The efficiency of using different fertilization systems in dryland and irrigated crop rotations on ordinary carbonate chernozems of the Central Ciscaucasia

The search for the rational use of fertile irrigated land in the steppe zone of Central Ciscaucasia and the determination of factors for the sustainable production of crop products, provided that soil fertility is maintained, remained as valid today as ever. The relevance of research is also increasing due to changes in climatic characteristics in specific agro-landscape conditions, including, an increase in average daily and annual air temperatures by 2 - 50С. The novelty of research is the establishment of the most efficient fertilization systems in dryland and irrigated conditions to increase winter wheat yields, to increase the productivity of 1 ha of crop area, as well as to maintain and reproduce soil fertility and to increase the productivity of irrigated crop rotation. The article contains the research results on the use of different fertilization systems and their influence on winter wheat yields and crop rotation productivity in dryland and irrigated agriculture on ordinary carbonate chernozems in specific agro-landscape, soil and climatic characteristics of the Central Ciscaucasia.


Introduction
Intensive use of arable land and accelerated mineralization of organic matter, together with a sharp decrease in the use of organic and mineral fertilizers, irrational use of irrigation water and an insufficient share of perennial grasses in crop rotation leads to a general decline in soil fertility and, as a result, a decline in crop yields and crop rotation efficiency [1]. In this regard, farming systems are focused on evidence-based crop rotation systems that reduce production costs, improve soil fertility, regulate the food, water and air regimes of the soil, without requiring additional material costs, which is very important for producing environmentally friendly crop products and reducing their cost [2].
Corresponding author: kbniish2007@yandex.ru  79  67  65  59  65  65  65  84  83  70  67  70  60  67  76  88  67  76  88  81  75  71  70  75  64  63  61  70.3   74  82  88  90  89  86  84  74  72  69  67  69  74  89  86  84  74  72  69  74  82  88  74  82  88  89  86  84  74  72  69  67  69  74 3 Results and discussion During the autumn of 2018 (from September to December inclusive), 51.2 mm of precipitation fell at a rate of 110.7 mm, which did not even allow winter wheat to grow in autumn, despite the optimal planting time. The scarcity of soil moisture was apparently not enough for wheat seed germination and smooth and timely sprouts. No snow cover was formed and was observed for only 1-3 days. The sprouts emerged slowly from late January through February and developed poorly. The yield of Cheget winter wheat in the option 1 -without fertilizer and irrigation (control) -after 69 years of the experiment averaged 18.6 dt/ha (Table 2), and for three different predecessors: alfalfa, maize, sunflower, it was almost identical, which is statistically proven. Recommended fertilization systems: mineral and organo-mineral in non-irrigated conditions (options 2 and 3), in 2018 provided, on average, a higher yield of Cheget winter wheat (51.3 and 58.4, respectively) than wheat yield in similar irrigated crop options (options 5 and 6) by 3.2-2.8 dt/ha, which is mathematically reliable, and is explained by the fact that soil fertility in dryland options is undoubtedly higher than in irrigated options, and the weather conditions favorable for winter wheat made it possible to realize the advantage of a higher humus and nutrient content in the root layer of the soil to produce a higher yield.
The estimated fertilization systems in the irrigated crop rotation (options 7 and 8) provided an increase in crop yield compared to the recommended fertilization systems of 5.5-7.6 dt/ha, which exceeded the LSD05 by 2.5-2.7 times.
The highest grain yield of Cheget winter wheat 60.0-63.2 dt/ha, depending on the predecessor, is obtained in option 8 on the estimated organo-mineral fertilization system aimed at reproduction of soil fertility. In 2018, a large yield of winter wheat in this option was achieved on the alfalfa predecessor, which is mathematically reliable ( Table 2).
Not only weather conditions have contributed to this yield, but also better timely soil preparation, planting of crops in optimal time and compliance of other agricultural practices.
It was found that with an optimal combination of accompanying factors, the efficiency of the studied fertilization systems increased more than 2 times. Thus, in the dryland crop rotation in 2018, mineral and organo-mineral fertilization systems achieved crop rotation productivity of 33.1 and 38.0 dt.g.u/ha with an average of 40 years of research (1970-2016) -32.1 and 34, 4 dt.g.u/ha. At the same time, the productivity of crop rotation without fertilization and irrigation was equal to 17.4 dt.g.u/ha with average productivity of dryland unfertilized crop rotation of 17.2dt.g.u/ha.
The climatic characteristics of the 2009 growing season were also unfavorable for the growth, development and production of all field crops. The sprouts emerged slowly from late January through February and developed poorly. From January to March 2019, precipitation fell only 58.1 mm, which was also less than the long-term average annual amount (63.3 mm) with temperatures significantly exceeding long-term ones by 3-40С. From April to August, 208.6 mm of precipitation fell, with a norm of 291.7 mm. Temperatures during the summer months were from 2.4 to 5.3о higher than the long-term average annual temperature, which contributed to the water scarcity for all crops. The relative air humidity in all months of growing season was less than the annual average by 2-14%. June 2019 was particularly unfavorable for climatic characteristics (Table. 1).
Such changes in climatic characteristics indicate a tightening of dryland cultivation conditions in comparison with previous decades. Low precipitation and high air temperatures are not only responsible for soil and air drought, but also for reduced crop yields.
The yield of Cheget winter wheat in option 1, without fertilizer and irrigation, after 70 years of the experiment averaged 19.8 dt/ha. In option 4, without fertilizers in irrigation, its average yield was 21.4 dt/ha (Table 3). In the non-irrigated crop rotation of the experiment in 2019, the influence of predecessors on winter wheat yields: alfalfa, maize, sunflower, was almost the same, the changes in yield indicators for all studied fertilization systems did not exceed the smallest significant difference.
Recommended fertilization systems: mineral and organo-mineral in non-irrigated conditions (options 2 and 3) provided, on average, lower winter wheat yields in 2019 than wheat yields in similar irrigated crop options (options 5 and 6) by 0.7 and 2.1 dt/ha, respectively, which is mathematically reliable (Table 3). Based on a comparative estimation of the soil fertility in these options under dryland and irrigated conditions, when the soil fertility in the dryland options, undoubtedly better, weather conditions unfavorable to winter wheat did not allow to realize the advantage of sufficient humus and nutrients in the root soil layer to produce a higher yield, since the decisive factor in its formation in an extremely dry year was the provision of plants with moisture.
The estimated fertilization systems in irrigated crop rotation, options 7 and 8, provided an increase in crop yield compared to the recommended fertilization systems of only 1.7-1.8 dt/ha, which exceeded the LCD05 for fertilizers by 2.3 times.
The highest grain yield of Cheget winter wheat is 38.7-39.2, i.e. 1.5 times less than in the previous year, depending on the predecessor, produced in option 8 on the estimated organomineral fertilization system aimed at reproduction of soil fertility. In 2019 the winter wheat yield in this option was almost the same for all studied predecessors, the difference in yield did not exceed the least significant difference for this factor (Table. 3). The importance of grain crop yields for crop rotation and crop rotation productivity in non-irrigated conditions in different years confirms their dependence on the amount of precipitation during the growing season and the year as a whole.
Without irrigation, the efficiency of the used fertilization systems is low. With the systematic use of the recommended mineral fertilizers N69Р63К45 (option 2) to the crop rotation culture in 2019, the crop rotation productivity was increased by 4.9 dt.g.u./ha to control or 75.4%. The systematic use of the organo-mineral fertilization system (option 3), manure 8 t/ha + N44P42K24, provided the increase in the productivity of dryland crop rotation 6.6 dt.g.u/ha to control or 101.5%.
The productivity of 1 hectare of crop rotation without fertilizers under irrigation (option 4) in 2019 was 19.6 dt.g.u. Irrigation increased the efficiency of the recommended mineral (option 5) and organo-mineral (option 6) fertilization systems and increased the annual average productivity of irrigated crop rotation by 55.6 and 86.7%, respectively, compared to the option without fertilizers in irrigation, and 3.7 and 4.6 times compared to the control, without fertilizer or irrigation. The use of estimated fertilization systems, mineral and organo-mineral (to preserve and reproduce soil fertility and to obtain the productivity of irrigated crop rotation 52-53 dt.g.u/ha) increased the productivity of 1 ha in irrigation by 71.4% and 132.7% respectively compared to the option 4, without fertilizer in irrigation (Table 5) and 4.2 and 6.0 times compared to control.
In 2019, the productivity of crop rotation without irrigation was significantly (almost 3 times) less than the long-term average annual productivity.
In 2020, the research results also confirmed the dependence of crop yields and productivity of non-irrigated crop rotation, primarily on the amount of precipitation during the growing season and the year as a whole, and then on the conditions of mineral nutrition.
From January to March 2020, precipitation fell 42.4 mm, which is 20.9 mm less than the long-term precipitation for the same period, at temperatures exceeding long-term ones. From April to August, 282.9 mm of precipitation fell, with a norm of 291.7 mm. The temperatures during the summer months were 0.7-3.8о higher than the average long-term temperature, which contributed to the development of moisture deficiency for spring crops.
The yield of Yuzhanka winter wheat in 2020 with fertilization without irrigation was relatively high, as against the other crop rotations, which was achieved due to the biological characteristics of the crop and its ability to efficiently use of available soil moisture.
In option 1, without fertilizer or irrigation, after 71 years of the experiment (Table 4), yields averaged 18.2 dt/ha and for three different predecessors: alfalfa, maize, sunflower, it was almost the same, which is statistically proven. In option 4, without fertilizers in irrigation, its average yield was 19.1 dt/ha.
Recommended fertilization system: mineral in non-irrigated conditions (option 2) in 2020, provided, on average, a lower yield of Yuzhanka winter wheat of 32.9 dt/ha than wheat yield in a same version of irrigated crop rotation (option 5 -34.3 dt/ha) by 1.4 dt/ha. The estimated fertilization systems in irrigated crop rotation, options 7 and 8 (33.1 and 39.7 dt/ha), provided an increase in crop yield compared to the recommended fertilization systems of 1.2-3.0 dt/ha.
The highest yield of Yuzhanka winter wheat grain is 38.0-39.7 dt/ha, depending on the predecessor, produced in option 8 from the estimated organo-mineral fertilization system aimed at reproduction of soil fertility (Table 4). In 2020, high yield of winter wheat in this option was achieved by the maize predecessor, which is mathematically relevant.