Management of the water regime of soil to increase the vegetable crops yield with different irrigation methods in the south of Russia

Long-term researches on the cultivation of vegetable crops with different methods of irrigation in the Volgograd region have shown that their yield was primarily closely related to the improvement of the water regime of the soil. Its efficiency using drip irrigation increased with the introduction of mineral fertilizers, and using subsurface irrigation with an improvement of the location of the irrigation network. The highest yield of beet with drip irrigation (82.4 t / ha) was obtained with an increase of the Soil Pre-Irrigation Moisture (SPIM) to 85% of Full Moisture Capacity (FMC) and fertilization doses to N235P140K130 kg/ha. The highest yield of courgettes with drip irrigation of 83.7 t / ha was obtained while maintaining the similar irrigation regime and the quantity of fertilizers N240P99K110 kg/ha.The maximum cabbage yield in our experience with drip irrigation of 83.1 t / ha was achieved using the option that combines the maintenance of the irrigation regime 80-90-80 %FMC with the application of fertilizers at doses of N110P50K140 kg / ha. The highest yield of radish with subsurface irrigation of 79.8 t / ha was obtained while maintaining SPIM 85 % FMC in the field with the location of subsurface humidifiers at a distance of 1.2 m from each other.


Introduction
Vegetable growing is the most important branch of agriculture in the Russian Federation. The Volgograd region is a typical region of the south of Russia, which is one of the main suppliers of vegetable products to various regions in our country. However, due to the strongly arid conditions, the cultivation of vegetable crops in this region is possible only with irrigation. The most common irrigation methods in the Volgograd region are sprinkling and drip irrigation. However, in our opinion, subsoil irrigation (subirrigation or subsurface irrigation) can also be successfully used for growing vegetable crops in this region.
The researches on the cultivation of vegetable crops at sprinkling, drip irrigation and subsoil irrigation in Volgograd State Agricultural University (Volgograd SAU) we have been conducting more than 20 years [27][28][29][30][31][32][33][34]. Their main goal is to develop a water regime for the soil to increase the yield of vegetable crops with different irrigation methods while maintaining soil fertility and environmental safety.

Materials and methods
The soils of the site are light brown, non-saline, medium loamy, low-humus. The humus content is no more than 1-2%. Groundwater is located at a depth of more than 3 m.
This Weather conditions during the study period were very stressful, especially in July and August. At this time, almost complete absence of rains, the highest air temperature and a large number of days with strong dry winds were observed.
Long-term researches have shown that the main component of the total water consumption of plants grown in the Volgograd region is the total consumption of irrigation water per season, that is, the volume of irrigation water. Consequently, it is possible to manage the water regime of the soil, as the main crop-forming factor, by selecting the most effective irrigation regime.
Therefore, all vegetable crops were studied with 3 options for irrigation regime on the background of 3 options for doses of mineral fertilizers and only for radish -on the background of 3 different options for the location of the irrigation network at SI.
For all other crops, 3 irrigation regimes were developed: one differentiated 75-85-75% FMC and two with a constant SPIM 75 and 85% FMC.
The change of the level of soil water in the variant with a differentiated drip irrigation regime for beet occurred sequentially in the next periods "seeding -7 leaf", "7 leaf -closing of leaves between the rows", "closing of leaves between the rows -harvesting; for vegetable marrow during the periods "sowing -flowering", "flowering -beginning of the fruit formation", "fruit formation -last harvest"; for radish with SI-during the periods of "seeding -beginning of the fruit formation", "fruit formation -technical ripeness", "technical ripeness -harvesting" .
The second study factor in the experiments with radish were 3 variants of the location of subsoil humidifiers with a distance of 1,2; 1,4 and 1,6 m between each other.

Results and Discussion
The irrigation rates for vegetable crops during the period of field researches are shown in the Table 1.  For subirrigation of radish in all variants of the experiment, the first watering at a rate of 5.0 mm / ha was done by sprinkling immediately after sowing for better seed germination.
The number of irrigations and volume of irrigation water for all variants of the experiments are shown in the Table 2. At the same time, the total number of drip irrigations during the season for beet increased on average from 34 to 112, for squash-from 31 to 69, for cabbage -from 16 to 29 units, and for radish with SI-from 18 to 33 pieces. As a result, the volume of irrigation water for beet increased from 455.6 to 537.6, for squash -from 334.8 to 374.4, for cabbage -from 308.0 to 360.0, and for radish -from 300.0 to 331.6 mm / ha.
The yield of vegetable crops is shown in the Table 3.
The science researches have shown that with drip and subsurface irrigation, the main factor influencing the yield of vegetable crops was the water regime of the soil.
In experiments with beet, an increase in the intensity of the drip irrigation regime from 75 to 85% FMC against the different agronomic background caused an increase in the yield of beet from 52.5 ..  The second factor influencing to the yield of radish with SI was the location of the irrigation network. A decrease in the distance between the humidifiers from 1.6 to 1.2 m stimulated an increase in its yield from 62.9 ... 71.0 to 72.2 ... 79.8 t / ha.

Conclusion
Long-term researches on the cultivation of vegetable crops with different methods of irrigation in the Volgograd region have shown that their yield was primarily closely related to the improvement of the water regime of the soil. Its efficiency using drip irrigation increased with the introduction of mineral fertilizers, and using subsurface irrigation -with an improvement of the location of the irrigation network.
The highest yield of beet with drip irrigation (82.4 t / ha) was obtained with an increase of the Soil Pre-Irrigation Moisture (SPIM) to 85% of Full Moisture Capacity (FMC) and fertilization doses -to N235P140K130 kg/ha. The highest yield of squash with drip irrigation of 83.7 t / ha was obtained while maintaining the similar irrigation regime and the quantity of fertilizers N240P99K110 kg/ha. The maximum cabbage yield in our experience with drip irrigation of 83.1 t / ha was achieved using the option that combines the maintenance of the irrigation regime 80-90-80 %FMC with the application of fertilizers at doses of N110P50K140 kg / ha.
The highest yield of radish with subsurface irrigation of 79.8 t / ha was obtained while maintaining SPIM 85 % FMC in the field with the location of subsurface humidifiers at a distance of 1.2 m from each other.