Vol 13, No 3 (2018)

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 m3/ha in the variant with 70% of FMC to 5105 m3/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 m3/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.

Rice plays an important role in the modern diet of Russian people. It occupies a leading position in area, yield, and gross grain harvest among all cereal crops. The aim of the research is development of optimal irrigation regimes that ensure rational use of water resources in southern agricultural zone of Amur Region. Setting and conducting field and laboratory experiments, system approaches and modern research methods were used. The article presents the results of studies on rice cultivation under different irrigation regimes. In the southern zone of Amur Region, along with water regimes of 70, 80, 90% of FMC, differentiated rice irrigation regimes were studied, combining differentiation of presumed humidity thresholds and wetting depth of active soil layer 75...85% of FMC (0.4 and 0.6 m); 80% of FMC (0.4 and 0.6 m). In addition, various flooding regimes of rice field (short and intermittent flooding), seeding rates, timing of sowing, rice cultivars were studied. Obtaining a rice grain yield of more than 4 tons per hectare is ensured by application of mineral fertilizers in the dose of N120P30K30 and seeding rate of 5 million seeds. Optimum seeding time was set from 20 to 25 May. Based on the results of the research, irrigation water was saved, as well as yield increased by optimizing irrigation rice regimes using sprinkling by differentiating presumed moisture thresholds and wetting depth. When rice was cultivated under flooding system of irrigation, it was established that regime of shortened flooding turned to be optimal. When sprinkling in conditions of southern agricultural zone of Amur Region, differential irrigation regime of 75...85% of FMC in active soil layer was 0.4 and 0.6 m.

Studies carried out in steppe zone of chernozem soils of Volgograd region have established that winter wheat after fallow and maize are the best precursors for maize, cultivated for grain under strip-till technology. Growing maize after sunflower annually led to a significant decrease in crop yields. N66P32K32 turned to be the best rate of mineral fertilizers. Seeding rate of 60 thousand seeds per ha was optimal for early maize hybrids. It was found that total water consumption over the three-year period was 2653 m³/ha with fertilizer rate N66P32K32, and corn and sunflower rose to 2,700 and 2,695 m³/ha. At N66P32K32, winter wheat plants used moisture most economically. The water consumption coefficient, which shows moisture consumption for creation of a ton of produce, was 421.0 m3/t. For corn, it increased by 34.1, and for sunflower by 247.7 m³/t. In control after all precursors, moisture consumption per ton of grain sharply increased: according to winter wheat, water consumption coefficient was equal to 551.9 m³/t, corn and sunflower were 53.0 and 360.1 m³/t more. The maximum values of dry matter accumulation in 2013 and 2015 were recorded at flowering stage: depending on precursor, after winter wheat - 9.07 and 7.24 t/ha, after maize - 8.67 and 6.77, and after sunflower - 6.64 and 4.76 t/ha, respectively. Over the research years the largest daily increasing of dry biomass during germination-flowering was observed after winter wheat - 452 and 361 kg/ha, decreased slightly after corn - 432 and 337 kg/ha, and a significant decrease was noted after sunflower - 331 and 237 kg/ha. In arid 2014 season, during the period of precipitation deficit, the indicators were significantly lower. The best yield results were obtained in more favorable 2013 and 2015 research years. The studies showed that the best maize precursor was winter wheat - 5.524 t/ha. The lowest yield was obtained after sunflower - 3,456 t/ha. Moreover, maximum yield was achieved at fertilizer application N66P32K32 - 5.324 t/ha, N50P16K16 - 4.813 t/ha and in the control - 4.015 t/ha.

Soils of the southern region of Chad are developed on wind-drawn sand and colluvio-alluvium deposits of two main rivers Logone and Chari. This region of Chad is principal agricultural zone of Chad. Evaluation of physical and chemical properties of sandy soils and their fertility in this region revealed that some soils have very high content of strontium. With aim to locate areas with high content of srontium in soil, and to study its dependence on physical properties of soil and translocation of strontium in soil profile nine pedons were dug on different fields intensively used for agricultural production. Using X-ray spectrometric analysis and radiometric measuring of soil samples it has been revealed that Sr content in soil samples varies from 10 to 270 mg/kg of soil depending on type of soil, depth of soil layers, clay and organic content. Strontium content negatively correlates with total content of calcium and phosphorus in layers of soil. Low CEC of soil may be a reason of translocation of strontium from higher to lower layers of soils. Strontium content in soils do not relates with level of radioactivity of soils under study. The highest content of strontium has been found in soils developed on colluvio-alluviumdeposits. Very wide Ca/St ratioin soil samples of alluvial hydromorphic soils may cause increase of Sr content in vegetable food and drinking water. This may be one of etiological factors which directly or indirectly may cause misbalance in mineral nutrition and severe diseases of a man. It worth of considering necessity of further studies of Sr dynamic in soils under different crop production systems and how to mitigate negative effect of natural pollution of soils with this element.