Effect of Irrigation Systems on the Water Requirements of Sweet Corn1-2

C. W. WENDT, A. B. ONKEN, O. C. WILKE, R. HARGROVE, W. BAUSCH, AND L. BARNES3

ABSTRACT bage (Brassica oleracea) may be reduced with trickle irriga-. . . . . . _, j _, . ,_ . „ . ,, tion and modified furrow irrigation compared to conven-A field study was conducted to determine the influence o f sprinkler , „ . . . . . . . , - ,

irrigation (Sp), furrow irrigation (F), subirrigation (Su), and an- tlonal furrOW ""gation, but that the consumptive use of thetomated subirrigation (ASu) on the water requirements of sweet corn cr°Ps would not be reduced under normal field conditions.(Zea mays L.). Irrigation water was applied to the SP, F, and Su plots Thus, the studies reported to date indicate that the major dif-when the soil water potential at the 30-cm depth in the row reached ferences in irrigation water requirements of different sys--40 cbars potential. The time and amount of water applied was based terns are due to the capability of the systems to deliver irri-on a combination of leaf area index (LAI) and potential evapotranspi- gation water efficiently and maintain salt in the root zones atration (ET,}. Water application to the ASu plots was controlled by a desirable levels rather than changing the consumptive use ofswitching tensiometer 30 cm deep set at -40 cbars potential. Soil me cropwater content changes were determined by gravimetrically sampling Another area of research that has received some emphasisthe surface 15 cm and obtaining neutron probe measurements of water js automated irrigation in which soil and plant sensors ori n t h e deeper depths. . , , . . . . 1 1 -c- -c . J-M •. j • .u • • .• . • * t time clocks activate irrigation systems to deliver water.Significant differences existed i n t h e irrigation water requirement o f , , , , , , , • fthe sweet corn irrigated by the different systems (F = 351 mm, SP = Such systems can be developed when adequate supplies of248 mm, Su = 248 mm, ASu = 142 mm). However, little difference in irrigation are always available. Fischback and Wittmus (5)consumptive use occurred between systems (F = 361 mm, Sp = 346 have developed automated surface irrigation systems usingmm, Su = 346 mm, ASu = 310 mm) due to differences in soil water valves developed by Haise and Paine (8). Davis (3) hasutilization. Automation of irrigation systems offers the possibility of described a system for automated subsurface irrigation.significantly enhancing irrigation water use efficiency in supplemen- Gustafson (7) reported that avocados watered with an au-tally irrigated areas. tomated drip irrigation system required only one-third to

one-half the irrigation water to make equal growth of avoca-Additional Index Words: consumptive use, furrow irrigation, df)S ̂ ^ americana} watered with a sprinkler system.

sprinkler irrigation, subimgation, automated subimgation, evapo- Most studies mvolv; automated systems aretranspiration, leaf area index, irrigation efficiency. _. . . , . . . ,from fully irrigated areas. Automated irrigation should otter

————————————————— a better opportunity to increase the efficiency or irrigation

GOLDBERG AND SHMUELi (6) reported that yields of vege- water application in supplementally irrigated areas becausetables grown on a saline, loamy sand soil with saline rainfa11 could be more efficiently utilized. The purpose of

water applied by drip irrigation were more than twice those tms study was to compare the water requirements of sweetfrom furrow and sprinkler irrigation. Davis and Pugh (4), corn m a supplemental irrigated area of Texas when the cornhowever, found little difference in vegetable yields in Cali- was watered with sprinkler irrigation, furrow irrigation,fornia between drip and furrow irrigation systems and also subirrigation, and automated subimgation systems.little difference in irrigation water requirement when therunoff from the furrow irrigation system was considered. MATERIALS AND METHODSBucks et al. (1,2) have reported that irrigation water The study was conducted on a Miles loamy fine sand (Udicrequirements of cotton (Gossypium hirsutum L.) and cab- Paleustalfs) located in Knox County, Texas. A description of the

irrigation systems used in the study is as follows.—————— /) Sprinkler Irrigation System (Sp)—The sprinkler irrigation

'Technical Contribution no. 13080, Texas Agnc. E x p S t n Texas t ljd ( ; triangular pattern with sprinklers locatedA&M Univ. Agnc. Res. and Extn. Center, Route 3, Lubbock, TX 79401. ,% ., , , . , °._, , , c, ,. ,Supported in part by EPA Grant no. 802806. 12-2 m aP.art alon§ the laterals. The laterals were 51-mm-diam alu-

2Mention of a proprietary product in this paper is used solely to provide minum with 19-mm-diam galvanized steel risers 1.83-in tall. Thespecific information and does not constitute an endorsement of this product sprinklers had 4.4-mm-diam brass nozzles. The flow was limitedby the Texas Agric. Exp.Stn. , Texas A&M Univ . , over other products not to each lateral by a 113-li ter/min flow control valve (accuracymentioned. ±5%). With this flow, each sprinkler discharged 18.9 liters/min at•JProressor, Associate Professor, Associate Protessor, Texas Agnc. Exp. , „ . , iStn., Texas A&M Univ. Agric. Res. and Ext. Center, Lubbock, TX, and Z'8 Bar lateral pressure-former research associates, Texas A&M Univ. Vegetable Res. Stn., Box 2) Furrow Irrigation System (F)—The turrow plots were lev-179, Munday, TX 76371. eled for even distribution of water through 152-mm-diam gated

786 SOIL SCI. SOC. AM. J . , VOL. 41, 1977

slip-joint Al irrigation pipe. Gates were 51-mm-diam butterflyvalves spaced 102-cm apart. The amount of water delivered toeach plot was metered through a 152-mm magnetic-drive flowmeter (accuracy ±3%).

3) Manual Subirrigation System (Su)—The subirrigation lateralswere installed with a modified chisel at an approximate depth of 30cm below the soil surface. There was a lateral under each row(rows on 102-cm centers). These laterals were made of 13-mm-diam polyethyene pipe with 0.6-mm-diam Whitney-type subirriga-tion orifices spaced 91-cm apart. The laterals were connected to51-mm PVC header lines on each end of the plot which were alsobeneath the soil surface.

Following filtering, the water entered headers on each end of theplot. The flow to each header line was controlled by a 56.7-li-ter/min flow control valve (accuracy ±5%). Thus, the total flow toeach plot was limited to 113 liters/min. Filter cartiridges (350 ^im)were used in the filtering system.

4) Automated Subirrigation System (ASu)—A 51-mm PVCmainline was installed from the pressure tank at the east well tofurnish water for these plots. The pressure switch on the tank wasset at a 2.8 to 4.1 bar pressure range. A 113-liter/min filter was in-stalled in the mainline to filter the water. Filter cartridges (100fj.m) were used in the filtering system. Materials, placement, andinstallation of the headers and laterals for the automated subirriga-tion system were the same as for the manual subirrigation systemdescribed above. The control valves for each plot consisted of a120 VAC normally closed solenoid valve, a 37.8-liter/min flowcontrol valve for each header pipe, and necessary gate valves forflushing. Controls for the plots are described in a publication byWendtet al. (14).

The meteorological equipment necessary to estimate ETV (po-tential evapotranspiration) according to the method of Jensen et al.(11) was located at the site. A Class A evaporation pan was alsolocated at the site near one of the irrigation wells. The fetch east ofthe pan was the corn in the irrigation study and the fetch west ofthe pan was an irrigated grain sorghum crop.

To determine leaf area index (LAI) on the plots, a relationshipbetween leaf area and stem diameter of the corn was developed, sothat leaf area measurements of a large number of plants could bemade. The equation developed was:

Log Y= -1.169 + 2.389 Log X r = 0.984where Y = leaf area and X = stem diameer 2.54 cm above theground.

The generalized water budget model used to compare the irriga-tion systems was:

hW = M + Ir-N-F- (E+T). {Hillel (9)}

Table 1—Water applied and yield of sweet corn irrigated by variousirrigation systems comparing the water efficiency of irrigation

systems in Knox County, Texas, 1973.

Parameter Method of measurementAW = Change in water content

M = PrecipitationIr = Irrigation water

N = Runoff

Gravimetric samples ofsurface 15 cm; calibratedneutron probe for deeperdepths. (Weekly neutronprobe measurementswere made in all plots attwo locations in eachplot. Each gravimetricsample consisted of 3-6cores near each neutronprobe access hole. If theSp, F, and Su plots wereirrigated, measurementswere made the day beforeand the day after the irri-gation.Rain gaugeTime and flow meter(Accuracy ±3%) or flowcontrol valves (Accuracy±5%)None during the growing

Irrigationsystemf

FSpSuASu

Irrigationwater

applied

mm351 a248 b248 b142 c

Number ofirrigations

553

25

Soil watercontent change

during thegrowing season

mm-10 a-98 b-98 b

-168 c

Total waterconsumptive

use ofthe crop

mm361 a346 a346 a310 a

Yield Jears/ha

38,918 a40,154 a43,242 a39,536 a

* Numbers not followed by the same letter are significantly different at the 5%level of probability.

t F - Furrow, Sp - Sprinkler, Su - Subirrigation, ASu - Automated Subirrigation.j A total of 83 mm of rainfall was received on 13 days during the growing season.

F = Deep percolationE+T = Evaporation -I- Transpirationor Evapotranspiration (ET)

of the crop

During the growing season, there was no runoff from the plots.Also, the location of peak concentrations of a bromide tracer (12)in the root zone remained nearly constant during the growingseason. This fact indicated that there was negligible deep percola-tion during this period. Since there was no runoff or deep percola-tion from the plots, the above equation become the following:

ET = M + Ir - AW.Tensiometers were used as the criteria for applying water

through the various irrigation systems. Water was applied whenthe potential at 30 cm decreased to -40 cbars to the Sp, F, and Suplots. Due to the porosity of the loamy fine sand soils, it was notpossible to apply < 76 mm of irrigation water per application withthe F system. In the Sp and Su plots, it was possible to apply a per-centage of £TP at each application varying according to the LAI—evapotranspiration relationship presented by Ritchie and Burnett(13). Water was applied as needed to the ASu plots when the po-tential at 30 cm decreased to -40 cbars until the potential in-creased above —40 cbars. Two replications of each system wereused for the study.

The plots were planted to sweet corn (Zea mays L.) var. Bo-nanza 2-4 May at the rate of 16.8-kg seed/ha. Each plot was 16-102-cm rows wide and 60,8-m long. There was a buffer zone of7-102-cm rows on each side of the rows from which data were ob-tained. Manufacturers recommended rates of Diazinon AG500 andDylox were applied as needed to control insects during the grow-ing season. Atrazine was also applied as recommended to controlweeds. All plots were fertilized with 22.4-kg N/ha at planting andtwo sidedress applications of 44.8-kg N/ha applied through the ir-rigation water during the growing season for a total of 112-kgN/ha. Eight replications of yield data were obtained from each irri-gation system on 16-18 July.

RESULTS AND DISCUSSION

The water use and the yield of the sweet corn in the studyare shown in Table 1. If only the irrigation water data areconsidered, it would appear tha a breakthrough in theamount of water required by sweet corn occurred. Essen-tially, the same yield of sweet corn was obtained when 142-mm irrigation water were applied with ASu, 248 mm withSu and Sp, and 351 mm with F. However, when the signifi-cant differences in change in soil water content in the soilprofile are considered there was no significant difference inthe consumptive use (CU) of the crop (F = 361 mm, Sp =346 mm, Su = 346 mm, ASu = 310 mm). These data thussupport the fact that irrigation systems do not change greatlythe CU of crop, previously pointed out by Bucks et al (1,2)and Hoare et al. (10).

WENDT ET AL.: IRRIGATION SYSTEMS & THE WATER REQUIREMENTS OF SWEET CORN 787

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fc . SPRINKLERV. IRRIGATION• 9'.» o FURROW

1 — " IRRIGATION

5 DAY POTENTIALEVAPOTRANSPIRATION

. 5 DAY PANEVAPORATION

Fig. 1—Potential evapotranspiration rates and pan evaporation com-pared to the measured consumptive use of corn irrigated by dif-ferent irrigation systems in 1973.

Also included in the table are the number of irrigationsapplied with each system. Only 3 irrigations were appliedwith Su system; 5 irrigations were applied with F and Spsystems. In the plots with ASu, 25 applications were ap-plied. In general, the amounts applied with ASu systemwere in the range of the amounts received in showers fromrainfall.

Figure 1 shows the PE (pan evaporation), ETV, and CU ofcorn from the different irrigation systems. The CU curve ofcorn of the automated subirrigation system followed the £TPcurve closer than the curves of the other systems from mid-June until the end of the study in July. This can be seen inmore detail from the crop coefficients (Table 2). Crop coef-ficients KET (observed evapotranspiration/potential evapo-transpiration) and Kp (observed evapotranspiration/panevaporation) were calculated. Mean values for KET for the19 June to 13 July period for the F, Sp, Su, and ASu were1.21, 1.18, 1.15 and 1.04. The mean ATET for ASu was thelowest (1.04) indicating that CU was closer to the £TP thanthe other three systems. It is possible that the values of KETmay be high due to low values of ETP. The wind run wasmeasured at a height of 2 m at a site near the corn crop.Some of the surrounding sweet corn approached a height of2 m late in the season which may have decreased the windrun values resulting in lower values for £Tp. Since the KET

Table 2—Ratios of measured consumptive use of different irrigationsystems in relation to potential evapotranspiration

(ATET) and pan evaporation (KD).

Furrowirrigation

Period

10-14 May15-19 May20-24 May25-29 May30 May-3 June4-8 June9-13 June14-18 June19-23 June24-28 June29 June-3 July4-8 July9-13 July

Average9 June-13 July

KET0.020.040.130.160.640.831.501.051.221.331.191.011.19

1.21

Kp

0.010.020.080.130.410.640.910.810.790.960.780.590.96

0.83

Sprinklerirrigation

KET0.020.040.130.160.640.831.401.071.161.261.131.041.18

1.18

Kp

0.010.020.080.130.410.620.840.780.960.910.740.570.94

0.82

Subirrigation

KET0.020.040.130.160.640.831.400.981.101.201.101.011.29

1.15

Kp

0.010.020.080.130.410.620.840.760.720.870.720.551.03

0.78

Automatedsubirrigation

KET

0.010.020.060.100.450.721.300.921.021.081.000.891.07

1.04

Kp

0.0050.010.040.070.300.550.800.710.660.780.660.490.88

0.71

— 2

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IRRIGATION SYSTEMS« FURROW" SPRINKLER.MANUAL

SUBIRRIGATION. AUTOMATED

SUBIRRIGATION

,-85.

IRRIGATION AMOUNTPOTENTIAL ET90,95 , 100

X100

10 20MAY

30 19 29 9 19JUNE JULY

Fig. 2—Leaf area index of corn irrigated by different irrigation sys-tems in 1973.

values for ASu were close to 1.0, major errors in estimating£TP probably did not occur. However, the importance ofstandardizing the environment around the evaporation panor the equipment used to estmate ETV cannot be overempha-sized. Errors in water content and irrigation measurement orundetected deep percolation losses may have caused higherKET values for the F, Sp, and Su systems.

Crop coefficients in relation to pan evaporation (Kp)followed a similar pattern in that ASu system was the lowest(0.71) followed by Su (0.78), Sp (0.82), and F (0.83) sys-tems. The value of 0.71 obtained for ASu was similar tothat obtained by Bucks et al. (2) for cabbage.

Values of LAI of the corn grown on the different systemsare shown in Fig. 2. The LAI values of corn from F andASu plots were slightly, but not significantly, lower thanLAI values of corn from Sp and Su plots from mid-Juneuntil early July. The systems thus had no significant influ-ence on leaf area development and amount.

The percentage of £TP used as a basis for applying irriga-tion water to corn grown on the F, Sp, and Su systems isshown on the same figure. Because the leaf area developedso fast it was difficult to use a percentage of ETp based onleaf area as a scheduling technique. Such an approach mayoffer more possibilities with a longer season crop in whichthe leaf area develops slower. In this study, the K^ ex-ceeded 1 during the 5-day period of 9-13 June (Table 2) dur-ing which the LAI varied from 2.23 - 2.8 (Fig. 2).

As previously indicated, gravimetric determinations weremade weekly and/or the day before and after irrigations andthe day after rainfall in the corn crop. The percent moistureof the surface 2.5 cm ranged from 2.0 - 2.5% prior to irriga-tion or rainfall. Pressure plate data showed that the potentialat this moisture percentage was < — 15 bars. It was thereforeconcluded that the corn roots were not active in the surface2.5 cm when water was applied. Moisture samples taken theday after irrigation or rainfall following drainage rangedfrom 8-9%. The decrease in percentage of moisture of sam-ples following drainage and of samples at which the mois-ture content stabilized after 3-4 days was attributed to soilrather than plant evaporation. The amounts attributed to soilevaporation in the various systems were subtracted from theconsumptive use for the various systems to obtain estimates

788 SOIL sci. soc. AM. J., VOL. 41, 1977•

•• more desirable than those which require LAI measure-ments.

__".- Corn irrigated by manually-operated irrigation systems10. !^*«""" had a higher CU than corn irrigated by the ASu system. One

^^"^« , reason for this difference could be errors in measurement..8 •?< ____RITCHIE AND Another possibility is more efficient use of water by the

s' " B U R N E T T 0 3 ) plants grown over the auomated system. The 30-45-cm&' /^ zone of this system was kept at rather constant potential4 /. IRR«FURROW SYSTEM through frequent additions of small amounts of water.

/ -SPRINKLER Under these conditions, it may have been possible for the/ 'SUBIRRIGATION t • ..,. .. • • ,, j .. ...2- / -AUTOMATED roots in this zone to remain more viable and active than in

"X SUBIRRIGATION tne omer systems where larger amounts of water were added° .4 .8 12 1.6 20 2.4 2B 3.2 35 less frequently.

LEAF AREA INDEX Another concept that needs further evaluation for supple-Fig. 3-Plant evaporation (Ep) of SWeet corn produced with different mental irrigated areas is that °f irrigating only a portion of

irrigation systems in relation to potential evaporation (Eo) as influ- the root zone SO as to leave a portion for storage of rainfallenced fcy LAI. to obtain more efficient utilization of irrigation water. Some

of plant evaporation. These data are compared to the rela- approaches to this would be to irrigate every other furrowtionship between the ratio of plant evaporation to potential WIth furrow irrigation systems and apply smaller amountsevaporation and LAI derived by Ritchie and Burnett (13) in more frequently with sprinkler irrigation systems. Produc-Fig. 3. Because the change between an LAI of 0.4 and 2.4 ers are using these practices to a certain extent, but theyoccurred so fast, few data points are available for this range could be further refined to increase irrigation water ef-of leaf area indices. For LAK0.4, all of the data points ficiency.were above the Ritchie and Burnett relationship. ForLAI>0.4, most of the data points from the ASu systemwere below the line while data points from other systemswere above the line, especially for leaf area indices > 2.6.The data also lend emphasis to previous statements that irri-gation systems do not change CU requirements of crops, butthey may change irrigation water requirement by deliveringthe water more efficiently.

In summary, although significantly different amounts ofwater were applied to corn irrigated with different irrigationsystems, the differences in total water requirement wereminor due to the differences in change in soil water contentbetween irrigation systems. However, automation of irriga-tion systems does afford the possibility of making more ef-ficient use of water stored in soil profiles. This factor shouldnot be discounted in those areas where supplemental irriga-tion rather than full irrigation is used. A zone of lower mois-ture content can be developed to store rainfall, yet the cropcan obtain adequate moisture and not become stressed. Au-tomation of furrow and sprinkler systems deserves furtherinvestigation as a means of increasing application ef-ficiency.

Irrigation return flow can be reduced in those areas that donot require a leaching requirement either by automating sys-tems or by using a measure of £Tp as a basis of irrigation.However, in most irrigated areas, leaching requirementscould be provided by automated systems or included withthe £TP. The sweet corn grew so fast in the study that it wasnot possible to fully evaluate the feasibility of using LAI inconjunction with £TP to schedule irrigations. Schedulingprocedures that use ETV estimates which project LAI are