Soil Nutritional Status of Tea Plantations In Plains of Sub Himalayan West Bengal, India

Tea is the most consumed beverages after water. In Terai and Dooars region of sub Himalayan West Bengal, India, tea plantations are around 150 years. Exploitation of tea garden soil over centuries has led to decline in soil fertility and crop productivity after all initiatives of external inputs. As nutrients play a crucial role in quality and quantity of manufactured tea,the present initiative has been designed to quantify the soil nutrient status of tea growing Terai and Dooars region. 79.62% (Terai) and 84.72% (Dooars) of the soil samples were found to have normal pH.47.21% (Terai) and 49.3% (Dooars) of soil samples was found to have normal organic carbon. 12.03% and 20.82% of soil from Terai and Dooars showed low total nitrogen. Both the organic carbon and nitrogen in soil are positively correlated.Phosphorus (as P2O5) content of soil is extremely site and depth specific. Almost all samples of the study area showed high potassium (as K2O) content. Monoculture, change in rainfall pattern and inorganic additives have contributed enormous stress to soil but despite of all these odds the overall nutritional richness of these tea growing regions seems to be satisfactory. Current Agriculture Research Journal www.agriculturejournal.org ISSN: 2347-4688, Vol. 8, No.(3) 2020, pg. 239-246 CONTACT Malay Bhattacharya malaytsnbu@gmail.com Molecular Biology and Tissue Culture Laboratory, Department of Tea Science, University of North Bengal, Siliguri, 734013, Darjeeling, India. © 2020 The Author(s). Published by Enviro Research Publishers. This is an Open Access article licensed under a Creative Commons license: Attribution 4.0 International (CC-BY). Doi: http://dx.doi.org/10.12944/CARJ.8.3.10 Article History Received: 14 May 2020 Accepted: 09 December 2020


Introduction
Tea is the most popular beverages and an important plantation crop cultivated in India along with many other areas of the world (Nath). 1 It is not only a much liked beverage of the people in the country but also fetches a good amount of foreign exchange (Karmakar and Banerjee). 2 Tea is produced from the leaves of tea plant scientifically called Camellia sinensis (L.) O. Kuntze. Tea plants are leafy perennial trees planted and pruned to desirable height with an objective of recurring harvest. The quality of tea leaf used for manufacturing is highly influenced by soil nutrients and tea clone. Concentration of nutrients in tea leaf is related with the soil environment (Özyazici et al., 3 ). Mineral contentof harvested tea depend on the soil properties on which it is grown along with itsagronomic practice (Kalita and Mahanta 4 ). So, the contents of nutrient element of tea plant are related with soil environments.
In India, the tea plant was discovered growing wild in upper Assam (India) in 1821 (Roy). 5 In West Bengal, the first tea garden was established in 1857 at Darjeeling, there after tea plantations started extending down to sub Himalayan Terai region from 1862 and Dooars from 1874 (Joseph). 6 So, tea plantations of Terai and Dooars are around 150 years old. Being a plantation crop, the land is utilized for monoculture of tea. More than a century longexploitation of soil under tea cultivation in Terai and Dooars has led to degradation of soil fertility. Maintenance of soil nutritional quality is a massive economic burden to the local tea growers in view of a huge amount of chemical inputs sharing a good proportion of manufacturing cost every recurring year. In addition injudicious application of chemical fertilizers in large quantities without having a fair qualitative knowledge of tea plantation soilresults in destabilization or decline of yields. Adequate soil testing can regulate the quantity of fertilizer loads providing a clear idea of how much exactly chemical inputs are required, and thus can restrict imprudent usage of excess soil nourishment agents.
Soil being one of the most important factors for quality tea produce has not been investigated to a great extent. There are some scattered literature on soil nutrient status of Mengding Mountain, China (Zheng et al., 7 ), Fujian Province, China (Ping), 8 Black sea region, Turkey, 3 Dibrugarh and Sivasagar district of Assam, India. 1 But, soil nutrient status of Terai and Dooars region are extremely lacking. So the present study was conducted to determine the pH, total nitrogen, phosphorus and potassium in tea plantations of Terai and Dooars region of sub Himalayan West Bengal, India.

Materials and Methods Study Area
Terai (plains of Darjeeling district)and Dooars (plains of Jalpaiguri and Alipurduar districts) regions are located inplains of sub Himalayan West Bengal, India. These two regions have cool winter with warm and humid summer. Rainfall is common almost throughout the year with heavy downpours during the rainy season. Six tea plantations of Terai and nine tea plantations of Dooars region were considered for the present study of soil nutritional status.

Soil Sampling
In our study area, a total number of 126 soil samples were collected by means of a screw type auger of which 54 samples were from Terai and 72 samples were from Dooars region. Each sample was gathered by mixing five presamples collected from the corners of an imaginary square of ten metres side and from its diagonal bisector. About five hundred grams of soil samples were brought to laboratory in airtight zipper bags for downstream analysis. Soil samplings were performed early in the morning before application of fertilizers. Topsoil (0-15 cm) and sub soil (15-30 cm) were dug under the canopies of tea bushes.

Preparation of soil Samples for Analysis
The collected soil samples were completely air dried. Debris from the samples like roots, pebbles etc were removed by hand. The clean air dried samples were passed through 2mm sieve and crushed with mortar and pestle. For organic carbon determination, the samples were further passed through final mesh sieve (0.5mm).

Estimation of Soil pH
pH of soil samples were measured on precalibrated pH meter following protocol of Baruah and Barthakur. 9

Determination of Soil Organic Carbon Content
Quantification of soil organic carbon was conducted by Chromic acid method proposed by Walkley and Black. 10

Determination of Total Soil Nitrogen, Available Phosphorus and Potassium
Total soil was determined by Kjeldhal method (Jackson). 11 Estimation of phosphorus as phosphate and potassium as potash requires diacid digestion of soil. One gram sample was subjected to diacid digestion. 9 Available phosphorus in the digested sample solution in form of phosphate was conducted by the protocol developed by Bray and Kurtz. 12 Determination of available potassium form of Poatash was conducted by the protocol developed by Chapman and Pratt. 13

Nutritional Index
Nutritional index for soil organic carbon, total nitrogen, available phosphorus (as P 2 O 5 ) and potassium (as K 2 O) were calculated to determine the soil nutritional status of Terai and Dooars region. Nutritional index was calculated following Sharma, et al., 14

Statistical Analysis
Descriptive statistics in the form of mean, minimum, maximum value and standard deviation (SD) were analysed using SPSS software and MS Excel.

Result and Discussion Soil ph
Soil reaction is measured by pH of a suspension of soil in water. In tea plantations the pH within the range of 4.5-5.5 has been recommended (https:// www.tocklai.org/activities/tea-cultivation/). The pH of the soil samples collected across the study area was variable (table I) The soil pH of Dooars region was found to be more than the Terai region. The influence of dolomite brought down by rivers from neighbouring Bhutan may be the main reason behind such pH. In both Terai and Dooars tea plantations, pH of the subsoil was found to be more than top soil. In top soil of Terai region the pH was lower than the recommended pH but pH of the sub soil was within the range. In the Dooars region the pH of both top and sub soil was within the recommended range.
Percentages of soil samples with low, normal and high pH are depicted in table II. 79% of the collected soil samples from Terai and 84.5% samples from Dooars region were found to have normal pH. Rest samples showed either low or high pH. The sub-Himalayan Terai region comprises of the plains of Darjeeling district. In this region the soils are mostly sandy, highly acidic, heavily leached and poor in plant nutrients (Bhattacharya). 15 In the Dooars region, rivers flowing from neighboring Bhutan carry a large quantity of dolomite dust along with silt that sediment on the soil of tea plantations during floods occurring in the rainy season. So this might be a reason for well maintenance of soil pH of this region by natural means.  17 Miller and Dick 20 : Bergstrom et al., 21 The application of chemical fertilizers to ensure fertility of soil and crop productivity may negatively act on the complex mechanism of biogeochemical cycle (Tilman et al., 22 ; Adesmoyce and Kloepper 23 ). The tea growing areas generally have moderately to highly acidic soil and it is well established that under the acidic or calcareous soil large amount of phosphorus is fixed (Gyaneswar et al., 28 ). The problem of phosphorus deficiency is of particular concern for acid soil like tea garden soil, as tea prefers a low pH (4.5-5.5)

Conclusion
The majestic beauty of sub-Himalayan West Bengal is for its landscape, forests and Tea gardens. The economy of this region is dependent on three T's-Tea, Timber and Tourism. The tea gardens spread over every corner of this region practice monoculture of tea which has partially declined the soil nutritional quality thereby adversely affecting quality of manufactured tea. Moreover change in rainfall pattern and deterioratedwaterholding capacity resulted in loss of soil biota and acidification. All these deteriorative features reduce plant root growth and plant health. The experimental findings too clearly depicts that proper pedological analysis can restrict use of excess chemical inputs and ascertain the soil nutrient level predicting which sort of nourishment elements are actually required for the benefit of the plantation providing a fiscal advantage to the tea growers. Thus, scientific fertility replenishment initiative must be implemented on an emergency basis to save tea plantations and boost the economy of the region.

Acknowledgement
The authors would like to acknowledge the Tea plantations for providing soil samples for analysis.

Funding
The corresponding author would like to acknowledge that the present study was partially supported by research fund (1954/R-2019) received by him.

Conflict Of Interest
There is no conflict of interest