture content at saturation. b θr = moisture content at permanent wilting point. c FC = ﬁeld capacity moisture content. d AWC = available water capacity. e ASWD = allowable soil water depletion. f Ksat = saturated hydraulic conductivity.

2. Materials and methods design with 4 replications for sap flow measurements. The irrigation scheduling treatments for conventional irrigation were as follows: 1) 2.1. Site description daily irrigation (Daily), 2) University of Florida Institute of Food and Agricultural Sciences recommended scheduling characterized by irri- The experiments were conducted at Ave Maria (lat. 26°16′N, long. gating every two days to replace water used by crop evapotranspiration 81°25′W) in the southwest Florida flatwoods (Collier county), Arcadia (IFAS), and 3) irrigation scheduled half the number of days between (lat. 27°13′N, long. 81°39′W) in the south-central flatwoods (Desoto irrigation recommended by IFAS and Daily (Intermediate). The total

County), and Avon Park (lat. 27°36′N, long. 81°31′W) in the central irrigation was designed to meet estimated crop water use (ETc) for ridge (Highlands county). The soils at Ave Maria are classified as mature citrus equaling 1127 mm per year in Avon Park (Florida Immokalee fine sand (sandy, siliceous, hyperthermic Arenic Automated Weather Network average from 1 January 2004 to 31 Haplaquods) (USDA, 1998a). The soil at Arcadia is classified as a December 2013 at Sebring, FL, 16 km from the study site), 1138 mm Smyrna fine sand (sandy, siliceous, hyperthermic Aeric Haplaquods) per year in Arcadia (Florida Automated Weather Network average from (USDA, 1998b) while the soil classification at Avon Park is Astatula 1 January 2006 to 31 December 2012, at Arcadia, 3 km from the study sand (hyperthermic, uncoated Typic Quartzipsamments) (USDA, site) and 1211 mm per year at Ave Maria (Florida Automated Weather 1998c). Network average from 1 January 2002 to 31 December 2012, at Immokalee, 9 km from the study site). Similar amounts of citrus water use were reported earlier (Morgan et al., 2006; Jia et al., 2007; Romero 2.2. Experimental design et al., 2009). The trees at all sites were spaced at 4.6 m x 7.6 m.

The experiment was arranged in a randomized complete block

273 D.M. Kadyampakeni, K.T. Morgan Scientia Horticulturae 224 (2017) 272–279

effective saturation could also be used to describe water retention characteristics. The amount of water retained in the soil at any given moment is dependent upon factors such as the type of plant cover, plant density, stage of plant growth, rooting depth, evaporation and transpiration rates, amount of water infiltrated, rate of wetting, nature of horizona- tion and the length of time since the last irrigation or rainfall event (Cassel and Nielsen, 1986). Amount of water available for plant use is determined through estimation of available water capacity, field capacity and permanent wilting point. The traditional field capacity for well-drained sandy soil under laboratory conditions is estimated at 10 kPa of soil water tension for a sandy soil and 33 kPa for medium or fine-textured soil (Obreza et al., 1997). The other retention parameters, including hydraulic conductivity, were conceptualized by van Genuchten (1980) as follows:

1/2 1/m m 2 K =−−KθS ee[1 (1θ ) ] (3)

θθ− r nm− θe = =+[1 (αh ) ] θθsr− (4)

1 m =−1 n

−1 where Ks is the saturated hydraulic conductivity (cm h ), θe (0 < θe< 1) is the effective saturation, θs and θr are saturated and − residual water contents (cm3 cm 3), respectively, h is the pressure head − (cm), α is related to the inverse of the air-entry pressure (cm 1) and n is a measure of the pore-size distribution. Pressures applied to un- Fig. 1. Soil moisture retention curves for 0–15-, 15–30-, and 30–45-cm soil depths in disturbed soil cores ranged from 0 to 100 kPa. three sandy soils of Florida. 2.4. Measurement of sapflow 2.3. Soil moisture determination Sap flow sensors (Dynamax Inc., Houston, TX, USA) were installed The soil properties that determine the behavior of soil water flow on four branches on each tree per irrigation schedule (each branch systems are the hydraulic conductivity and water retention character- serving as a replicate). Measurements of branch diameters were taken istics. The relation between soil water content and the soil water suc- prior to installation of the sensors. The sap flow sensors were connected tion is a fundamental part of the characterization of the hydraulic to a data logger (CR 1000, Campbell Scientific Inc., Logan, UT, USA) to properties of soil (Klute, 1986). The conductivity of a soil depends on record data every hour. Flow data obtained from the data logger were − − pore geometry and the properties of the fluid flowing through or re- then converted to water flow per unit leaf area (g cm 2 d 1)in tained in the pores. Viscosity and density are the two properties that Summer 2013, Fall 2013 and Spring 2014. The sap flow measurements directly affect hydraulic conductivity while soil porosity and water were done for 5–14 days. Stem and leaf areas are presented in Table 1 retention function are determined by soil texture and structure (Klute below. and Dirksen, 1986). Soil water sensors were used to measure volumetric soil moisture content at the three sites (EC-5 and 10-HS, Decagon De- 2.5. Stem water potential measurement vices, Pullman, WA). Soil moisture was measured hourly at 15- and 30- cm depths using the EC-5 soil moisture sensor and the HS10 sensor at Stem water potential was measured using 4 leaves per tree. Leaves 45-cm depth. Each block contained one data logger for recording soil were wrapped in plastic and aluminum foil the day prior to data col- fl −1 moisture content. Unsaturated water ux (q, cm h ) was estimated lection to allow the water potential of the leaves to equilibrate with the ’ using Darcy s law: water potential of the stem. Wrapped leaves were cut at the petiole with q=−K(θ)∇H (1) a razor blade and stem water potential was measured using a pressure chamber (Model 1000, PMS Instrument Co., Corvallis, OR) that was − where K is the unsaturated hydraulic conductivity (cm h 1), θ is soil pressurized at 1 MPa/30 s using compressed nitrogen. − volumetric water content (cm3 cm 3), and ∇H is the total hydraulic head gradient (cm), which was calculated by dividing the difference in 2.6. Visual survey analysis and polymerase chain reaction assays the total potential (cm; sum of matric and gravitational potentials) between one sampling depth layer and another (e.g., the top and middle Trees were visually evaluated for any visual HLB symptoms. Trees layers) by the thickness of the two layers (cm). The matric potential was that were asymptomatic for HLB were identified and used for the study. calculated from the moisture release curve developed for the three soils. Thereafter, real-time polymerase chain reaction (PCR) assay to de- The driving force was expressed as the negative gradient of the hy- termine C. Liberibacter asiaticus infection was used on the selected trees draulic head composed of the gravitational head, z, and the pressure every six months. head, h, mathematically given as:

H = h + z (2) 2.7. Statistical analysis

Mualem (1986) also explained that there are some independent The data were analyzed using GLM Mixed Model Type III proce- variables of interest that describe soil water retention characteristics dures using SAS (version 9.3 for Windows; SAS Institute, Cary, NC) ff θ such as the degree of saturation (S), e ective water content ( e), when assumptions for analysis of variance were satisfied. Differences in

274 D.M. Kadyampakeni, K.T. Morgan Scientia Horticulturae 224 (2017) 272–279

Fig. 2. Soil moisture distribution at Arcadia, Ave Maria, and Avon Park using Intermediate, IFAS and Daily irrigation schedules in summer 2013.

sap flow and stem water potential between irrigation schedules, sites contents at Ave Maria and Arcadia were largely between 0.03 and − and interactions between sites were established. 0.15 cm3 cm 3 at all depths though IFAS irrigation schedule showed greater soil moisture contents than the other two irrigation schedules at 3. Results 30–45-cm depth in Summer 2013, Fall 2013 and Spring 2014. Soil moisture at 15- and 45-cm depths at Arcadia (Figs. 2 and 3) 3 −3 3.1. Soil moisture retention characteristics and distribution pattern by varied between 0.025 and 0.25 cm cm and remained below 3 −3 depth, irrigation schedule and site 0.10 cm cm at 30-cm depth, largely due to greater moisture ex- traction because most citrus roots are concentrated in the top 30-cm Average soil physical properties (Table 2; Fig. 1) showed saturated (Alva and Syvertsen, 1991; Zang et al., 1996; Alva et al., 1999; − moisture contents varying between 0.35–0.39 cm3 cm 3 at Ave Maria, Kadyampakeni et al., 2014b). − − 0.32–0.40 cm3 cm 3 at Avon Park, and 0.44–0.45 cm3 cm 3 at Ar- cadia. Residual moisture content (assumed to be equal to the moisture 3.2. Sap flow and stem water potential between irrigation schedules and − content at permanent wilting point) average 0.01 cm3 cm 3, sites − − 0.009 cm3 cm 3 and 0.01 cm3 cm 3 at Ave Maria, Avon Park and Ar- cadia, respectively. Field capacities (FC) and available water capacity Daily values of sap flow were done by summing the hourly values, − − (AWC) varied between 0.062 cm3 cm 3 to 0.11 cm3 cm 3, with AWC as recommended by Cohen (1991), and truncating values collected estimated to be 86% to 91% of FC. Irrigation set points for irrigation from 000 h to 500 h since the accuracy of dynagage technique is limited scheduling were estimated using methods described by Obreza et al. at very low sap flow values. Sap flows measured using the dynagage (1997) at 33 and 50% of allowable soil water depletion (ASWD). heat pulse method are directly correlated with water use, and thus give − Overall 33% ASWD varied between 0.020 and 0.033 cm3 cm 3 while first approximation of water use in irrigated plants. Daily irrigation − 50% ASWD varied between 0.031 and 0.050 cm3 cm 3. schedule showed higher water use at the Ave Maria in Summer 2013 − Soil moisture contents were below 0.07 cm3 cm 3 at 15- and 30-cm and Avon Park in Summer 2013 and Fall 2013 (Fig. 4). Intermediate soil depths (Fig. 2) at Avon Park probably because this is an excessively was greater than IFAS and Daily at Arcadia in Summer 2013 (Fig. 4). No drained Entisol with very low water holding capacity (Morgan et al., differences in daily water use were observed in Fall 2013 at Arcadia and 2006; Obreza et al., 1997). The soil moisture contents at 45-cm depth at Avon Park, and in Spring 2014 at all 3 sites though Daily irrigation − Avon Park varied between 0.025 and 0.18 cm3 cm 3. The patterns at consistently showed greater sap flow at both Ave Maria and Avon Park Avon Park were similar in Fall 2013 and Spring 2014. The moisture than IFAS and Intermediate irrigation schedules (P < 0.001)(Fig. 4).

275 D.M. Kadyampakeni, K.T. Morgan Scientia Horticulturae 224 (2017) 272–279

Daily > Intermediate > IFAS. We found signiﬁcant interaction (P<0.0001) between site and irrigation schedule possibly due to diﬀerences in soil characteristics. The soil at Avon Park are well drained Entisols while the soils at Arcadia and Ave Maria are poorly drained Spodosols and this might have impacted water use. The PCR assays showed that the Intermediate irrigation block at Ave Maria, and Daily and Intermediate irrigation blocks at Arcadia were HLB positive. All the trees at Avon Park were asymptomatic and HLB negative during the period of the study.

4. Discussion

4.1. Soil moisture distribution patterns

We consistently observed cycling trends in increments of soil moisture following irrigation events at the three sites which is typical for irrigated soils using controllers and microsprinkler irrigation systems (Morgan et al., 2006; Fares and Alva, 2000). Fares and Alva (2000), using a different type of capacitance probe on a Candler fine sand, also found that soil water content in the root zone exceeded the full point during periods of irrigation and/or rainfall, and it drained rapidly within 24–48 h after the end of such events. At all the three sites, moisture contents in the 30–45 cm soil depth largely exceeded 33%ASWD and FC but remained below saturation. According to Alva et al. (1999), water fluxes tend to be greater at depths where root distribution or density are minimal. Also, the sand soil characteristic with > 95% sand content in Florida explains while water fluxes might be greater due to downward drainage of irrigation or rainwater once the hydraulic gradient is sufficient to trigger water movement. Assess- ment of the three irrigation schedules suggests that soil moisture might be optimized with any of the three systems because all the soils re- sponded with elevated levels of soil moisture immediately following irrigation applications, and receded as a result of root uptake and drainage. Runoff losses were considered negligible since most of the soils are well drained in the top 60 cm and would not lose excess water to surface runoff. Of the three depths, 15–30 cm soil depth tended to show the least soil moisture contents at all sites compared with either – – Fig. 3. Soil moisture distribution at Arcadia between 1 December 2013 and 10 March 0 15- or 30 45-cm soil depths largely due to the typically higher sand 2014. content associated with the E-horizon of Spodosols or Entisols, and negligibly low organic matter and/or clay contents compared with the Daily water use largely varied between 0.02 and 0.18 g/d/cm2 in other two depths (Obreza and Collins, 2008). Good irrigation man- Summer 2013, 0.01–0.15 g/d/cm2 in Fall 2013 and 0.01 and 0.24 g/d/ agement of the sandy soils, thus, contributes to good stewardship of cm2 in Spring 2014.Estimation of water use hourly showed that Daily water and nutrient resources (Parsons and Boman, 2006) by sub- schedule, particularly at Avon Park and Ave Maria was higher than stantially reducing leaching and evaporation losses of water. Intermediate and IFAS between 600 h and 1600 h, while in Arcadia, all seasons followed the same trend but Fall 2013, though no clear dif- 4.2. Sapflow and stem water potential dynamics ferences were established (Fig. 5). Hourly sap flows peaked to 8, 5.8 and 6 mg/h/cm2 at Avon Park, Ave Maria and Arcadia in Summer Though no correlation was found between hourly sap flow mea- 2013, respectively. surements and soil moisture content, sap flow trends monitored hourly In Fall 2013, peak sap flows were 5.5, 9.2 and 7 mg/h/cm2 re- showed that frequent irrigation events placed between 900 h and spectively at Avon Park, Ave Maria and Arcadia. In Spring 2014, 1800 h should result in increased water uptake with minimal drainage highest sap flows ranged from 2.5 and 5; 2 and 3.7, and 2 and 7 mg/h/ losses. Comparison of the 3 irrigation schedules showed that Daily ir- cm2 Avon Park, Ave Maria and Arcadia, respectively. Overall, strongly rigation schedule, would likely result in improved water use for both significant quadratic relationships (P < 0.01) were found between HLB positive and HLB asymptomatic trees. The 1-day and/or 1.5-day hourly sap flow and time of day with R2 largely varying between 0.60 break in irrigation schedule for the IFAS and Intermediate irrigation and 0.93 (Table 3). Quadratic model described hourly sapflow better schedule showed that trees might have intermittent occasions of water for tree branch for mature > 10-year-old trees compared to the cubic stress. On average, greater stem water potential was noted at Avon model for young < 6-year-old trees reported by Kadyampakeni et al. Park, followed by Ave Maria, and then Arcadia, suggesting the im- (2014c) for whole trees. portance of good and frequent irrigation management particularly on Stem water potential was greater for Daily than Intermediate but the extremely well drained Candler fine sand. Except for Ave Maria, similar to IFAS (P<0.05) at Arcadia (ranging between 0.3 and where stem water potential was greater for Daily (which was somewhat 0.5 MPa) and Avon Park (varying between 0.5 and 0.8 MPa) suggesting surprising), than Intermediate > IFAS, the other two sites consistently that Daily irrigation schedule resulted higher water use than showed stem water potential of the expected order Intermediate (Fig. 6). At Ave Maria, the trend was surprisingly different Intermediate ≈ IFAS > Daily, since Daily irrigation maintained soil (P < 0.01), ranging from 0.4 to 0.9 MPa, following the order: moisture at levels close to FC most of the day. Based on the observations on the two sites of Arcadia and Avon Park, Daily irrigation would

276 D.M. Kadyampakeni, K.T. Morgan Scientia Horticulturae 224 (2017) 272–279

Fig. 4. Daily sap ﬂow patterns for mature citrus at Avon Park (left) Arcadia (middle) and Ave Maria (right) in Fall, 2013 and Spring 2014 measured per leaf area basis.

Fig. 5. Hourly sapﬂow for mature citrus at Avon Park (left) Ave Maria (middle) and Arcadia (right) in Summer 2013, Fall, 2013 and Spring 2014 measured per unit leaf area.

reduce water stress in the HLB aﬀected trees and would be appropriate 5. Conclusions to implement on Florida’s sandy soils without aﬀecting tree productivity assuming a good nutrition program, pest and disease man- Field capacities (FC) and available water capacity (AWC) varied − − agement strategy. between 0.062 cm3 cm 3 to 0.11 cm3 cm 3, with AWC estimated to be 86% to 91% of FC. Irrigation set points for irrigation scheduling were

277 D.M. Kadyampakeni, K.T. Morgan Scientia Horticulturae 224 (2017) 272–279

Table 3 Regression analysis of quadratic relationships of hourly water use per unit leaf area with respect to time of day across the three seasons in Avon Park, Ave Maria, and Arcadia in Florida.

b 2 Site Irrigation Yo ab RRMSE P schedulea

Summer 2013 Avon Park IFAS −4.740 0.009 −0.0000030 0.78 0.42 *** Avon Park Intermediate −5.642 0.011 −0.0000036 0.90 0.33 *** Avon Park Daily −16.012 0.030 −0.0000100 0.84 1.18 *** Pooled −8.798 0.016 −0.0000058 0.48 1.44 *** Ave Maria IFAS −7.786 0.015 −0.0000049 0.88 0.48 *** Ave Maria Intermediate −4.437 0.009 −0.0000032 0.93 0.23 *** Ave Maria Daily −13.069 0.025 −0.0000088 0.86 0.94 *** Pooled −8.430 0.016 −0.0000056 0.62 1.09 *** Arcadia IFAS −5.608 0.010 −0.0000035 0.82 0.44 *** Arcadia Intermediate −9.582 0.018 −0.0000060 0.82 0.73 *** Arcadia Daily −10.442 0.020 −0.0000069 0.70 1.19 *** Pooled −8.544 0.016 −0.0000055 0.67 0.96 ***

Fall 2013 Avon Park IFAS −5.151 0.010 −0.0000035 0.61 0.74 *** Fig. 6. Stem water potential between Intermediate irrigation, IFAS irrigation and daily Avon Park Intermediate −5.571 0.011 −0.0000038 0.74 0.60 *** irrigation at Ave Maria, Arcadia and Avon Park. Error bars represent 1 standard deviation Avon Park Daily −10.029 0.020 −0.0000069 0.75 1.05 *** of four replicates. Pooled −6.917 0.014 −0.0000048 0.58 1.00 *** − − Ave Maria IFAS 8.628 0.016 0.0000056 0.78 0.78 *** citrus trees at diﬀerent fertilization and irrigation rates while main- Ave Maria Intermediate −8.470 0.016 −0.0000056 0.78 0.77 *** Ave Maria Daily −17.822 0.033 −0.0000115 0.76 1.71 *** taining good pest and disease management would be critical to devise Pooled −11.640 0.022 −0.0000075 0.59 1.56 *** appropriate nutrient management recommendations for HLB positive Arcadia IFAS −2.104 0.004 −0.0000015 0.79 0.07 *** trees in Florida, and similar agro-ecologies for citrus. Arcadia Intermediate −13.127 0.026 −0.0000093 0.69 1.68 *** − − Arcadia Daily 3.827 0.006 0.0000017 0.45 0.86 * Acknowledgements Pooled −6.354 0.012 −0.0000004 0.26 1.72 ***

Spring 2014 − − The authors would like to thank the support of grower cooperators Avon Park IFAS 7.055 0.013 0.0000044 0.77 0.63 *** fi ffi Avon Park Intermediate −7.197 0.013 −0.0000042 0.78 0.61 *** at Paci c Co., Orange Co. and Ben Hill Gri n Inc. Avon Park Daily −11.876 0.022 −0.0000075 0.81 0.96 *** Pooled −8.710 0.016 −0.0000054 0.69 0.91 *** References Ave Maria IFAS −6.709 0.013 −0.0000046 0.84 0.54 *** Ave Maria Intermediate −3.612 0.008 −0.0000030 0.66 0.58 *** Albrigo, L.G., Syvertsen, J.P., 2015. Status of citrus fruit drop in relationship to HLB. Ave Maria Daily −7.757 0.015 −0.0000053 0.87 0.53 *** Citrus Ind. 95, 14–17. Pooled −6.026 0.012 −0.0000042 0.73 0.65 *** Alva, A.K., Syvertsen, J.P., 1991. Irrigation water quality affects soil nutrient distribution, − − Arcadia IFAS 4.786 0.009 0.0000033 0.77 0.48 *** root density, and leaf nutrient levels of citrus under drip irrigation. J. Plant Nutr. 14, − − Arcadia Intermediate 9.561 0.019 0.0000065 0.82 0.81 *** 715–727. Arcadia Daily −13.467 0.025 −0.0000087 0.79 1.17 *** Alva, A.K., Prakash, O.M., Fares, A., Hornsby, A.G., 1999. Distribution of rainfall and soil Pooled −9.271 0.018 −0.0000061 0.61 1.22 *** moisture content in the soil profile under citrus tree canopy and at the dripline. Irrig. Sci. 18, 109–115. *, *** Significant at 0.05 and 0.001 levels of probability. Bassanezi, R.B., Montesino, L.H., Stuchi, E.S., 2009. Effects of Huanglongbing on fruit – a Irrigation schedule: IFAS = University of Florida Institute of Food and Agricultural quality of sweet orange cultivars in Brazil. Eur. J. of Plant Pathol. 125, 565 572. Sciences (IFAS) recommended scheduling; Daily − daily irrigation; Intermediate − ir- Cassel, D.K., Nielsen, D.R., 1986. Field capacity and available water capacity. In: Klute, A. rigation scheduled half the number of days between irrigation recommended by IFAS and (Ed.), Methods of Soil Analysis Part 1, 2nd edition. Agronomy Ser. 9. Madison, Wisconsin, USA, pp. 901–926. Daily. All the irrigation schedules targeted replacing full crop evapotranspiration each Cohen, Y., 1991. Determination of orchard water requirement by a combined trunk sap day. flow and meteorological approach. Irrig. Sci. 12, 93–98. b ffi 2 ffi Yo is the Y-intercept, a and b are regression coe cients, R is the coe cient of de- Dagulo, L., Danyluk, M.D., Spann, T.M., Valim, M.F., Goodrich-Schneider, R., Sims, C., termination, RMSE is the root mean square error and P is the probability. Rouseff, R., 2010. Chemical characterization of orange juice from trees infected with citrus greening (Huanglongbing). J. Food Sci. 75, C199–C207. estimated at 33 and 50% of allowable soil water depletion (ASWD) Fares, A., Alva, A.K., 2000. Evaluation of capacitance probes for optimal irrigation of fi – 3 −3 citrus through soil moisture monitoring in an Entisol pro le. Irrig. Sci. 19, 57 64. varied between 0.020 and 0.033 cm cm while 50% ASWD varied Gottwald, T.R., da Graça, J.V., Bassanezi, R.B., 2007. Citrus Huanglongbing: the pathogen 3 −3 between 0.031 and 0.050 cm cm . and its impact. Plant Health Prog. 23 (June), 2014. http://dx.doi.org/10.1094/PHP- Daily water use largely varied between 0.02 and 0.18 g/d/cm2 in 2007-0906-01-RV. fi – 2 Graham, J.H., Johnson, E.G., Gottwald, T.R., Irey, M.S., 2013. Presymptomatic brous Summer 2013, 0.01 0.15 g/d/cm in Fall 2013 and 0.01 and 0.24 g/d/ root decline in citrus trees caused by Huanglongbing and potential interaction with 2 cm in Spring 2014. Water use pattern was largely of the order Phytophthora spp. Plant Dis. 97, 1195–1199. Daily > IFAS > Intermediate. On average, greater stem water potential Irey, M.S., Gast, T., Gottwald, T.R., 2006. Comparison of visual assessment and poly- was noted at Avon Park, followed by Ave Maria, and then Arcadia, merase chain reaction assay testing to estimate the incidence of the Huanglongbing pathogen in commercial Florida citrus. Proc. Fla. State Hortic. Soc. 119, 89–93. suggesting the importance of good and frequent irrigation management Irey, M., Mai, P., Graham, J., Johnson, J., 2008. Data trends and results from an HLB particularly on the extremely well drained sandy soils of Florida. The testing laboratory that has processed over 64,000 commercial and research samples results showed that Daily irrigation would reduce water stress in the over a two-year period in Florida. Abstract IRCHLB Proc. 103. ff ’ Jia, X., Swancar, A., Jacobs, J.M., Dukes, M.D., Morgan, K., 2007. Comparison of eva- HLB a ected trees and would be appropriate to implement on Florida s potranspiration rates for flatwoods and ridge citrus. Trans. ASABE 5, 83–94. sandy soils without affecting tree productivity assuming a good nutri- Kadyampakeni, D.M., Morgan, K.T., Schumann, A.W., 2014a. Root density distribution tion program, pest and disease management strategy. These findings and water uptake of citrus trees infected with Huanglongbing. Proc. Fla. State Hortic. Soc. 127, 37–41. should improve our understanding in estimating irrigation water de- Kadyampakeni, D.M., Morgan, K.T., Schumann, A.W., Nkedi-Kizza, P., 2014b. Effect of mand and development of a sustainable irrigation management strategy irrigation pattern and timing on root density of young citrus trees infected with to sustain citrus productivity of HLB affected trees in Florida and other Huanglongbing disease. Horttechnology 24, 209–221. Kadyampakeni, D.M., Morgan, K.T., Schumann, A.W., Nkedi-Kizza, P., Obreza, T.A., citrus producing regions. Further investigation into the performance of

278 D.M. Kadyampakeni, K.T. Morgan Scientia Horticulturae 224 (2017) 272–279

2014c. Water use in drip- and microsprinkler-Irrigated citrus trees. Soil Sci. Soc. Am. Obreza, T.A., Collins, M.E., 2008. Common soils used for citrus production in Florida. J. 78, 1351–1361. Univ. Florida Coop. Ext. Serv. SL. 193 Gainesville, FL. Kadyampakeni, D.M., 2012. Citrus Advanced Production System: Understanding Water Obreza, T.A., Pitts, D.J., Parsons, L.R., Wheaton, T.A., Morgan, K.T., 1997. Soil water and NPK Uptake and Leaching in Florida Flatwoods and Ridge Soils. Univ. Florida, holding characteristics affect citrus irrigation strategy. Proc. Fla. State Hort. Soc. 110, Gainesville Ph.D. Diss. 36–39. Klute, A., Dirksen, C., 1986. Hydraulic conductivity and diffusivity: laboratory methods. Parsons, L., Boman, B., 2006. Best management practices for Florida citrus. In: Klute, A. (Ed.), Methods of Soil Analysis. Part 1. Physical and Mineralogical HortTechnology 16, 389–393. Methods. Agronomy No. 9., 2nd ed. American Society of Agronomy, Madison, WI, pp. Romero, C.C., Dukes, M.D., Baigorria, G.A., Cohen, R., 2009. Comparing theoretical ir- 687–734. rigation requirement and actual irrigation for citrus in Florida. Agric. Water Manage. Klute, A., 1986. Water retention: laboratory methods. In: Klute, A. (Ed.), Methods of Soil 96, 473–483. Analysis. Part 1. Physical and Mineralogical Methods Agronomy No. 9, 2nd ed. USDA, 1998a. Soil Survey of Collier County Area. Florida. 20 June 2014 http://ufdc.u- American Society of Agronomy, Madison, WI, pp. 635–662. fl.edu/UF00026060/00001/6j. Manjunath, K.L., Halbert, S.E., Ramadugu, C., Webb, S., Lee, R.F., 2008. Detection of USDA, 1998b. Soil Survey of DeSoto County Area. Florida. 20 June 2014 http://ufd- ‘Candidatus Liberibacter asiaticus’ in Diaphorina citri and its importance in the man- c.ufl.edu/UF00026091/00001. agement of citrus Huanglongbing in Florida. Phytopathology 98, 387–396. USDA, 1998c. Soil Survey of Highlands County Area. Florida. 20 June 2014 ufdc.ufl.edu/ Morgan, K.T., Obreza, T.A., Scholberg, J.M.S., Parsons, L.R., Wheaton, T.A., 2006. Citrus UF00026062/00001. water uptake dynamics on a sandy Florida Entisol. Soil Sci. Soc. Am. J. 70, 90–97. USDA, 2016. Florida Citrus Statistics. National Agricultural Statistics Service Florida Field Mualem, Y., 1986. Hydraulic conductivity of unsaturated soils, predictions and formulas. Office, Florida, US. Methods of soil analysis, Agronomy Monograph, chap. 31, vol. 9. Am. Soc. of Agron., van Genuchten, M.Th., 1980. A closed-form equation for predicting the hydraulic con- Madison, WI, pp. 799–823. ductivity of unsaturated soils. Soil Sci. Soc. Am. J. 44, 892–898.

279