WATER SAVING IRRIGATION REGIMES FOR VEGETABLE CROP PRODUCTION UNDER CONDITIONS OF VOLGA DON INTERFLUVE

Irrigation regimes and rates of mineral fertilizers for obtaining the expected yields of vegetable crops under conditions of light chestnut soils of the Volga-Don interfluve are considered in the study. We established that irrigation regimes and norms of mineral fertilizers proposed in our field study for table beet (Beta vulgaris) and carrot (Daucus carota) cultivation allow yielding in the range of 60...80 t/ha. Thus, for example, the maximum yield of table beet 84.1 t/ha was obtained in the variant with 80% pre-irrigation soil moisture and N230P180K100 fertilizer at a variable depth of soil moistening (0.3...0.5 m). Changes in fertilizer dose from N130P80K20 to N230P180K100 contributed to 63.7...84.1 t/ha yield increase, which is 10—20% higher compared to other variants. Change in soil moisture from 70—80—70 to 80—80—80% of FMC in combination with fertilizer dose from N150P70K180 to N210P100K260 increased carrot yields from an average of 57.9 to 81.6 t/ha. The highest yields (81.6 t/ha) were obtained when maintaining pre-irrigation soil moisture of 80—80—80% of FMC and applying N210P100K260 fertilizer rate. In general, beet and carrot cultivation on light chestnut soils using drip irrigation is the most efficient. To maintain water regimes of the soil adopted by the experiment, a different irrigation frequency was required. When increasing humidity level from 70 to 90% FMC frequency of irrigation increases, and irrigation rate decreases. The total consumption of moisture in the experiments increased with an increase in moisture content — from 4,417 m/ha in the variant with 70% of FMC to 5105 m/ha in the variant with 90% of FMC. The largest total water consumption of table beet was noted in the variant with a differentiated depth of soil wetting and averaged 4,530—5,105 m/ha. The share of irrigation water in the total water consumption of plants increased from 73.3 to 75.7%. Application of mineral fertilizers reduces water consumption of table beet. The smallest coefficient was obtained in the second irrigation regime variant, when humidity was maintained at 80% of FMC with different wetting depth. This situation was observed in all variants of irrigation regimes and fertilizer applications. This confirms that differentiating wetting depth according to table beet growth stage makes it possible to use irrigation water more economically at all rates mineral fertilizer application.


INTRODUCTION
Currently, when growing vegetables, optimization of irrigation regime as a factor of integral significance has the first importance. It determines productivity per hectare and yield quality, total costs, water and energy resources demand, and public health situation. So, irrigation regime, irrigation technique, mechanization and automation should be improved, and new, more productive methods of irrigation should be created in order to increase efficiency of irrigation reclamation. Hence, experience of advanced farms of the region and the data of research institutions show that proper farming practices and optimal irrigation regime result in high and stable yields of vegetable crops. It is well known, that irrigation water costs, soil properties and plant productivity change depending on the irrigation methods used. Therefore, drip irrigation is promising in vegetable crop growing [1-5, 6, 7].
Cultivation of vegetable crops, in particular carrots and beetroot, on irrigated lands of the Volgograd region is important. Hence, we are conducting research, which purpose is to determine optimal combination of irrigation regime and fertilizer application in order to obtain carrot and table beet yields at the level of 60, 70, 80 t/ha.

MATERIALS AND METHODS
The research was conducted during 2015-2017 on two plots of Gorodishchensky district of Volgograd region, located in the zone of unstable moistening according to the generally accepted recommendations of B.A. Dospekhov, V.N. Pleshakov, G.F. Nikitenko [8][9][10]. The soils are light chestnut heavy loam, slightly waterpermeable. Humus content in 0-0.5 m soil layer is 1.87...2.02%, soil density is 1.31 t/m 3 , field moisture capacity (FMC) of dry soil is 22.93%. Soils of the experimental plots have 7.0...8.3 pH and are not saline.
The content of available forms of nitrogen in the first and second plots is characterized by low availability, mobile phosphorus has medium and high availability, exchangeable potassium has high and medium availability. Doses of mineral fertilizers were determined by a conventional method, according to V.I. Filin [11].
To obtain the expected yields of vegetable crops, there were two factors in the experiment: the first one is water regime of the soil (factor A), the second onefertilizer dose (factor B).
In the first plot we studied optimal water and fertilizer regimes of the soil for cultivating table beet cultivar 'Bordo' from 2015 to 2017. A field two-factor experiment was conducted on the territory of individual entrepreneur 'Kolesnikov' in the Kuzmich village of Gorodishchensky district according to the following scheme: 1) irrigation regime -water regime of the soil was studied: irrigation was carried out along with humidity decrease to 70, 80 and 90% of FMC in active soil layer. 2 variants of soil wetting depth were planned: the first -0.3 m during 'plantingroot formation' and 0.5 m during 'root formation -technical ripeness' and the second -0.5 m; 2) mineral fertilizers: rates of mineral fertilizers were calculated by the balance method for yields of 60, 70, 80 t/ha. In all variants according to the irrigation regime, they had the following rates: 1) N 130 P 80 K 20 ; 2)N 180 P 130 K 60 ; 3) N 230 P 180 K 100 .
In the second plot investigations were carried out from 2015 to 2016 to study the effect of differentiated irrigation regimes and various fertilizer rates on carrot yields. The experiments were carried out on the territory of the Kuzmich village of "Kuzmichevsky' farm in Gorodishchensky district. The experiments were based on a two-factor scheme: The first factor -irrigation regime: 70-80-70; 70-90-80; 80-80-80% of FMC (Table 1). The second factor -fertilizer application. The rates of mineral fertilizers were calculated by the balance method for yields of 60, 70, 80 t/hа. In all irrigation regime variants these rates were as following: 1-st -N 150 P 60 K 180 ; 2-nd -N 180 P 80 K 220 ; 3-rd -N 210 P 100 K 260 (80 t/gа).
In both studies season irrigation was carried out using drip irrigation. During carrot cultivation active soil layer was 0.5 m. The irrigation rates were 250...300 m 3 /ha, 208...300 m 3 /ha and 250 m 3 /ha. Carrots 'Mayor F1' hybrid seeds were sown using common regional agricultural techniques.

RESULTS AND DISCUSSION
The results of three-year research on light chestnut soils of the Volga-Don interfluve have shown that the applied irrigation regimes and the application rates of mineral fertilizers along with drip irrigation make it possible to obtain expected yields of table beets and carrots at a level of 60...80 t/ha.
In our experiment, to maintain the water regimes of the soil a different number of irrigations were required. The data shown in Table 2 indicate that increase in humidity from 70 to 90% of FMC results in increase in number of irrigations and irrigation rates, and irrigation rate decreases. Irrigation regime, crop yield and meteorological conditions of the growing season have a decisive influence on the amount of total water consumption. The total consumption of moisture in the experiments increased with an increase in water availability from 4,417 m 3 /ha in the variant with 70% of FMC to 5,105 m 3 /ha in the variant with 90% of FMC. The highest total water consumption of table beet was in the variant with a differentiated wetting depth and averaged 4,530...5,105 m 3 /ha. Share of irrigation water in total water consumption of plants increased from 73.3 to 75.7%, as water availability improved (Table 3).  Our experiments showed that different irrigation regimes and fertilizer applications had a significant impact on yield and water consumption of root crops. The maximum table beet yield of 84.1 t/ha was obtained when soil wetting depth was 0.3-0.5 m, soil moisture was 80% of FMC and N 230 P 180 K 100 fertilizer rate (Table 4).

АГРОТЕХНОЛОГИИ И МЕЛИОРАЦИЯ ЗЕМЕЛЬ
Depending on the variant, table beet yield increased by 8.8...11.5 t/ha after N 180 P 130 K 60 application and by 25.6...29.2 t/ha after N 230 P 180 K 100 application compared to N 130 P 80 K 20 fertilizer application.
While maintaining wetting depth at the level of 0.3...0.5 m and increasing soil moisture level from 70 to 90% of FMC, table beet yield varied from 54.9 to 84.1 t/ha. In all variants of the experiment, the highest table beet yield was obtained when pre-irrigation soil moisture was 80% of FMC and fertilization rate -N 230 P 180 K 100 . Decrease or increase of pre-irrigation soil moisture in active soil layer to 70 or 90% of FMC reduced yields of root crops by 10-15%.
According to the data obtained, mineral fertilizers also reduce beet water consumption. The lowest coefficient was in the second variant of irrigation regimes, when soil moisture was maintained at 80% of FMC with differentiated wetting depth. We observed it in all variants of irrigation regimes and fertilizer applications. This confirms that differentiation of wetting depth of the soil according to table beet growth stages makes it possible to use irrigation water more economically at all rates of mineral fertilizers ( Table 5). In the second plot, carrots were sown on May 15. During the research years, meteorological conditions had a great influence on irrigation frequency and rates. So, for example, depending on the variant, 15...20 waterings were conducted, which amounted to irrigation rate of 4,050...4,780 m 3 /hа (Table 6).
According to the data of Table 7, differentiating pre-irrigation soil moisture and different fertilizer rates had a significant impact on carrot yield and water consumption. The data obtained show that changes in carrot productivity under drip irrigation correlate with changes in total water consumption and water consumption coefficient. In addition, carrots are very responsive to mineral fertilizer application. The maximum carrot yield of 81.6 t/ha can be obtained by maintaining constant soil moisture at the level of 80-80-80% of FMC and applying fertilizers at the following rate -N 210 P 100 K 260 .  The irrigation water was most effectively used at soil moisture levels of 80-80-80% of FMC, since there was the lowest water consumption and averaged 72.18 m 3 /hа over research years.

АГРОТЕХНОЛОГИИ И МЕЛИОРАЦИЯ ЗЕМЕЛЬ
Carrot yield 60 t/hа is achieved in the variant with pre-irrigation soil moisture of 70-80-70% of FMC in combination with fertilizer application N 150 P 60 K 180 . So, irrigation rate was 4,050 m 3 /hа, and total water consumption was 5,678 m 3 /hа.
For carrot yields of 70 t/ha irrigation rate increased to 4,780 m 3 /ha, and total water consumption increased to 5,781 m 3 /ha. The maximum carrot yield 81.6 t/ha was obtained when soil moisture was 80-80-80% of FMC and fertilizer rate was increased to N 210 P 100 K 260 .