Introduction

Cucumber (CucumissativusL.) is a widespread, popular, daily used in fresh and processed form vegetable crop. Cucumber fruits are in great demand among the population and processing enterprises. It is cultivated worldwide due to a short vegetation period and intensive yield formation with mass fruiting.

Cucumber is a low calorie food product, a complete source of vitamin C and carotene. The main component of young fruit is water – 94-95%. In addition to vitamin C and β-carotene, cucumber contains a small amount of sugar (1.5-2%), protein (1%), cellulose (0.75%), vitamin B₂ (riboflavin), nicotinic acid (PP), thiamine (B₁), as well as aromatic substances. Cucumber fruits contain more iodine than other vegetables and potatoes do (1, 2).

Cucumber is a main crop cultivated in sheltered ground, it takes from 50 to 70% of the greenhouse area, due to the high early emergence of fruit, yielding and high profitability. In recent years, the area of sheltered ground in the Republic has significantly increased (3). This is facilitated by state subsidies for the development of greenhousefacilities.Thus, the Program “Agrobusiness-2020” provides subsidies for the area of vegetables in sheltered ground in the following amounts: 2014 – 364 hectares, 2015 – 394 ha, 2016 – 424 ha, 2017-2020 – 461 ha (in each year). Also the mineral fertilizers (NPK), purchased by farmers, will be subsidized in the amount of from 255.8 thousand tenge (2014) to 412.7 thousand tenge (2020). So, the state creates conditions for the development of production and reduce imports. The volumes of consumption of vegetable and melon production in fresh and processed form are about 3.2 million tons, of which the share of imports is about 6% (4).

The application of mineral fertilizers under drip irrigation increases crop yields. But only the consistent and correct use of fertilizers (rates and methods) in combination with resource-saving agricultural methods will create favorable conditions for the proper development of plants (5).

The formation of vegetative mass and root system of cucumber in a greenhouse depends to a significant extent on the types of soils and amounts of applied fertilizers. Because only they determine the conditions of mineral nutrition of plants, accordingly, the productivity of cucumber.

In sheltered ground cucumber generates significantly more yield than in open ground, the difference may be 10-15 times or more. It should be taken into consideration that in greenhouses the depth of soils is limited, is about 20-25 cm, in the food plan the soils do not contain a large diversity of macro- and microelements, as wild (natural) soils of open ground. Therefore, in the cultivation of greenhouse cucumber a special approach to the system of fertilizer application is required (6).

Soils (substrates) in sheltered ground are very important in agronomic, economic, phytosanitary and environmental terms. Soils should provide favorable conditions for the growth and development of greenhouse crops (cucumber) and the formation of their high yields. At the same time soils (substrates) must be accessible and affordable. In the process of annual use in microflora of greenhouse soil the parasitic forms begin to dominate, i.e. pests and pathogens accumulate. To fight infection it is necessary to change the greenhouse soil often or to perform disinfection (sanitation), which leads to considerable economic and environmental costs (7).

For successful implementation of the set tasks, a very significant role is assigned to highly productive greenhouse varieties (hybrids) of cucumber and highly efficient agrotechnologies of crop cultivation in shelteredground. In this aspect, our research, aimed at increasing the yield and improving the quality of greenhouse cucumber with a substantial reduction in material costs and environmental impact on people and the environment, is relevant.

Materials and methods

The research was conducted in 2013-2015 in the greenhouse of the Kazakh Research Institute of Potato and Vegetable Growing (KazRIPVG). The greenhouse is equipped with all modern mechanisms of regulation of the microclimate (temperature, humidity) and lighting, instruments and equipment for drip irrigation, mineral nutrition and other methods (using Korean technology). The total area of the greenhouse is 3420 m².

KazRIPVG is located in the piedmont of South-Eastern Kazakhstan (950-1050 m above sea level), in the village of Kainar of Karasai District of Almaty Region.

The climate of the region is sharp continental. The warm period is 240-275 days, the frost-free period – 140-170 days. The sum of effective temperatures is 3100-3400⁰С. The hydrothermic coefficient is 0.7-1.0. The mean annual precipitation is 350-600 mm. The soil is dark-chestnut, medium-loamy, the humus content is 3%. The greenhouse soil is a standard substrate and has the following basic composition: perlite – 40%; coir – 30%; peat – 30%.

Sample preparation and analytical methods

In experiments with soils and fertilizers the classical methods are used: the agrochemical methods of soil studies (8); methodologyof agrochemical research(9); methodologyof field experience (10); methodology of experimental work in vegetable and melon growing (11).

The qualitative indicators of cucumber fruits are defined by the following methods: dry matter – gravimetric method (drying); total sugars – by Bertrand; vitamin C and carotene – by Murri.

The objects of our research were greenhouse cucumber, types of soils, types, amounts and combinations of fertilizers. The experiments used F1-hybrid of greenhouse cucumber Aibyn (selections of KazRIPVG) approved for use in all 14 regions of Kazakhstan (12).

To determine the effect of the studied processing methods on the growth and development of plants of greenhouse cucumber the phenological observations and biometric research were conducted on test plots in the greenhouse.

The phenological observations were made to establish the time of occurrence and completion of a certain phase of plants development by the method of A.I. Rudenko (1950).

During biometric research of greenhouse cucumber: the length of the main stem; the number of leaves; the number of ovaries; the number, length, diameter and weight of fruits (in the period of mass fruiting) were taken into account.

The technology of greenhouse cucumber cultivation was carried out in accordance with the recommendations of KazRIPVG (13, 14).

Results and Discussion

The formation of vegetative mass and root system of cucumber in a greenhouse depends essentially on the types of soil substrate (soil) and fertilizer amounts, as these factors determine the conditions of mineral nutrition and productivity of cucumber (15-18).

In sheltered ground cucumber generates significantly more yield than in open ground, the difference may be 10-15 times or more. It should be taken into account that in greenhouses the depth of soils is limited, is about 20-25 cm, in the food plan the soils do not contain a large diversity of macro- and microelements, as wild (natural) soils of open ground. Therefore, in the cultivation of greenhouse cucumber a special approach to the system of fertilizer application is required.

In sheltered ground cucumber is grown off season, when adverse weather conditions make it difficult to cultivate plants in the field. And in greenhouses the outer meteorological indicators have a certain impact on the growth and development of cucumber plants. If the microclimate inside a greenhouse is not regulated, which requires large expenditures, the plants will lag behind in development or occurrence and passage of phenological phases of development will be delayed. Thus, cloudy weather for a long time, which often takes place in winter and early spring periods, has a certain negative impact on the process of formation of vegetative biomass of plants and yield of cucumber young fruits. The negative impact of external factors can to some extent be offset through the creation of optimal conditions of crop mineral nutrition (19).

Taking the above into account, we conducted phenological observations and biometric research, defined the dynamics of the formation of greenhouse cucumber yield. Both the impacts of weather conditions (by years of research) and greenhouse soils and various types and amounts of fertilizers were taken into consideration.

In table 1 the data of phenological observations in the greenhouse, during which the dates of occurrence and passage of the main phases of growth and development of cucumber plants are fixed, is given.

Cucumber sowing in winter-spring greenhouse turnover was made in late January – early February (by years of research), seeds directly in the soil. The appearance of single seedlings was observed in 5-8 days after sowing, and mass seedlings – in 8-14 days. The first true leaf was observed only in 2-3 weeks after sowing and the second leaf – in 6-9 days more after the first leaf. The appearance of 3-4 true leaves of plants was recorded in 2013 in 23 days after sowing, in 2014 – in 31 days (1 month), and in 2015 –in 36 days (more than one month). The relatively slow development of plants of greenhouse cucumber in the beginning period of vegetation is associated with adverse weather conditions of the winter months (cold and cloudy weather). The phenological phases of cucumber development “5-6 true leaves” and “8-10 true leaves” accounted for the II decade of February in 2013, I-II of March – in 2014, II-III of March – in 2015.

Later, after the incoming of spring with relatively favorable weather conditions, there was more intense development of cucumber in the greenhouse. Mass flowering of crop (75% of plants) was observed in late March – early April (by years). In the phenological phase “mass fruiting” the plants entered in the II and IIIdecades of April. Mass ingathering of cucumber young fruits was conducted in April and May. Cucumber harvesting continued till the month of June in all years of research.

The durations of certain phenological phases of development and overall vegetation period of greenhouse cucumber were considerably different. The period from sowing cucumber seeds in the greenhouse soil to the appearance of mass seedlings ranged from 8 to 14 days. The period from mass seedlings of cucumber to the first ingathering of young fruits amounted to 74-77 days. The fruiting period, i.e. the time interval between the first and lastingathering, was equal on the average to 68-70 days. The duration of the vegetation period of cucumber, which includes the period from mass germination of seeds to the last harvesting of crops in the greenhouse, amounted to about 155-165 days.

Table 1: Phenological observations in experiments with greenhouse cucumber

In forming well-developed vegetative biomass and high yields of cucumber fruits in sheltered ground a significant role is given to soils and mineral fertilizers. In this regard, we conducted research to assess the effectiveness of different types of soils, amounts and combinations of macro- and micronutrients in the greenhouse of KazRIPVG.

It should be noted that in the greenhouse of KazRIPVG for mineral nutrition of cucumber a special fertilizer system, involving the use of a complex of all macro- and microelements, essential for plants, through the drip irrigation system, is used. The types, amounts and combinations of fertilizers, the frequency of their application under greenhouse cucumber are regulated depending on the phenological phase of crop growth and development for balanced plant nutrition (table 2).

Table 2: The system of cucumber fertilization used in the greenhouse of KazRIPVG

This special complex system of application of fertilizers is costly, because their cost several times higher than the cost of conventional mineral fertilizers. Because such complex fertilizers are produced in far-abroad countries (Turkey, Finland, etc.). Due to high cost of fertilizers production, high expenses for their transportation and customs duties, the special fertilizers are very expensive for the greenhouse facilities of the Republic. Therefore, many farmers use mineral fertilizers produced in Kazakhstan (nitrogen and phosphate) and in the countries of the Customs Union (potash). The fertilizers are often applied without consideration of the needs of plants and the level of generated greenhouse yield, which leads to wastes of important fertilizer elements and contamination of soils and products with toxic substances (20).

Proceeding from the foregoing, we conducted research to evaluate the effectiveness of various amounts and combinations of macronutrient fertilizers (NPK) on the crop of cucumber in sheltered ground (greenhouse). Since cucumber, like other vegetables, is grown in artificial soil (hydroponics) in the greenhouse, a clean control (without fertilizers) was not provided in the experiments. As a background variant of the experiment a variant, in which a special complex system of cucumber fertilization with generalizing conventional name “Kristalon” was applied, was taken. Fertilizer “Kristalon” can be of different brands (“Special”, “Cucumber”, etc.), includes various types and combinations of water-soluble macro- and micronutrients (for different phenophases of cucumber).

When using the special (standard) complex fertilizer system for mineral nutrition of cucumber during the vegetation period per 1 ha of greenhouse area 1740 kg of fertilizers in the physical mass are applied in total. If we convert it to the active substance, this gives a total of 1039 kg/ha of a.s. of NPK fertilizers. Of these, the proportion of nitrogen (N) is 177 kg, of phosphorus (P₂O₅) – 276 kg, of potassium (K₂O) – 586 kg. The NPK ratio is 1:1.56:3.31.

The standard set of water-soluble complex fertilizers (Kristalon) was taken as a background variant (fertilized control). There was no unfertilized control in the experiment as the typical soil of the greenhouse (perlite, coir, peat) does not contain enough of all nutrients, necessary for cucumber. In this case, the greenhouse cucumber plants will grow very poorly, will significantly lag behind the fertilized plants, they will not give a full yield of young fruits. Accordingly, the research results obtained will be biased and unreliable. Therefore, to all experimental variants the fertilizers to create conditions for optimal and balanced mineral nutrition of cucumber were applied.

It should be noted that when the cucumber yield was 15 kg from 1 m² per 1 turnover of the greenhouse (converted 150 t per 1 ha), on the formation of biomass and yield of plants on the average 450 kg of nitrogen, 225 kg of phosphorus and 600 kg of potassium (in active substance) are spent.

Therefore, in the calculation of fertilizer amounts under the greenhouse cucumber, it is necessary to take into account the amounts of the removal of nutrients by the crop yield by all means.

The standard complex range of fertilizers for cucumber, recommended by the manufacturers and used in the greenhouse of KazRIPVG, provides the need of plants in 2 main macroelements – P₂O₅ and K₂Oalmost completely. The removal of phosphorus is compensated by 123% and of potassium – by 98%. In this fertilizer system lack of nitrogen is manifested. The costs of this important macronutrient are compensated for only 39%.

For balanced nutrition of cucumber plants the standard (special) complex fertilizer Kristalon was added with nitrogen fertilizer (reimbursement of nitrogen increased from 39% to 75-100%). These variants (Kristalon + N_160-210) made the second and third variants of our experiment. In the scheme of the experiment the variants with various amounts of industrial NPK fertilizers, traditionally used by farmers (ammonium nitrate, ammophos, potassium sulfate), were also included. These ones include predominant (75%) and full (100%) consumption of nutrients for yield formation of cucumber young fruits in sheltered ground of South-Eastern Kazakhstan. Thus, to uphold the principle of the only difference the fertilizers were applied to all 4 studied variants similar to the background in the same vegetation periods of cucumber plants through the drip irrigation system of the greenhouse.

The results of biometric research showed that the formation of vegetative biomass of greenhouse cucumber plants is closely interrelated to the conditions of crop mineral nutrition (table 3).

Applying the background variant, when the standard complex fertilizer Kristalon had been used, the following indicators were recorded: plant height – 245 cm, the number of leaves of 1 plant – 30.6 pieces, diameter (largest) of leaves – 26.3 cm, the number of ovaries of 1 plant – 12.8 pieces, the number of formed fruits of 1 plant – 5.4 pieces (average of 10 accountable plants).

Table 3: The impact of different types, amounts and combinations of mineral fertilizers on the formation of biomass of greenhouse cucumber plants

Using the experiment variants, when the background variant (Kristalon) had been added with nitrogen fertilizer in the amounts of 160-210 kg/ha (of a.s.), the following biometric indicators of cucumber were recorded: plant height – 267-281 cm, the number of leaves of 1 plant – 33.7-34.9 pieces, diameter of leaves – 28.0-29.2 cm (largest leaf), the number of ovaries of 1 plant – 14.1-14.5 pcs, the number of formed fruits of 1 plant – 5.6-6.3 pcs. That is, the amplification of the special complex greenhouse fertilizer by adding nitrogen fertilizer contributes to more intensive development of cucumber plants and formation of a large biomass.

Applying the experiment variants, when for mineral nutrition of cucumber the conventional industrial fertilizers in the amounts of N₃₄₀P₁₇₀K₄₅₀ and N₄₅₀P₂₂₅K₆₀₀had been used, the indicators of growth and development of plants were slightly lower, and this was due to a narrow range of nutrients in the applied fertilizers. In this case, the height of the cucumber plant was equal to 230-243 cm, the number of leaves of 1 plant was 27.4-31.0 pieces with diameter of 23.5-25.9 cm (maximum diameter of the leaf), and on the accounting day 1 plant formed 10.2-11.6 pieces of ovaries and 3.8-4.7 pieces of fruits.

The more intensive development of cucumber plants contributed to the formation of higher yields of fruits (table 4).

Applying the background variant of the experiment, when the special complex fertilizer (Kristalon) for greenhouses had been used, the yield of cucumber was 17.4 kg/m² (for 1 turnover of the greenhouse). As for the experiment variants, when Kristalon had been added with nitrogen fertilizer in the amounts of 160 and 210 kg/ha (of a.s.), the yield of cucumber increased by 13.8 and 20.1%. In this case, 19.8 and 20.9 kg of fruits were gathered from 1 m² of the greenhouse. A quite high agronomic effect of amplification of nitrogen nutrition of the crop was marked.

Using the experiment variants, when the cucumber plants in the greenhouse were fertilized with simple combination of conventional nitrogen (ammonium nitrate), phosphate (ammophos) and potash (potassium sulfate) fertilizers in the amounts of N₃₄₀P₁₇₀K₄₅₀ and N₄₅₀P₂₂₅K₆₀₀, the crop yields decreased by 9.8-19.5% compared to the background. Nevertheless, the fairly good levels of fruit yields were obtained. As for the variant of amount N₃₄₀P₁₇₀K_450,that covers the removal of nutrients (NPK) by 75%, for one turnover of the greenhouse, 14.0 kg/m² of product were grown. And when using the variant of amount N₄₅₀P₂₂₅K₆₀₀,that covers the removal of nutrients (NPK) by 100%, for one turnover of the greenhouse 15.7kg/m²of young fruits were grown. That is, replacing the expensive special complex greenhouse fertilizer by conventional fertilizers it is possible to obtain good yields of cucumber.

Table 4: Yield and quality of young fruits of greenhouse cucumber depending on the types, amounts and combinations of mineral fertilizers

* Note: for one turnover of the greenhouse.

The quality of the product is essential for proper and safe nutrition of the population (12). This is especially important for vegetable growing in sheltered ground. On this basis, the biochemical analyses of cucumber fruits were carried out.

The quality indicators of the fruits, when applying the background variant, were higher. It is associated with better nutrition of plants. The water-soluble complex fertilizer Kristalon provided plants with full mineral nutrition, delivering to them all the necessary macro- and microelements. The cucumber fruits, that were grown using this variant, contained 4.10% of dry matters, 0.95% of the total sugars and 4.6% of vitamin C. The use of Kristalon with the addition of N₁₆₀ also contributed to the considerable improvement of the biochemical composition of the cucumber yield: dry matter – 4.10%, total sugars – 1.36%, ascorbic acid (vitamin C) – 3.9 mg%. The increase in the amount of nitrogen (Kristalon + N₂₁₀) led to some reduction of dry matters (3.38%) and vitamin C (3.9 mg%) in the fruits, and the content of total sugars (0.95%) was at the level of the background variant. Applying the experiment variants, when the plants were fertilized with conventional simple types of NPK fertilizers, the quality indicators of the product were not much different from the yields when using the variants of greenhouse fertilizer Kristalon. Applying NPK variants the cucumber fruits contained 3.74-3.78% of dry matters, 0.90-1.21% of sugars and 3.3-4.2 mg% of ascorbic acid.

In sheltered ground for normal, healthy growing of cucumber plants soils are of great importance. In modern greenhouses of industrial type the artificial substrates (soils) are mostly used. They are imported from far-abroad countries, and are costly to the greenhouse facilities. The frequent replacement of soils with further acquisition of new substrates from foreign countries imposes large costs on producers of greenhouse products. So, this poses the question of the development of inexpensive soils from local materials.

In the conditions of the greenhouse of KazRIPVG we prepared and studied the composition of the soil consisting of the following components: 30% – mountain black soil (piedmont dark-chestnut soil), 30% – rotted manure (humus) and 40% – sand. These local components are available to farmers.

The results of the research of greenhouse cucumber showed rather high effectiveness of the studied soils. We observed the normal development of plants and the formation of their full biomass. The cucumber plant, grown in the artificial greenhouse soil (perlite, coir, peat), had the following biometric data: the length of the main shoot (stem) – 256 cm, one plant formed 32.7 pieces of leaves; 13.4 pieces of ovaries and 5.8 pieces of fruits (table 5).

Table 5: The impact of greenhouse soils on the formation of biomass of cucumber plants (phenophase – mass fruiting)

* Note: on the day of accounting (biometrics of cucumber plants)

The cucumber plants, grown in natural soils, maximum close to wildland soils (based on black and chestnut soils) were significantly superior to the plants, grown in artificial soils, by the measured biometric indicators. When using these variants of the experiment the plants were higher, leafy and they formed greater numbers of ovaries and fruits. This is due to the presence of humus and nutrients for plants in these natural soils.

Table 6: The impact of greenhouse soils on the cucumber productivity

The intensive development of plants in natural soils contributed to the formation of higher levels of cucumber yields. As we can see from table 6, using the variant “Soil-1” the yield of young fruits was 20.4 kg/m², using “Soil-2” – 19.1 kg/m² and 18.2 kg/m² when applying the variant of the artificial substrate, accordingly.

Thus, soils for greenhouses, made from natural local components, provide the formation of a highly developed biomass of greenhouse cucumber plants and high yields of fruits.

Conclusions

The results of the analyses showed that the qualitative indicators of cucumber young fruits to a certain extent depend on the conditions of mineral nutrition. The amplification of the special complex water-soluble greenhouse fertilizer Kristalon by adding nitrogen fertilizer (160-210 kg/ha) contributed to more intensive development of plants and formation of a large biomass. When using the conventional mineral fertilizers (N₃₄₀P₁₇₀K₄₅₀; N₄₅₀P₂₂₅K₆₀₀)for the cucumber nutrition the biometric indicators of plants were slightly lower, due to the limitation of nutrients in these fertilizers.

The composition of the soil, consisting of local, available to farmers, components, was studied: 30% – black soil and dark-chestnut soil, 30% – humus and 40% – sand. The cucumber plants, grown in the natural soil, were significantly superior to those ones, grown in the artificial substrate, by biometric indicators: they were higher, leafy and formed greater numbers of ovaries and fruits. This is due to the presence of humus and nutrients in the natural soil.

Acknowledgment

This work was supported by the Kazakh Research Institute for Plant Protection and Quarantine. We are grateful to the workers of the greenhouse, especially to the Master of Agriculture, NusupovaAigulOrysbekovna for their assistance.

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