(1) Distribution of Longjing Tea in West Lake
Hangzhou West Lake Longjing Tea is located in the West Lake Scenic Area, where "spring, summer, autumn and winter are beautiful, rain, snow, sunny and cloudy are strange". Traditional producing areas are distributed in hills and low mountains below 500 meters above sea level, which are horseshoe-shaped and surrounded by mountains. According to the Regulation on the Protection of Longjing Tea Base in Hangzhou West Lake, the Longjing tea base and reserve base in Hangzhou West Lake include West Lake Scenic Area and West Lake District, starting from Hupao and Maojiabu in the east, reaching Yangfu Temple, Longmenkan and hejia village in the west, Shejing and Fushan in the south and Laodongyue and Jinyujing Tea Farm in the north. Among them, the first-class protection area of West Lake Longjing Tea Base covers Nanshan Village in the east, Lingyin and meijiawu in the west, Fancun in the south and Xinyuquan in the north. There are 459.2hm2 of tea fields in this area, which are included in the protection base area of 328.6hm2, and the protection rate is 7 1.6%, which is included in the protection base area of 41.7hm2. The second-class protection area of West Lake Longjing Tea Base is outside the first-class protection area of West Lake Longjing Tea Base. The existing tea area is 932.5hm2, which is included in the protection base area of 583.3hm2, and the protection rate is 62.6%, which is included in the protection base162.4hm2..
Hangzhou West Lake Longjing tea production area is adjacent to West Lake in the east and Qiantang River in the south. Affected by "one lake, one river" water and air regulation and southeast monsoon, the climate is warm, with an annual average of 16. 1℃, ≥ 10℃ active accumulated temperature of about 5 100℃, frost-free period of 250d and precipitation of 65438.
Due to the difference of weathering and erosion resistance of sandstone, limestone and shale, and the influence of geological structure, Tianzhu Mountain (4 13m), Beifeng (3 14m), Ren Mei Peak (355m) and tianmashan (275m) were formed around Hangzhou West Lake. Nanfeng (257m), Fenghuang Mountain (157m), Baoyun Mountain (10/8m), Geling (125m), Baoshishan (7m), Dingjiashan (49m) and Wu Shan (63m).
The soil in tea-producing areas is mainly yellow red soil and its varieties, mainly yellow sandy soil, and the soil pH value is 4.5 ~ 6.0. Evergreen deciduous broad-leaved mixed forests with evergreen broad-leaved trees or deciduous broad-leaved trees as surrounding vegetation, and artificially cultivated Pinus massoniana and Phyllostachys pubescens forests. Hupao Creek, Jiuxi Creek, Meiwu Creek and Bailongtan Creek originate from the mountains of the West Lake, flow through the tea area and enter the Qiantang River. Groundwater resources are abundant and often appear as springs. Well-known are Tiger Running Spring (a fissure spring), Longjing Spring (a karst spring) and Yuquan Spring (a pore spring). The unique ecological environment provides good natural conditions for high-quality tea.
(2) Geological background of Longjing tea producing area in West Lake.
Hangzhou area belongs to the Yangtze River-Qiantang River quasi-fold belt and the early Paleozoic quasi-geosyncline area. On the secondary unit, Hangzhou happens to be at the junction of Qiantang quasi-geosyncline anticline and Taihu-Wusong inland fault depression, which has the characteristics of structural fluctuation from southeast to northwest. The geological structure in the western mountainous area of Hangzhou is dominated by NE-SW folds, which is called "West Lake Syncline". The fold axis strikes northeast and tends to northeast. Syncline is composed of 1 1 single fold, which constitutes the topographic characteristics of hills and mountains. Monomer folds are short-axis asymmetric declination folds, synclines are generally complete, and anticlines are often broken. The northeast end of the West Lake syncline is covered by Quaternary. Secondly, a series of NE-trending and NW-trending fault structures have developed in this area. Controlled by the West Lake syncline, the terrain of Hangzhou gradually decreases from southwest to northeast, and the east is connected with Hangjiahu Plain.
Hangzhou area belongs to the stratum area in the northwest of Zhejiang Province, and strata are exposed from Proterozoic to Quaternary. The distribution of strata in the Longjing tea producing area of West Lake and its vicinity is mainly controlled by the West Lake syncline. The two wings of syncline are mainly sedimentary clastic rocks such as Silurian and Devonian sandstone, fine sandstone, mudstone and glutenite, and the core is Carboniferous-Permian limestone.
(3) Geochemical characteristics of Longjing tea producing area in West Lake.
In order to know the geochemical characteristics of Longjing tea producing areas in West Lake in detail, based on the systematic collection of basic geological and soil data and the distribution of main Longjing tea producing areas in West Lake, four main Longjing tea producing areas of Jiulisong, Laodongyue, Shifeng and meijiawu were selected for comparative study (Figure 3-5).
Figure 3-5 Schematic Diagram of Geological Background of West Lake Longjing Tea Producing Area
Q4- four yuan; JBOY3-Upper Jurassic intermediate-acid pyroclastic rocks; C-P- Carboniferous-Permian carbonate rocks; D3- Upper Devonian sandstone; S3- Upper Silurian purplish red fine sandstone; S2— Middle Silurian argillaceous sandstone
1. Soil and tea sampling
In the early spring tea-picking season, three samples of young leaves and three samples of corresponding mature leaves were collected from each tea garden, and soil samples were collected by layers (10 ~ 20 cm, 60 ~ 80 cm) (Shifeng only collected one layer of 10 ~ 30 cm).
Tea samples were collected, dried and crushed to 80 meshes, and more than 20 elements were determined by X-ray fluorescence, atomic fluorescence and atomic absorption spectrometry.
After the soil sample is collected, it is sieved by 20 meshes and ground to 80 meshes, and the total amount and effective amount of elements are analyzed. The total amount of elements is determined by conventional geochemical analysis methods and quality requirements, and the extraction and determination of effective amount refer to the methods commonly used in agricultural departments.
2. Element geochemical characteristics of parent rocks
The soil-forming parent material in Longjing tea producing area of West Lake is mainly distributed in Paleozoic-Mesozoic sedimentary strata except that it is partially covered by Quaternary system. The main lithology of Silurian is argillaceous sandstone (S2) and purplish red fine sandstone (S3), Devonian is timely sandstone (D3), Carboniferous-Permian is carbonate rock (C-P), and local Jurassic is intermediate-acid pyroclastic rock (JBOY3).
Table 3- 1 1 lists the average element contents of several main soil-forming parent materials in Longjing tea area of West Lake. As can be seen from the table, the contents of trace elements in different kinds of rocks vary greatly. Compared with different soil-forming materials, except limestone, other soil-forming materials have the characteristics of high silicon, low potassium and low calcium. Limestone is characterized by low silicon and high calcium. The element content characteristics of soil-forming parent materials provide a basis for the migration and enrichment of elements in soil.
Table 3- 1 1 Contents of Main Elements in Soil-forming Parent Rock in Longjing Tea Area of West Lake
Note: The content unit of oxide is%, and the rest is mg/kg.
3. Geochemical characteristics of soil elements
The soil in Longjing tea producing area of West Lake mainly includes yellow sandy soil, yellow sandy soil and stony sandy soil. Yellow-red soil subtype, with some blue soil in some areas. Laodongyue and Jiulisong mainly develop yellow soil, while Lionbees and meijiawu mainly develop yellow sand. Yellow soil has heavy adhesiveness and poor air permeability, which is not conducive to the transformation and migration of nutrients, the development of plant roots and the effective utilization of nutrients. Yellow sandy soil has good air permeability and water holding capacity, which is beneficial to the absorption and utilization of nutrients by plant root development.
Table 3- 12 gives the average content of soil trace elements in Longjing tea area of West Lake. Compared with Table 3- 1 1, the content of soil elements largely inherits the characteristics of parent rocks in subtropical humid climate. In the weathering process of parent rock, elements with strong supergene activity such as K, Na, Ca and Mg are relatively leached, while Fe and Al are relatively enriched.
Table 3- 12 Contents of Soil Macroelements in Longjing Tea Producing Area of West Lake
Note: The content of oxide and OM is%, and the rest is mg/kg; The number of samples is 3.
Soil properties also have a certain influence on the depletion or enrichment of geochemical elements. The yellow sand soil has better air permeability and water permeability, stronger leaching effect and greater element leaching loss than the yellow sand soil. The weathering of rocks makes the element distribution tend to be uniform. The properties of soil also show the influence on the element-enriched layer. Most elements in light soil (yellow sandy soil) are deeply enriched due to strong leaching, while clay soil (yellow sandy soil) is weakly enriched due to leaching. Except for iron, sulfur, lead and mercury, boron, molybdenum, cobalt and phosphorus are shallowly enriched, and the enrichment horizons of most elements vary.
4. Geochemical environment and tea quality
Previous studies have shown that the soil-forming parent rock is high in silicon, phosphorus and potassium, and low in calcium, manganese and magnesium, which is beneficial to the growth of tea trees and is a high-quality factor. Tea tree is a "calcium-loving crop". More than 10× 10-3 of Ca in soil is harmful to tea tree, and more than 80× 10-3 of available Mn will cause Mn poisoning.
As we all know, the quality of young leaf tea is better than that of adult leaf tea. Table 3- 13 shows that young leaves are rich in beneficial elements such as K, Zn, P, Se, Ni and Co, while the contents of al, Hg, Cd, As and Sb are much lower than those of adult leaves. This shows that different qualities of tea not only have their own characteristics in appearance characteristics (shape, taste, fragrance and color), but also have their own characteristics in element content.
Table 3- 13 Comparison of Element Contents between Young Leaves and Adult Leaves of West Lake Longjing Tea
Note: the contents of cadmium, mercury, antimony and selenium are ng/g, and the rest are mg/kg; The number of samples is 12.
The difference of parent rock type and soil physical and chemical properties is an important factor that determines that Shifeng and meijiawu tea are superior to Laodongyue and Jiulisong. In terms of the total content and effective amount of soil elements, the contents of iron, zinc and molybdenum in Shifeng and meijiawu tea gardens are moderate, while the contents of mercury, aluminum and lead are low, while the effective amount of phosphorus and potassium is high, while the contents of calcium, horse, magnesium and copper are moderate or low, and the nutritional elements are basically balanced, which is beneficial to the growth and quality of tea trees. As can be seen from Table 3- 14, Shifeng and meijiawu teas are rich in phosphorus, potassium, zinc, chlorine and selenium, with moderate contents of calcium, manganese and magnesium and low contents of aluminum and arsenic. In contrast, the contents and available amounts of Ca and Mn in Laodongyue and Jiuli pine are too high, while the available amounts of P and K in Laodongyue tea garden are too low, and the contents of Hg and Pb in Jiuli pine are too low.
The above results show that the growth and quality of Longjing tea are closely related to soil-forming parent rock, soil properties and element geochemical characteristics, and suitable parent rock types, soil properties and element content are the basic natural conditions for high-quality tea. For Longjing tea in Hangzhou, the medium yellow sand soil developed on Devonian quartzite is a suitable soil type for developing high-quality tea.
Table 3- 14 Comparison Table of Element Contents in Young Leaves of West Lake Longjing Tea Producing Area
Note: the contents of cadmium, mercury, antimony and selenium are ng/g, and the rest are mg/kg; The number of samples is 12.