SEASONAL CHANGES OF MACRO- AND MICROELEMENTS CONTENT IN SOILS OF GREEN TEA FARMING FROM RIZE (TURKEY)

Abstract. During 2014 year, 60 soil samples at the point of 30 soil samples in the spring and 30 soil samples in autumn were taken from the localities of Fındıklı (41°16’14.40”N 41°08’24.13”E), Pazar (41°10’50.06”N 40°53’11.35”E) and Sabuncular (41°04’20.79”N 40°43’13.51”E) from Rize (Turkey), where green tea has been cultivated. The value of pH, content of the organic matter, and amount of macroand microelements amount were determined in sampled soils and the seasonal changes were investigated. According to the obtained results, it was established that, in general, the values of pH, as well as the content of macroand microelements in spring were higher than those recorded in autumn.


Preparation of soil samples
Four basic stages, which help to determine the representativeness and reliability of approach, were defi ned as follows: Stage 1 -pre-sampling assessment and plan; Stage 2 -soil sampling; Stage 3 -soil pre-analysis treatment (which includes soil preparation and storage); and Stage 4 -soil analysis [1]. The samples were collected from the three different sampling points (Sabuncular, Pazar and Fındıklı in Rize (Turkey)) during two different seasons (April (I) and November (II)). The most soil samples are collected using a specifi c corer or auger. These primary samples are subsequently either combined (composite/aggregated) or kept and analysed separately ( Figure 2).
The logistics, costs, obtained information and interpretation that is likely to be gained from both of these two approaches is very different [1]. The number and relative position of the sampling points depend on the scope of sampling and, thus, on the particular sampling strategy chosen, which can be selected on a statistical basis [1]. When these primary samples are mixed together, a composite/aggregate sample is obtained. A sample ready for the laboratory can be obtained either directly from the primary sample or from the composite sample [1]. [5].

Methods
All chemicals used in this study were purchased from Merck and were of analytical grade. The value of pH, organic matter content, amount of the macro-and microelements were determined in all soil samples. Each determination was repeated 3 times. pH value The pH measurement was carried out after pH meter electrodes were plunged in the suspension of soil, according to the recommendations presented in [6][7].

Organic matter content
Organic matter in soil sample was digested by oxidation with acid-dichromate solution. The excess of dichromate was titrated with KMnO 4 solution, using ferrous(II) sulphate solution as indicator [8].

Nitrogen content
The soil sample was subjected to digestion with concentrated H 2 SO 4 and solubilisation mixture (Na 2 SO 4 or K 2 SO 4 + CuSO 4 •5H 2 O + FeSO 4 •7H 2 O). The soil extract was titrated with boric acid in micro-Kjeldahl apparatus and the nitrogen content was calculated by the corresponding formula [8].

Phosphorus content
Phosphorus content in soil samples was determined after digestion by extraction solution (NH 4 F + 0.5N HCl). Phosphorus content was determined in fi ltrate solution after adding ammonium molybdate in the presence of aqueous tin(II) chloride, at 660 nm wave length [8].

Potassium content
Potassium content was determined, after digestion of soil sample by ammonium acetate, in fl ame photometer device [8].

Calcium content
Solution after digestion by ammonium acetate was titrated with 0.01N EDTA in the presence of ammonium purpurate in alkaline medium. The calcium content was calculated by the corresponding formula [8].

Calcium + magnesium content
Solution after digestion by ammonium acetate was titrated with 0.01N EDTA in the presence of eriochrom black -T indicator. The magnesium content was calculated by the corresponding formula [8].

Iron, manganese, zinc and copper content
The soil sample was subjected to digestion with DTPA solution (diethylene triaminepentaacetic acid + CaCl 2 + triethanolamine). The content of iron, manganese, zinc and copper was determined in soil extracts by using atomic absorption spectrometry (AAS) at 248.3 nm, 279.5 nm, 213.9 nm and 324.7 nm respectively.

Replaceable aluminium
Aluminium was determined by atomic absorption spectrometry (AAS) at 309.3 nm wavelength, after soil treatment with a solution of potassium chloride.

Results and discussion
In this study, soil samples were taken from the region of Sabuncular, Pazar and Fındıklı in Rize (Turkey) during April and November, 2014. A total of 30 soil samples was obtained from 10 different manufacturers in each region. Twelve separate analyses of each of these soil samples were performed (a total of 360).

pH value
The pH value of the tea agricultural land in Rize ranged from mild to exceptionally acidic. The pH value ranged from 3.42 to 6.12. It was determined that the pH value in the most cases was below of 4.50. In 86.6% of the soil samples the value of pH was recorded between 4.50 and 6.00, which is considered ideal for tea growing. In 76.6% of samples the exceptionally acidic pH value was registered, while 23.4% of samples had the ideal value of pH. The results for each zone and season are given in the Tables 1-3.
According to the results presented in Tables 1-3, the higher values of pH were observed in soil sampled during April. Organic fertilizers used in spring are considered as one of the reasons. It has led to the rise of pH due to the properly processing of the soil containing the applied organic fertilizer, by rainfall. In the autumn, the effect of organic fertilizer is reduced. Secondly, the drop in the pH value during November is caused by pollution through rainwater contaminated with organic fertilizer. It has led to the emergence of a signifi cant negative effect that can be considered in the literature of the uncontrolled use of agricultural chemicals in our country and uncontrolled of manufacturers in this topic. Our tea producers have applied ammonium sulphate ((NH 4 ) 2 SO 4 ) fertilizer in excessive quantity and onesidedly despite all warnings. Consequently, more than 95% of our tea soils in 30 years have gained an excessive level of acidity and the pH of soil has dropped below the lower limit of pH (4.5). As a result, it appears to be compatible with the average values of pH obtained in April for tea cultivation, considering pH value of 4.5 -6.0. The pH variation in soils of Sabuncular region is presented in Figure 3.  Table 1 Results of soil samples analyses, taken from the green tea farming in the region of Sabuncular during April (I) and November (II).

Organic matter content
In 13.3% of soil sampled during April the organic matter content was at high level, while in 86.7% of samples was at very high level. During November there were registered the following results: in 16.7% of samples the organic matter content was at medium level, in 73.3% -at high level and in 10.0% -at very high level. Similar results were identifi ed in another study in Rize [9]. The values of organic matter content vary widely in soil of tea garden during April and November. This is explained by the fact that each month is characterized by abundant rainfall and low temperatures. Dynamics of organic matter content registered in Sabuncular region is shown in Figure 4.

Nitrogen content
The nitrogen content in soil samples ranged from 1.1 g/kg to 8.6 g/kg. In 10% of soil sampled during April the nitrogen content was at high level, while in 90% of samples was at very high level. During November there were registered the following results: in 16.7% of samples the nitrogen content was at medium level, in 56.7% -at high level and in 10.0% -at very high level. The nitrogen ratio was similar to organic matter content. Thus, we can conclude that nitrogen is originated from organic matter in the soil.
A dynamics of nitrogen content in a study conducted between 1978 -1982 years for 1667 soil samples at same region was reported [10]. Also, Müftüoğlu et al. determined the nitrogen content of the tea garden soils, classifying them as group of low, medium, high and very high [11]. There were identifi ed the following groups: 3.78% low, 16.09% medium, 40.59% high and 39.53% very high in a study of soil samples [12]. It appears that these values are compatible with our results. The variation of nitrogen content recorded in Sabuncular region is presented in Figure 5.

Phosphorus content
The phosphorus content in soil sampled in April and November ranged from 0.0030 g/kg to 0.1286 g/kg. Comparing the obtained results with results performed in another study in the same region, which include research of 1815 soil samples [10], the increasing of phosphorus content in the soil was observed.
The phosphorus amount in samples taken in November was lower than the phosphorus content in samples collected in April. The reason is a reduction of pH value in soils. In soil phosphorus reacts with Al, Fe, Mn and insoluble hydrated oxides of these elements under acidic conditions, with Ca and Mg -in alkaline conditions. Phosphorus is a nutrient, being the most affected by the soil reaction.

Potassium content
In soil sampled during April in 46.7% of samples the potassium content was at low level, while in 26.7% of samples was at suffi cient level, and in 26.6% -at high level. During November there were registered the following results: in 16.7% of samples the potassium amount was at very low level, in 46.7% -at low level, in 26.6% -at suffi cient level and in 10.0% -at very high level. By comparing our results with the results of another study in the same region, which include research of 1678 soil samples [13], it is observed an increasing the potassium amount in the soil.
Potassium content in the samples taken in November was lower than the potassium levels in April. It can be stated that decreasing the pH value, increasing the precipitation quantity and freeze-thaw phenomena in the soil are the reasons for this fact. It is not exactly determined that increasing the potassium level in the soil depends on the pH value. It is accepted as a general rule that the potassium level increases in the conditions of high pH [14]. Potassium amount dynamics in soils sampled from Pazar region is presented in Figure 7.

Calcium content
The calcium content in soil sampled in April and November ranged from 0.424 g/kg to 47.304 g/kg. Calcium content values in soil samples were higher than the normal values during both seasons. In 36.7% of the samples taken in the spring and in 40.0% of the samples taken in the autumn the calcium content had the desirable values. The dynamics of calcium content in soils sampled in Pazar region is shown in Figure 8.

Magnesium content
In soil sampled during April in 3.3% of samples the magnesium content was at suffi cient level, while in 33.4% of samples was at high level, in 60.0% -at very high level. During November there were registered the following results: in 10.0% of samples the magnesium amount was at suffi cient level, in 50.0% -at high level, in 33.3% -at very high level. The values of magnesium content in the soil samples were higher than the normal values during both seasons. In 3.3% of the samples taken in the spring and in 10.0% of the samples taken in the autumn the magnesium content had the desirable values. A dynamics of magnesium content in soils sampled in Pazar region is shown in Figure 9.

Iron content
The iron content of samples taken in April was at medium level in 6.7% of samples, at a high level in 40.0% of samples and at a very high level in 53.3% of samples. In November the iron amount was registered at medium level in 3.3% of samples, at a high level in 26.7% of samples and at a very high level in 70.0% of samples. In 40.0% of samples taken in the spring and in 26.7% of samples collected in the autumn the iron content had the desirable values. The reason is the decline of pH value between the two seasons. The higher values of pH in the spring cause the iron content decreasing, whereas the fall in pH values in autumn causes the iron content increasing above the normal values.
It was determined that the values of iron content ranged between 0.0036-0.0448 g/kg in a study conducted in 8 gardens between the years of 1977-1978 in the same region [14]. Taking into account these data, it seems to be an increase in values of iron amount in our tea land. Toxic effects causing an excess of soluble iron in plants, which lack of useful iron content, contribute to excessive iron defi ciency in some soils. The variation of iron content in soil sampled in Pazar region is presented in Figure 10.

Manganese content
The manganese content in samples taken in April was at medium level in 76.7% of samples and at a very high level in 23.3% of sample. In November the manganese content in 36.7% of samples was at medium level, in 40.0% of samples -at high level and in 23.3% of samples -at very high level. In 23.0% of samples taken in the spring and in 40.0% of samples taken in the autumn the manganese amount had the desirable values. It is determined the manganese values ranged between 0.0019-0.0405 g/kg in a study conducted in 8 gardens between the years of 1977-1978 in the same region [15]. As a result, an increase in the value of manganese content was observed in samples taken in November. The variation of the manganese amount in soil sampled in Fındıklı region is shown in Figure 11.

Zinc content
The zinc content in samples taken in April was at medium level in 20.0% of samples and at a very high level in 80.0% of samples. In November the zinc amount was at medium level in 40.0% of samples and at a high level in 60.0% of samples. In 80.0% of samples taken in the spring and in 60.0% of samples taken in the autumn the zinc amount had the desirable values. The amount of zinc ranged between 0.12-4.05 mg/kg in a study conducted in 8 gardens between the years of 1977-1978 in the same region [15]. As a result, a decrease in the value of zinc content was observed in samples collected in November. The variation of zinc content in soil sampled in Fındıklı region is shown in Figure 12.

Copper content
The copper content in samples taken in April was in 16.7% of samples at medium level, in 80.0% -at a high level and in 3.3% -at a very high level. In November the copper content was in 46.7% of samples at medium level and in 53.3% -at a high level. The copper content ranged between 0.06-5.93 mg/kg in a study conducted in 8 gardens between the years of 1977-1978 in the same region [15]. As a result, an increase in the value of the copper amount was observed in soil sampled during two seasons. Dynamics of the copper amount in soil sampled in Fındıklı region is presented in Figure 13.

Aluminium content
The aluminium content in samples taken in April was at low level in 63.3% of samples and at medium level in 36.7%. In 53.3% of samples it was at low level and in 46.7% at medium level during November. The variation of aluminium content in soil sampled in Fındıklı region is shown in Figure 14.

Conclusions
Commercial fertilizers, especially on the basis of nitrogen and phosphorus, are often used unconsciously in tea growing areas in Turkey. Soil reaction has been gradually acidic and the soil productivity began to be lost as a result of manufacturers, especially using ammonium sulphate fertilizer alone and overmuch. The amount of products to be received per unit area will be high-quality as long as soil fertility status is at an appropriate level. Therefore, the promotion and protection of soil productivity level is important.
Despite the depletion or decrease in the use of ammonium sulphate fertilizer in many platforms and the expression used for the location of compound fertilizer, tea manufacturers have not outgrown their habits but continued to use ammonium sulphate fertilizer for years. In order to avoid the acidity increasing of the soil it is recommended to use composite fertilizer (with ammonium sulphate) instead of using ammonium sulphate alone.