Vegetable Irrigation: Sweet Pepper and Tomato

Transcription

1 May 2015 Hrticulture/Vegetables/ Vegetable Irrigatin: Sweet Pepper and Tmat Tiffany Maughan, Dan Drst, and L. Niel Allen Prper irrigatin is critical fr sweet pepper and tmat prductin. Optimal irrigatin management leads t healthy plants, maximum yields, and high quality fruit. Under-irrigatin results in a reductin f yield, blssm end rt, and ther fruit quality issues. Over-irrigatin increases disease susceptibility, nutrient leaching, and water lss. Fr ideal fruit set and develpment, a cnsistent misture supply thrughut all grwth stages, but particularly at blm and during fruit sizing, is necessary. Sweet peppers and tmates are sensitive t water stress while flwering as under-irrigatin at this time leads t blssm end rt, a calcium deficiency exacerbated by a lack f water. Uneven watering during fruit sizing leads t cracking in tmat fruit. Water stress als creates cnditins leading t mre sunburn f fruits. Different irrigatin methds are cmmnly used t irrigate a sweet pepper r tmat crp, each with different management cnsideratins. Furrw irrigatin is quite cmmn but many grwers are beginning t use drip irrigatin t save water and imprve plant grwth and prductivity. Regardless f the irrigatin system used, there are sme basic principles t understand that will help ensure prper irrigatin. This fact sheet will discuss these basic principles. Prperly managing irrigatin is analgus t managing mney. In additin t knwing yur current bank balance (sil water cntent), it is imprtant t track bth expenses (evaptranspiratin) and incme (rainfall and irrigatin). Bank Balance (Sil Water Cntent) Hw big is my bank accunt? Water hlding capacity First, sme terminlgy: Field Capacity is the amunt f water that can be held in the sil after excess water has perclated ut due t gravity. Permanent Wilting Pint is the pint at which the water remaining in the sil is nt available fr uptake by plant rts. When the sil water cntent reaches this pint, plants die. Available Water is the amunt f water held in the sil between field capacity and permanent wilting pint (Figure 1). Allwable Depletin (readily available) is the pint where plants begin t experience drught stress. Depending n sil type, the amunt f allwable depletin fr sweet peppers and tmates is abut 25% f the ttal available water in the sil (Figure 2). The gal f a well-managed irrigatin prgram is t maintain sil misture between field capacity and the pint f allwable depletin, r in ther wrds, t make sure that there is always readily available water and that plants d nt experience water stress. Wet Sil Water Cntent Dry Bank Accunt Saturated sil Field Capacity Available Permanent Wilting Pint Unavailable Allwable Depletin (Beginning f Plant Stress) Figure 1. Sil water cntent frm saturated t dry. Optimal sil misture levels fr plant grwth are between field capacity and allwable depletin.

2 The amunt f readily available water is related t the effective rting depth f the plant, and the water hlding capacity f the sil. The effective rting depth depends n sil cnditins and variety. Abut 70% f sweet pepper and tmat rts are in the tp ft f sil, with 30% in the secnd ft. The water hlding capacity within that rting depth is related t sil texture, with carser sils (sands) hlding less water than fine textured sils such as silts and clays (Table 1). A deep sandy lam sil at field capacity, i.e., wuld cntain 0.6 t 0.75 inch f readily available water in an effective rting depth f 1 ft. What s in the bank? Measuring Sil Misture In rder t assess sil water cntent, mnitr sil misture at tw depths: 12 inches deep and near the bttm f the effective rting depth (apprximately 24 inches deep). One f the mre cst effective and reliable methds fr measuring sil misture is by electrical resistance blck, such as the Watermark TM sensr (Irrmeter C., Riverside CA). These blcks are permanently installed in the sil, and wires frm the sensrs are attached t a handheld unit that measures electrical resistance. Resistance measurements are then related t sil water ptential, which is an indicatr f hw hard the plant rts have t pull t btain water frm the sil. Figure 2. The amunt f allwable depletin, r the readily available water, represents abut 30% f the ttal available water. Table 1. Available water hlding capacity fr different sil textures, in inches f water per ft f sil. Ttal available water is the amunt f water in the sil between field capacity and permanent wilting pint. Allwable depletin (readily available water) is the amunt f water the plant can use frm the ttal available befre experiencing drught stress. Allwable depletin is apprximately 30 percent f ttal available fr peppers and 40 percent fr tmates. Ttal Available Allwable Depletin inches (30 % Readily available) Sil Texture Water inch/ft In tp1 In tp1.5 Sands and fine sands Lamy sand Sandy lam Lam Silt lam, silt Silty clay lam Sandy clay lam, clay lam The handheld unit reprts sil misture cntent in centibars, where values clse t zer indicate a wet sil and high values represent dry sil. The relatinship between sil water ptential and available water differs by sil type. The range f the sensr is calibrated t 0 t 200 centibars (higher values indicate drier sil), which cvers the range f allwable depletin in mst sils. The sensrs are less effective in carse sandy sils, and will verestimate sil water ptential in saline sils. Remember that allwable depletin is 25% f available water, which rughly crrespnds t sil water ptentials f 22 centibars fr a lamy sand sil, and 40 centibars fr a lam (Table 2, 30% depletin values fr each sil texture). Table 2. Recmmended Watermark sensr values at which t irrigate. Sil Type Irrigatin Needed (centibars) Lamy sand Sandy lam Lam Silt lam, silt Clay lam r clay TM Watermark is a registered trademark f Irrmeter, C., Riverside, CA. Expenses Evaptranspiratin Water is lst frm the field thrugh surface runff, deep perclatin (mving belw the rt zne), evapratin frm the sil surface, and transpiratin thrugh the

3 leaves f the plant. Of these, the biggest lsses are typically due t evapratin and transpiratin, cllectively knwn as evaptranspiratin r ET. Deep perclatin frm excess irrigatin can be anther large lss. Estimates f ET are based n weather data, including air temperature, relative humidity and wind speed. Table 3 lists average daily reference ET values fr several cities acrss Utah. Many mre sites are mnitred in the state. If yur city is nt listed, visit climate.usurf.usu.edu t find a lcatin near yu. Sme weather statins in Utah are prgrammed t calculate and reprt the ET estimates fr alfalfa as a reference crp (ET ref r ET r ). The ET f yur crp can be determined by multiplying the ET r by a crrectin factr r crp cefficient (K crp ) that is specific t yur crp and its stage f develpment. ET crp = ET r K crp The K crp fr sweet peppers and tmates is shwn in Table 4. The K crp varies depending n current grwth stage. Water use increases gradually as the crp develps until the full canpy is established. After maturity is reached and early fruits begin t ripen, irrigatin is ften slightly reduced fr bth crps with tmat irrigatin reductin being mre significant. Sme misture stress at this time increases fruit sluble slid cncentratin. Irrigatin requirement can be reduced by abut 20 percent when tmates and peppers are grwn under mulch. Table 3. Daily ttal alfalfa reference evaptranspiratin (ETr) fr nine Utah cities expressed in (A) inches per day, (B) gallns per acre per day, and (C) drip-irrigated gallns per 100 feet f bed length per day. Mnth Lgan Brigham City Ogden Farmingtn Salt Lake City Spanish Frk Richfield Cedar City St. Gerge (A) Inches per day Mar Apr May Jun Jul Aug Sep Oct (B) Gallns per acre per day. Amunts need t be adjusted by Crp Cefficient and Irrigatin Efficiency. 1 Mar Apr May Jun Jul Aug Sep Oct (C) Drip-irrigated gallns per 100 feet f bed length per day based n 4-ft bed spacing. Irrigatin amunts need t be adjusted by Crp Cefficient and Irrigatin Efficiency. 2 Mar Apr May Jun Jul Aug Sep Oct Cnversin t gallns per acre per day (B) = (A) x * / Calculatin fr drip-irrigatin (C) = (B) x 4 ft.(bed spacing) / If different bed spacing is used, adjust calculatin. Calculated frm lng-term mnthly evaptranspiratin values frm Hill, 2011.

4 Table 4. Descriptin f stages f grwth and crp cefficient estimates fr pepper and tmat crps. Crp Planting Date t 10% Grund Cver 10% t 70% Grund Cver Maturity t Harvest Sweet Pepper 1 Kcrp Tmat 1 Kcrp Frm Crp Cefficients fr Use in Irrigatin Scheduling adjusted fr alfalfa reference ET. Incme Irrigatin and Rainfall In Utah s high elevatin desert climate, rainfall nly cntributes a small fractin f the in-seasn water requirements f the crp. Therefre, regular irrigatin is needed t supply plant water needs. This irrigatin water can be supplied by furrw r drip lines. Whichever irrigatin system yu utilize, it is imprtant t calibrate yur system s that yu knw precisely hw much water is being applied. When trying t determine applicatin unifrmity, it is best t measure utput at bth ends f yur irrigatin system. Als, if yur planting is n a slpe, yu shuld measure utput at the highest and lwest pints f yur field. Elevatin differences and the distance the water travels thrugh the irrigatin lines bth affect water pressure, and cnsequently the flw rate at the nzzle. Drip irrigatin tape cmes with recmmended perating pressures, a variety f emitter spacings, and varius flw rates. Mst drip tapes perate at 10 psi. Emitters may be spaced frm 4 t 36 inches apart and cme in a variety f flw rates. Peppers d well with 12 t 18 inch emitter spacing and tmates with 18 t 24 inch spacing. Flw rates are cmmnly reprted in gallns per100 feet f tape per hur (GPH) r gallns/emitter/hr. Fr a tape with a 12-inch emitter spacing, 24 gallns/100ft/hr = 24/100 = 0.24 gallns/emitter/hr. Pressure cmpensating emitters (PC) prvide the best unifrmity. Flw rate frm each emitter and emitter spacing can be used t calculate rate per area (Table 3). Drip irrigatin systems are usually perated every day r every few days t maintain ptimal sil misture. The efficiency f yur system is a measure f hw much yu have t ver-water the wettest spts in the field t get adequate water t the dry spts. Efficiency is related t the unifrmity f applicatin and t the amunt f evapratin that ccurs befre the water can mve int the sil. A well-designed drip system can be 70 t 90% efficient while fld and furrw irrigatin is typically 30 t 50% efficient. If yur water supply is limited, a mre efficient system can make a large difference in water savings and crp prductivity. Case Study Fllwing is an example f hw t calculate water needs fr a tmat crp in Farmingtn, Utah, with a full canpy in July. The sil is a deep sandy lam with drip irrigated rws every 4 feet. Water use (Expenses) ETr values are 0.27 inch /day (Table 1, weather statin data). Crp cefficient is 0.66 (Grwth stage = Full Cver, frm Table 4). ET crp = ET r K crp ET crp = 0.27 inch/day * 0.66 = 0.18 inches/day Sil strage capacity (ptential bank balance) The ttal strage capacity fr readily available water ver the 1.5 ft effective rting depth is 0.68 inches (Table 1) inches / 0.18 inch per day = 3.7 (3) days between irrigatins. In 3 days replace 0.68 inches. Restated, the sil misture in the rtzne will g frm field capacity t plant stress levels in 3.7 days. T recharge the sil prfile, yu will need t add a net f 0.68 inches f water every 3 days. Assuming a drip irrigatin system with an efficiency f 90%, 0.75 inches f water applicatin will be required fr each watering. If yu are perating yur drip system n a daily basis yu wuld set yur system t apply 0.25 inch per day. Summary Gd irrigatin management requires: 1. An understanding f the sil-plant-water relatinship 2. A prperly designed and maintained irrigatin system, and a knwledge f the efficiency f the system 3. Prper timing based n a. Sil water hlding capacity b. Weather and its effects n crp demand c. Stage f crp grwth. Each f these cmpnents requires a cmmitment t prper management. Prper management will lead t the maximum yields per applied irrigatin water, and will ptimize the lng term health and prductivity f yur crp.

5 Irrigatin Applicatin Rates Surface Irrigatin (flw usually in cubic feet per secnd) Inches/hur = cubic feet per secnd (cfs) / acres Example: 4 cfs/ 5 acres = 0.8 inches/hur Drip Irrigatin (flw per emitter is usually in gallns per hur) Inches/hur=1.6 *gallns per hur (gph)/emitter spacing (feet^2) Example: 1.6*0.5 gph / (1 feet* 4.5 feet) = 0.18 inches/hur Irrigatin Set Times Set time (hurs) = Grss Irrigatin Need (inches) / applicatin rate (inches/hur) Example: 3 inches / 0.28 inches/hur = 10.7 hurs Cnversins 1 cfs= gpm 1 gpm= 60 gph 1 acre = 43,560 feet^2 Additinal Resurces Crp cefficients fr use in irrigatin scheduling. Water Cnservatin Factsheet. N British Clumbia Ministry f Agriculture and Fd. Octber Hartz, T., and B. Hansn Drip irrigatin and fertigatin management f prcessing tmat. Vegetable Research and Infrmatin Center, University f Califrnia. Hill, R.W Crp and Wetland Cnsumptive Use and Open Water Surface Evapratin fr Utah. Utah Ag. Exp. Stn. Res. Rpt. #213. Utah State University, Lgan UT. Available n the Web at Hill, R.W Cnsumptive Use f Irrigated Crps in Utah. Utah Ag. Exp. Stn. Res. Rpt. #145. Utah State University, Lgan UT. Available n the Web at ITRC. Rw crp drip irrigatin n peppers study High Rise Farms. ITRC Reprt N. R LeBeuf, J., R. Shrtt, C. Tan and A, Verhallen Irrigatin Scheduling fr tmates an intrductin. Ministry f Agriculture, Fd and Rural Affairs. Ontari, Canada. Order N Utah State University is cmmitted t prviding an envirnment free frm harassment and ther frms f illegal discriminatin based n race, clr, religin, sex, natinal rigin, age (40 and lder), disability, and veteran s status. USU s plicy als prhibits discriminatin n the basis f sexual rientatin in emplyment and academic related practices and decisins. Utah State University emplyees and students cannt, because f race, clr, religin, sex, natinal rigin, age, disability, r veteran s status, refuse t hire; discharge; prmte; demte; terminate; discriminate in cmpensatin; r discriminate regarding terms, privileges, r cnditins f emplyment, against any persn therwise qualified. Emplyees and students als cannt discriminate in the classrm, residence halls, r in n/ff campus, USU-spnsred events and activities. This publicatin is issued in furtherance f Cperative Extensin wrk, acts f May 8 and June 30, 1914, in cperatin with the U.S. Department f Agriculture, Kenneth L. White, Vice President fr Extensin and Agriculture, Utah State University.