Table of Contents
Introduction to Eucalyptus
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 a 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 up to 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 agroforestry programmes during the seventies and early eighties. Raising of Eucalyptus on field boundaries under different patterns of agroforestry 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.
SEE ALSO: Management of Eucalyptus Species
Propaganda About Eucalyptus Water Consumption
Some pseudo-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 having a decisive effect on land use pattern of agroforestry, 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 rumours floated against Eucalyptus plantation that it adversely affects the soil moisture regime.
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.
Study of the Research 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 meters 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 meters above mean sea level). Both the sites have a semi-arid subtropical climate of an extreme type. The minimum and maximum temperatures show wide fluctuations at both the experimental sites. In order to make a comparison, the blank area (control with no plantation) as close to the plantation site as possible was also selected at both the places.
Physico-chemical characteristics of the soil of Study Area
The physico-chemical characteristics of the soil at both the experimental sites, as analysed at Forest Research Institute, Kanpur are presented in Table- 1.
|Sl. No.||Parameters||Soil at Billhaur (Kanpur) site||Soil at Mathura site|
|A. Chemical Characteristics:|
|2||E.C. (1:2.5)||3.00 ds/m||0.204 ds/m|
|B. Physical Characteristics:|
|1||Water holding capacity||52.08%||38.12%|
|6||Soil texture||Clay loam||Sandy loam|
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.
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 D4 , 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).
ALSO READ: Pros and Cons of Eucalyptus Tree Plantation
Result 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. 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 per cent 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 a 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 the water table, several researchers have investigated its root behaviour also in different soil conditions. George (1977) noticed that taproot 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 taproot 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 taproot 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.
The research can be summed up in the following points:
- 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 the 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.
So, what do you think of Water Consumption of Eucalyptus vs. Other Species. Let us know in the comments section below.
By Ram Jee Srivastava, Ashwani Kumar and K. Prasad
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