Irrigation and Drainage Systems12: 265–288, 1998.© 1998Kluwer Academic Publishers. Printed in the Netherlands.

Lysimeter study on the use of biodrainage to controlwaterlogging and secondary salinization in (canal)irrigated arid/semi-arid environment

R. CHHABRA & N.P. THAKURDivision of Soil and Crop Management, Central Soil Salinity Research Institute,Karnal-132001, Haryana, India

Accepted 21 August 1998

Abstract. The study describes the capacity of trees to control the rise in water table andthus prevent the formation of waterlogged soils and development of secondary salinizationin canal irrigated areas. It was conducted in RCC lysimeters of 1.2 m dia. and 2.5 m depthfilled with sandy loam alluvial soil (Typic Ustochrept), with provisions to maintain watertable depth at 1, 1.5 and 2 m from the surface and groundwater salinity at 0.4, 3, 6, 9 and 12dS m−1. The amount of water biodrained by eucalyptus (Eucalyptus tereticornis) and bamboo(Bambusa arundinacea) at the given water table depths and groundwater salinity levels wasmonitored over four years by daily measuring the water needed for maintaining the watertable. The trees continued to absorb and transpire water throughout the year, the capacitybeing more in summer and rainy than that was in the winter season. The eucalyptus plantcould biodrain 2880, 5499, 5518 and 5148 mm of water in the first, second, third and fourthyear of study period, from non-saline groundwater and a water table depth of 1.5 m. Theamount of water biodrained was more at 1.5 m as compared to 1 and 2 m water table depths.The biodrainage capacity of trees was significantly affected by the salinity of the groundwater.However, even at salinity of 12 dS m−1, the eucalyptus plant biodrained 53% of that undernon-saline conditions. It was calculated that biodrainage could control water table rises upto1.95, 3.48, 3.76 and 3.64 m in first, second, third and fourth year, respectively. The secondarysalinity developed in the root zone, upto 45 cm depth, did not exceed 4 dS m−1 even at watertable depth of 1 m with salinity of 12 dS m−1. The volume of water biodrained by bambooincreased with time and could control water table rises upto 1.09, 1.86, 2.46 and 2.96 m infirst, second, third and fourth year of growth, respectively.

This study indicates that due to high transpiration capacity and an ability to extract waterfrom deeper layers containing saline groundwater, the trees can control the rise in water tablein irrigation command areas and prevent the formation of waterlogged and eventually thesaline wastelands.

Key words: biodrainage, eucalyptus, bamboo, water table depth, groundwater salinity, canalirrigation, waterlogging, secondary salinization

ir475.tex; 13/11/1998; 14:27; p.1DISK/CP/PALM/kb; IRRI475; PIPSNR.: 188316 (irrikap:bio1fam) v.1.1

266

Introduction

Provision of irrigation has long been recognized as one of the key inputs forincreasing and sustaining agricultural production under arid and semi-aridenvironments. To achieve this, large investments are being made in majorand minor irrigation projects to create a substantial irrigation potential bymost of the countries. However, this development has not been without itsmisgivings. Despite best efforts put in, the adverse effects of irrigation havebeen observed in many irrigation command areas. One of the early symptomsis the rise in water table due to seepage caused from the canals and inadequateon-farm water management. All these factors contribute to the groundwaterwhich starts rising after the introduction of canal irrigation. Rises of 0.3 to1.0 m year−1 in water table have been observed in most of the irrigationcommand areas in India. As a consequence, 2.46 million ha of productiveland has become waterlogged in different states of India alone (Anonymous1991).

To prevent the rise of water table above the critical level, attempts areusually made to lower it by installing drainage systems. Such systems areexpensive, cannot be adopted by individual farmers, require energy to operateand pose a disposal problem of salty drainage effluent.

An alternative to this engineering solution can be bio- drainage, which isdefined as the process of removing the excess soil water through transpirationusing bio-energy of the plant. It is an option to prevent the development ofwaterlogged and saline soils especially in land locked areas where there isno possibility of disposing saline drainage effluent. For the past seventeenyears trees have been used to biodrain an excess of urban effluent (sewagewater) and utilize their nutrient and irrigation potential for biomass produc-tion (Chhabra & Baddesha 1985; Chhabra 1987, 1988, 1990 and 1991) at theCentral Soil Salinity Research Institute, Karnal and at many other places inIndia.

The present study was undertaken to determine the biodrainage capacityof eucalyptus and bamboo, two fast growing tree species which also haveconsiderable economic and industrial use, for controlling waterlogging andsalinity in irrigated lands.

Materials and methods

A series of lysimeters made from reinforced cement concrete (RCC) humepipes NP2, approved by the Bureau of Indian Standards, with a dia. of 1.2 mand a depth of 2.5 m were installed in an experimental field at the CentralSoil Salinity Research Institute, Karnal, India. The site has monsoon type of

ir475.tex; 13/11/1998; 14:27; p.2

267

climate with maximum and minimum temperatures of 45 and 0◦C, respec-tively. The potential evaporation (Eo) is highest (12 mm day−1) in summerand lowest in winter (1.1 mm day−1). For four years of the experiment therainfall was 822, 1076, 1075 and 891 mm while the Eo was 1424, 1388, 1461and 1307 mm, respectively.

PVC perforated supply pipes, covered with nylon gauze were inserted inthe lysimeters at a depth of 1.0, 1.5 and 2.0 m, respectively to supply waterof desired salinity from a plastic reservoir. This inlet pipe was also used fordrawing samples of groundwater from the lysimeter to check on its salinitylevel during conduct of the experiment. Using stands, these reservoirs (20liter capacity) were placed at the required heights, to maintain water table inthe lysimeters at the specific depths (Figure 1). After the construction andtesting for water proofing, each lysimeter was filled with sandy loam alluvialsoil (Typic Ustochrept), having pH 8.2 and EC 0.4 dS m−1 (Table 1). The soilwas packed to a bulk density of 1.50 g cm−3. The excavated soil was filledback around the buried lysimeters to minimize temperature fluctuations in theroot zone.

Each lysimeter was planted with a three months old sapling of eucalyp-tus or bamboo. These were raised earlier in 20 cm deep polyethylene bagsand transplanted in the center of the lysimeter in the month of March, 1993following standard silvicultural practices. Except for the initial six months,when irrigation was also applied at the surface to help in establishment of thetrees, all the water was applied in the reservoir and thus entered the lysimetersfrom below.

The water in the reservoir was replenished every day and taken as a mea-sure of the water lost through evapo-transpiration. The lysimeters with treeswere not covered and all the rainfall was allowed to enter and accounted forwhile computing the water balance. In the rainy season there was mostly a gapbetween rainy and non-rainy days. As a result of that rain water which wasallowed to enter the lysimeters though increased the soil moisture content tosaturation and also accumulated in the reservoir yet never came out of it. Thataccumulated leachate in the reservoir again entered the lysimeter during non-rainy days to maintain water table depth. As a result of that less water wasadded from outside to maintain water table depth during that period. Anotherset of lysimeters, with similar combinations of water table and salinity levelsbut without trees were used to monitor the loss of water through evaporation(Es) alone. The amount of water biodrained (Wb) by the tree was calculatedby subtracting the evaporation (Es) from the evapo-transpiration (ET) i.e. ET-Es = Wb. However, due considerations may be given to the fact that Es of thesoil under tree canopy will be less than that from non-vegetated soil becauseof:

ir475.tex; 13/11/1998; 14:27; p.3

268

Figure 1. Design of lysimeters with facility to maintain different water table depths.

− mulching effect of forest litter on the soil,− decrease in temperature,− increase in relative humidity, and− low moisture content of the surface soil (caused by depletion by the tree

roots).

To be on conservative side, the loss of moisture from the lysimeters havingno trees but with similar depth of water table and groundwater salinity wassubtracted from the observed ET to arrive at the net transpiration by the trees

ir475.tex; 13/11/1998; 14:27; p.4

269

Table 1. Physico-chemical characteristics of the soil used in lysimeters.

Characteristics Value

pH (1:2, soil:water suspension) 8.20

E.C., dS m−1 (1:2, soil:water supernatant) 0.40

Organic carbon,% 0.40

CaCO3, % 0.41

Cation exchange capacity, me 100 g−1 10.22

Soluble salts in 1:2, soil:water ratio, me 100 g−1

Cl− 0.15

SO42− 0.32

CO32− absent

HCO3− 0.04

Na+ 0.72

Ca2+ 0.10

Mg2+ 0.30

Exchangeable cations, me 100 g−1

Ca2+ 6.25

Mg2+ 2.32

Na+ 1.50

K+ 0.37

Available nutrients, kg ha−1

N 127.57

P 7.13

K 288.00

Particle size,%

Clay 9.20

Silt 14.30

Sand 76.30

(Wb). Hence the Wb calculated through this method may be relatively under-estimated. Potential evaporation (Eo) was measured every day from the openpan evaporimeter installed at the Institute Meteorology Observatory and com-piled for each month and year.

The moisture content of the soil was monitored in situ through Neutron

ir475.tex; 13/11/1998; 14:27; p.5

270

Probe Gauge using a calibration curve. For that an aluminum access pipe wasinstalled in each lysimeter to a depth of 2.5 m.

Treatments

Treatments imposed are listed below:

a) Tree species : 2; Eucalyptus (Eucalyptus tereticornis),Bamboo (Bambusa arundinacea)

b) Water table depths : 3; 1.0, 1.5 and 2.0 m from the surface ofthe lysimeter

c) Salinity levels of groundwater : 5; 0.4 (control), 3, 6, 9 and 12 dS m−1

d) No. of replications : 2

e) Total nos. of lysimeters

with trees : 60

without trees : 30

The groundwater salinity was maintained by applying saline watercontaining Ca2+: mg2+ and SO2−

4 : Cl− in the ratio of 1:2 and 1:3, respec-tively. It had no residual sodium carbonate (RSC) and sodium adsorptionratio (SAR) was less than 5. This composition was similar to that of thegroundwater found in most of arid and semi-arid areas.

Before start of the experiment, soil upto the imposed water table depthwas brought in equilibrium with the required groundwater salinity by repeat-edly draining and renewing it with fresh saline water and monitoring for thedesired level. After that the depleted water (due to ET) was compensated bynon-saline water. This was done to keep the salinity of the groundwater at theimposed level which otherwise would have risen due to the depletion of waterin a closed lysimeter.

Statistical analysis

Statistical analysis was done using two factor randomized block design inaccordance with the methods outlined by Panse and Sukhatme (1967) usingMSTAT C software package. Least significant difference (LSD) was calcu-lated for comparing the treatments at 5% level of probability.

ir475.tex; 13/11/1998; 14:27; p.6

271

Results and discussion

Effect of water table depth and its salinity on biodrainage capacity ofeucalyptus

Effect of water table depthThe biodrainage capacity of eucalyptus was significantly affected by watertable depth (Table 2). In first year, the maximum volume of biodrained waterwas 2420 mm at 1.5 m followed by 2284 and 1799 mm at 1.0 and 2.0 m depth,respectively. In spite of higher soil moisture content at 1 m, the trees grownat 1.5 m biodrained the most. An improved performance at 1.5 m water tabledepth is conceived to be due to a better root environment. The biodrainagecapacity of eucalyptus decreased significantly as the water table depth be-came deeper (2.0 m) which seems due to the fact that in first year the rootshad not reached to that depth. Greenwood and Beresford (1979) also foundthat transpiration rate of eucalyptus increased significantly when the rootsreached the zone of higher water content. Similarly, Calder (1986) reportedthat eucalyptus species can use very high quantities of water if planted inareas where water table is shallow because there is no stomatal control whenthere is abundant amount of water supply in the root zone. Heinrich and Sands(1990) reported that ET by eucalyptus plant was a function of soil moisturecontent as the leaf water potential controlling ET was low when grown in wetas compared to that in dry soil.

In second year the amount of water biodrained by eucalyptus plant was3572, 3698, 2902 mm at the water table depth of 1.0, 1.5 and 2.0 m, respec-tively. That increased to 3873, 3955 and 3190 mm, respectively in third year.The maximum amount (3698 and 3955 mm) of water biodrained by euca-lyptus was again at 1.5 m water table depth. On comparing the biodrainagecapacity of eucalyptus tree in first year with that in second and third year,it was found that it had increased almost one and half times and seems to bewell correlated with plant growth. But in fourth year, the biodrainage capacityat each depth of water table was slightly lower (3596, 3730 and 2820 mm).The growth (27.8 cm girth at 1.35 m height) of the eucalyptus trees within thelysimeter was less than those trees planted outside the lysimeters in the non-experimental area (55 cm girth at 1.35 m height). In third year the girth was26.7 cm and increased non-significantly to 27.8 cm in fourth year. The heightalso was almost similar in third and fourth years, which appears to be due tothe stagnation of the root growth in relatively limited space in the lysimeter.Sharma (1984) had also described pattern of root distribution as the majorfactor affecting evapo-transpiration of eucalyptus trees.

ir475.tex; 13/11/1998; 14:27; p.7

272

Table 2. Biodrainage capacity (Wb), mm, of eucalyptus for different water table depths andgroundwater salinity.

1st year 2nd year

Groundwater

Salinity Water table depth, m

dS m−1

1.0 1.5 2.0 Mean 1.0 1.5 2.0 Mean

0.4 2449 2880 2133 2487 4342 5499 3466 4435

3.0 2388 2305 1872 2188 3902 3641 3099 3547

6.0 2256 2399 1683 2112 3502 3277 2764 3181

9.0 2097 2334 1652 2028 3124 3114 2638 2958

12.0 2231 2185 1653 2022 2988 2959 2543 2830

Mean 2284 2420 1799 – 3572 3698 2902 –

LSD at P=0.05 for

Water table depth 50 24

Salinity levels 64 35

Interaction 111 53

3rd year 4th year

Groundwater

Salinity Water table depth, m

dS m−1

1.0 1.5 2.0 Mean 1.0 1.5 2.0 Mean

0.4 5098 5518 3746 4787 4958 5148 3787 4631

3.0 4014 3985 3398 3799 3885 4189 3183 3752

6.0 3874 3675 3125 3558 3447 3502 2629 3193

9.0 3319 3369 2908 3199 3078 3139 2357 2858

12.0 3061 3230 2774 3021 2612 2673 2140 2475

Mean 3873 3955 3190 – 3596 3730 2820 –

LSD at P=0.05 for

Water table depth 92 60

Salinity levels 119 78

Interaction 205 135

ir475.tex; 13/11/1998; 14:27; p.8

273

Effect of groundwater salinityThe volume of water biodrained in first year was 2487, 2188, 2112, 2028 and2022 mm at salinity levels of control, 3, 6, 9 and 12 dS m−1, respectively.These results showed that the biodrainage was highest when the groundwatersalinity was lowest. Its magnitude decreased with increase in salinity of thegroundwater. There was no significant difference between the volume of wa-ter biodrained at salinity of 9 and 12 dS m−1.

In second, third and fourth years, these effect of groundwater salinitywere more pronounced at every level irrespective of the depth of water table(Table 2). This was due to an increase in the salinity of the lower soil layers(Figure 4) as a result of extraction of water by the roots from those zones.These observations are in contrast to those reported by Hanada and EL-Enany(1994) who observed a reduction in transpiration rate only for increasingsalinity of the shallow groundwater. Eucalyptus tree biodrained 2022, 2830,3021 and 2475 mm of water in first, second, third and fourth years at ground-water salinity of 12 dS m−1. That was respectively 81, 64, 63 and 53% ofthat observed under non-saline conditions. Tanji and Karajeh (1993) alsoobserved a decrease in the efficiency of eucalyptus to extract soil water whenthe salinity in the soil built up, which in their case was due to the continuoususe of saline drainage effluent as a source of irrigation. These results are inagreement with those of Sumayao et al. (1977), Babla and Soliman (1978)and Roberts (1983) who all reported that evapo-transpiration decreases withan increase in salinity level in the growth medium.

Effect of water table depth and its salinity on biodrainage capacity ofbamboo

Effect of water table depthThe volume of water biodrained by bamboo species increased with time. Infirst year its capacity was 1358, 1327 and 1277 mm at 1.0, 1.5 and 2.0 mdepth of water table, respectively. However, in second, third and fourth yearthe biodrainage capacity of bamboo increased to 2180, 2852 and 3166 mm,respectively at the water table depth of 1.5 m (Table 3). It was a result of anincrease in root mass and in canopy over time.

The biodrainage capacity of bamboo species was less when the water tabledepth was deeper as compared to when it was shallower. In first year, themaximum volume (1358 mm) of water was biodrained under shallow depth(1.0 m) while it was significantly less (1277 mm) under deeper depth (2.0 m).Being shallow rooted and a surface feeder, bamboo plant exhibited a higherbiodrainage capacity when the water table was within the effective root zone.However, in the second, third and fourth years of its growth the maximumamount of water biodrained was at the water table depth of 1.5 m. The amount

ir475.tex; 13/11/1998; 14:27; p.9

274

Table 3. Biodrainage capacity (Wb), mm, of bamboo for different water table depths andgroundwater salinity.

1st year 2nd year

Groundwater

Salinity Water table depth, m

dS m−1

1.0 1.5 2.0 Mean 1.0 1.5 2.0 Mean

0.4 1351 1401 1393 1382 2225 2551 2339 2372

3.0 1335 1343 1229 1303 2169 2369 2133 2224

6.0 1352 1305 1178 1279 2158 2218 1901 2092

9.0 1407 1259 1285 1317 2112 2027 1760 1966

12.0 1347 1328 1298 1324 1929 1736 1637 1767

Mean 1358 1327 1277 – 2118 2180 1954 –

LSD at P=0.05 for

Water table depth 30 29

Salinity levels 37 37

Interaction 66 65

3rd year 4th year

Groundwater

Salinity Water table depth, m

dS m−1

1.0 1.5 2.0 Mean 1.0 1.5 2.0 Mean

0.4 3109 3489 2805 3134 3727 4233 3330 3764

3.0 2687 3157 2565 2803 3397 3854 2981 3411

6.0 2547 2732 2398 2559 2760 3014 2640 2805

9.0 2489 2479 2364 2444 2498 2531 2194 2407

12.0 2408 2401 2228 2346 2190 2196 1831 2072

Mean 2648 2852 2472 – 2914 3166 2595 –

LSD at P=0.05 for

Water table depth 170 130

Salinity levels 241 168

Interaction 99 291

ir475.tex; 13/11/1998; 14:27; p.10

275

of water biodrained in fourth year was 2914, 3166, 2595 mm at 1.0, 1.5 and2.0 m water table depths, respectively which was almost one and half to twotimes more than in first year. This must be due to the increase in the root massand canopy of the plant enhancing its total transpiration capacity.

The biodrainage capacity of eucalyptus was maximum in third year anddecreased slightly in fourth year of its growth. That might be due to the factthat eucalyptus being deep rooted tree might have already covered the limitedspace of the lysimeter within two to three years. In fourth year, there wasno further root proliferation and development resulting in stagnation, causingslight reduction in its biodrainage capacity. In case of bamboo the biodrainagecapacity increased with an increase in the growth period. As mentioned, bam-boo is a surface feeder and being shallow rooted plant the space for its rootproliferation in the lysimeter seems to be enough upto four years of growth.

The data show that eucalyptus tree biodrained almost one and half to twotimes more water than bamboo in the initial two years, and thus was moreeffective for biodrainage of waterlogged soils. This is assumed to be dueto its deeper roots, resulting in more water uptake even from deeper watertable depth and higher transpiration capacity resulting in more loss of water.Eucalyptus plants have an open canopy and the leaves do not overlap eachother. Due to this it provides an ideal condition for transpiration of the ex-tracted water at relatively high rates even from the lower storey leaves. Thiscapacity of eucalyptus plants to extract high amounts of soil water and to actas bio-pumps has previously been highlighted (Chhabra & Baddesha 1985;Rawat et al. 1985 and Calder 1986). Alvares (1982) contended that for thisreason eucalyptus may even cause desertic conditions in areas with low wateravailability.

Effect of groundwater salinityTable 3 shows that groundwater salinity level affected the biodrainage capac-ity of bamboo to a relatively small extent in first year but that in second, thirdand fourth year of growth it was significantly reduced with an increase ingroundwater salinity.The effect of groundwater salinity on the amount of wa-ter biodrained by bamboo was less as compared to that of eucalyptus. Whencompared with the control (non-saline conditions), the biodrainage capacityof bamboo in fourth year decreased to 45% against 47% for eucalyptus atgroundwater salinity of 12 dS m−1, showing that it is slightly more tolerantto groundwater salinity than eucalyptus.

Effect of biodrainage by trees on water table depth

The amount of water lost through evaporation from the non-vegetative soil(Es) was maximum from shallow (1 m) and minimum from deep (2 m) water

ir475.tex; 13/11/1998; 14:27; p.11

276

Table 4. Ratio of Wb/Eo, Wb/Es and Eo/Es as affected by depth of water table and its salinityunder eucalyptus plantation in the fourth year.

Salinity Wb/Eo Wb/Es

levels, Water table depth, m

dS m−1

1.0 1.5 2.0 Mean 1.0 1.5 2.0 Mean

0.4 3.79 3.94 2.90 3.54 13.85 17.75 21.16 17.59

3.0 2.97 3.21 2.44 2.87 10.76 15.99 15.68 14.14

6.0 2.64 2.68 2.01 2.44 9.63 15.70 12.95 12.76

9.0 2.36 2.40 1.80 2.19 9.65 13.13 16.84 13.21

12.0 2.00 2.05 1.64 1.89 7.46 12.43 16.34 12.08

Mean 2.75 2.85 2.16 2.59 10.28 15.01 16.67 13.96

Salinity Eo/Es

levels, Water table depth, m

dS m−1

1.0 1.5 2.0 Mean

0.4 3.65 4.50 7.30 5.15

3.0 3.62 4.98 6.45 5.02

6.0 3.65 5.85 6.45 5.32

9.0 4.10 5.46 9.35 6.30

12.0 3.73 6.09 10.0 6.61

Mean 3.75 5.38 7.91 5.68

table depth. The mean Eo/Es increased from 3.75 to 7.91 with an increasein water table depth from 1 to 2 m (Table 4). Hence, water lost from thebarren soil will be much less and thus the natural drying of the soil will notbe able to control the rise in water table. Further, with increase in groundwatersalinity from 0.4 (Control) to 12 dS m−1, Eo/Es increased from 5.15 to 6.61(Mean of three water table depths). The loss of soil water was minimum fromdeeper water table with highest groundwater salinity level resulting in highestEo/Es of 10.0. These results indicate that for a given depth of water tablean increase in groundwater salinity will further limit the loss of soil waterthrough evaporation.

As a consequence of biodrainage by trees, loss of moisture from the soilwas much higher resulting in the mean Wb/Eo ratio of 2.59 in fourth year.Since the moisture loss in this case was from the groundwater and not from

ir475.tex; 13/11/1998; 14:27; p.12

277

the free water standing on the surface, it was more meaningful to derive theWb/Es which came to mean value of 13.99 (Table 4) showing that under treecanopy the soil lost moisture 14 times more than that when it was left fallow.This was due to the fact that the tree roots had access to soil moisture, insitu, at deeper depths and thus could extract it with ease leading to highertranspiration and did not depend upon the water conductance in the soil.While the loss of water from the soil surface (Es) as such had to meet theinternal resistance of the soil leading to a decrease in evaporation. Further,the results show that Wb/Eo and Wb/Es were significantly affected by thesalinity of the groundwater.

After converting the volume of the water transpired (biodrained) by thetree into depth of water (cm), through dividing it by the surface area of thelysimeter (1.1314 m2), the water table rise controlled in the soil, was cal-culated by dividing it with drainable porosity fraction. For the sandy loamsoil used in the experiment a drainable porosity of 18 per cent was taken asreported by the United States Bureau of Reclamation (1984).

In first year eucalyptus plant biodrained 2487 mm water, mean value ofthree water table depths from the non-saline (control) treatment. That amountsto control of 13.82 m rise of water table in the lysimeter. Scaling up thisvalue to the field situations where the plant to plant and row to row distancewill be 2 m and 4 m respectively, i.e. an effective area of 8 m2 instead of1.1314 m2, eucalyptus plant will be able to control a water table rise of 1.95 m(13.82× 1.1314/8).

Table 5 gives the capacity of the eucalyptus and bamboo plantation tocontrol water table rise in first, second, third and fourth year, respectivelyunder non-saline conditions. Data show that while the maximum biodraingecapacity for eucalyptus trees was attained in third year it continued to in-crease over the time in bamboo plantation. That is, as explained earlier, dueto the difference in the rooting pattern of the two species. That was furtherconfirmed by Wb/Eo which increased with time for bamboo but levelled ofin case of eucalyptus plants (Figure 2). When extrapolated over a large areaof farm land and considering the rise in water table to be controlled upto0.5 m year−1 (which is the common observed rate of rise in most of the canalirrigated areas in India) one will require one ha of plantation for every 7 haof farm land to be kept free from waterlogging.

In areas with saline groundwater, four years old eucalyptus and bambooplant can control the rise in water table upto 1.94 and 1.63 m even at ground-water salinity of 12 dS m−1 (Table 6). This control in rise of water table willprevent the secondary salinization due to groundwater. Similar observationshave been reported by Greenwood et al. (1985) for Australia where by plant-ing eucalyptus, water table is deliberately being lowered to prevent problemof salinity.

ir475.tex; 13/11/1998; 14:27; p.13

278

Table 5. Control of water table rise, m, due to biodrainage by eucalyptus and bamboo undernon-saline groundwater conditions.

Period of growth, year

Species

1st 2nd 3rd 4th

Eucalyptus 1.95 3.48 3.76 3.64

Bamboo 1.09 1.86 2.46 2.96

Figure 2. Ratio of water biodrained (Wb) to pan evaporation (Eo) in different growth periodsof eucalyptus and bamboo

Effect of season on the biodrainage capacity of trees

In all the four years of the experimentation, the amount of water lost throughWb, Eo and Es was affected by the season. In fourth year (Figure 3), theamount of water biodrained was maximum in summer (April to September)and minimum in winter (October to March) indicating that environmental fac-

ir475.tex; 13/11/1998; 14:27; p.14

279

Table 6. Control of water table rise, m for fourth year due to biodrainage by eucalyptus andbamboo as affected by the depth of water table and its salinity.

Eucalyptus Bamboo

Groundwater

Salinity, Water table depth, m

dS m−1

1.0 1.5 2.0 Mean 1.0 1.5 2.0 Mean

0.4 3.90 4.04 2.98 3.64 2.93 3.33 2.62 2.96

3.0 3.05 3.29 3.50 2.95 2.67 3.03 2.34 2.68

6.0 2.71 2.75 2.07 2.51 2.17 2.67 2.07 2.20

9.0 2.42 2.47 1.85 2.25 1.96 1.99 1.72 1.89

12.0 2.05 2.10 1.68 1.94 1.72 1.73 1.44 1.63

Mean 2.82 2.93 2.22 – 2.29 2.49 2.05 –

tors like radiation and temperature are the most important factors controllingthe biodrainage capacity of the plantations. Rawat et al. (1984) also observedthat transpiration by eucalyptus was a function of atmospheric aridity. Thougheucalyptus tree is evergreen plant yet it has maximum leaf shedding in themonth of September causing the lowest Wb as compared to that in the monthof December and January when the temperature was the lowest. Contraryto that, Eo and Es were much affected by climatic factors as compared totranspiration showing there by that simple energy calculations are not ap-plicable to active transpiration process leading to effective control of watertable. Their values were lowest for the months of December and Januaryand corresponded with the lowest temperature of the year. Due to these rea-sons Wb/Eo (Figure 3) was maximum in the winter (October–March) thansummer (April–September). Sharma (1984) also reported a higher ET/Eo foreucalyptus canopies during winter than summer in Western Australia. Botheucalyptus and bamboo, being evergreen trees, transpired throughout the yearat all salinity levels and were thus able to biodrain soil water continuouslyeven during the rainy season. Sharma (1984) argued that high transpirationrate by eucalyptus even in the rainy season may be due to the evaporationof intercepted water being higher than the transpiration from a dry canopy. Incomparison to trees, role of annual crops for biocontrol of water table is ratherlimited. The water uptake by annual crops is more variable and is mostlyextracted from the surface shallow layers. Crops also do not need much water

ir475.tex; 13/11/1998; 14:27; p.15

280

Figure 3. Seasonal variations in Wb, Eo, Es and ratio of Wb/Eo for eucalyptus plantations inthe fourth year

either during early stages of plant growth or at maturity. There is also a clearlean period when no water is absorbed because there are no crops in the field.

Biodrainage in relation to control of soil salinity

Since there was no outlet in the lysimeters, no salt was allowed to go outexcept that absorbed by the growing trees. After an equilibrium had been

ir475.tex; 13/11/1998; 14:27; p.16

281

reached, constant salinity of the groundwater was maintained by replacingthe depleted amount (as a result of biodrainage) by non-saline water.

Figure 4 shows that not only under deep water table depth of 2.0 m butalso under shallow water table depth of 1.0 m and high salinity (12 dS m−1)of the groundwater there was no appreciable increase in salinity in the rootzone under tree canopy. Even at shallow water table depths of 1 and 1.5 m,the ECe remained below 4 dS m−1 in the upper 45 cm depth of the soil whichwas in strong contrast with the pronounced salt accumulation in the surface30 cm in the lysimeter without trees (Figure 5). This difference was due to thefact that salt laden groundwater being drawn to the surface by the capillarypores was not allowed to reach the top layer and was intercepted by the treeroots. Water was absorbed and finally transpired through the leaves leavingthe salts in the lower layers of the soil. This observation was supported by thesoil moisture profile (Figure 6) which showed much lower moisture contentsin the surface 60 cm soil in lysimeters with trees as compared to those withno tree. Biodrainage therefore also controlled the phenomenon of secondarysalinization. The zone of maximum salt accumulation in the lysimeters withtrees was between 45 to 120 cm, 45 to 150 cm and 60 to 210 cm in case of 1,1.5 and 2 m depths of water table, respectively (Figure 4). This was apparentlythe zone of maximum water uptake by the roots leading to increase inconcentration of the salts. In contrast, the zone of maximum salt accumulationin lysimeters without trees, was in the surface 30 cm soil when the watertable depth was at 1 and 1.5 m depth (Figure 5). From the salinity profile(Figure 7), it appeared that bamboo plant was more effective in preventingthe development of secondary salinization in the surface layers as comparedto eucalyptus. This may be due to its finer roots being more effective in inter-cepting the capillary movement of the groundwater as is indicated from thesoil moisture profile (Figure 6).

Even the small amounts of salts reaching the surface got leached downduring the rainy season making the upper soil layer free of salts, ECe< 2dS m−1 (Figure 8). Salinity fluctuations in the root zone were governed bythe upward salt movement from the groundwater by capillary rise, and itssubsequent downward flushing during rainy season. Under field conditionsthe depletion of water from the effective root zone as a result of biodrainageby the trees will result in lowering of water table but increase in the saltconcentration. These salts will however, be washed down by rain water andget equilibrated in the aquifer. The actual control under field conditions andsustainability of the biodrainage will depend upon the climatic conditions(rainfall and Eo), irrigation practices, and the growth rate of trees. Undersituations where there are light textured soils and the salts are transported dueto horizontal movement of the groundwater, trees by reducing the volume of

ir475.tex; 13/11/1998; 14:27; p.17

282

Figure 4. Soil salinity profiles as affected by the depth of water table and its salinity after 4 years of eucalyptus plantation

ir475.tex;13/11/1998;

14:27;p.18

283

Figure 5. Soil salinity profiles as affected by depth of water table and its salinity after 4 years in the non-tree lysimeters

ir475.tex;13/11/1998;

14:27;p.19

284

Figure 6. Soil moisture profiles, before rainy season, of non-tree lysimeters and those with eucalyptus and bamboo plantation in the fourth year underdifferent depths of water table

ir475.tex;13/11/1998;

14:27;p.20

285Figure 7. Soil salinity profiles as affected by the depth of water table and its salinity after 4 years of bamboo plantation

ir475.tex;13/11/1998;

14:27;p.21

286

Figure 8. Soil salinity profiles after rainy season as affected by depth of water table and its salinity under eucalyptus plantation after 4 years

ir475.tex;13/11/1998;

14:27;p.22

287

drainable water will check the movement of the salts from higher to the lowerelevation areas as well as waterlogging in the depressions.

Conclusions

This study, conducted in lysimeters showed that the trees could absorb andtranspire water throughout the year, from water table depth upto 2 m, thecapacity being more in summer and rainy season than in winter. Four year oldeucalyptus and bamboo plants could check a rise of water table of upto 3.64and 2.96 m, respectively. Though the capacity of the trees to lower down thewater table was affected by the level of groundwater salinity yet eucalyptusplant could biodrain effectively even at 12 dS m−1 salinity of groundwater.Development of secondary salinization in the root zone, even under shallowwater table depth of 1 m, was checked by depletion of soil moisture and itsprevention to reach the surface.

Trees only help in removing the drainable surplus water by absorbing itthrough the roots and transpiring from the leaves. By doing so, these highwater transpiring trees help in lowering the water table and counteract theharm done by excessive irrigation or seepage of the water through the canals.These trees do not bioharvest the salts as such and thus do not remove thesalts from the soil. But by controlling the rise in water table and decreasingthe capillary water fringe, help in preventing the accumulation of salts in theroot zone.

Acknowledgement

The authors are thankful to the Department of Wastelands Development, Min-istry of Rural Development, Government of India, New Delhi for the financialgrant to support this study. Constant encouragement from Dr. N.T. Singh,Director, and cooperation of Dr. O.P. Singh, Head Division of Drainage andWater Management and Dr. S.P. Gupta in construction of the lysimeters andthe technical assistance received from Mr. Rati Ram and Mr. Jog Dhiyan isacknowledged.

References

Alvares C. 1982. Social forestry – the likely distortions.Bio. Energy Res. News1(1): 1–6.Anonymous. 1991. Report on problem identification in irrigated areas with suggested remedial

measures. Ministry of Water Resources, Government of India, New Delhi.

ir475.tex; 13/11/1998; 14:27; p.23

288

Babla A.M. & Soliman M.F. 1978. Evaluation of the relative specific effect of cations on plantgrowth and nutrient absorptions.11th Intern. Soil Sci. Congr. Edmonton1: 319–320.

Calder I.R. 1986. Water use of eucalyptus – a review with special reference to South India.Agric. Water Management11: 333–342.

Chhabra R. 1987. Forestry - a cure for sewage pollution.Aquaworld11(6): 185–187.Chhabra R. 1988. Conservation of nutrients and irrigation potential of domestic waste waters

sans pollution.J. Soil Water Conser, India 32: 113–123.Chhabra R. 1990. Preventing sewage pollution of water bodies through afforestation.J. of the

Institute of Public Health Engineers, India 2: 1–14.Chhabra R. 1991. Sewage water utilization through forestry. Brochure No. 15. Central Soil

Salinity Research Institute, Karnal, India.Chhabra R. & Baddesha H.S. 1985. Sewage water for afforestation.Proc. National Seminar

on Man, Forest and Environment, Haryana Forest Department, Karnal, India.Greenwood E.A.N. & Beresford J.D. 1979. Evaporation from vegetation in landscape de-

veloping secondary salinity using the ventilator chamber technique (1) Comparativetranspiration from juvenile eucalyptus above saline ground water seeps.J. Hydrology42:369–382.

Greenwood E.A.N., Klein L., Beresford J.D. & Watson G.D. 1985. Differences in annualevaporation between grazed pasture and eucalyptus species in plantations on a saline farmcatchment.J. Hydrology78: 261–278.

Hanada A.M. & El-Enany A.E. 1994. Effect of NaCl salinity on growth and mineral elementcontents and gas exchange of plants.Biologia Plantarum36(1): 75–81.

Heinrich P.A. & Sands R. 1990. Water use by trees. Woodlots Workshop, Proceeding No. 32,Victoria, Australia. pp 47–52.

Panse V.G. & Sukhatme P.V. 1967.Statistical Methods for Agricultural Workers. ICAR, NewDelhi.

Rawat P.S., Gupta B.S. & Rawat J.S. 1984. Transpiration asaffected by soil moisture ineucalyptus.Indian Forester110(1): 35–39.

Rawat P.S., Negi D.S., Rawat J.S. & Gurumurti K. 1985. Transpiration, stomatal behaviorand growth ofEucalyptus hybridunder different soil moisture levels.Indian Forester111:1097–1111.

Roberts J. 1983. Forest transpiration: A conservative hydrological process.J. Hydrology66:131–141.

Sharma M.L. 1984. Evaporation from a eucalyptus community.Agric. Water Management8:41–56.

Sumayao C.R., Kenemasu G.T. & Hodges T. 1977. Soil moisture effects on transpiration andnet CO2 exchange of sorghum.Agric. Meteorology18: 401–408.

Tanji K.K. & Karajeh F.F. 1993. Saline drain water reuse in agroforestry system.J. Irrigationand Drainage Engineering119(1): 170–180.

U.S. Bureau of Reclamation. 1984.Drainage Manual. U.S. Department of the Interior, Bureauof Reclamation, Denver, Colorado, 2nd edition. pp 286.

ir475.tex; 13/11/1998; 14:27; p.24