EFFECTS OF SUBSURFACE DRAINAGE AND SUBIRRIGATION ON THE

YIELDS OF FOUR CROPS

Sie-Tan Chieng1, J. Keng2, and M. G. Driehuyzen3

JBio-Resource Engineering Department, University of British Columbia, Vancouver, B.C. V6T1W5;2Agassiz Station, Agriculture Canada, Agassiz, B.C. VOM1A0; and3Soil Branch, B.C. Ministry ofAgriculture and Food, Surrey, B.C.

Received 2 June 1986, accepted 16 September 1986

Chieng, S.-T., J. Keng, and M. G. Driehuyzen.of four crops. Can. Agric. Eng. 29: 21-26.

1987. Effects of subsurface drainage and subirrigation on the yields

Field experiments demonstrated that subsurface drainage increased crop yield on low, flat alluvial soil in the LowerFraser Valley. Subsurface drainage not only increased crop yield; it also advanced soil trafficability and workability.Successful subirrigation can be practiced through a subsurface drainage system but no significant increase in yield wasobserved in 1983, 1984 and 1985 field trials.

INTRODUCTION

The climate and topography in low, flatalluvial areas such as the Lower Fraser

Valley, Pemberton Valley and the meadows of the Cariboo area in British Colum

bia are such that drainage has traditionallyformed the main element of water management of agricultural land, particularly inthe winter months when total precipitationexceeds evapotranspiration. During the

growing period, drainage is required onlyfor abnormally wet periods because evapotranspiration exceeds rainfall and noexcess water is generated.

Figure 1 compares the monthly precipitation of 1983,1984 and 1985 to that ofthe 30-yr average monthly precipitationand potential evapotranspiration of an arealocated in the western end of the Lower

Fraser Valley (Chilton 1981; Environment

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Canada 1982). It clearly indicates a needfor drainage from September to April and awater deficit from May to August. Becausewater stored in the soil profile is availableto crops at the commencement of the growing season, not all the fields in these areasneed irrigation. Generally, only soil with alow water-holding capacity needs supplemental irrigation. Features of these areasthat indicate that subsurface drainage and/

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JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC

MONTHS

Figure 1. Comparison of total monthly precipitation of 1983, 1984 and 1985 to the 30-yr meanmonthly precipitation and evapotranspiration for Delta Ladner South Weather Station.

CANADIAN AGRICULTURAL ENGINEERING, VOL. 29, NO. 1, WINTER, 1987

SECTION A - A

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or subirrigation may be beneficial and feasible are:

(1) The uneven distribution of precipitation during the year, which causesexcess water in the field during fall, winterand early spring, and deficit conditionsduring the summer;

(2) Ground water tables which are generally high in the cool seasons;

(3) Land which is relatively flat;(4) A large supply of low cost and high

quality water available for subirrigation.Subirrigation has been practiced for

many years on some sandy soils in theFraser Valley by controlling the water levels in the open ditches. Currently, sub-irrigation, by using the existing subsurfacedrainage system, is receiving increasingattention because of the followingadvantages:

(1) Labor and maintenance costs areminimal for a well-designed subsurfacedrainage system performing the dual functions of drainage and subirrigation.

22

Figure 2. Experimental field layout.

(2) When an existing subsurface drainage system is used for subirrigation noadditional irrigation system is required.

(3) Evaporative loss of water from thesoil surface is minimal. This is one of the

great attractions for areas where evaporation is high.

(4) Soil compaction and leaching ofnutrients from the upper root zone can bereduced.

In order to demonstratethe benefits that"can be gained from subsurface drainage,and to show that subirrigation can indeedbe carried out through an existing subsurface drainage system, a full scale fieldexperiment was conducted.

EXPERIMENTAL LAYOUT

The experimental site was located atBoundary Bay, Delta, British Columbia.The soil was classified as Ladner series; ahumic luvic gleysol at an average elevationof approximately 1.2 m above mean sealevel. The soil was mostly silty clay loam

(NOT TO SCALE)

REGIME D

and was moderately poor to poorlydrained.

Polyethylene 100-mm-diameter drainswere installed at an average depth of 1.1m,a spacing of 14 m, a length of 100 m; thedrains were backfilled with refuse and

wood chips. Drains discharged into anopen ditch which had been constructed inthree segments. The three ditch segmentsare interconnected and could be controlledseparately with overflow standpipes forsubirrigation (see Fig. 2(a)).

The experiment consists of four watermanagement regimes as shown in Fig. 2(b).Water was removed from regimes A, B andC during periods of high precipitation andlow evapotranspiration by means of drainsand the use of a pump.

During the summer, water was introduced into the soil in regimes B and C bymeans of subdrains during periods whenirrigation was needed. Water levels in theditch were controlled with overflow stand-

pipes which were set at an appropriate

CANADIAN AGRICULTURAL ENGINEERING, VOL. 29, NO. 1, WINTER, 1987

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Figure 3. Watertable height versus time for Regimes A, B, C and D, 1 Jan. to 30 Apr. 1984.

level for each regime. Regime D was acontrol-plot with neither drainage nor sub-irrigation at any time. The four water management regimes may be summarized asfollows:

Regime A — drainage at all times;water table is controlled at or below sub-

drains.

Regime B — drainage during high precipitation periods and subirrigation to alevel of 60 cm below ground surface during periods of water deficit.

Regime C — drainage during high precipitation periods and subirrigation to alevel of 30 cm below ground surface during periods of water deficit.

Regime D — no drainage and no sub-irrigation at any time.

Four crops (corn, potatoes, grass andstrawberries) were planted across the fourwater regimes (see Fig. 2) to determinetheir responses to each regime.

RESULTS AND DISCUSSION

Groundwater Table Fluctuation

Continuous water table positions midway between two drain lines for each

regime have been recorded by means ofwater table recorders. Since the largeamount of figures cannot be given completely in this paper, 1984 has beenselected for illustration. Conclusions are

based on findings from 1983, 1984 and1985. Figures 3, 4 and 5 provide a comparison between four water regimes for1984. The water table in the undrained

regime (D) remained at or close to theground surface from late fall to earlyspring. The area was often flooded duringthe winter months.

In the drained regimes (A, B and C),sharp "rises" (peaks) in the water table areevident. These peaks correspond to heavyrainfall events. However, the excess rainwater was rapidly drained and the watertable "drops" in a very short time. Theaverage water table depth in these regimeswas generally below the 50 cm level.

Removal of excess water is most critical

during spring. To produce top yields it isimportant to be able to work the soil earlyand prepare a good seedbed without excesssoil compaction and degradation of soilstructure (Bertrand et al. 1984). Excesswater prevents field access, and, therefore,

CANADIAN AGRICULTURAL ENGINEERING, VOL. 29, NO. 1, WINTER, 1987

TABLE I. OPPORTUNITY DAYS

(1 March to 31 May)

Years

Regime 1983 1984 1985

A

B

C

D

Opportunity daysgained (i.e., A-D)

83

75

80

19

64

90

59

54

4

86

89

80

74

29

60

reduces the number of opportunity days towork the land. An opportunity day in thisstudy is defined as a day when the groundwater table is 50 cm or more below the soil

surface and the field is workable. Table 1

indicates the opportunity days for theperiod between 1 March and 31 May in1983, 1984 and 1985. In 1983, 1984 and1985 there were 64, 86 and 60 more opportunity days, respectively, on the drainedarea as compared to the undrained area.

Effect of Drainage on Crop YieldsAlthough all four crops (corn, potatoes,

forage grass and strawberries) wereplanted in 1983, 1984 and 1985, no yield

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TABLE II. CROP YIELDS

(tonnes per hectare)

Regime

Crop A B C D

(1) (2)t (3) (4) (5)

Potatoes 37.1 38.3 40.1 41.1

Cornt 16.3 18.7 17.8 10.1

Forage grasst 12.1 12.5 12.1 8.8

Strawberries 6.6 6.0 4.5 0.8

tDry matter yields.%Numbers in parentheses are column numbers.

data for grass and strawberries were collected in 1983. The average potato andcorn yields for 1983, 1984 and 1985, andthe average grass and strawberry yields for1984 and 1985 are presented in Table II.

Table II clearly shows the benefits ofdrainage for corn, grass and strawberrycrops. Crop yields from regimes withdrainage (A, B and C) are consistentlyhigher than those from regime D withoutdrainage improvement. In the case ofpotatoes, a slight decline in yield wasrecorded. More field trials are needed tosubstantiate this finding.

Columns 2 and 5 in Table II compare theyields from regime A with those fromregime D (i.e., drained versus undrained;both with no subirrigation). The results

i r r 1 1 f r 1 1 r

90 120 150 180 210 240 270 300 330 360 390

TIME, days of year

Water table in Regime A (drainage and no subirrigation), Regime B (drainage andsubirrigation to a level of 60 cm below soil surface) and Regime C (drainage andsubirrigation to a level of 30 cm below soil surface) in 1984.

suggest, in the absence of any irrigationoperation, that subsurface drainageincreased corn, forage grass and strawberry yields by 61, 38 and 725%, respectively. However, it decreased potato yieldby 10%.

Effect of Subirrigation on Crop YieldsIn this study, the responses of the water

table in subirrigated regimes (B and C)were measured at mid-spacing betweendrain lines. Figures 3, 4 and 5 show thewater table response to subirrigationduring the 1983, 1984 and 1985 summerperiods. The rapid response of the watertable suggests that successful subirrigationcan be carried out by using the existingsubsurface drainage system. This findingindicates the potential feasibility of usingexisting subsurface drainage systems forsubirrigation of agricultural fields in theLower Fraser Valley.

Columns 2, 3 and 4 in Table II comparecrop yields from regime A (drainage, nosubirrigation) to those from regimes B andC (drainage, subirrigation). The resultsshow that subirrigation had little effect oncrop yield. In the case of potato, corn andforage grass, a slight increase in yield dueto subirrigation was found.

It should be noted that subirrigation had

no effect on strawberry yield becauseberries were harvested before subirrigationwas started. However, more field trials areneeded to see whether the subirrigationduring the previous growing season hasany effect on crop yield in the followingyear.

CONCLUSIONS

A full-scale field experiment to demonstrate the benefits that can be gained fromsubsurface drainage for the Lower FraserValley condition was carried out. Subirrigation was conducted by using the existingsubsurface drainage system. The resultsshow that drainage is a good investmentfor crop production. Subsurface drainagenot only increased crop yield but, additionally, it advanced soil trafficability andworkability by more than 60 days for theLower Fraser Valley climatic region. Successful subirrigation can be practicedthrough a subsurface drainage system;however, no significant increase in yieldwas observed from this experiment. Morefield trials are needed to confirm this

observation.

ACKNOWLEDGMENTSWe gratefully acknowledge the financial

support provided by the ARDSA program, aswell as technical assistance provided by

CANADIAN AGRICULTURAL ENGINEERING, VOL. 29, NO. 1, WINTER, 1987 25

D. Pedersen, Soil Branch, B.C. Ministry of cultural land drainage on soil characteristics of Environment of British Columbia, Van-Agriculture and Food. and crop growth. Third Annual Western couver, B.C.

„ Provincial Conference, 20-22 Nov. 1984, ENVIRONMENT CANADA. 1982. Cana-Kfc*fcKfcJNCk& Winnipeg, Man. dian climatic normals. Vol. 3, Precipitation

BERTRAND, R. A., M. G. DRIEHUYZEN, CHILTON, R. H. 1981. A summary of cli- 1951-1980. Environment Canada, Ottawa,and D. PEDERSON. 1984. Effect of agri- matic regimes of British Columbia. Ministry Ont.

26 CANADIAN AGRICULTURAL ENGINEERING, VOL. 29, NO. 1, WINTER, 1987