0500-B2

Studies on Soil Moisture Variations under Eucalyptus Plantation

Ram Jee Srivastava, Ashwani Kumar and K. Prasad ¹

ABSTRACT

Eucalyptus is one of the first forest species largely domesticated throughout the world. Eucalyptus trees were first introduced in India as early as 1790, at Nandi Hills in Karnataka. In India, about 170-species of Eucalyptus have been tried upto 2200 m. altitude with an annual rainfall range of 400- 4000 mm. There are nearly 600 known species of Eucalyptus distributed globally. It was given immense importance in large-scale afforestation especially in social forestry and agro- forestry programmes during seventies and early eighties. 

During early eighties some psuedo-environmentalists started advocating strong propaganda, though not based on scientific research, that Eucalyptus dries out the sub-soil water consequently, lowering the water table. With a view to have decisive effect on land use pattern of agro-forestry, which has suffered a setback, the present investigation was carried out in field plantations of Eucalyptus tereticornis (Eucalyptus hybrid) of various age groups at two different sites (Mathura and Billhaur) during the year 1995-1997.

From the present investigation it was concluded that there was significant variation in soil moisture within the soil depths and also between the months at both the sites. The soil moisture at different depths under Eucalyptus plantation of various age groups was found to be higher at Billhaur site as compared to Mathura in respective soil depths. The similar trend was observed in control of respective sites. The study revealed that it is the edaphic factors especially soil texture including environmental conditions, which play an important role in variation of soil moisture level. Thus, the unscientific myth about Eucalyptus species that it dries up the sub-soil moisture thus lowering the water table proves to be categorically wrong.

INTRODUCTION

Eucalyptus is one of the first forest species largely domesticated throughout the world. No other tree genus except Eucalyptus has ever been so widely propagated throughout the world since it contains remarkably wide range of tree species in regard to adaptation to site, types of management systems and multipurpose uses (Zacharin, 1978). Eucalyptus trees were first introduced in India as early as 1790, at Nandi Hills in Karnataka. In 1843, it was successfully introduced in Nilgiri Hills. In India, about 170 species/ varieties/ provenances of Eucalyptus have been tried upto 2200 m. altitude with an annual rainfall range of 400- 4000 mm. Eucalyptus hybrid is an admixture of mainly Eucalyptus tereticornis and Eucalyptus camaldulensis (Shyam Sunder, 1979).

Eucalyptus can grow in a wide variety of soil conditions but requires deep, fertile, well-drained loamy soil with adequate moisture for best growth. Eucalyptus was given immense importance in large-scale afforestation especially in social forestry and agro- forestry programmes during seventies and early eighties. Raising of Eucalyptus on field boundaries under different patterns of agro- forestry had been a common practice adopted by the farmers. The small farmers along with activist groups all over the country vis-à-vis environmentalists started raising alarm against the expansion of Eucalyptus monoculture in the arid and semi-arid regions. Later on some psuedo-environmentalists started advocating strong propaganda, though not based on scientific research, that Eucalyptus dries out the sub-soil water consequently, lowering the water table. With a view to have decisive effect on land use pattern of agro-forestry, which has suffered a setback, the present investigation was carried out in field plantations of Eucalyptus tereticornis. Thus, the present study will present a scientific basis with respect to the rumors floated against Eucalyptus plantation that it adversely affects the soil moisture regime.

MATERIALS AND METHODS

The present study was undertaken in the field plantation of Eucalyptus tereticornis (Eucalyptus hybrid) of various age groups at two different sites during the year 1995-1997.

Location of the study area

For the study of soil moisture variations at different depths, the areas were selected under Eucalyptus plantations of different age groups along with control (without plantation) at two different soil types in Mathura and Kanpur (Billhaur) districts respectively.

Geographically, Billhaur (Kanpur) is located in between the latitude 25.26⁰ and 26.58⁰ North and longitude 79.31⁰ and 80.34⁰ East (200 meter above mean sea level). Mathura district is located in between the latitude 27.33⁰ and 27.67⁰ North and longitude 77.75⁰ and 78.25⁰ East (180 meter above mean sea level). Both the sites have a semi- arid sub-tropical climate of extreme type. The minimum and maximum temperatures show wide fluctuations at both the experimental sites. In order to make comparison, the blank area (a control with no plantation) as closed to the plantation site as possible was also selected at both the places.

Physico-chemical characteristics of the soil of experimental sites

The physico- chemical characteristics of the soil at both the experimental sites, as analysed at Forest Research Institute, Kanpur are presented in Table- 1.

Table 1 : Chemical characteristics of the soil at Billhaur (Kanpur) and Mathura experimental sites

Soil moisture measurements

The soil moisture regimes at various depths (0-60cm, 61-90cm, 91-120 cm and 121-150 cm.) were directly measured using Electronic Soil Moisture Meter. At each site under investigation, holes of approximately 5.0 cm diameter for above-mentioned depths were dug in the middle of the selected blocks with the help of a manual earth auger. The Moisture Meter directly gave the percentage of moisture in the soil at the specified depth and location. Based on these observations, the variation in the soil moisture regime at various depths and also according to the monthly variation were computed and compared with the control. The observations were recorded every month on a fixed date for a period of two years.

Statistical analysis

The observations on soil moisture levels were statistically analysed. Under the present investigation, the factorial analysis with control was applied (Underwood, 1997). There were four moisture levels at depths D₁ to D_{4 ,} three age groups (5-7 years, 7-9 years and 11-13 years) and two sites. Analysis of variance was calculated according to Snedecor & Cochran (1967).

RESULTS AND DISCUSSION

The mean soil moisture variation (in per cent) at different soil depths under Eucalyptus plantation of three age groups (5-7 years, 7-9 years and 11-13 year) including control at both the sites have been depicted in graphic representations (Fig.1 to 4). It is revealed from the graphs that mean values for soil moisture in per cent at all the four depth were generally higher under Eucalyptus plantation in all the age groups as compared to control at Billhaur as well as Mathura sites. At both the sites, the maximum moisture percent was observed during the rainy months and month wise decreasing trend of soil moisture level at Billhaur and Mathura sites. The low values for soil moisture were observed in the month of April to June at both the sites. It is further revealed that soil moisture per cent was generally low in all the twelve months at Mathura site as compared to Billhaur. It is interesting to note that the moisture level at depths D₃ and D₄ remained higher under Eucalyptus plantation in all the three age groups as compared to their control throughout the year which indicates that the Eucalyptus plantation did not deplete the soil moisture from the sub-soil surface at both the sites.

On making comparison regarding soil moisture variations between Eucalyptus plantation of different age groups with control, it was revealed that the control exhibited the lower values of soil moisture at both the sites. The soil moisture level was found to be maximum at all the depths under Eucalyptus plantation of age group 7-9 years at both the sites. However, the soil moisture per cent at all the four depths under plantation of age group 5-7 years and 11-13 years have almost identical values at Billhaur site whereas it was observed to be more at all the depths under age group 5-7 years than that of age group 11-13 years at Mathura site.

The mean value of soil moisture per cent at all the four depths was generally higher at Billhaur site as compared to that of Mathura. Table-2 represents the analysis of variance (ANOVA) for the months, age groups, soil depths, and their respective interactions.

The above findings are well in consonance with the findings as reported by Kumar et al. (1995) where they studied the soil moisture per cent at various soil depths and age groups of tree species e.g. Eucalyptus tereticornis, Acacia nilotica, Prosopis juliflora, Dalbergia sissoo as well as in open land (Control). In Eucalyptus species, the soil moisture level for the age group 3-5 and 7-9 years has been appreciably higher than the other three species and even in the control.

Poore and Fries (1987) reported that drawing of soil moisture depends on stand density, soil and environmental conditions.

Srivastava (1993) has estimated that the Eucalyptus has high water holding capacity in the soil. There was more soil moisture under Eucalyptus than a nearby open area even after three consecutive drought years. Abbasi and Vinithan (1997) have established that Eucalyptus hybrid plantations do not deplete soil moisture and their performance in their report always compared favourably with plantation of other tree species.

Regarding complaints against Eucalyptus that it draws water from water table, several researchers have investigated its root behaviour also in different soil conditions. George (1977) noticed that tap root of Eucalyptus hybrid had descended to a depth of 3 m and the lateral roots had spread up to 3.5 m. These findings are also supported by Rao (1984) and Davidson (1985) in a study made in 10 year old plantations of Eucalyptus globules and Pinus radiata near Rome reporting that the tap root of the former reached a depth of 4.20 m and of the latter a depth of 2.20 m and the lateral roots a radius of 11 m and 5 m respectively. It has mentioned that in semi-arid tracts, generally the water table is situated rather very deep in ground, probably below 10 to 30 m and it is very clear that tap root of Eucalyptus hybrid goes down to 3 to 4 m. Such being the case, it is hard to believe that it can reach the water table and lower its level.

Foley and Bernard (1984) reported that whether Eucalyptus plantation would affect the water table depends greatly on the hydrological and physical properties of the soil. Dinesh Kumar (1984) has refuted the allegation that Eucalyptus has a high transpiration rate. According to him, Eucalyptus being a xerophyte, has a low transpiration rate and it controls stomatal openings according to water availability without serious reduction in biomass production, similar findings have also been reported by Brown et al., (1976), Ackerson (1980) and Singh et al. (1993).

As far as the comparative water requirement and biomass production of some tropical tree species is concerned, Chaturvedi et al.,(1984 and 1988) reported that out of ten species tested, Eucalyptus tereticornis was found to consume the most water overall and also to be the most efficient in biomass production per litre of water consumed.

Gurumurthi and Rawat (2000) reported that the transpiration in Eucalyptus is dependent on soil moisture availability. Eucalyptus has the inherent capacity for luxury consumption of water when moisture is abundantly available. The high rate of transpiration in Eucalyptus is thus an adaptability mechanism operative under adequate soil moisture only.

CONCLUSION

• From the present investigation it was concluded that the variation in soil moisture within the soil depths and also between the months was found to be significant.
• It was also noticed that in the month of March, April and May, the water table itself goes down and when it gets recharged after the onset of monsoon, the moisture requirement of Eucalyptus for different age groups and sites are very well met. During this period, it was also noticed that Eucalyptus plantation did not affect the moisture content in sub-soil adversely.
• The trend of variation in the soil moisture over the year at Mathura and Billhaur sites remained almost similar.
• The trend of decrease or increase in the soil moisture under plantation as well as in control was similar in respective soil depths.
• The soil moisture at different depths under Eucalyptus plantation of various age groups was found to be higher at Billhaur site as compared to Mathura site in respective soil depths. This indicates that it is the edaphic factor especially soil texture including environmental conditions, which play an important role in variation of soil moisture level.

Thus, the unscientific myth about Eucalyptus species that it dries up the sub-soil moisture rapidly proves to be categorically wrong.

ACKNOWLEDGEMENT

Authors express their grateful thanks to Principal Chief Conservator of Forests, U.P. for the encouragement to carry out the present study. We are highly thankful to Dr. Prabhaker Dubey, Silviculturist, Southern Region, U.P., Kanpur for providing full support and facilities during the studies. We are deeply thankful to Sri Nikhil Shringirishi, Sri Narendra Shukla and Sri Somesh Gupta Research Fellows for their help and cooperation in statistical analysis and manuscript.

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Table-2 Comparison table for Analysis of variance of interactions of soil moisture variation

C1 - Control
C2 - 5-7 years age groups
C3 - 7-9 years age groups
C4 - 11-13 years age groups
D1 - 0-60cm
D2 - 61-90 cm
D3 - 91-120cm
D4 - 121-150cm