Irrigating With High Salinity Water 1

Transcription

1 BUL322 Irrigating With High Watr 1 Dorota Z. Haman 2 In humid aras such as Florida, salinity concrns ar diffrnt than in arid aras sinc larg amounts of rainfall will wash out salts concntrating in th soil profil. Howvr, managmnt may b rquird clos to th coast whr groundwatr salt contnt is frquntly high. managmnt also may b rquird during xtndd drought priods. In arid climats, whr most of th crop watr rquirmnt is supplid through irrigation and th watr oftn contains larg amounts of dissolvd salts, salinity control is frquntly a major objctiv of irrigation managmnt. Irrigation with various typs of wast watr (municipal, industrial, tc.) can also crat salinity hazards or toxicity problms. Abov crtain concntrations, sodium, chlorid, boron, and othr ions ar toxic to many plants. Sinc watr is a vry good solvnt, all irrigation watrs contain som dissolvd salts. Elctrical conductivity is a rliabl indx of salt concntration in th watr. A conductivity of 1 ds/m (dcisimns pr mtr) indicats a salt concntration of approximatly 700 ppm (parts pr million)(soil and Containr Mdia Elctrical Conductivity / IFAS Circular 1092). This valu will vary to som xtnt with tmpratur and typ of salts. is also frquntly xprssd in mg/l (milligrams pr litr). Th numbr of mg/l is quivalnt to ppm. Dcisimns pr mtr is th SI unit for conductivity. Th common English unit is millimhos pr cntimtr (mmho/cm). On ds/m is qual to on mmho/cm. Th salt concntration in th plant root zon is usually highr than that of irrigation watr. Salts ar concntratd du to vaporation and plant transpiration which slctivly rmov watr laving salts in th soil. Ths salts can b rmovd from th plant root zon by laching. Effcts rstricts th availability of watr to plants by lowring th total watr potntial in th soil. also has an impact on crop physiology and yild. Visibl injury can occur at high salinity lvls. Usually, crop yild is indpndnt of salt concntration whn salinity is blow som thrshold lvl, thn yild gradually dcrass to zro as th salt concntration incrass to th lvl which cannot b tolratd by a givn crop. This rlationship is prsntd graphically in Figur This documnt is BUL322, on of a sris of th Agricultural and Biological Enginring Dpartmnt, Florida Cooprativ Extnsion Srvic, Institut of Food and Agricultural Scincs, Univrsity of Florida. Original publication dat Fbruary Rviwd April Visit th EDIS Wb Sit at 2. Dorota Z. Haman, Associat Profssor, Agricultural and Biological Enginring, Gainsvill, FL, Institut of Food and Agricultural Scincs, Univrsity of Florida, Gainsvill, Th Institut of Food and Agricultural Scincs (IFAS) is an Equal Opportunity Institution authorizd to provid rsarch, ducational information and othr srvics only to individuals and institutions that function with non-discrimination with rspct to rac, crd, color, rligion, ag, disability, sx, sxual orintation, marital status, national origin, political opinions or affiliations. U.S. Dpartmnt of Agricultur, Cooprativ Extnsion Srvic, Univrsity of Florida, IFAS, Florida A. & M. Univrsity Cooprativ Extnsion Program, and Boards of County Commissionrs Cooprating. Milli Frrr, Intrim Dan

2 Irrigating With High Watr 2 Tabl 2 lists xampls of crops in ach of thos tolranc rating groups. Control Figur 1. A gnral function of yild rspons to salinity. Various crops show diffrnt snsitivitis to diffrnt salinity lvls. Som crops ar much mor tolrant than othrs. Plants ar gnrally dividd into four salinity rating groups: snsitiv, modratly snsitiv, modratly tolrant, and tolrant (Tabl 1). Tabl 1. Thrshold and zro yild salinity lvls for four salinity groups. Rating Thrshold ds/m Zro Yild Lvl ds/m Snsitiv Modratly Snsitiv Modratly Tolrant Tolrant (adoptd from Jnsn, 1980) Tabl 2. Exampl of crops in four salinity rating groups. Snsitiv Modratly snsitiv Modratly tolrant Tolrant almond alfalfa rd bt sugarbt appl broccoli safflowr cotton avocado cabbag oliv dat palm ban tomato soyban brmudagrass carrot lttuc what grapfruit corn rygrass orang cucumbr whatgrass lmon grap wildry okra panut onion potato strawbrry radish pach ric plum sugarcan (adoptd from Jnsn, 1980) In salin conditions, soil watr availability to th crop can b accomplishd through svral stratgis such as; laching salts from th soil profil, maintaining high soil watr contnt in th root zon, slcting mor salt tolrant plants, improving drainag in th fild, changing irrigation mthod, and adjusting planting practics in som cropping systms. Laching salts from th root zon In arid climats irrigation must supply all watr rquirmnts of th crop for th growing sason. Additional watr must b applid to rmov th salts from th root zon in ordr to avoid a build-up of salts which will xcd th thrshold lvl for a givn crop and rsult in yild rduction. Th amount of additional watr is usually xprssd as a laching fraction which is a dimnsionlss numbr. Th laching rquirmnt for sprinklr and surfac irrigation can b xprssd by ( Equation 1 ). Equation 1. whr: LF -laching fraction (dimnsionlss) -dpth of watr draind (inchs or mm) - dpth of watr applid through irrigation (inchs or mm) Ec i - lctrical conductivity of irrigation watr (mmho/cm or ds/m) EC d -lctrical conductivity of drainag watr (mmho/cm or ds/m) In humid aras th rainfall partially rducs th salinity problms du to irrigation with salin watr. Total dpth of watr applid is a sum of irrigation dpth and th rainfall dpth minus runoff as sn in, Equation 2.

3 Irrigating With High Watr 3 Equation 2. whr: -dpth of irrigation (inchs or mm) D r -dpth of rainfall minus runoff (inchs or mm) D a -dpth of th total watr application (inchs or mm) Th wightd avrag lctrical conductivity for th watr applid through irrigation and th rainfall which prcolats through th root zon must b takn into considration. Th wightd avrag lctrical conductivity of th total watr applid can b calculatd from Equation 3 : Irrigation watr conductivity is 1.5 ds/m. From Tabl 2, w know that broccoli is a modratly snsitiv crop which will b affctd by th soil saturatd xtract salinity lvl EC in th root zon highr than 3.0 ds/m (Tabl 1). This will allow us to calculat LF (Equation 1). Th total watr applid through th irrigation systm during ach irrigation vnt ( ) is th croop watr rquirmnt (CR) plus a drinag dpth ( ) du to th laching rquirmnt: = CR +. Using Equation 1: LF = / = EC i /(5EC - EC i ) = 1.5/13.5 = 0.11 and sinc: Equation 3. In humid climats such as Florida's, thr ar many larg rainfall vnts. Most of th watr infiltrats quickly du to th sandy txtur of th soils. During th rainy sason th dpth of rainfall in Equation 3 is much largr than th dpth of irrigation, and th lctrical conductivity of th wightd avrag is low. As a rsult, salts and frtilizr nutrints ar washd from th root zon bfor salinity concntration can significantly incras. Howvr, salinity may b a problm during xtndd dry priods whn watr is applid only through irrigation. During this tim, an additional amount of watr should b applid with ach irrigation vnt to assur salt rmoval from th plant root zon. Th amount of additional irrigation watr can b calculatd using Equation 1. Exampl 1: Calculat th laching rquirmnt for broccoli during an xtndd dry wathr priod in Florida (assum that all th watr rquirmnt is supplid through irrigation) knowing: Amount of watr that must b applid to fulfill crop watr rquirmnt (CR) is 1 inch (25 mm) pr irrigation vnt. = x LF and = x LF and = CR+ = (CR + ) x LF = (CR + ) x 0.11 = = 0.11 = 0.12 in = = 1.12 in. A simpl chck of calculations can b prformd using quation (1): / = LF 0.12/1.12 = 0.11 Answr: During dry sason, th total amount of irrigation watr which must b applid during ach irrigation vnt in ordr to maintain th soil salinity lvl blow 3.0 ds/m is 1.12 inch (28 mm). From this total amount, 0.12 inch (3 mm) will drain du to th rquird laching fraction LF = Undr Microirrigation Du to th continous high watr contnt in th root zon undr microirrigation, highr salt contnt can b tolratd in th soil than undr sprinklr irrigation without yild rduction. Equation 4 is usd to calculat laching fraction undr microirrigation.

4 Irrigating With High Watr 4 Equation 4. whr: Max EC can b found in Tabl 3. Hanlon, E.A., B.L. McNal and G. Kiddr Soil and Containr Mdia Elctrical Conductivity Intrprtation. Florida Cooprativ Extnsion Srvic, IFAS, Univrsity of Florida, Gainsvill, FL. Circular Availabl onlin: LF calculatd from Equation 4 can b usd in Equation 1 to calculat (dpth of additional watr to b applid). Undr high frquncy irrigation (microirrigation) salts that accumulat blow th mittrs can b almost continuously flushd. Whn LF > 0.1, it is rcommndd that additional watr is usd for flushing to kp salts from concntrating in th plant root zon. Th minimum EC is a usful paramtr for stimating th ffct of microirrigation on crop yild. If EC i <= min EC, thr will b ssntially no rduction in yild. Rclamation of Salt-Affctd Soils Rclamation is dfind as a procdur rquird to rstor productivity loss of th soil du to svr salinity problms. Th only provn solution to a high concntration of solubl salts in a soil profil is laching. Laching rquirs good drainag so that th salts can b rmovd from th fild. Dpnding on th condition, if th natural drainag is not adquat, artificial drains (surfac or subsurfac) must b constructd. A gnral rul is that to rmov 80% of solubl salts initially prsnt in a soil profil, th dpth of watr qual to th dpth of this profil must b applid. A rclamation should b don by application of watr ovr th ntir ara as uniformly as possibl through flooding or sprinkling. Rfrncs Jnsn, M.E Dsign and Opration of Farm Irrigation Systms. An ASAE Monograph. Amrican Socity of Agricultural Enginrs, 2950 Nils Road, St. Josph, MI Jams, L.G Principls of Farm Irrigation Systm Dsign. John Wily & Sons, Inc. Nw York.

5 Irrigating With High Watr 5 Tabl 3. Spcific minimum and maximum balus of EC for Various crops. Fild crops EC,dS/m EC,dS/m Crop Min 1 Max 2 Crop Min 1 Max 2 Cotton Corn Sugar bts Flax Sorghum Broadbans Soyban Cowpas Sugarcan Bans Fruit and nut crops Dat palm Apricot Fig, oliv Grap Pomgranat Almond Grapfruit Plum Orang Blackbrry Lmon Boysnbrry Appl, par Avocado Walnut Raspbrry Pach Strawbrry Vgtabl crops Zucchini squash Swt corn Bts Swt potato Broccoli Pppr Tomato Lttuc Cucumgr Radish Cantaloup Onion Spinach Carrot Cabbag Bans Potato Turnip aftr Ayrs and Wscott (1985). 1 Minimum EC dos not rduc yild. 2 Maximum EC rducs yild to zro.