The biometric data viz., diameter at breast height, tree height and tree volume was evaluated and were correlated with climatic and edaphic factors to assess the influence of edapho climatic factors towards productivity of farm grown teak
Biometric attributes in block plantations of farm grown teak
The different biometric attributes of block plantations observed in four age classes of the three different agroclimatic zones are presented in tables 1, 2, 3 and 4.
The diameter at breast height in block plantations of high rainfall zone in all four age classes considered for study ranged between 0.024 m and 0.314 m, whereas for southern zone the range of values were 0.041 m to 0.264 m. In case of cauvery delta zone the variation in diameter at breast height was between 0.049 m and 0.277 m (Fig.1). These results strongly suggest that with the increase in age the diameter at breast height also increases progressively. This study was in line with (Durai, 2021), whose study proved that the mean diameter at breast height increased linearly with increase in age. Further Shahapurmath et al. (2016) revealed that tree age plays a crucial role in determining the growth of teak trees raised in farmlands. Similarly, the studies of Sabastin et al. (2018) revealed that increase in diameter growth occurs with increase in tree age for teak raised in farmlands.
In terms of tree height, among all four age classes maximum tree height was recorded in the age class 15-20 years, with value of 12.50 m, 11.50 m, 11.50 m for high rainfall zone, southern zone and cauvery delta zone respectively (Fig.2) the increased tree height growth in high rainfall zone is mainly due to the influence of favourable climatic variables and optimum edaphic properties. Similar study carried out by (Arunkumar, 2011) revealed that better growth in terms of tree height was depicted by trees growing in high rainfall areas and deep fertile soils. The results were also in accordance with the findings of Thompson and Nagabhushanam, (1998) that teak height growth was influenced to a certain extent by edaphic factors. Climatic factors had a strong impact on height growth of scots pine in Finland (Jansons et al., 2013).
Tree volume in block plantations of three agroclimatic zones in four age classes shown a range from 0.002 m3 to 0.927 m3 in high rainfall zone, 0.004 m3 to 0.623 m3 in southern zone and 0.005 m3 to 0.693 m3 in cauvery delta zone (Fig.3). The results agree with the findings of (Ravi et al., 2019) in Ailanthus excelsa, that tree volume varied with respect to age classes and growth conditions. Comparably, (Sureshkrishnan et al., 2017) studied and determined the volumes of Tectona grandis, Melia dubia, Gmelina arborea and Ailanthus excelsa in cauvery delta zone of Tamil Nadu for nine age classes in farmlands.
Biometric attributes in boundary plantations of farm grown teak
The different biometric attributes of block plantations observed in four age classes of the three different agroclimatic zones are presented in tables 5, 6, 7 and 8.
The results of the present investigation portrayed that the growth biometry of boundary plantations for the age class of 15-20 years was maximum in all three agroclimatic zones when compared to block plantations. The maximum values recorded in terms of diameter at breast height, tree height and tree volume in boundary plantations of high rainfall zone (0.366 m, 13.00 m and 1.369 m3) where higher when compared to block plantations (0.314 m, 12.50 m and 0.927 m3) of the same age class. Similar trend was observed by Krishnan et al. (2022), in cauvery delta zone of Tamil Nadu, where growth attributes viz., diameter at breast height, tree height and tree volume of boundary plantations in age class of 15-20 years showed better growth performance than block plantations in teak.
The diameter at breast height, with reference to boundary plantations of four different age classes under three agroclimatic zones brought to light that, the maximum of value of diameter at breast height for high rainfall zone, southern zone and cauvery delta zone were 0.366 m, 0.293 m and 0.314 m respectively (Fig.4). The study outcomes expose that diameter at breast height increases with increase in age. The study results are in accordance with the findings of (Vijayabhama et al., 2022) in casuarina plantations of different age classes of cauvery delta zone revealed that diameter at breast height increases with the increase in age of trees.
In terms of tree volume, the mean values of boundary plantations of high rainfall zone (1.369 m3), southern zone (0.838 m3) and cauvery delta zone (1.004 m3) were comparatively higher than that of block plantations (Fig.5), (Fig.6). The increase in tree volume of boundary plantations was mainly due to wider spacing and less competition for light, space, nutrients and other resources used by the individual trees when compared to block plantations. The wider spacing in boundary plantation promotes better increment of tree volume in comparison to closer spacing of block plantation. Supporting the present study Zahabu et al. (2015) inferred wider spacing favoured better growth for teak , that was raised in plantations of Tanzania. The variation in tree volume of three agroclimatic zones was attributed to heterogeneity of climatic variables and edaphic influences in different agroclimatic zones. The results agree with the findings of Reddy et al., (2014) that the assessment of teak tree volume in three different agroclimatic zones of Karnataka, the northern transition zone had an optimum mean annual rainfall of 749 mm and the presence of favourable medium black soil has shown better volume and productivity as compared to other zones taken for productivity studies in Teak.
The overall investigation of biometric attributes of farm grown teak in both block and boundary plantations for four age classes viz., 0-5, 5-10, 10-15 and 15-20 years in three agroclimatic zones of Tamil Nadu brought to light that 15-20 years age class is the most favourable age class for obtaining maximum yield in terms of tree volume. Thus with respect to boundary and block plantations of different agro climatic zones, better growth performance was evident in boundary plantations due to several factors like climatic variables, edaphic influences, lesser competition for resources, wider spacing and better silvicultural and management interventions adopted by the tree growing farmers.Hence it is concluded that irrespective of the agroclimatic zones, the plantations of age class 15-20 years is recommended for commercial exploitation in teak grown in farmlands.
Correlation of climatic and edaphic influence on growth of farm grown teak
Climatic variables in three agro climatic zone of Tamil Nadu
The climatic variables of High Rainfall Zone, Southern Zone and Cauvery Delta Zone were collected for a period of 20 years (2001-2021) and presented in Tables 9 to 11. The mean annual rainfall for 20 years was documented as 1248.83 mm in high rainfall zone, 908.15 mm in southern zone and 803.34 mm in cauvery delta zone. The maximum temperature during this period ranged between 35.900C to 39.750C for high rainfall zone, whereas for southern zone and cauvery delta zone the maximum temperature range was recorded between 38.830C to 43.330C and 40.080C to 43.600C respectively. The minimum range of temperature was observed between 14.640C to 17.290C in high rainfall zone, 13.640C to 16.800C in southern zone and 15.080C 17.050C in cauvery delta zone. The mean relative humidity during this period was registered as 79.65% in high rainfall zone, 69.25% in southern zone and 68.90% in cauvery delta zone.
Correlation Analysis
Karl Pearson’s correlation coefficient was employed to correlate the climatic parameters viz., mean annual rainfall (mm), mean maximum temperature (ºC), mean minimum temperature (ºC) and mean relative humidity (%) with biometric attributes viz., diameter at breast height, tree height and tree volume in both block and boundary plantations of farm grown teak in High Rainfall Zone, Southern Zone and Cauvery Delta Zone of Tamil Nadu (Tables 12 to 17).
Correlation of climatic influence with growth of teak raised in block plantations
The results of correlation studies for tree volume of block plantations in high rainfall zone showed positive correlation with mean annual rainfall (r = 0.279) whereas negative correlation was observed with mean maximum temperature (r = -0.002) and mean minimum temperature (r = -0.316). Since high rainfall zone possess a mean annual rainfall of 1248.83 mm, the result suggests that teak grows well in regions with optimum rainfall. This result was supported by the findings of Seth and Khan, (1958) in which conclusions were drawn that teak exhibit better growth in areas with annual rainfall range of 800-2500 mm in tropics. Further the studies of Yeh and Wensel (2000) expressed that climatic variables in terms of annual precipitation had direct impact in growth of coniferous trees in temperate regions
With reference to block plantations of southern zone and cauvery delta zone, positive correlation was observed between tree volume and mean annual rainfall (r = 0.417) and (r = 0.170), mean maximum temperature (r = 0.118) and (r = 0.107) , mean minimum temperature (r = 0.183) and (r = 0.133), mean relative humidity (r = 0.189) and (r = 0.120). The results are complementary to the research outcomes of Ravi et al. (2019) in Ailanthus excelsa that inferred positive correlation was observed between annual rainfall, temperature and humidity with tree volume in Cauvery delta zone and Western agroclimatic zone of Tamil Nadu.
Correlation of climatic influence with growth of teak raised in boundary plantations
The findings in relation to correlation studies of growth attributes with climatic parameters viz., rainfall, temperature and humidity in boundary plantations of high rainfall zone in four age classes (0-5, 5-10, 10-15 and 15-20 years) detailed that tree volume has shown positive correlation with average annual rainfall (r = 0.388) and relative humidity (r = 0.423) whereas highly significant negative correlation was expressed with minimum mean temperature (r = -0.641**) and negative correlation was noticed with mean maximum temperature (r = -0.241). The results conclude that extreme temperature fluctuations affect the growth of teak raised in farmlands. The findings of Haq et al. (2021) were in accordance with the present study which infers that extremes of temperature had a negative impact on the growth of Dalbergia sisoo. Comparably, the results of Yang et al. (2004) in Pinus radiata p demonstrated the negative correlation between tree volume and maximum temperature. Thus conclusions can be drawn that fluctuations in temperature has significant negative impact on growth of trees. Interestingly, the study of Apurva et al. (2017) on Terminalia arjuna, was incompatible with the present result, suggesting that increase in temperature is directly proportional to the growth attributes at juvenile stage.
Tree volume with respect to boundary plantations of southern zone and cauvery delta zone shown positive correlation with climatic variables viz., mean annual rainfall mean (r = 0.321) and (r = 0.187), mean maximum temperature (r =0.081) and (r = 0.082), mean minimum temperature (r= 0.250) and (r = 0.153), mean relative humidity (r = 0.096) and (r = 0.131). The result was in accordance with the findings of Raviperumal et al. (2018) for Azadirachta indica and Albizia lebbeck plantations in Western agro climatic zone of Tamil Nadu, that positive correlation was observed between growth attributes and climatic variables namely mean annual rainfall, temperature and relative humidity in farmlands.
Edaphic variables in selected agroclimatic zones of Tamil Nadu
The soil physico-chemical properties viz., soil pH and Electrical conductivity (dSm-1) along with, Organic carbon (%), Available nitrogen (kg ha-1), Available phosphorus (kg ha-1) and Available potassium (kg ha-1) were investigated from the soil samples collected from High Rainfall Zone, Southern Zone and Cauvery Delta Zone of Tamil Nadu and the results are presented in table 18.
Soil physico-chemical properties in surface soils of three agroclimatic zones of Tamil Nadu
With reference to surface soils, the pH ranged between 7.2 to 7.74 for high rainfall zone, 7.43 to 8.23 for southern zone and 7.56 to 8.03 for cauvery delta zone. Electrical conductivity varied in the range of 0.12 dS/m to 0.17 dS/m, 0.16 dS/m to 0.23 dS/m and 0.14 dS/m to 0.21 dS/m for high rainfall zone, southern zone and cauvery delta zone respectively. In regard to organic carbon, the maximum and minimum values were recorded as 0.46% and 0.62 % for high rainfall zone, 0.44% and 0.54 % for southern zone and 0.45% to 0.60 % for cauvery delta zone.
The range of values for available nitrogen, available phosphorous and available potassium were recorded as 181 Kg ha-1 to 197 Kg ha-1, 17 Kg ha-1 to 22 Kg ha-1 and 265 Kg ha-1 to 340 Kg ha-1 for high rainfall zone, followed by 171 Kg ha-1 to 192 Kg ha-1, 15.5 Kg ha-1 to 21.5 Kg ha-1 and 255 Kg ha-1 to 295 Kg ha-1 for southern zone. In cauvery delta zone, the values were tabulated between 174 Kg ha-1 to 189 Kg ha-1, 15 Kg ha-1 to 19 Kg ha-1 and 260 Kg ha-1 to 290 Kg ha-1 respectively.
Soil physico-chemical properties in sub surface soils of three agroclimatic zones of Tamil Nadu
For sub surface soils (15-30 cm), the range of pH value was recorded between 7.34 to 7.89 for high rainfall zone, 7.54 to 8.30 for southern zone and 7.67 to 8.19 for cauvery delta zone. The variations in electrical conductivity was noted in the range of 0.13 dS/m and 0.16 dS/m for high rainfall zone, 0.18 dS/m and 0.24 dS/m for southern zone, 0.14 dS/m and 0.19 dS/m for cauvery delta zone. The maximum values of organic carbon for high rainfall zone, southern zone and cauvery delta zone were 0.56%, 0.48% and 0.51% respectively.
The available nitrogen varied between 177 Kg ha-1 to 193 Kg ha-1 in high rainfall zone, 165 Kg ha-1 to 189 Kg ha-1 in southern zone and 172 Kg ha-1 to 185 Kg ha-1 in cauvery delta zone. The values of available phosphorous was recorded between 15 Kg ha-1 to 20.5 Kg ha-1, 15.5 Kg ha-1 to 18.5 Kg ha-1 and 14.5 Kg ha-1 to 17 Kg ha-1 for high rainfall zone, southern zone and cauvery delta zone respectively. With reference to available phosphorous the values documented were between 258 Kg ha-1 to 328 Kg ha-1 for high rainfall zone, 240 Kg ha-1 to 289 Kg ha-1 for southern zone and 245 Kg ha-1 to 281 Kg ha-1 for cauvery delta zone.
Correlation analysis
Karl Pearson’s correlation coefficient was used to determine the relation between growth attributes of farm grown teak and soil parameters viz., pH, Electrical Conductivity (dSm-1), Organic Carbon (%), Available Nitrogen (kg ha-1), Available Phosphorus (kg ha-1) and Available Potassium (kg ha-1) for four different age classes (0-5, 5-10, 10-15 and 15-20 years) in three agroclimatic zones of Tamil Nadu viz., High Rainfall Zone, Southern Zone and Cauvery Delta Zone. The correlation studies with respect to block and boundary plantations have been listed in tables 19 and 20.
Correlation of edaphic influence with growth parameters in block plantations of farm grown teak
The correlation of biometric attributes with soil properties in block plantations brought to light that, tree volume exhibited significant positive correlation with organic carbon (r = 0.446*), The results thus conclude that, soil organic carbon is one among the most important parameter that has greater impact on growth of teak. The results were harmonious with the findings of Watanabe et al. (2010), that soils rich in organic matter with good water holding capacity is amenable for increased growth in teak, making it the most important factor for tree growth. Similarly, Gupta et al. (2009) observed positive correlation between soil organic matter and growth biometry in poplar and inferred that soil organic matter is highly crucial for better growth performance of poplar. Boonkird et al. (1960) also with the opinion of growth attributes of teak was positively correlated and influenced by soil organic carbon.
The tree volume witnessed positive correlation with available nitrogen (r = 0.305), available phosphorous (r = 0.351) and available potassium (r = 0.233). The results were in line with the findings of Boonkird et al. (1960) inferred that available nitrogen had positive correlation with growth of teak. In contrast, Adekunle et al. (2011) revealed that available phosphorous had negative correlation with growth attributes of teak. In addition, the tree volume reflected negative correlation with pH and electrical conductivity in block plantations. Result was in line with the findings of Kumi et al. (2022) a that the soil electrical conductivity had increasingly negative impact on tree volume. Meanwhile the study outcomes of (Ezenwa, 1988) on teak were contradictory to the present investigation that positive correlation was exhibited between the tree volume and soil pH.
Correlation of edaphic influence with growth parameters in boundary plantations of farm grown teak
With reference to boundary plantations, the results highlighted that tree volume was positively correlated with soil organic carbon (r = 0.063), available nitrogen (r = 0.355), available phosphorous (r = 0.320) and available potassium (r = 0.295), while negative correlation was observed with pH (r = -0.084) and electrical conductivity (r = - 0.028). Complementing the present study results, the studies on growth of teak in drought conditions by Santosa et al. (2022) revealed that available phosphorous had a major role in improving the growth attributes of teak in comparison to available nitrogen and available potassium. The results are apparent with the findings of Aparanji, (2000) in teak plantations, where positive correlation was observed between edaphic factors and tree volume. Similar positive correlation with volume and edaphic influences were observed in Ailanthus excelsa plantations (Rajasugunasekar et al., 2014). Further, increase in growth biometry of Eucalyptus grandis plantations was directly proportional to the increase in available nitrogen and available phosphorous (Subrahamanyan, 1998). Paradoxical to the current study, significant negative correlation was observed between available potassium and tree volume of Melia dubia plantations (Nanda et al., 2021).