High-density grpefruit production in open hydroponics system Rhunito S. Ferrrezi, Kyl A. Thomson, Mrk A. Ritenour, nd Aln L. Wright University of Florid, Institute of Food nd Agriculturl Sciences, Indin River Reserch nd Eduction Center, Fort Pierce, FL 34945. Corresponding uthor: rferrrezi@ufl.edu Astrct Precise irrigtion nd fertigtion mngement provide less-limiting environment to roots while minimizing over irrigtion nd leching of nutrients. This concept cn improve tree growth in the presence of HLB nd help optimize wter nd nutrient use. Higher tree density cn increse fruit yield per re under high HLB pressure. This study evluted the efficiency of open hydroponics on Ry Ruy grpefruit production under different irrigtion systems nd tree density. We tested comintion of rootstocks (Sour ornge nd US897), tree spcing [stndrd nd high density stggered (HDS)], fertiliztion (dry grnulr nd fertigtion), nd irrigtion systems (drip nd microjet), rrnged on five tretments: ) SO + stndrd spcing + dry grnulr fertilizer + micro jet, ) SO + HDS + fertigtion + drip, ) US897 + HDS + fertigtion + microjet, ) US897 + HDS + fertigtion + drip, nd ) SO + HDS + fertigtion + microjet. Folir nutrient, insecticide nd fungicide were spryed using stndrd prctices. We scouted for psyllids, lef minors nd other citrus pests monthly. HLB incidence reched % fter five yers of plnting. Trunk dimeter nd cnopy volume incresed over time, nd were higher on compred to other tretments. Totl numer of fruit nd fruit yield were 226% nd 183% higher in 216 compred to 215. yielded 7,39 kg/h in 217 compred to n verge of 22,153 kg/h for other tretments. Solule solid contents, cidity, nd rtio were not significnt (p>.5). Totl solids per hectre ws lwys low in. High density stggered (HDS) plnting resulted in higher fruit yield, irrespective of rootstock nd irrigtion system, representing n importnt dvnce to the grpefruit production system. However, lor cost nd effect on plnt growth over time still need to e determined for commercil recommendtion. Keywords High density, plnt performnce, fruit yield, fruit qulity. 1
Introduction Citrus (Citrus spp.) is Florid's most importnt griculturl commodity. The stte produces citrus for different mrkets: round ornges (C. sinensis) for juice; nvels, mndrins (C. reticult), grpefruit (C. prdisi) nd lemons (C. limon) for the fresh fruit industry; nd lemons for extrcting peel oil for processing. However, citrus production in Florid hs declined drsticlly since 25 due to citrus greening or Hunglonging (HLB), cused y Cndidtus Liericter siticus (CLs), in ddition to cnker (Xnthomons xonopodis), urn development, nd recent hurricnes (Morgn et l., 29; Kdympkeni et l., 216). The decline in citrus productivity hs resulted in n ggregte loss of $ 3 illion in citrus growers revenue from 26 through 214 (Hodges et l., 214). The Indin River Citrus District mintins pproximtely 13.5% of Florid s totl citrus crege inventory since 2/1 (excluding the crop yers 24/5 due to hurricne dmge) with drstic reduction in recent yers. The numer of grpefruit trees plnted hs incresed since 2/1; conversely, totl ering crege nd totl ering trees in the stte hve oth declined y 38% in the lst decde (USDA, 217). The totl numer of oxes of grpefruit produced in Florid hs decresed from 4.9 million in 23/4 to.8 million in 215/16 (USDA, 217). Excluding seson 24/5, Florid s verge grpefruit yield is quickly decresing over time from 497 oxes/cre in 2/1 to only 288 oxes/cre in 216/17 (USDA, 217). Once citrus is ffected y HLB, it ecomes grdully less productive. HLB lters the plnts physiology (reducing photosynthesis nd xylem flux) nd morphology (e.g. phloem trnsloction, loted nd corky veins, root length nd density) ffecting nutrient uptke, trnsloction, nd utiliztion (Kdympkeni et l., 214). Nutrients re vitl in disese control s nutrients influence plnt resistnce nd pthogen growth (Hndique et l., 212). Hunglonging inhiits root growth, reduces nutrient uptke, promotes lef nd fruit drop, results in deformed fruit with unplesnt flvor, nd results in whole tree decline tht is often lethl (Hndique et l., 212). Firous root length nd density re not consistent in HLB-ffected trees nd re ffected y distnce from the tree trunk (lterl nd verticl), type of rootstock, nd ge of the tree (Kdympkeni et l., 214). Moreover, HLB induced reduction in root density reduces wter nd nutrient uptke (Grhm et l., 213). The decline in firous density is mnifested s wek cnopy volume, poor fruit qulity, nd yield losses. Precise irrigtion nd fertigtion mngement provide non-limiting environment to roots while minimizing over irrigtion nd leching of nutrients. This concept cn improve tree growth in the presence of HLB nd help optimize wter nd nutrient use. Higher tree density cn increse fruit yield per re under high HLB pressure. This study evluted the efficiency of open hydroponics on grpefruit cultivted under different tree spcing (stndrd nd high-density), fertilizer sources (dry grnulr nd wter-solule fertilizer) nd irrigtion methods (drip nd micro jet). Mteril nd Methods 2
Averge dily temperture ( o C) The study ws conducted t the UF/IFAS Indin River Reserch nd Eduction Center in Fort Pierce, FL (lt. 27 o 26 1.8 N, long. 8 o 26 49.8 W nd elevtion m). Ry Ruy grpefruit trees were plnted in Sept/213 (totl of 2,769 trees in 3.23 hectres). 35 3 25 2 15 5 214 215 216 217 1/1 2/1 3/1 4/1 5/1 6/1 7/1 8/1 9/1 /1 11/1 12/1 Fig. 2. Averge dily temperture during the 214-217 experiment. Fort Pierce, FL. We tested comintion of rootstocks { Sour ornge [C. urntium] nd US897 [Cleoptr (C. reticult) Flying Drgon (Poncirus trifolit)]}, tree spcing [stndrd nd high-density stggered plnting (HDS)], fertiliztion (dry grnulr nd wter-solule fertilizer), nd irrigtion systems (drip nd micro jet), rrnged on five tretments: ) Ry Ruy on Sour Ornge + stndrd spcing (3.8 7 m, 358 trees/h) + 16N-2.2P-8.3K dry grnulr fertilizer pplied in-ground + micro jet (one emitter per tree; lue microsprinklers - 4.5 LPH @ 2 psi) ) Ry Ruy on Sour Ornge + HDS [(2.74 1.5.9 m) 6.1 m, 953 trees/h)] + 15N-2.6P-22.4K pplied y fertigtion + drip irrigtion (four emitters per tree, instlled on doule rows; lue dripper - 3.8 LPH) ) Ry Ruy on US-897 + HDS + 15N-2.6P-22.4K pplied y fertigtion + micro jet (sme s ove) ) Ry Ruy on US-897 + HDS + 15N-2.6P-22.4K pplied y fertigtion + drip (sme s ove) ) Ry Ruy on Sour Ornge + HDS + 15N-2.6P-22.4K pplied y fertigtion + micro jet (sme s ove) The experimentl design ws completely rndomized with five replictions. We mesured HLB incidence, tree size, lef mcro nd micronutrient concentrtions, totl numer of fruit nd fruit yield, fruit qulity prmeters (solule solid contents, cidity, nd rtio) nd clculted totl solids per hectre. Hunglonging dignosis of mture leves for CLs titer nd ctivity ws mesured nnully y using the quntittive polymerse chin rection (q-pcr) (Li et l. 26). A totl of 4-6 mture leves ws collected from summer flush in ech of ll four crdinl sections per tree, from which the petiole/midris ws used for CLs detection. Tree size ws ssessed every yer y mesuring trunk dimeter (~8 cm ove the ud 3
union), tree height to top of cnopy (not including height of vigorous shoots tht extend significntly pst the top of the cnopy), nd cnopy dimeter (in prllel nd perpendiculr to the tree row). Cnopy volume ws clculted using the formul: [(dimeter prllel to row dimeter perpendiculr to row) height] 4. Lef nd soil nutrient concentrtions ws determined nnully in August (on spring flush). Approximtely 2-3 mture leves were collected in different prts of the tree. Lef tissue smples were dried for 72 h t 65 o C nd nlyzed y Inductively Coupled Plsm Atomic Emission Spectroscopy (ICP-AES) (Orez nd Morgn, 28). Totl numer of fruit nd fruit dimeter were determined y hrvesting ll tree fruit nd pssing them through n opticl sorter (Autoline, Reedley, CA) mounted on triler. Mesurements were converted into numer of fruit per crton within commercil ctegory. Totl fruit yield ws determined y direct weighing ll the fruit per tree. Rndom smples of 2 fruit from ech experimentl unit were collected for fruit qulity nlysis on ech yer. The fruit smples were weighed, nd fruit dimeter t the equtor ws mesured with digitl cliper. The fruit were weighed nd juiced using press juicer; then, juice ws weighed, nd expressed s percentge of the totl fruit weight. Totl solule solids content ws determined with digitl refrctometer (HI9681; Hnn Instruments, Woonsocket, RI) using few drops of juice. The totl cidity ws determined y titrtion of 5 ml of fruit juice with.1 N sodium hydroxide (NOH) to ph 8.1. Totl solids per hectre ws clculted s: (% juice in fruit ) (solule solids content ) Yield (kg/h). Folir nutrient, insecticide nd fungicide were spryed using stndrd prctices. We scouted for psyllids, lef minors nd other citrus pests monthly. Dt were nlyzed y normlity (Proc univrite), nlysis of vrince (ANOVA) (Proc GLM), nd Tukey s multiple comprisons test (Proc lsmens) using SAS (v. 9.4; SAS Institute, Cry, NC). Proility vlues.5 were considered sttisticlly significnt. Results nd Discussion HLB incidence incresed over time, reching % fter 5 yers of plnting (Fig. 2). The disese progression wrrnts the rpid HLB spreding in the stte of Florid. Trunk dimeter nd cnopy volume incresed over time, nd were higher on compred to other tretments (p<.1, Fig. 3). Such response ws expected, since trees plnted on lower densities receive more solr rdition, wter nd nutrients, not competing with surrounding trees s the high density plntings. Lef mcro nd micronutrient concentrtions were influenced y tretment nd smpling dte (dt not shown). Totl numer of fruit nd fruit yield were 226% nd 183% higher in 216 compred to 215. yielded 7,39 kg/h in 217 compred to n verge of 22,153 kg/h for other tretments. In 217, dt ws compromised y Hurricne Irm, which cused 5%-7% fruit drop (visul oservtion) (Fig. 4). 4
HLB incidence (%) 12 8 6 4 2 214 215 216 217 218 P =.6127 P =.76 P =.532 P =.623 P = 1. Fig. 2. Hunglonging (HLB) incidence of Ry Ruy grpefruit trees. Tretments: ) Sour Ornge (SO) + stndrd spcing [358 trees/h] + dry grnulr fertilizer + micro jet, ) SO + high density stggered (HDS) [(953 trees/h)] + fertigtion + drip, ) US-897 + HDS + fertigtion + micro jet, ) US-897 + HDS + fertigtion + drip, nd ) SO + HDS + fertigtion + micro jet. Trunk cliper (mm) 12 8 6 4 2 214 215 216 217 P =.3 P =.473 P =.13 P <.1 c c Cnopy volume (m 3 ) 14 12 8 6 4 2 214 215 216 217 P =.17 P =.8554 P =.1 P <.1 c c c Fig. 3. Trunk cliper nd cnopy volume of Ry Ruy grpefruit trees. Tretments: ) Sour Ornge (SO) + stndrd spcing [358 trees/h] + dry grnulr fertilizer + micro jet, ) SO + high density stggered (HDS) [(953 trees/h)] + fertigtion + drip, ) US-897 + HDS + fertigtion + micro jet, ) US-897 + HDS + fertigtion + drip, nd ) SO + HDS + fertigtion + micro jet. c c c 5
Totl numer of fruit >64 (No.) 8 7 6 5 4 3 2 32 28 215 P =.1296 216 P =.8834 217 215 P =.163 216 P =.17 217 P =.96 P =.55 Yield (kg/h) 24 2 16 12 8 4 Fig. 4. Totl numer of fruit nd fruit yield of Ry Ruy grpefruit trees. Tretments: ) Sour Ornge (SO) + stndrd spcing [358 trees/h] + dry grnulr fertilizer + micro jet, ) SO + high density stggered (HDS) [(953 trees/h)] + fertigtion + drip, ) US-897 + HDS + fertigtion + micro jet, ) US-897 + HDS + fertigtion + drip, nd ) SO + HDS + fertigtion + micro jet. Fruit qulity prmeters were mesured in 216 nd 217 only. Solule solid contents, cidity, nd rtio were not significnt (p>.5). Totl solids per hectre ws constntly low in (Fig. 5). In 217, ll prmeters were considerly lower thn 216 due to the negtive effects of Hurricne Irm on fruit qulity. Conclusions High density stggered (HDS) plnting resulted in higher fruit yield, irrespective of rootstock nd irrigtion system, representing n importnt dvnce to the grpefruit production system. However, lor cost nd effect on plnt growth over time still need to e determined for commercil recommendtion. 6
Solule solids content (%) Acidity (ml cid/smple) kg solule solids/hectre Rtio (%) 11 9 8 7 6 5 4 3 2 1 1.2 1..8.6.4.2. 13 12 11 9 8 7 6 5 4 3 2 1 16 14 12 8 6 4 2 216 P =.8333 217 216 P =.551 217 216 P =.1729 217 216 P =.82 217 P =.2246 P =.93 P =.515 P =.114 Fig. 5. Solule solids content, cidity, rtio nd solule solids per hectre of Ry Ruy grpefruit trees. Tretments: ) Sour Ornge (SO) + stndrd spcing [358 trees/h] + dry grnulr fertilizer + micro jet, ) SO + high density stggered (HDS) [(953 trees/h)] + fertigtion + drip, RR/897_HDS_fert_ MS) US-897 + HDS + fertigtion + micro jet, ) US-897 + HDS + fertigtion + drip, nd ) SO + HDS + fertigtion + micro jet. 7
Acknowledgements We thnk R. Cve, R. Burton, C. King, R. Lesmes, D. Phuyl, H. Tom Jmes, T. Medows, J. Stephens nd D. Dvis for technicl ssistnce; nd KeyPlex micronutrients, Vlent, Tessenderlo Group, UPI, Byer, Hunter, FMC. Hrrell s, ICL Specilty Fertilizers, Plnt Food Systems nd Aryst LifeScience for product dontion toferrrezi s Citrus Horticulture L. Funding for this reserch ws provided y UF/IFAS, UF/IFAS Citrus Inititive, USDA-FDACS-SCBG (wrd #92195). References Grhm, J.H., E.G. Johnson, T.R. Gottwld, nd M.S. Irey. 213. Presymptomtic firous root decline in citrus trees cused y hunglonging nd potentil interction with Phytophthor spp. Journl of Plnt Disese 97:1195 1199. Hndique, U., R. Eel, nd K.T. Morgn. 212. Influence of soil-pplied fertilizer on greening development in new growth flushes of sweet ornge. Proc. Fl. Stte. Hort. Soc. 125:112:9 14. Hodges, A.W., M. Rhmni, T.J. Stevens, nd T.H. Spreen. 214. Economic impcts of the Florid citrus industry in 212-13. Ginesville, Florid. Kdympkeni, D.M., K.T. Morgn, A.W. Schumnn, nd P. Nkedi-Kizz. 214. Effect of irrigtion pttern nd timing on root density of young citrus trees infected with hunglonging disese. HortTechnology 24:29 221. Kdympkeni, D.M., K.T. Morgn, nd A.W. Schumnn. 216. Biomss, nutrient ccumultion nd tree size reltionships for drip- nd microsprinkler-irrigted ornge trees. Journl of Plnt Nutrition 39:5, 589 599. Li, W., J.S. Hrtung, nd L. Levy. 26. Quntittive rel-time PCR for detection nd identifiction of Cndidtus Liericter species ssocited with citrus hunglonging. Journl of Microiologicl Methods 66(1) 4-115. Morgn, K.T., T.A. Wheton, S.C. Willim, nd L.R. Prsons. 29. Response of young nd mturing citrus trees grown on sndy soil to irrigtion scheduling, nitrogen fertilizer rte, nd nitrogen ppliction method. HortScience 44:145 15. Orez, T.A. nd K.T. Morgn. (eds.) 28. Nutrition of Florid Citrus Trees. Univ. Florid, Inst. Food Agr. Sci., Electronic Dt Info. Source, SL 253. U.S. Deprtment of Agriculture. 217. Florid Citrus Sttistics 215-216. 31 My 217. Aville t https://www.nss.usd.gov/sttistics_y_stte/florid/pulictions/citrus/citrus_sttist ics/215-16/fcs1516.pdf 8