Сельское хозяйство / 3. Земледелие, грунтоведение и агрохимия

L.S. Malyukova, Z.V. Pritula

The All–Russian Scientific and Research Institute of Floriculture and Subtropical Crops, 354002, Krasnodar region, Sochi, Yana Fabritsiusa str. 2/28

Effect of boron and zinc-containing fertilizers on quality of tea leaf on Russian Black Sea Coast

The Black Sea coast of Russia is the only one in the country and the world's most northern area where tea is cultivated on an industrial scale. This culture was introduced to the zone in 1878 for the first time, and the first tea plantation was founded in 1901, which has been operated up to the present. Industrial cultivation of this crop was in a period of 1970-1980. Prolonged use of mineral fertilizers has led (due to the increased soil acidity) to the increase in the mobility of some elements (Ca, Mg, Mn, Fe, Al, Cu, Zn), changed the balance of nutrition elements in soil-absorbing complex and some other soil properties [6, 7, 9]. Furthermore, applying high doses of mineral macrofertilizers in fertilizer systems of tea usually leads to declines in tea quality [3, 8, 11], one of the reasons is reduce of microelements in tea raw materials. In this regard, the task is to develop the most effective agrochemical methods of increasing yield, quality of tea leaves as well as to preserve fertility in unique soils. Multicomponent mineral nutrition of tea plants is considered as one of the most promising areas, including the use of micronutrients. The most significant role in ensuring high productivity and quality of tea raw material is experimentally proved by many tea-producing regions and belongs to such micronutrients as boron and zinc [2, 5, 10, 12, 14, 15]. Boron and zinc play an important role in the physiological and biochemical processes concerning plant growth, particularly in phenolic and carbohydrate metabolisms, respiration and plant resistance to abiotic stress factors [1, 14-16].

The aim of this research was to study the effect from soil fertilizers containing boron and zinc on biochemical indicators of quality in tea raw material in conditions of Russian Black Sea coast.

The studies were conducted during 2008-2013 based on the field experiment, which was pledged on a tea plantation in 2003 and included a regionalized cultivar called Colkhida (planted in 1983). Zinc sulfate (Zn - 4,3 kg/ha of active substance) and boric acid (B - 6 kg/ha of active substance) were added to the soil surface on the background nitrogen rate (240 kg N·ha), phosphorus (70 kg P₂O₅·ha) and potassium rates (90 kg K₂O ha). As a control, there was an option with the introduction of macrofertilizers nitrogen rate (240 kg N·ha), phosphorus (70 kg P₂O₅·ha) and potassium rates (90 kg K₂O ha). The size of experimental plots was 10 m². The frequency - 3-fold. The soil is brown forest acidic with low humus content and powerful, on eluvium-deluvium of mudstone. Before setting the experiment, the soil was characterized by acidic reaction of medium of the soil solution (pH 3,2-3,3 ), average supply with hydrolyzable nitrogen ( 80-100 mg/kg), mobile phosphorus (300-400 mg/kg) and potassium (200 - 300 mg / kg). Biochemical indicators in raw materials quality were evaluated by two parameters: the content of tannin and extractives in 3-leaf fleches. Fleshes sampling was carried out according to the test options in the periods of tea leaves mass collecting: the third ten-day period in May, the first ten-day period in July; the repetition was 3-fold. Samples for biochemical studies made up 100 g of 3-leaf fleches. Tea raw material was fixated by wet steam for 3 minutes in Koch apparatus; drying was carried out first outdoor, then - in an oven at a temperature of 60˚C up to air-dry state. Tannin content was determined by a method based on tannin oxidation with potassium permanganate, with the participation of indigo carmine as an indicator, according to Standart 19885-74 [14], using a conversion factor 5.82 by K.M. Dzhemukhadze [4]. Determination of extractives was performed by extraction of water soluble substances from tea sample by boiling and quantitative determination of a dried extract (ISO 1574-80).

Synthesis of secondary metabolites such as polyphenolic compounds, including tannin, in a 3-leaved shoot is one of the most important indicators of both quality of the obtained products and activity of redox processes, enzymatic reactions, as well as carbohydrate and phenolic exchanges.

Studies have shown that the use of zinc and to a lesser extent boron-containing fertilizers increased tannin content, which characterized tea leaves quality, especially during the first harvest (Table). This regularity was recorded almost every year and confirmed by the average data.

Table - Content of tannin and extractives in 3-leaf fleches of tea plant

(average for 2011-2013yy.)

Option	Tannin, %		Extractives
	May	July	May	July
control	25,3 ± 1,9	31,3 ± 1,0	41,3 ± 0,9	43,1 ± 1,0
B	25,7 ± 1,7	31,6 ± 1,6	41,4 ± 1,2	43,5 ± 1,0
Zn	27,0 ± 2,4	32,3 ± 1,2	41,9 ± 1,3	44,2 ± 2,0
LSD 0,05	1,1	0,9	0,3	1,0

In general, synthesis of tannins increased in July, in comparison with May, and their content in a 3-leaf fleches increased up to 4-8% for all test variants for all the research years.

According to the content of extractives in 3-leaf fleches, impact from micronutrients was recorded to a lesser extent. Thus, the experimental options had a quite stable content of extractives in May, which ranged from 40 to 43% in different years of observations. In July (the second wave of growth), the content of extractives was from 42 to 47% in different studying years. There was a greater accumulation of extractives in treatments where zinc was used.

The research has shown that soil fertilization with boron and zinc (6 and 4,3 kg/ha of active substance, respectively) on the Black Sea coast of Russia increase of catechins (tannins, less extractives) in the content of 3-leaved shoots, which characterize the quality of tea raw material indicates that these fertilizers contributed to plant antioxidant capacity.

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