Irrigation Costs for Tomato Production in Florida * 1

Transcription

1 AE74 Irrigtion Costs for Tomto Production in Florid * 1 D.J. Pitts, A.G. Smjstrl, D.Z. Hmn nd G.A. Clrk 2 Seepge irrigtion is the most common method of irrigting tomtoes in Florid tody. This method pplies wter to the field through lterl ditches. From these ditches, wter flows horizontlly eneth the surfces to form perched wter tle nd then moves upwrd to the plnt's root zone y cpillry ction. With seepge irrigtion, wter is sometimes conveyed from the wter source to the field through open ditches. Significnt wter loss my occur due to evportion nd deep percoltion. Some growers use underground pipe distriution systems, which reduce these losses; this type of seepge irrigtion is known s "semi-closed." Due to the reltively low irrigtion efficiencies nd high pumpge requirements with oth seepge irrigtion methods, there is interest in micro (drip) irrigtion s n lterntive. Microirrigtion is the controlled, slow ppliction of wter through devices clled emitters directly to the plnt's root zone from network of plstic pipes. The term "microirrigtion" includes irrigtion methods such s drip, trickle, microsprinkler, micro-spryer, nd some forms of susurfce irrigtion. Drip irrigtion is the form of microirrigtion most often used in the production of tomtoes. The mjority of tomtoes grown in Florid re produced for the fresh mrket. Culturl prctices for production usully include rised eds for dringe, plstic mulch, nd stking. If drip irrigtion is employed with this production system, the lterl tuing used to distriute the wter to the plnt is plced eneth the plstic mulch nd within 12 inches of the plnt row. In this puliction, the cost of drip irrigtion is compred to the irrigtion costs of the two forms of seepge irrigtion under typicl Florid conditions. IRRIGATION EFFICIENCY Efficiency is n importnt fctor. It influences the cost of operting n irrigtion system. Irrigtion ppliction efficiency is the rtio of wter stored in the root zone of the plnt to the totl wter pumped. Wter losses my occur through conveynce, deep percoltion, nd runoff (tilwter). Overll irrigtion efficiency is ffected y mny fctors, including the method of conveynce, distnce from the wter source to the field, soil chrcteristics, ge nd type of crop, wether conditions, requirements for leching to prevent slt uildup, method of ppliction, nd, perhps most importntly, how the 1. This document is AE74, one of series of the Agriculturl nd Biologicl Engineering Deprtment, Florid Coopertive Extension Service, Institute of Food nd Agriculturl Sciences, University of Florid. Originl puliction dte Jnury Reviewed July Visit the EDIS We Site t 2. Former Assistnt Professor, Southwest Reserch nd Eduction Center, Immoklee, Professor nd Associte Professor, Agriculturl Engineering, Ginesville, Associte Professor, Gulf Cost Reserch nd Eduction Center, Brdenton, respectively; Coopertive Extension Service, Institute of Food nd Agriculturl Sciences, University of Florid, Ginesville. The Institute of Food nd Agriculturl Sciences (IFAS) is n Equl Opportunity Institution uthorized to provide reserch, eductionl informtion nd other services only to individuls nd institutions tht function with non-discrimintion with respect to rce, creed, color, religion, ge, disility, sex, sexul orienttion, mritl sttus, ntionl origin, politicl opinions or ffilitions. U.S. Deprtment of Agriculture, Coopertive Extension Service, University of Florid, IFAS, Florid A. & M. University Coopertive Extension Progrm, nd Bords of County Commissioners Cooperting. Lrry Arrington, Den

2 Irrigtion Costs for Tomto Production in Florid* 2 irrigtion system is mnged. More informtion on irrigtion efficiency is ville in IFAS Extension Bulletin 247. Wter-Conveynce Efficiency Wter losses in conveynce from the irrigtion pump to the field cn e significnt fctor in irrigtion costs. Efficiencies of vrious conveynce methods re given in Tle 1 for comprison. Pumping Cpcity The pumping cpcity required is function of the mximum dily evpotrnspirtion (ET m ), the net re to e irrigted, irrigtion system efficiency, nd mximum dily hours of irrigtion system opertion. Pumping cpcity ws clculted from: where: P = Pumping cpcity, (gpm) ET m = Mximum dily evpotrnspirtion (inches) A = Tle 1. Typicl efficiencies of irrigtion conveynce methods. Conveynce Method Underground Pipe Efficiency, percent 100 Aove-ground Aluminum Pipe 85 to 95 Concrete-lined Ditches 80 to 90 Erth Ditches 40 to 80 ssumes no lekge. depends hevily upon soil properties; vlues cn e very low for Florid's sndy soils. Wter-Appliction Efficiency Wter-ppliction efficiency is the rtio of the volume of wter stored in the root zone (nd ville to the plnt) to the volume of wter pplied to the field. This efficiency cn vry significntly due to the irrigtion system, soil type, nd mngement prctices. Seepge irrigtion wter ppliction efficiencies cn rnge from 25 to 60 percent depending on production system, soil type, nd hydro-geologicl properties including restrictive soil lyers, existing wter tle, size of field, etc. Drip irrigtion wter ppliction efficiencies re normlly much less vrile for well-designed nd well-mnged systems, nd typiclly rnge from 80 to 90 percent. COSTS OF IRRIGATION The costs of drip irrigtion for tomtoes re compred to the costs of the two forms of seepge irrigtion. Mny site-specific fctors influence these costs. For this nlysis, three 100-cre fields (open-ditch seepge, semi-closed seepge, nd drip) were compred. In ddition, ssumptions were mde with regrd to pumping cpcity, net production crege, hours of opertion, nd sesonl pumping requirements. Are, (net irrigted cres) Eff = Overll efficiency, (deciml) H o = Mximum dily hours of opertion C = 450, ( constnt to convert to gpm) The mximum dily evpotrnspirtion (ET m ) is function of temperture, reltive humidity, dy length, crop nd culturl prctices (such s plstic mulch nd row spcings), wind speed, nd solr rdition. It cn e estimted s 75 percent of pn evportion or from ET estimtion equtions. Mximum hours of opertion is function of soil wter-holding cpcity, wetted volume of soil, mngement nd lor skills, nd reliility of electricl nd mechnicl systems. Often, seepge systems must e operted nerly continuously during dylight hours to e effective. Drip systems must hve the cpcity to pply wter frequently, more often thn once per dy if necessry. Mximum hours of opertion for sizing purposes must e less thn 24 hours to llow for mintennce nd repir of the system. Therefore, the mximum hours of dily opertion ws ssumed to e sixteen for ech of the systems. Net production crege is less with the open-ditch system thn with either drip or semi-closed systems due to the field re llocted to conveynce ditches nd to wider lterl ditches. The

3 Irrigtion Costs for Tomto Production in Florid* 3 drip irrigtion systems lso require field spce for dringe ditches nd drive lnes for hrvesting. Pumping system cpcity for the drip irrigtion system is function of the plnt row nd emitter spcing nd the flow rte per emitter. In this exmple, the row spcing ws 6 feet, the flow rte ws 24 gph/100 ft, nd there were 5600 ft of row per gross cre. Further, the drip irrigted field ws ssumed to e divided into four suunits, with only one unit to e irrigted t time. These ssumptions result in wter pumping cpcity requirement of 560 gpm. The specific ssumptions tht were mde for this nlysis with regrd to pumping cpcity, efficiency, nd field lyout re shown in Tle 2. Initil Cpitl Investment In ddition to efficiency nd the vilility of wter, the initil cpitl requirement is n essentil fctor tht influences the cost of opertion of n irrigtion system. In computing the initil cpitl requirements for the three 100-cre fields, the irrigtion systems were seprted into two ctegories: the wter supply system nd the distriution system. Economic Anlysis Tle 4 provides listing of the estimted initil cpitl outlys for the three 100-cre systems. Well depth, pump cpcity, nd power requirements were ssumed sed on common wter yield chrcteristics of underground wter-ering formtions in Florid. It ws ssumed tht the drip system could e designed in zones, thus the required pumping cpcity is 5.6 gpm/cre (sed on gross crege). The drip system must hve seepge irrigtion cpcity since the field must often e wetted to llow for ed formtion. In this exmple, however, there is only sufficient wter to wet pproximtely one hlf of the field t time. Totl fixed costs for the 100-cre drip irrigtion system ws estimted t $67,400. The wter supply system consists of the well, nd the pump nd power unit. The distriution system consists of field conveynce ditches, filter systems, underground PVC pipe nd fittings, chemicl injection unit, meters, ckflow prevention, controllers, nd utomtic nd mnul vlves. The requirements for these components will vry depending on the system used. In ddition, since totl pumping hed requirements my e different with ech system, the ssumptions in Tle 3 were mde. The seepge systems, ecuse of lower ppliction efficiencies nd other fctors, would require more pumping cpcity thn the drip irrigtion systems. For exmple, with the open ditch seepge system, wter use is ner potentil ET over the entire field. This is cused y seepge round ditches nd the wet ground surfce in the row middles. Therefore, three wells, pumps, nd power units were required for this seepge irrigtion system. Bsed on Eqution (1), the 100-cre, semi-closed seepge irrigtion system required two wells to provide the necessry pumping cpcity since conveynce losses were eliminted with this system. Totl fixed costs for the seepge irrigtion systems were estimted to e $61,140 nd $55,500 for the semi-closed nd open-ditch systems, respectively. Tle 5 provides rekdown of the nnul fixed costs for the three irrigtion systems. Deprecition ws computed sed on 10-yer lon period. Totl nnul cost includes deprecition, interest, insurnce, txes, nd repirs. Estimted totl nnul fixed costs for the drip, semi-closed, nd open-ditch seepge systems were $11,458, $10,234, nd $9,381, respectively. A summry of nnul fixed nd vrile costs re given in Tle 6. Vrile costs include pumping nd lor. However, for the drip system, the lrgest component of vrile costs is the cost of the disposle lterl tuing tht must e replced ech yer. Totl nnul costs for the three 100-cre irrigtion systems were $24,344, $13,031 nd $12,202 for the drip, semi-closed nd open-ditch systems, respectively. Since more net production cres result from the semi-closed thn the open-ditch system, the lowest nnul irrigtion cost per production cre occurred with the semi-closed irrigtion system. This nlysis ssumes equl production per cre from ech system which my not occur. For exmple, flooding the field with seepge irrigtion provides some frost protection; this is not possile with the drip system. On the other hnd, the cpcity to

4 Irrigtion Costs for Tomto Production in Florid* 4 provide fertilizers to the plnt through the drip irrigtion system my reduce fertilizer costs nd increse production over the seepge systems. SUMMARY The cost of irrigtion is function of the initil cpitl outly for the irrigtion system, irrigtion requirements, vilility of wter, mrket interest rtes, nd fuel costs plus the costs ssocited with lor nd other site-dependent vriles. Assuming common Florid conditions nd current interest rtes nd fuel costs, nnul irrigtion costs were estimted t $363, $195 nd $214 per net irrigted production cre for the drip, semi-closed nd open-ditch irrigtion systems, respectively.

5 Irrigtion Costs for Tomto Production in Florid* 5 Tle 2. Assumptions used in the economic nlysis. Assumption Open-ditch Semi-closed Drip ET m (inches) Net Production Are (cres) Irrigted ET re (cres) Efficiency (percent) Dily Hours Operted Pump Cpcity (gpm) Numer of Wells Seson Pumpge (c-in) Tle 3. Irrigtion pumping hed required. Assumption Open-ditch Semi-closed Drip Drwdown Sttic Wter level Friction (pumping) Opertion Pressure Totl pumping hed given s feet of hed, where 2.31 ft= 1 psi. ssumes specific yield of 25 gpm/ft of drwdown. Tle 4. Initil cpitl investment($) for 100 cre Tomto Drip, Semi closed nd Seepge Irrigtion Systems. Item Drip Semi-closed Open-Ditch Wter supply system 1 well 2 wells 3 wells Well(s) 10-inch, 140ft deep 8,000 16,000 24,000 Pumps(s) 6,000 12,000 18,000 Power Unit(s) 3,500 6,000 9,000 3-inch PVC pipe 4,500 8,000 4-inch PVC pipe 6,000 6,000 6-inch PVC pipe 9,000 7,500 8-inch PVC pipe 13,500 Fittings 4,000 2,000 Conveynce ditches 3,000 Vlves 4,500 2, Filtrtion 2,000 Chemicl injection 1,000 Meters 2, ,200 Bckflow prevention 1, Controller 2,000 Totl ($) 67,400 61,140 55,500 well dimeter nd specific yield will vry with loction. does not include the costs of lnd forming.

6 Irrigtion Costs for Tomto Production in Florid* 6 Tle 5. Annul Fixed Cost ($) for 100 cre Drip, nd Semi-closed nd Open ditch Seepge Irrigtion Systems for Tomtoes. Item Drip Semi-closed Open ditch New cost 67,400 63,140 55,500 Averge cost 33,700 31,570 27,750 Yers of life Deprecition c 6,740 6,314 5,500 Interest d 3,370 3,157 2,775 Insurnce e Txes f Repirs g Totl 11,458 10,734 9,381 new cost - slvge vlue divided y 2 (ssumes no slvge vlue). sed on 10 yer lon. c new cost divided y yers of life. d verge cost x 10 percent e new cost x 0.5 percent f verge cost x 1 percent g new cost x 1 percent Tle 6. Annul Fixed, Vrile nd Pumping Costs ($) for 100-cre Drip nd, Semi closed nd Open ditch See ge Irrigtion System for Tomtoes. Item Drip Semi-closed Open ditch Fixed cost 11,458 10,734 9,381 Vrile Costs: Irrigtion tuing 10, Pumping Costs c 859 1,568 1,664 Lor Costs d Totl nnul costs e 24,344 13,031 12,202 Totl per cre f from Tle 5 560,000 $19/1000 ft c t $0.08 per KWH d t $5.00 per hour e sed on 90-dy growing seson. f net production cres.