Vegetable Irrigation: Melon

Transcription

1 Available Unavailable February 2015 Vegetable Irrigatin: Meln Tiffany Maughan, Dan Drst, Niel Allen and Brent Black Hrticulture/Vegetables/ Prper irrigatin is essential t grwing a healthy and prductive meln crp. Fr ideal fruit develpment, a cnsistent misture supply thrughut the seasn is necessary. T little irrigatin will result in weak plants with under-sized fruits and reduced quality. Over irrigatin can lead t disease prblems and nutrient leaching. There are a number f irrigatin systems that can be used t irrigate a meln crp, each with different management cnsideratins. 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 melns is abut 50% 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 Allwable Depletin (Beginning f Plant Stress) Permanent Wilting Pint Figure 1. Sil water cntent frm saturated t dry. Figure 1. Sil water cntent frm saturated t dry. Optimal levels fr plant Optimal grwth sil are misture between field capacity levels and fr allwable plant grwth depletin.y are between field capacity and allwable depletin. 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 meln rts are in the tp ft f sil, with 30% in the secnd ft and the tap rts extend dwn t 3 feet. 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.

2 What s in the bank? -- Measuring Sil Misture In rder t assess sil water cntent, ne needs t mnitr sil misture at several depths, frm just belw the sil surface (2 t 3 inches), t the bttm f the effective rting depth (1.5 feet). 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 50 percent 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 50 percent f ttal available. Ttal Available Allwable Depletin inches (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 50% f available water, which rughly crrespnds t sil water ptentials f 50 centibars fr a lamy sand sil, and 70 centibars fr a lam (Table 2, 50% depletin values fr each sil texture). 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 leaves f the plant. Of these, the biggest lsses are 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. 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.

3 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 cantalupe and watermelns are shwn in Table 4. The K crp varies depending n current grund cver relative t the rw width, which prvides an estimate f percent grund cver. Grund cver can be estimated by placing a yard stick under the canpy f the plant and cunting the number f inches that are shaded. Measurements shuld be taken when the sun is directly verhead. When the vine cvers 20% f the grund, a field f cantalupes is using abut 30% f the amunt f water used by the alfalfa reference crp. Water use increases gradually as the canpy develps until the full canpy is established. Fr melns, reducing the amunt f water applied in the last week befre harvest by abut 10 t 15% will imprve flavr and quality. Hwever, it is imprtant t remember that meln fields may be harvested ver several weeks, s sustained water reductin may affect later develping fruit size and yield. Table 3. Daily ttal alfalfa reference evaptranspiratin (ET r) fr seven 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 Farmingtn Spanish Frk Salt Lake City Green River Mab St. Gerge (A) Inches per day Mar Apr May Jun Jul Aug Sep Oct (B) Gallns per acre per day. Irrigatin 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 6-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 6 ft. (bed spacing) / If different bed spacing is used, adjust calculatin accrdingly. Calculated frm lng-term mnthly evaptranspiratin values available at climate.usurf.usu.edu.

4 Table 4. Descriptin f grwth (percent f grund cvered) and crp cefficient estimates fr melns grwn in a plasticulture system. Grund Cver (%) Crp Crp cefficient Cantalupe 1 K crp Watermeln 2 K crp Grattan, et al., 1998 (adjusted fr alfalfa reference ET). 2. Ministry f Agriculture and Fd. Octber 2001 (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, impact sprinklers, drip lines r micrsprinklers. Whichever irrigatin system yu utilize, it is imprtant t calibrate yur system s that yu knw precisely hw much water is being applied. With sprinklers and micrsprinklers, the simplest way t d this is t place catch cans in multiple lcatins in yur planting and cllect water fr a set perid f time. The amunt f water cllected ver time will give yu an applicatin rate (inches per hur), and differences in water cllected amng the catch cans will tell yu hw unifrm the applicatin is within yur planting. 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 perates at 10 psi. Emitters may be spaced frm 4 t 36 inches apart and cme in a variety f flw rates. 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 micrsprinkler r drip system can be 70 t 90% efficient. Overhead sprinkler systems are typically 60 t 75% 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 cantalupe crp with a full canpy. The sil is a deep sandy lam with drip irrigated rws every 6 feet. Water use (Expenses) ETr values are 0.30 inches per day (weather statin data). Crp cefficient is 0.80 (Grwth stage = 100, frm Table 4). ET crp = ET r K crp ET crp = 0.30 inches/day * 0.8 = 0.24 inches/day Sil strage capacity (ptential bank balance) The ttal strage capacity fr readily available water ver the 2-ft effective rting depth is 1.1 inches (Table 1). 1.1 inches / 0.24 inches per day = 4.6 (4) days between irrigatins. In 4 days replace 0.96 inches. Restated, the sil misture in the rtzne will g frm field capacity t plant stress levels in 4.6 days. T recharge the sil prfile, yu will need t add a net f 0.96 inches f water every 4 days. Assuming a drip irrigatin system with an efficiency f 80%, 1.2 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 0.3 inches per day (0.24/0.80). Fr a tw day irrigatin interval apply 0.6 inches (2*0.24/0.80). Summary Gd irrigatin management requires: 1. An understanding f the sil-plant-water relatinship

5 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. Additinal Resurces AgriMet Crp Cefficients. Pacific Nrthwest Reginal ffice f the Bureau f Reclamatin.US Dept. f the Interir Crp cefficients fr use in irrigatin scheduling. Water Cnservatin Factsheet. N British Clumbia Ministry f Agriculture and Fd. Octber Grattan, S.R., W. Bwers, A. Dng, R. Snyder, J. Carrll and W. Gerge New crp cefficients estimate water use f vegetables, rw crps. Califrnia Agriculture 52:1p 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 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 Sprinkler Irrigatin (flw is usually in gallns per minute) Inches/hur=96.24 *gallns per minute (gpm)/area (ft^2) Example: 96.24*7 gpm / (40 feet*60 feet) = 0.28 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*.5 gph / (1 feet* 2.5 feet) = 0.32 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 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.