INTRODUCTION

The main economic crops cultivated on more than 80% of arable lands in the Central Chernozem Region are winter wheat, spring barley, corn maize, sunflower, soybeans, sugar beet, green maize, peas, and buckwheat. The average share of lands used for cultivation of the most important grain crops (winter wheat and spring barley) varied over the last 10 years from 38% in Belgorod oblast to 47% in Kursk and Tambov oblasts. On average, 17.4% of lands used for cultivation of winter wheat, barley, and corn maize nationwide are located in the Central Chernozem Region. In 2012–2019, some 33.3% of corn grain, 18.8% of winter wheat, and 26.7% of barley were produced in the Central Chernozem Region. In recent years, the climatic conditions in the region changed significantly [1, 2], which can affect its bioclimatic potential [3]. The climatic [4, 5], soil, and agrotechnical conditions have the greatest effect on the yield of agricultural crops and arable land productivity; therefore, preliminary assessments of agroclimatic productivity resources [6, 7] and comprehensive soil quality assessments are mandatory elements of soil fertility management and rational use of agricultural resources.

The purpose of this study was to perform a comprehensive analysis of natural, soil–climatic, and agrotechnical conditions determining the yield of main crops cultivated in the Central Chernozem Region.

MATERIALS AND METHODS

The works were performed at the Agrochemistry and GIS Laboratory, Kursk Federal Agricultural Research Center, and included the systems analysis of the conjugated complex of agroclimatic and soil parameters, agrochemical properties, and crop productivity. The study uses data provided by the Federal State Statistics Service for Belgorod, Voronezh, Kursk, Lipetsk, and Tambov oblasts [8]. The yield productivity of cultures occupying the greater part of cultivated lands in the Central Chernozem Region (winter and spring wheat, barley, oats, maize, sugar beet, sunflower, buckwheat, peas, and soybeans), as well as fertilization, were taken into account. Data on the heat and moisture supply were taken from the weather records [9]. The agroclimatic potential of arable land productivity was computed on the basis of average annual values of agroclimatic heat and moisture resources during the active growing season and the potential consumption of productive moisture [10]. A comprehensive soil quality assessment was performed for arable lands taking into account agrochemical properties and using approaches presented in earlier studies [11].

To assess the production capacity of arable lands in oblasts of the Central Chernozem Region, sequential computations of the basic yield productivity (YPb) that can be achieved without the application of fertilizers and the actually possible yield (APY) of agricultural crops were performed based on a comprehensive assessment of agrochemical parameters and the climate-assured yield (CAY) taking into account the average annual agroclimatic parameters.

$${\text{Y}}{{{\text{P}}}_{{\text{b}}}} = {{{\text{C}}}_{{\text{A}}}}{\text{CAY}}\frac{{{\text{S}}{{{\text{F}}}_{i}} - {\text{S}}{{{\text{F}}}_{{\min }}}}}{{{\text{S}}{{{\text{F}}}_{{\text{A}}}} - {\text{S}}{{{\text{F}}}_{{\min }}}}},$$
(1)
$${\text{APY}} = {\text{Y}}{{{\text{P}}}_{{\text{b}}}} + ({\text{S}}{{{\text{F}}}_{i}} - {\text{S}}{{{\text{F}}}_{{\min }}})\frac{{{\text{CAY}} - {\text{Y}}{{{\text{P}}}_{{\text{b}}}}}}{{{\text{S}}{{{\text{F}}}_{{{\text{max}}}}} - {\text{S}}{{{\text{F}}}_{{\min }}}}},$$
(2)

where CA is the agrotechnics coefficient; CAY is the climate-assured yield of cultivated crops; and SFi, SFA, SFmax, and SFmin are the integral soil quality (fertility) scores: score of the assessed site, average score for the study area, maximum score, and minimum score, respectively.

The agricultural production dynamics was assessed based on the absolute variation parameters of levels of crop yield time series (mean linear and square deviations) as well as relative characteristics: the stability coefficient of the statistical series levels and the stability parameter of the crop dynamics trend (i.e., correlation index reflecting the conjugation degree between the yield variation and the totality of factors that increase the yields over time [12–14]).

RESULTS AND DISCUSSION

Analysis of the agroclimatic conditions in the Central Chernozem Region over the period of 1960–2019 shows that, in terms of heat supply, its oblasts form the following series: Tambov < Lipetsk < Kursk < Belgorod < Voronezh (Table 1). In terms of moisture supply, the greatest numbers of years with optimal conditions were registered in Belgorod (60.3%), Kursk (53.4%), and Lipetsk (63.2%) oblasts; the greatest numbers of arid years were in Voronezh (46.6%) and Tambov (48.3%) oblasts.

Table 1.   Agroclimatic conditions in oblasts of the Central Chernozem Region (1960–2019)
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Integral agroclimatic parameters (i.e., HTC) reflect the yield formation conditions more objectively. According to our data, the optimal HTC levels were registered most often in Belgorod and Lipetsk oblasts (60.3–63.2% of years) and less often in Tambov and Voronezh oblasts (44.8% of years in both federal subjects).

In 1996–2019, the highest arable land productivity per harvested area in all categories of farming enterprises (grain yield units per ha) was registered in Belgorod (1700–5300) and Kursk (1400–5600) oblasts, while the lowest productivity was in Lipetsk (1500–4900), Voronezh (1300–4500), and Tambov (1300–4400) oblasts. It is necessary to note a significant yield increase trend registered for all agricultural crops in recent years. The observed changes in the dynamics are closely related to weather conditions and reflect both dry and excessively wet periods (Fig. 1).

Fig. 1.
figure 1

(a) Arable land productivity dynamics and (b) periodicity of changes in the yield in relation to the hydrothermal conditions in the period with temperatures over 10°C.

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The results of spectral analysis indicate that the periodicity of changes in the annual humidity index and the Selyaninov hydrothermal coefficient (HTC) is 4–5 and 11–12 years, respectively. The parabolic correlation between the arable land productivity and HTC reaches the point of extremum at HTC = 1.32.

Due to the significant effect of mineral nutrition conditions on the yield of agricultural crops [15], it is necessary to take into account the arable land saturation with fertilizers (kg of NPK primary nutrients (p.n.) per ha) as a production intensification parameter.

Overall, the arable land productivity dynamics (grain yield units per ha) in districts constituting oblasts of the Central Chernozem Region can be described by the following dependence:

$${\text{Y}} = -11.0 + 1.17{{{\text{X}}}_{1}} + 36.7{{{\text{X}}}_{2}}-13.96{\text{X}}_{2}^{2} + 0.066{{{\text{X}}}_{3}},$$
$${\text{F}} = 168.1,\,\,\,\,{\text{R}} = 0.93,\,\,\,\,p < {{10}^{{-4}}},$$

where X1 is the time series ordinal number (1–60, 1960–2019), X2 is the Selyaninov hydrothermal coefficient, and X3 is the amount of fertilizers (kg of NPK p.n. per ha).

The average annual increase in arable land productivity with time amounts to 120 grain yield units per ha due to the improvement of agrotechnics and strain renovation. The application of 1 kg of primary nutrients increases the productivity by 6.6 grain yield units.

In 2012–2019, the climate-assured arable land productivity level in oblasts of the Central Chernozem Region varied from 3400 to 7100 grain yield units per ha (14.5%) (Fig. 2, Table 2). Based on the hydrothermal conditions determining the climate-assured arable land productivity, oblasts of the Central Chernozem Region can be arranged in the following order: Kursk (5400–7100) > Belgorod (4200–6300) > Lipetsk (5000–6100) > Tambov (4200–5600) > Voronezh (3400–6200 grain yield units per ha).

Fig. 2.
figure 2

Climatic potential of arable land productivity in oblasts of the Central Chernozem Region (thousand grain yield units per ha).

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Table 2.   Climatic and soil parameters in oblasts of the Central Chernozem Region (2012–2019)
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The quality of soils in the Central Chernozem Region is primarily determined by the content of mobile phosphorus and potassium and acidity. In terms of the integral soil fertility score (Fig. 3, Table 2) oblasts of the Central Chernozem Region form the following series: Belgorod (84.60 ± 4.30) > Voronezh (79.40 ± 3.90) > Kursk (77.40 ± 8.36) > Lipetsk (74.50 ± 4.30) > Tambov (72.80 ± 6.40).

Fig. 3.
figure 3

Distribution of districts constituting oblasts of the Central Chernozem Region by the integral soil fertility score.

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The actually possible yield productivity in oblasts of the Central Chernozem Region varies from 2890 to 6110 grain yield units per ha (15.1%). Based on this parameter (Fig. 4, Table 2), the oblasts can be ranked as follows: Kursk (5.22 ± 0.41) > Belgorod (5.15 ± 0.46) > Voronezh (4.08 ± 0, 54) > Lipetsk (4.77 ± 0.22) > Tambov (4.03 ± 0.41 grain yield units per ha).

Fig. 4.
figure 4

Actually possible yield productivity of arable lands in oblasts of the Central Chernozem Region (thousand grain yield units per ha).

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The territorial variation of the actual crop yields is determined by differences in the sets of natural and anthropogenic factors (Table 2). Production intensification analysis performed for the period of 2012–2019, taking into account the saturation of arable lands with mineral fertilizers (kg of NPK p.n. per ha), shows that the effects caused by fertilization or by the increasing soil quality are manifested consistently with the climatic productivity potential. This is reflected in the positive interaction of the above factors. The economic return of fertilizers on soils richer in nutrients decreases, which is reflected in negative interactions (Tables 3, 4).

Table 3.   Average yields of main agricultural crops in the period of 2012–2019 in oblasts of the Central Chernozem Region (centners per ha)
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Table 4.   Relationships between yields of agricultural crops and agroclimatic, soil, and agrotechnical factors in the Central Chernozem Region
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The yield of agricultural crops is formed by the interaction of natural and agrotechnical factors. The strength of the relationship between this parameter and the computed actually possible yield (APY) is determined by statistically significant paired correlation coefficients (R = 0.49–0.80). Analysis of dynamic yield series for the period of 1996–2019 shows that agricultural crops cultivated in the Central Chernozem Region can be arranged based on their stability coefficients (%) into the following increasing series: peas (72.2) < buckwheat (72.9) < soybeans (74.2) < maize (74.6) < winter wheat (79.9) < barley (80.1) < sugar beet (82.2) < sunflower (83.9); this order is primarily determined by the biology of the crops and duration of the active growing season. Concurrently, crops that underwent greater genetic changes and strain renovation are distinguished by both their stability degree and by the long-term yield growth dynamics (based on the correlation index): peas (0.641) < winter wheat (0.729) < barley (0.755) < buckwheat (0.771) < soybeans (0.845) < maize (0.851) < sugar beet (0.889) < sunflower (0.931).

CONCLUSIONS

Agroclimatic conditions are among the main factors determining territorial differences in the stability of agricultural production and its growth dynamics. Based on the stability of the yield growth trend, oblasts of the Central Chernozem Region form the following hierarchy: Kursk (0.865) > Belgorod (0.815) > Voronezh (0.795) > Tambov (0.793) > Lipetsk (0.740).

Variations in crop yields in the Central Chernozem Region are determined by the cumulative effect of climatic conditions, agrotechnics, and soil quality (the multiple correlation coefficient R = 0.52–0.81). The analysis of natural productivity resources makes it possible to rank the territorial objects in accordance with the priority of measures required to increase the soil fertility, enhance the structure of cultivated lands, and optimize the agrotechnics.