Available online at Wetting Patterns and Nitrate Distributions in Layered-Textural Soils Under Drip Irrigation

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1 Agriculturl Sciences in Chin 2007, 6(8): Avilble online t *:? ScienceDi rect August 2007 Wetting Ptterns nd Nitrte Distributions in LyeredTexturl Soils Under Drip Irrigtion LI Jiusheng, JI Hongyn, LI Bei nd LIU Yuchun Deprtment of Irrigtion nd Dringe, Chin Institute of Wter Resources nd Hydropower Reserch, Beijing 0044, P.R. Chin Abstrct Lbortory experiments were conducted in different sequence nd thickness of the soil lyers to investigte the effects of lyeredtexturl soils on wetting ptterns nd wter nd nitrte distributions from surfce point source under vrious csmbintions of ppliction rte nd pplied volume. Three lyered soils, including sndyoversndy lom (SL), sndy lomoversndy (LS), nd sndy lomsndysndy lom (LSL), nd two uniform soils ( uniform sndy lom nd uniform sndy soil) were tested. In the experiments, the ppliction rte ws vried from 0.69 to 3.86 L h1 nd the pplied volume from.7 to 12.1 L. The experimentl results demonstrted tht the wetting ptterns nd wter nd nitrte distributions were gretly ffected by the sequence nd thickness of soil lyers s well s the ppliction rte nd volume pplied. An interfce existing in the lyered soils, whether fineovercorse or corseoverfine, hd common feture of limiting downwrd wter movement nd of incresing horizontl wter movement. For the fineovercorse lyered mils of LS nd LSL, wter nd nitrte were uniformly distributed t given depth in the top lyer soil. For corseoverfine lyered soil of SL, however, wter ccumulted in the sublyer soil underneth the interfce nd zone of lower nitrte concentrtion ws observed. The effect of ppliction rte on wter distribution pttern ws dependent upon soil lyering. A minor influence of ppliction rte on wter distribution for the fineovercorse lyered soils (LS nd LSL) thn for the uniform sdils ws found. To obtin greter wetted depth through selecting the emitters hving smller ppliction rte, which is common method in the system design for uniform soil, my not be necessrily pplied for the lyered soils. Mesurements of nitrte distribution showed tht nitrte ccumulted towrd the boundry of the wetted volume for both the uniform nd the lyered soils. This suggests the importnce of optiml mngement of drip fertigtion becuse nitrte is susceptible to the movement out of the root zone by mismngement of fertigtion. The informtion obtined from this reserch is useful in the design, opertion, nd mngement of drip fertigtion system. Key words: drip irrigtion, fertigtion, lyeredtexturl soil, soil wter. nitrte INTRODUCTION Drip irrigtion hs priority in selecting n pproprite irrigtion method in rid nd semirid regions becuse of its potentil of precisely pplying wter nd chemicls both in quntity nd position through field. A proper design nd mngement of drip fertigtion system is, to some extent, dependent upon better understnding of wetting ptterns nd wter nd solute distributions in soil under different combintions of soil type nd lyering, emitter ppliction rte, nd volume pplied. Mny reserchers hve ddressed wetting ptterns from surfce point source, usully represented by the depth of wetting nd the rdius of the wetted volume. Bsed on the solutions of twodimensionl flow eqution presented by Bresler (1978), for exmple, Schwrtzmn nd Zur (1986) developed series of equtions relting Received 20 Mrch, 2007 Accepted June, 2007 Correspondence LI Jiusheng, Ph D, Professor, Tel: Fx: Emil: lijs@iwhr.com CD CMS. All Qht~ reserved. PuMlshed by Elsevler Lld

2 Wetting Ptterns nd Nitrte Distributions in LyeredTexturl Soils Under Drip Irrigtion 97 1 the width nd depth of the wetted volume to the emitter ppliction rte, the sturted hydrulic conductivity, nd the mount of wter in the wetted volume. The experiments conducted by BrYosef nd Sheikholslmi (1976) nd Li et l. (2004) demonstrted tht the increse in the surfce wetted rdius with the volume pplied from surfce point source could be represented by power function with power vlue of bout 0.3 for wide rnge of soil textures, from snd to cly. Cook et l. (2003) developed softwre progrm, WetUp, to disply pproximte wetting ptterns from drippers by using the nlyticl solutions of Philip (1984). In recent yers, the studies on wter flow nd nitrte trnsport under drip irrigtion re incresing becuse of the concern bout the contmintion of ground nd surfce wter sources cused by mismngement of nitrogen fertilizers. Simunek et l. (1999) developed softwre pckge, Hydrus2D, tht enbles implementtion of three dimensionl, xilly symmetric wter flow, solute trnsport, nd root wter nd nutrient uptke. The softwre ws then used to simulte the dynmics of wter nd solute in soil under vrying vribles of drip irrigtion nd to develop the best mngement strtegies for drip irrigtion systems (Cote et l. 2003; Li et l. 200; Grdens et l. 200). However, most of the experimentl nd simultion reserches regrding wter infiltrtion nd solute trnsport from n emitter were conducted on uniform soil (Khn et l. 1996; Revol et l. 1997; Mmolow nd Or 2000; Thorburn et l. 2000; Li et l. 2004). In fct, most field soils re lyered s result of geologicl processes. Extensive ttention hs been given to onedimensionl infiltrtion into lyered soil in the lst severl decdes (Hnks nd Bowers 1962; Hill nd Prlnge 1972; Hchum nd Alfro 1980; Li et l. 1986; Wng et l. 1999). However, few studies hve investigted the infiltrtion into lyered soil under drip irrigtion, which is usully considered s two or threedimensionl problem (Cote et l. 2003). A more precise design of field drip irrigtion system requires further understnding of the wetting ptterns nd chemicl distributions in lyered soils from drip emitter. Although wetting ptterns under drip imgtion in lyered soil cn be obtined by numericl simultion (Cote et l. 2003; Li et l. 200), the experimentl dt to verify the simultion model under such conditions re still lcking. The objectives of this study were to investigte the effects of soil lyering on the wetting ptterns nd nitrte distributions under vrious combintions of emitter ppliction rte nd volume pplied through lbortory experiments nd to give recommendtions for design nd mngement of drip irrigtion systems. MATERIALS AND METHODS Soil lyering tested 'lko soils, medium permeble sndy lom soil (referred to s the fine soil) nd highlypermeble sndy soil (referred to s the corse soil), were used in the experiments. The soils were seprtely collected in different fields just fter winter whet ws hrvested. For ech soil, lrge volume of soil ws obtined nd irdried for the sme length of time nd'the sme temperture. Prticle size nlysis yielded n verge of 66.% snd, 33.4% silt, nd 0.1% cly for the sndy lom soil, nd n verge of 93.39% snd, 6.8% silt, nd 0.03% cly for the sndy soil. The field cpcity nd sturted soil wter content were 0.33 nd 0.2 cm3 ~ mfor the ~ sndy lom soil, nd 0.23 nd 0.43 cm3 ~ mfor the ~ sndy soil, respectively. The sturted hydrulic conductivity predicted by the Rosett rtificil neurl network model (Schp et l. 2001) ws 118 cm d' for the sndy lom soil nd 709 cm d* for the sndy soil. Three lyered soils with different sequences nd thickness of soil lyers were tested. The fmt tested soil consisted of n upper 9 or 19cm lyer of sndy soil nd lower or 20cm lyer of sndy lom soil (referred to s SL9 nd SL19, respectively), the second soil consisted of n upper 9cm lyer of sndy lom soil nd lower cm lyer of sndy soil (referred to s LS), nd the third soil consisted of n upper 9cm lyer of sndy lom soil, middle cm lyer of sndy soil, nd lower 2 cm lyer of sndy lom soil (referred to s LSL). The uniform sndy lom (referred to s L) nd sndy soil (referred to s S) were lso tested. Thus, totl of five lyering soil structures were studied in this study. Experimentl setup The experiments were conducted using 1" wedge CAAS.Alliightsreserved. PublishedbyElsevierl.

3 972 LI Jiusheng ef nl. shped plexiglss continers, cm in height with 41cm rdius (Li et l. 2003), under n ssumption tht ech continer represented one twentyfourth of the complete cylinder. This ssumption ws verified by Lu (2000) who investigted the influence of the ngle of the wedgeshped continer on wter nd solute movement, nd found tht there ws no significnt difference between the 1" wedgeshped continer nd the 90" one. The completely mixed irdry soils were pssed through 2mm sieve nd pcked in the continer with 4 or cm increments to obtin constnt bulk density of 1.3 g cm3 for the sndy lom soil nd of 1.0 g ~ mfor the ~ sndy soil. For ll experiments conducted, n pproximtely similr initil soil wter content ws used, 0.06 to 0.8 cm3 ~ mfor the ~ sndy lom soil nd 0.0 to cm3 cm" for the sndy soil (Tble 1). The wter ws dded to the soil through no. 7 needle connected to Mriotte tube with flexible hose. The outlet ws locted on the soil surfce t the comer of the soil continer. To mintin zero evportion, the soil ws covered with polyethylene sheet. Ammonium nitrte (NH,NO,) solutions prepred on weight (NH,NO,)/volume (w/v) bsis were used in ll the experiments. During ech experiment, the positions of the moving wetting front on the soil surfce nd in the verticl plne s well s the sturted entry zone on the surfce were recorded visully t severl times. After predetermined volume of wter hd been pplied, the verticl plne of the continer ws plced on horizontl surfce to void redistribution of wter in the soil. The continer ws then opened nd smpled with metl tube (inside dimeter 3 cm). When the soil ws smpled the tube went completely through the section. The smpling lyout hd rdil intervls of cm, 2. cm strting from the point of ppliction nd moving outwrd to the edge of the wetted surfce. The sme cm intervls for verticl dt points were fixed up to the wetting front, but the first smpling leg ws 2 cm from the soil surfce. Sometimes, the outer end smple ws less thn cm from the next to the end smple to obtin the soil smple for the wetting front. Grvimetric soil smples were tken outside of the wetted volume to estblish the initil condition of wter content nd nitrte concentrtion. The soil smpling time for ech experiment ws bout 1 min nd the fresh weight of ech smple vried from to 1 g, depending on its position. Five grms of ech smple were tken for determintions of nitrte (NO;) nd the remining smple volume ws used for grvimetric wter content determintion. A g smple of soil ws extrcted with 0 ml of 1 mol LI KC1 to obtin the NO; concentrtion in the soil. All NO; concentrtions in vrious solutions were determined using n utonlyzer (AA3) nd re presented s mg of N in NO; per liter of soil wter (NO;N). Three vribles ffecting wter flow nd solute trnsport, including emitter ppliction rte, volume pplied, nd input concentrtion, were considered. The vribles re presented on the bsis of completely cylindricl system in this rticle. The ppliction rte nd volume pplied were obtined by multiplying the ctul vribles by 24. In totl, 17 experiments were conducted with ppliction rtes vrying from 0.69 to 3.86 L hi, volumes pplied from.7 to 12.1 L, nd input concentrtion of 0 mg L', which were determined bsed on the commercil instlltions (Fu et l. 1988). One repliction ws used for ech experiment. Different ppliction rtes were obtined by chnging the height differentil between the Mriotte tube nd the outlet. Tble 1 summrizes the ppliction rte, volume pplied, input concentrtion, soil lyering, nd initil wter content nd initil nitrte concentrtion for ech of the 17 experiments. As there existed some difficulty to control the ppliction rte t exctly the sme vlue between the comprble experiments, the dt obtined from the experiments with n pproximtely equl ppliction rte were used to evlute the effects of pplied volume. For exmple, exp. nos. 6, 7, nd 8 were used to evlute the effects of pplied volume for the SL soil. Grphicl softwre pckges (Autodesk, Inc. 2000; Golden Softwre, Inc. 2000) were used for clculting the volume of wter nd plotting the contours of wter content nd nitrte concentrtion. The difference before nd fter experiments for wter volumes were clculted to determine the percentge of the pplied volume recovered. RESULTS Movement of wetting front Monitoring of surfce wetting reveled tht the wter 02007, CAAS. All dgms resewed. PuMlshed by Elwvkr Ltd.

4 Wetting Ptterns nd Nitrte Distributions in LyeredTexturl Soils Under Drip Irrigtion 973 spred outwrd in circulrrc shped sturted zone on the surfce for the uniform sndy lom soil (L) nd LS nd LSL lyered soils, but no sturted entry zone ws observed under the ppliction rtes nd volume pplied for the soils hving highly permeble soil s top lyer (uniform sndy nd SL soils). The dimensions of the sturted entry zone on the soil surfce were controlled by the ppliction rte nd soil lyering (Fig. 1). For given lyered soil, greter ppliction rte produced lrger rdius of the sturted zone. For exmple, the ultimte rdius of the sturted zone ws 8.2, 12.1, nd 22.2 cm for the ppliction rtes of 0.92, 1.90, nd 3.86 L h' fter dding L of wter for the LS soil. It cn lso be seen in Fig.1 tht both lyered soils of LS nd LSL resulted in greter ultimte rdius of the sturted entry zone thn the uniform sndy lom soil. The ultimte rdii of the sturted zone t n pproximte ppliction rte of 1 L h' were, for exmple, 8.2, 8.2, nd 6.4 cm for the LS, LSL, nd uniform sndy lom soil, respectively. For the infiltrtion from surfce point source hving ponded entry zone, wetting front forms within the top lyer nd dvnces downwrd continuously in response to the combined mtric nd grvittionl potentil grdients. When the wetting front reches the interfce between soil lyers, the wetting front stops nd the infiltrtion rte slows down since the mtric potentil for the sublyer of sndy soil is substntilly higher thn the top lyer of sndy lom soil t n pproximtely equl initil soil wter content. This cn explin the fct tht greter sturted entry zone formed on the surfce of the lyered soil thn on the surfce of the uniform soil. Surfce wetted rdius nd verticl wetted depth s function of time for the fineovercorse lyered soils hving 9cm top lyer of sndy lom soil (LS nd LSL) re illustrted in Fig.2. For both lyered soils, greter ppliction rte llows wter to move fster both horizontlly nd verticlly. A minor effect of soil LS q = 0.92 L hl.lsq= 1.90Lh' LS q = 3.86 L 11.' LSLq=1.16Lh' = LSL q = 2.00 L h ' LSL q = 3.82 L h ' Lq=0.Y3Lh' Elpsed time (min) Fig. 1 The sturted wetted rdius on the surfce s function of time for the lyered soils of sndy lomoversndy soil (LS), sndy lomsndysndy lom (LSL), nd the uniform sndy soil (L) t different ppliction rtes. Tble 1 Summry of the soil. lyering, ppliction rte (q), totl volume pplied (Q), initil conditions of soil wter nd solutions, nd ctul wter volume pplied nd recovered for ech of the 17 experiments Exp. Soil 92) Q*l Initil wter content (cm3 cm3) Initil NO,N (mg Ll) Volume Volume Percentge no. lyeringl) (Lhl) (L) Lomsoil Sndy soil Lom soil Sndy soil pplied (ml) recovered (ml) recovered 1 L L I S S ) SL I SL ) SL ' SL b 98 93) SL ') SL LS LS LS LSL LSL LSL LSL Men (N I) L, S. SL, LS, nd LSL represent uniform sndy lom soil, uniform sndy soil, sndyoversndy lom soil, sndy lomoversndy soil, nd sndy lomsndysndy lom soil, respectively. 2, Actul vlue multiplied by The thickness of the top lyer soil is 19 cm for these SL experiments. 'I The thickness of the top lyer soil is 9 cm for this SL experiment , CMS. All mht regerved. P umii by Elsevier Ltd.

5 ~~ 914 LI Jiushenn et l. lyering on the movement of horizontl wetting front ws observed. Power equtions were fitted to estimte horizontl wetting front movement nd the prmeters re summrized in Tble 2. The dt indicted tht the power vlue for different ppliction rtes vried within rnge of 0. to 0.39, with n verge of 0.3. This result is similr to previous finding obtined from the experiments cdnducted on uniform lom soil (Li et l. 2003). The movement of the verticl wetting front ws dominted by the soil lyering (Fig.2B). When wetting front reched the interfce between soil lyers, the movement of wetting front slowed down. As infiltrtion continued, wter content t the wetting front incresed nd so did the wetting front wter potentil, correspondingly. After period of time, the wetting front wter potentil incresed to certin vlue, the wetting front moves downwrd cross the interfce into the sublyer soil. For exmple, for n ppliction rte of 0.92 L h' of the LS soil, wetting front moved 9 cm downwrd to the interfce between the sndy lom nd the sndy soil in the initil 60 min of infiltrtion. But it took bout 180 min (from 60 to 2 min) for the wetting front to dvnce from 9 to cm depth cross the interfce. After the wetting front penetrting the interfce nd entering the sublyer soil, the dvncing of the wetting front becme fster gin, resulting in n 8 cm downwrd movement (from to 18 cm) in the following 4 min (from 2 to 660) of infiltrtion (Fig.2B). In other words, the verged downwrd movement rtes for the wetting front were 0.1, 0.006, nd cm mini for the initil 60 min, middle 180 min, nd finl 4 min of infiltrtion, respectively. Accordingly, the reduction of downwrd dvncing rte of the wetting front cused reduced infiltrtion, resulting in n expnding of the surfce sturted entry rdius (from to 6.3 mm) while the Tble 2 Prmeters for estimtion of surfce wetted rdius (R,, = btd) nd corresponding determintion coefficients (Rz) for the lyered soils of LS nd LSL Soil lverine (L h1) b d RZ LS LS LS LSL LSL LSL wetting front penetrted the interfce from 60 to 2 min of infiltrtion (Fig.1). These results reveled tht fineovercorse lyered soil reduced the dvncing rte of the wetting rte nd infiltrtion while the front penetrted the interfce between the soil lyers. The decrese in verticl wetted depth is evident for the LSL soil when ppliction rte incresed from q = 1.16 L h' to q = 2.00 L h' for given volume of wter pplied, but not from q = 2.00 to 3.82 L h' (Fig.2B). Even minor differences were detected for the LS soil. The observed trends of the verticl wetted depth decresing with ppliction rte re similr to the results observed for the uniform soils (Li et l. 2003), but the effects of ppliction rte on the verticl wetted depth ws minor for the lyered soils thn for the uniform soils. In drip irrigtion system design, lrger wetted depth cn be obtined by selecting emitters hving smller ppliction rte for uniform soil. But this method might not be necessrily effective for the fineovercorse lyered soils, especilly when ppliction rte exceeds 2 L h' for the lyered soils of LS nd LSL tested. The minor influence of ppliction rte observed on the verticl wetted depth my lso be ssocited with the experimentl errors rising from the differences in soil compction nd initil soil wter contents, the edge effect of the soil continers, nd time elpsing A h g. 3 : 3 2 B 20 z : '..,.. * *.. x. *LSq=O92Lh' =LSq=190Lh' A D LSq386Lh' 1 j C * ' LSLq=1.16Lh1 ; I. = LSLq=2.00Lh1 % : *LSLq=382Lh' m. 01 ' ' ' ' ' ' ' * ' Elpsed time (min) Elpsed time (min) Fig. 2 Surfce wetted rdius nd verticl wetted depth s function of time for the lyered soils of LS nd LSL t different ppliction rtes.. Q 2007, CAAS. All rlghts resenred. PuMished by Elsevier Ltd

6 J Wetting Ptterns nd Nitrte Distributions in LyeredTexturl Soils Under Drip Irrigtion 97 between the end of the experiment nd the time of smpling. Fig.3 shows the surfce wetted rdius nd verticl wetteddepth s function of time nd ppliction rte for corseoverfine lyered soil of SL s 6 L of wter ws pplied. No prticulr chnge in dvncing rte of verticl wetting front ws observed s the wetting front moved cross the sndsndy lom interfce locted t 19cm depth. The substntilly higher initil wter potentil for the top lyer of sndy soil thn tht for the sublyer of sndy lom soil mde the wetting front penetrte the interfce fster. For given volume pplied, the three ppliction rtes tested produced comprble surfce wetted rdius. A decresing trend of the ultimte wetted depth with ppliction rte ws observed when the rte incresed from 0.9 to 2.08 L hi, but the rtes of 0.69 nd 2.08 L h' produced n pproximtely similr wetted depth (Fig.3B). Agin, this result my be ssocited with the experimentl errors nd the edge effects of the soil continers. The observed wetted rdius nd verticl wetted depth nd time reltion ws fitted to power eqution nd the regression prmeters re presented in Tble 3. An verged power vlue of 0.36 ws obtined for the surfce wetted rdius nd vlue of 0.34 ws obtined for the wetted depth. The power vlues for the surfce wetted rdius re in greement with the results obtined from the experiments conducted on quite sme sndy soil (Li et l. 2004), but the power vlues for the wetted depth re smller for the SL soil thn for the uniform sndy soil. The reduced infiltrtion resulting from the underlying lom soil cn ccount for this difference. Surfce wetted rdius nd verticl wetted depth s function of time for different soil lyering structures hving sme top lyer thickness of 9 cm re compred in Fig.4. At n pproximte ppliction rte of 2 L h', the surfce wetted rdius followed the trend of LS > LSL > SL > S, while the verticl wetted depth followed the trend of S > SL > LSL > LS. Comprison of Figs. 4A nd 4B leds one to find tht the effect of soil lyering on the verticl wetted depth ws much more significnt thn on the surfce wetted rdius. For given volume of L pplied, the mximum difference of the surfce wetted rdius mong the five lyering soils tested ws.4 cm (31.1 cm for the LS soil nd 2.7 cm for the sndy soil), while the mximum difference of the verticl wetted depth reched 16.0 cm (33.9 cm for the sndy soil nd 17.8 cm for the LS soil). Wter nd nitrte distributions The percentge of pplied wter recovered for ll experiments rnged from 86 to 7% with n verge of 99% (Tble 1). It is therefore confirmed tht the mesurement of soil wter distribution hs reltively high ccurcy. Wter loss during the process of soil smpling nd the smpling errors re minly responsible for the smll difference between the recovered nd the + SL q = 0.69 L hl SL q = 0.9 L h' SL q = 2.08 L h' 0 " " " " " m Elpsed time (min) * 01 " " ' " " ' Elpsed time (min) Fig. 3 Surfce wetted rdius nd verticl wetted depth s function of time for the lyered soils of sndyoversndy lom (SL) t different ppliction rtes. b Tble 3 Prmeters for estimtion of surfce wetted rdius (Rh = btd) nd verticl wetted depth (R, = b,tdl) nd corresponding determintion coefficients (R2) for the lyered soil of SL q (L h9 R, = btd R, = b,tdi h d R2 b. d. R= Q2007,CAAS.Allrightsreserved. PuMibyElsevierLtd.

7 976 LI Jiushene et l. pplied wter. Chnges in volumetric wter content for ppliction rtes of 0.92, 1.90, nd 3.86 L hi fter dding L of wter re illustrted in Fig. for the fineovercorse lyered soil of LS. No significnt difference of surfce wetted rdius nd verticl wetted depth s well s wter distribution in the wetted volume ws observed s ppliction rtes incresed from 0.92 to 3.86 L hl. As discussed in the previous section of this rticle, when the verticl wetting front reches the interfce between soil lyers, the wetting front stops until the wetting front wter potentil increses to certin vlue. This mde more wter distribute in the horizontl direction, resulting in uniformly rdil wter distribution (isolines of wter content prllel to the soil surfce). The wter distributions for ppliction rtes of 1.16, 2.00, nd 3.82 L hi s 12 L of wter ws pplied re illustrted in Fig.6 for the threelyered soil of LSL. The ppliction rte of 1.16 L hl produced greter wetted depth thn the other two ppliction rtes tested, but n pproximtely similr wter distribution ws observed. A uniformly rdil wter distribution ws lso found in the 9cm top lyer of sndy lom soil. Wter ccumultion underneth the sndysndy lom interfce (locted t 14cm depth) ws noticed for ll ppliction rtes tested. Compring the wetting ptterns nd wter distributions in the lyered soils tested in the current study (Figs.3,, nd 6) nd the ptterns in uniform lom soil (Li ef l. 2003) nd in uniform sndy soil (Li et l. 2004), one cn find tht the effects of ppliction rte on wetting ptterns nd wter distributions for uniform soils re more obvious thn for lyered soil. This result cn be helpful for selection of emitter rtes in system design. The effects of pplied volume on wter distribution ptterns re described in Fig.7 for the corseoverfine soil of SL. A common feture for the distributions ws tht wter ccumultion occurred in the sublyer soil just below the interfce between soil lyers. Both horizontl nd verticl wetted distnces show n I, * b e LS q = I YY L h'. Q= 0 L ' LSq= 1 YO L h',q= I L LSL q = I Y L h I, Q= 0 L Sq=2 I L h'. Q= 0 L " Elpsed time (min) Elpsed time (min) Fig. 4 Surfce wetted rdius nd verticl wetted depth s function of time for different lyered soils t n pproximte ppliction rte of 2 L h rn A 0 B o co E I e LS soil LS soil LS soil q =O.Y2 L h' q = 1.90 L h' q = 3.86 L h I 3 Q =.0 L 3 Q=.1 L 3 Q =.0 L Fig. Chnge in volumetric wter content distribution for 0.92, 1.90, nd 3.86 L h1 ppliction rtes fter dding L of wter for the lyered soil of LS. E I 02007, CAAS. All Cht reserved. PuMied by Elwvler Ltd.

8 Wetting Ptterns nd Nitrte Distributions in LyeredTexturl Soils Under Drip Irrigtion 917 incresing trend with the volume pplied. For.7, 8.0, nd.0 L of wter pplied, the line of no chnge in volumetric wter content (0) ws t 27, 31, nd 32 cm of surfce rdius, nd ws t,3 1, nd 34.8 cm depth. Fig.8 compres wter distribution ptterns for the four lyered soils tested t n ppliction rte of bout 2.0 L h' nd volume pplied of L. In the figure, the top lyer thickness ws 9 cm for the lyered soils of SL, LS, nd LSL. Compring the wter distributions between the lyered soil nd the uniform soil, one cn find tht the interfce between soil lyers, whether fineovercorse or corseoverfine, hs common feture of limiting downwrd wter movement nd of incresing horizontl wter movement. For exmple, the line of no chnge in wter content ws t 28 nd 37 cm depth for the SL soil nd the uniform sndy soil (Fig.8A, B). Wter stored in 014 cm depth represented 98, 9, nd 6% of the totl wter pplied for the LS, LSL, nd SL lyering soil, respectively, while only 6% of the pplied wter remined in this lyer for the uniform sndy soil. It cn be recognized tht the zone for the gretest wter content increse occurred in the top lyer t the proximity of the emitter for the fineovercorse lyered soils, while the zone occurred in the sublyer soil just below the interfce for the corseoverfine lyered soil. The dimensions of the wetted volume for different lyered soils were lso clerly different. A nrrowdeepshped wetted volume ws formed for the corseoverfine lyered soil of SL nd the uniform sndy soil, but wideshllowshped wetted volume ws obtined for the fineovercorse lyered soils of LS nd LSL nd the uniform sndy lom soil. For exmple, the surfce rdius to depth rtio for the lines of no chnge in wter content ws 0.70, 1.13, 1.62, nd 1.83 for the S, SL, LS, nd LSL soils, respectively. It cn be inferred from the foregoing results tht the lyered soil, especilly the fineovercorse lyered soil, my form constrint Kdil distnce (cnl) Kdil distnce (cin) Kdil distnce (cm) A 0 BO c0 I I) I 0 IS 1 E I S f 20 c P : LSL soil LSL soil LSL soil q= 1.lhLhl q = 2.00 L h' q=3.82lh1 3 Q = 12.0 L 3 Q= 12.1 L 3 Q = 12.0 L 4(J Fig. 6 Chnge in volumetric wter content distribution for 1.16, 2.00, nd 3.82 L h1 ppliction rtes fter dding 12 L of wter for the lyered soil of LSL A 0 1 f 20 2,t Kdil distnce (cm) 3S SL soil q = 0.9 L hl Q =.1 L B SL soil 3 t q = 0.92 L h' Q = 8.0 L. C c B Q =.0 L Fig. 7 Chnge in volumetric wter content distribution for.7, 8.0, nd.0 L of wter pplied t n pproximte ppliction rte of 1 L h1 for the lyered soil of SL. 02M)7, CAAS. All rights resewed. Published by Elsevler LM.

9 978 LI Jiushene ef l. Rdil distncc (cm) A 0 IS IS E s' 20 8 n 2 1 q 3 = I.YY L h' Q =.0 L I * f 20 e c 2 LS sod q= 190Lh' 3 Q=lOlL Rdil distncc (cm) c D 0 IS Lsi soil q=l.ylk 3 Q =.0 L Fig. 8 Chnge in volumetric wter content distribution for different lyered soils t n pproximte ppliction rte of 2 L h i nd volume of L pplied. IS 20 2s 3s for wter nd nutrient uptke of plnts since such soil lyering restrict the wter to distribute into the sublyer of the soil. As n exmple, Fig.9 compres the distributions of nitrte (NO;N in mg LI) for different lyered soils t n ppliction rte of bout 2 L h' nd volume of L. Other experiments gve similr distribution ptterns (not shown in the figures). The ccumultion of nitrte t the boundry of the wetted volume ws observed for both uniform nd lyered soils. This result is in greement with the findings from the previous reserches (BrYosef nd Sheikholslmi 1976; Li et l. 2003, 2004). Compring Figs.8 nd 9 leds one to find tht nitrte distribution pttern is highly ssocited with wter distribution. An ccumultion of wter underneth the interfce between soil lyers for the SL soil (Fig.8A) led to zone of lower NO,N concentrtion (Fig.9A). For the LS soil, the uniform wter distribution in the top lyer (Fig.8B) resulted in uniform NO,N distribution (Fig.9B). DISCUSSION AND CONCLUSION Wetting ptterns nd nitrte distributions in lyered soils from surfce point source were investigted under vrious combintions of ppliction rte nd pplied volume s well s sequence nd thickness of the soil lyers. The results indicted tht the movement of wter in the soil is ffected by ll vribles tested nd nitrte trnsport is highly ssocited with wter flow. Both wetting front movement nd wter nd nitrte distributions in lyered soil re significntly different from those in uniform soil. An interfce existing in the lyered soils, whether fineovercorse or corseoverfine, hs common feture of limiting downwrd wter movement nd of incresing horizontl wter movement. Wter nd nitrte distribution ptterns re lso ffected by the sequence of soil lyers. For the fineovercorse lyered soils of LS nd LSL, wter nd nitrte were uniformly distributed t given depth in the top lyer soil. For corseoverfine lyered soil of SL, however, wter ccumulted in the sublyer soil Q2007, CAAS. All dghts resewed. Published by Usevler Ltd.

10 Wetting Ptterns nd Nitrte Distributions in LyeredTexturl Soils Under Drip Irrigtion 919 A SL soil q = 1.99 L h' Q =.0 L Co = 0 mg L' 2 3 LS soil q= 1.Y0Lh' Q =.1 L Co = 0 mg L ' p I C J! U v LSL 3 LSL soil q = I.Y L h' Q=.0L Co = 0 mg L' ' " E, B Sndy soil q=214lh' Q =.0 L Co = 0 mg L Fig. 9 The distributions of nitrte (NO,N in mg LI) for different lyered soils t n pproximte ppliction rte of 2 L hl nd volume of L pplied. Co represents the input concentrtion of NH,NO,. just below the interfce nd zone of low NO,N concentrtion ws observed. The effect of ppliction rte on wter distribution pttern ws dependent upon soil lyering. A minor influence of ppliction rte on wter distribution ws observed for the fineovercorse lyered soils of LS nd LSL. To obtin greter wetted depth through selecting the emitters hving smller ppliction rte, which is common method in the system design for uniform soil, my not be necessrily pplied for the lyered soils. The effects of soil lyering on wetting pttern nd wter nd nitrte distribution under drip irrigtion should therefore be crefully considered in system design; otherwise it my constrin crop wter nd nutrient uptkes. Mesurements of nitrte distribution showed tht nitrte ccumulted towrd the boundry of the wetted volume for both uniform nd lyered soils. This suggests the importnce of optiml mngement of drip fertigtion becuse nitrte is susceptible to the movement out of the root zone by mismngement of fertigtion, thus leding to nitrte contmintion of surfce nd ground wter sources nd soil. Initil soil wter content is n importnt fctor ffecting wter movement nd nitrte trnsport in the soil. An pproximtely equl initil wter content (round irdried wter content), which is substntilly lower thn the vlue used in drip irrigtion mngement, ws used for ll experiments in the study. A higher initil soil wter content cn ccelerte the movement of wter CAAS.AllrigMsresew6d. PubliibyUsevierLtd.

11 980 LI Jiushen et l. nd nitrte in the soil nd expnd the wetted volume, thus incresing the potentil of wter nd nitrte leching out of the root zone. The quntittive nlysis of the effect of initil wter content tht my be conducted by simultion using dynmic model is deserved. Acknowledgements This work ws finncilly supported by the Ntionl Nturl Science Foundtion of Chin (079077) nd the Key Lbortory of Plnt Nutrition nd Nutrient Cycling, Ministry of Agriculture, Chin. References Autodesk, Inc AUTOCAD User s Guide. Sn Rfel, Cliforni. BrYosef B, Sheikholslmi M R Distribution of wter nd ions in soils irrigted nd fertilized from trickle source. Soil Science Society of Americ Proceedings,,782. Bresler E Anlysis of trickle imgtion with ppliction design problems. Irrigtion Science, 1, 317. Cook F J, Thorburn P J, Fitch P, Bristow K L WetUp: A softwre tool to disply pproximte wetting ptterns from drippers. Irrigtion Science, 22, Cote C M, Bristow K L, Philip B C, Cook F J, Thorburn P J Anlysis of soil wetting nd solute trnsport in subsurfce trickle irrigtion. Irrigtion Science, 22, Fu L, Dong W, Zheng Y Guidelines for Microirrigtion Design. Wter Resources nd Power Press, Beijing. (in Chinese) Grdens A I, Hopmns J W, Hnson B R, Simunek J Twodimensionl modeling of nitrte leching for vrious fertigtion scenrios under microirrigtion. Agriculturl Wter Mngement, 74, Golden Softwre, Inc SURFER Version Reference Mnul. Golden, Colo. Hchum A Y, Alfro J F Rin infiltrtion into lyered soils: Prediction. Journl of Irrigtion nd Dringe Division, ASCE, 6, Hnks R J, Bowers S A Numericl solution of the moisture. flow eqution for infiltrtion into lyered soils. Soil Science Society of Americ Proceedings, 26,34. Hill D E, Prlnge J Y Wetting front instbility in lyered soils. Soil Science Society of Americ Proceedings, 36, Khn A A, Yityew M, Wrrick A W Field evlution of wter nd solute distribution from point source. Journl of Irrigtion nd Dringe Engineering, ASCE, 122, Li J, Zhng J, Ro M Modeling of wter flow nd nitrte trnsport under surfce drip fertigtion. Trnsctions ofthe ASAE, 48, Li J, Zhng J, Ro M Wetting ptterns nd nitrogen distributions s ffected by fertigtion strtegies from surfce point source. Agriculturl Wter Mngement, 67, 894. Li J, Zhng J, Ren L Wter nd nitrogen distribution from point source of mmonium nitrte. Irrigtion Science, 22, 19. Li Y Z, Lu J W, Hung Cly lyer nd soil wterslt trnsport under evportion. h: Shi Y C, Li Y Z, Lu J W, eds, Wter nd Slt Trnsport in Sltffected Soils. Beijing Agriculturl University Press, Beijing. pp (in Chinese) Lu D Experimentl study nd simultion of wter nd slt movement in the soil. MSc disserttion, Xi n University of Science nd Technology, Xi n, Shnxi, Chin. (in Chinese) Mmolw K, Or D Wter nd solute dynmics under dripirrigted crop: Experiments nd nlyticl model. Trnsctions of the ASAE, 43, Philip J R Trvel times from buried nd surfce infiltrtion point sources. Wter Resources Reserch, Revol P, Clothier B E, Mihol J C, Vchud G, Vuclin M Infiltrtion from surfce point source nd drip irrigtion. 2. An pproximte timedependent solution for wetfront position. Wter Resources Reserch, 33, Schp M G, Leij F L, vn Genuchten M T ROSETTA: computer progrm for estimting soil hydrulic prmeters with hierrchicl pedotrnsfer functions. Journl of Hydrology, 21, Schwrtzmn M, Zur B Emitter spcing nd geometry of wetted soil volume. Journl of Irrigtion nd Dringe Engineering, ASCE, 112, Simunek J, Sejn M, vn Genuchten M T HYDRUS2D Simulting wter flow, het, nd solute trnsport in two dimensionl vribly sturted medi. Interntionl Ground Wter Modeling Center, Riverside, Cliforni. Thorburn P J, Cook F J, Bristow K L Soildependent wetting from trickle emitters: Implictions for system design nd mngement. Irrigtion Science, 22, Wng Q, Sho M, Horton R Modified greenmpt models for lyered soil infiltrtion nd muddy wter infiltrtion. Soil Science, 164,4443. (Edited by ZHAO Qi)