Assessment of humus and nitrate content in soils and dynamics of their changes in the conditions of agricultural work in Kostanay region

Avaliação do teor de húmus e nitrato nos solos e dinâmica das suas alterações nas condições de trabalho agrícola na região de Kostanay

Abstract

The goal of the study was to assess the humus and nitrogen status of the main arable soils of Kostanay region and to identify signs of soil degradation associated with long-term agricultural use. The research was based on the generalization of long-term agrochemical monitoring data (2012–2023) and included the analysis of humus content and nitrate nitrogen in ordinary and southern black soils, as well as dark chestnut soils, using standard laboratory methods and statistical evaluation of spatial and vertical variability. The results showed that the humus content in arable soils is generally reduced compared to virgin analogues and corresponds mainly to medium- and low-humus levels, with clear differentiation across soil types and administrative districts. Nitrate nitrogen availability was found to be low or very low in a significant proportion of agricultural lands, indicating insufficient plant nutrition and ongoing depletion processes. The study also revealed spatial variability of agrochemical indicators and a predominantly accumulative profile distribution with maxima in the arable horizon. In conclusion, the obtained results confirm the development of degradation processes in the soils of Kostanay region and highlight the need for systematic soil monitoring and the implementation of sustainable land management practices aimed at restoring soil fertility and maintaining agricultural productivity.

Keywords:
agrocenoses; agrochemical indicators; common black soil; southern black soil; darkchestnut soils

Resumo

O objetivo do estudo foi avaliar o estado do húmus e do nitrogênio nos principais solos aráveis da região de Kostanay e identificar sinais de degradação do solo associados ao uso agrícola de longo prazo. A pesquisa baseou-se na generalização de dados de monitoramento agroquímico de longo prazo (2012–2023) e incluiu a análise do teor de húmus e do nitrogênio nitrato em solos negros comuns e do sul, bem como em solos castanho-escuros, utilizando métodos laboratoriais padronizados e avaliação estatística da variabilidade espacial e vertical. Os resultados mostraram que o teor de húmus nos solos aráveis é, em geral, reduzido em comparação com seus análogos virgens e corresponde principalmente a níveis médios e baixos, com clara diferenciação entre tipos de solo e distritos administrativos. A disponibilidade de nitrogênio nitrato foi considerada baixa ou muito baixa em uma proporção significativa das terras agrícolas, indicando nutrição insuficiente das plantas e processos contínuos de esgotamento. O estudo também revelou variabilidade espacial dos indicadores agroquímicos e uma distribuição de perfil predominantemente acumulativa, com máximos no horizonte arável. Em conclusão, os resultados obtidos confirmam o desenvolvimento de processos de degradação nos solos da região de Kostanay e destacam a necessidade de monitoramento sistemático dos solos e da implementação de práticas sustentáveis de manejo da terra voltadas à restauração da fertilidade do solo e à manutenção da produtividade agrícola.

Palavras-chave:
agrocenoses; indicadores agroquímicos; solo negro comum; solo negro do sul; solos castanho-escuros

1. Introduction

Land degradation is one of the major global problems of the 21st century and a serious threat to agricultural production, caused by the combined impact of natural and anthropogenic factors. Among the main human-induced drivers are agricultural intensification, expansion of arable land, irrational land use, deforestation, and climate change. These processes lead to desertification, erosion, salinization, acidification, dehumification, agricultural depletion, and declining productivity. According to UNEP, about 33% of the global land surface is degraded to some extent. Arid regions of Asia, Africa, Australia, and North America are particularly vulnerable. Each year, the area of degraded soils continues to increase, and signs of degradation are observed in about 30% of forests, 20% of agricultural land, and more than 10% of pastures.

The stable functioning of agriculture is essential for food security and national stability. In Kazakhstan, Kostanay region is one of the main agricultural regions due to its favorable soil and bioclimatic conditions. At the same time, the issue of sustainable and safe land use is especially important here, since the average share of agricultural land reaches 56%, while in some farms it rises to 99%, and the share of arable land may exceed 90% of the total area. Under such conditions, a comprehensive assessment of agricultural soils is necessary for the development of balanced land management strategies. Thus, this study aims to evaluate the humus and nitrogen status of the principal arable soils of Kostanay region and to determine the extent of soil degradation resulting from prolonged agricultural use.

In Kostanay region, the area of land used in agriculture is 11.073 million ha (Republic of Kazakhstan, 2023b). Arable land (6.346 million ha) and pastures (4.376 million ha) together account for 96.8% of all agricultural land. The total sown area reaches 5.258 million ha, or 22.7% of the total sown area of Kazakhstan (BNS, 2023). The region annually produces more than 54 million centners of cereals and legumes, about 25% of the country’s total output, and over 5 million centners of oilseeds, about 17% of national production.

The soil cover of Kostanay region includes both highly fertile soils and soils that are more sensitive to degradation under agricultural pressure. The main agricultural soils are ordinary and southern black soils (Calcic Black soils) and chestnut soils (Gypsic Kastanozems) (IUSS, 2022). In many areas, these soils are also affected by salinization, forming saline (Sodic) varieties within each subtype (Baisholanov, 2017; IUSS, 2022).

Agrochemical surveys in Kostanay region are conducted annually on 804–1173 thousand ha of arable land (Ministry of Agriculture of the Republic of Kazakhstan, 2020, 2021, 2022, 2023a). Two types of monitoring are used: production and scientific. Production monitoring, conducted by the state agrochemical service, covers agricultural lands periodically and focuses on key agrochemical indicators such as humus, easily hydrolyzed nitrogen, and mobile phosphorus and potassium. Scientific monitoring is carried out on the fields of agricultural research institutions and includes a wider range of soil properties (Saparov et al., 2017).

2. Methods

2.1. Methods for determining agrochemical and physico-chemical properties of soils

To determine the agrochemical and physico-chemical quality indicators of soil samples from arable lands of Kostanay region, control methods were used that meet the regulatory requirements of the state system for ensuring the uniformity of measurements of the Republic of Kazakhstan.

Determination of the limits of agrochemical and physico-chemical parameters of soils was carried out in the conditions of accredited research and testing laboratories. In order to ensure the reliability of research results, some of the measurements of soil samples were carriedout in specialized centers accredited in accordance with GOST ISO/IEC 17025-2019 (Russia, 2019) or in laboratories that have .

Determination of the content of soil organic matter (humus) was carried out by the Tyurin method, which is based on the oxidation of organic matter with a solution of potassium dichromate in sulfuric acid, followed by the determination of trivalent chromium equivalent to the content of organic matter on a spectrophotometer (Russia, 1991). Measurement range: 0.1-15.0%, relative error – 10%.

3. Results

3.1. Assessment of humus content in soils of agricultural lands of Kostanay region

3.1.1. Vertical distribution of humus in the main types and subtypes of arable soils of Kostanay region

As a result of soil studies conducted in 2012-2023 on agricultural lands of the Kostanay region, morphological and chemical properties of horizons were studied by profiles of the main types and subtypes of soils (Abdykhalykov et al., 2012; Almanova et al., 2021, 2023; Dzhalankuzov, 2014; Dzhalankuzov and Nazanova, 2015; Kenzhegulova et al., 2022, 2023). Reference soilsections and humus distribution profiles for ordinary black soil were studied at the Karabalyksky hospital, for southern black soil – at the Talapkersky hospital, and for dark chestnut soil-at the Kamystynsky hospital.

Ordinary black soils of the Karabalyksky station are characterized by a fairly high humus content (Figure 1), the amount ofwhich in horizon A is 7.8-8.0%, in the underlying horizons B1 and B2 gradually decreases to 4.3 and 2.7%, respectively, while the revealed thickness of the humus-containing layer (horizons A+AB) of the horizon averages 56 cm (Dzhalankuzov, 2014). Southern black soils of the Talakpersky station (22 km south of Kostanay) were characterized by an average humus content of 5.8% in the upper horizon A% with a sharp decrease in this indicator down the profile (Dzhalankuzov and Nazanova, 2015). The thickness of the humus horizon in the studied southern black soil profile was heterogeneous,gorizont A was isolated within the 0-20cm layer, and humushorizon AB lies to a depth of 50-55cm. The humus content in the upper horizon A of the arable dark chestnut soil studied in the Kamystyn region (Almanova et al., 2023) was low, amounting to about 2%. In the underlying horizons B1 and B2, it decreases to 1%. In the studied sections of dark chestnut soils, the depth of humus horizons A+AB was 29-34-cm.

Figure 1
Vertical distribution of humus content in the profiles of ordinary black soil, southern black soil and dark chestnut soil on agricultural lands of Kostanay region, according to stationary studies (Almanova et al., 2023; Dzhalankuzov, 2014; Dzhalankuzov and Nazanova, 2015).

Thus, in terms of the average content and profile distribution of humus, arable black soils and chestnut soils, on the one hand, and subtypes of arable black soils of ordinary and southern, on the other, differ significantly from each other, which confirms the decisive contribution of the natural component to the formation of the level of soil fertility.

3.1.2. Spatial variation of humus content

Spatial variability of agrochemical indicators in the arable horizon on individual agricultural lands was studied by employees of the Agricultural Experimental Station "Zarechnoye" in the Fedorovsky and Kostanay districts of the Kostanay region (Abuova et al., 2019, 2022; Tulkubaeva et al., 2020, 2022). The obtained statistical indicators of variation in the humus content characterize the average level, range, and coefficient of variation (Table 1). On all the studied agricultural lands, the spatial distribution of humus content in the arable horizon satisfies the normal law according to the results of statistical testing and according to the Wilk-Shapiro criterion (at the significance level p=0.05).

Table 1
Statistical characteristics of the variability of humus content (%) in the arable horizon of ordinary and southern black soils on certain agricultural lands of Kostanay region.

District, soil	Economy, field	Sample size	Average	Minimum	Maximum	Coefficient of variation, %
Fedorovsky, Troyana common black soil	“Trojan”	21	4.77	4.35	5.27	5.6
Kostanay, Lugovoye southern black soils	No. 11704	15	2.77	1.92	3.75	19.4
	“Lugovoye”, No. 14	13	3.20	2.73	3.72	8.4
	“Zarechnoye”, No. 91	39	3.29	2.64	3.96	10.8
	“Zarechnoye”, No. 132	30	3.74	3.32	4.15	6.1
	“Zarechnoye”, No. 133	35	3.31	2.82	4.07	9.1

At the same time, in the semiarid conditions of the Fedorovsky district with ordinary black soils, the minimum, average and maximum levels of humus content in the arable horizon correspond to the average gradation of humus content (4-6%). At the same time, in the arid conditions of the Kostanay region - with southern black soils, these statistical parameters for the studied agricultural fields are in the gradation of low humus content (2-4%). On all the surveyed are as of arable agricultural land, the effects of variation in the humus content dare residual low, which suggests a predominantly geogenic nature of the formation of spatial heterogeneity of the indicator against the background of a uniformly distributed agrogenic load. Indeed, in the course of agrotechnical tillage of the soil in the arable horizon, as a rule, there is an alignment of properties in the vertical and lateral directions.

3.1.3. Humus content in arable soils of Kostanay region

The soil cover of Kostanay region is confined to natural zones that change in accordance with the law of latitudinal zonation from steppe to semi-desert. Agrochemical studies conducted on the main subtypes of arable soils in Kostanay region (Ismuratov et al., 2020) revealed humus content levels for agricultural land in various administrative districts.

In the northern administrative regions of Kostanay region, the common black soil subtype dominates: Karabalyk (with an area of 6.9 thousand^km2), Uzunkolsky(7.2 thousand^km2), Fedorovsky (7.2 thousand^km2), Mendykarinsky (6.6 thousand^km2), Sarykolsky (6.1 thousand^km2) (Medeu, 2006). The highest levels of humus content in the upper horizon of arable land were recorded in Uzyuznkolsky district-on average about 5.1% (Figure 2a), while the range of variation of this indicator is quite narrow: from 4.85 to 5.36%. However, lower levels of humus content were observed in three other districts (Karabalyk, Fedorovsky, and Sarykolsky) with arable common black soils, where the crednande values were equal to 4.50-4.58%. Such average levels, maximum and minimum values of humus content in the arable horizon for Uzunkulsky, Karabalyksky and Sarykolsky districts belong to the gradation of medium-humus (4-6-6%) soils. Fields with a high (6-8%) level of humus content of the arable horizon. Contradicts the data in Section 3.1.2 and Table 1.

Figure 2
Mean values (Mean), standard deviation (SD), minimum (Min) and maximum (Max) values of humus content in the arable soil horizon in various districts of Kostanay region: (a) on ordinary black soils; (b) on southern black soils; (c) on dark chestnut soils, and their comparison with humus content levels (medium, low, very low) (according to Ismuratov et al., 2020).

Arable black soils of the Fedorovsky district are characterized by a large range of the indicator of the content of soil organic matter between individual surveyed points. It is possible that the marked minima of the indicator mark the areas of distribution of arable southern black soils on the territory of the region, which are characterized by an average availability of humus.

Much lower levels of humus content were recorded in arable soils of the Mendykarinsky district: the average level is 3.42%, the minimum level is 2.82%, corresponding to the gradation of low-humus (2-4%) soils. At the same time, on some lands of this region, average humus arable horizons of ordinary black soils are also noted, this is evidenced by the upper limit of the standard deviation (SD) and the maximum value of 4.68% (Figure 2a). Thus, in the subzone of the distribution of ordinary black soils in the territory of Kostanay region, the following series of areas was recorded for reducing the average humus content in the arable horizon: agricultural soils: Uzunkulsky > Karabalyksky > Fedorovsky > Sarykolsky > Mendykarinsky.

The southern black soil subtype dominates the soil cover of the central part of Kostanay oblast in six administrative districts: Altynsarinsky (with an area of 6.2 thousand^km2), Kostanay (7.5 thousand^km2), Denisovsky (6.8 thousand^km2), Beimbet Mailina (formerly Taranovsky) (7.6 thousand^km2), Zhitikarinsky (7.3 thousand km²), Karasusky (12.8 thousand^km2). The average humus content in the arable horizon for all regions of the southern black soil subzone belongs to the category of low-humus (2-4%) soils (Figure 2b). By decreasing the average value of humus content in the arable horizon, these regions form the following series: Denisovsky > Kostanay > Zhitikarinsky > Karasusky > Altynsarinsky > Taranovsky. In Denisovsky and Kostanay districts, about 15-20% of arable soils belong to the category of medium-humus (4-6%). In the Zhitikarinsky and Taranovsky districts, no medium-humus soils were found in the composition of agricultural land. The largest variation in the humus content in the arable horizon is observed on agricultural lands of Denisovsky and Kostanay districts. Minimum levels of humus content in the arable horizon of southern black soils, which amounted to only 2.6-2.7%, were recorded on separate agricultural lands in Denisovsky and Altynsarinsky districts (Figure 2b).

The subtype of dark chestnut soils dominates the soil cover in three administrative districts: Auliekolsky (with an area of 11.1 thousand^km2), Kamystinsky (12.1 thousand^km2), and Naurzumsky (15.2 thousand^km2). Humus levels in the arable horizon of dark chestnut soils in these areas correspond to low-humus (2-4%) soils (Figure 2c). In the Auliekolko district, about 15% of the surveyed lands are characterized by very low (<2%) humus content. Dark chestnut soils had a lower natural thickness of the humus horizon than black soils, so arable land in the dry steppe zone lacks humus. By decreasing the average value of humus content in the arable horizon, the regions of the dark chestnut soil subzone form the following series: Kamystynsky > Naurzumsky > Auliekolkosky (Figure 2c).

3.2. Assessment of nitrate nitrogen content in arable soilsof Kostanay region

Nitrogen is the most important element of plant nutrition. The main part of soil nitrogen is part of the organic matter of soils – humus, at the same time, the main mineral forms of nitrogen are the direct source of plant nutrition: nitrates_(NO3⁻), nitrites (NO22−) and ammonium (NH4₄⁺). In agrochemical studies conducted in Kostanay region, in most cases only nitrate nitrogen was determined.

3.2.1. Vertical distribution of nitrate content in the main types and subtypes of arable soils of Kostanay region

The profile distribution of nitrates in black soils and dark chestnut soils of Kostanay region has been studied in a number of studies (Almanova et al., 2021, 2023; Kenzhegulova et al., 2022). The distribution of nitrates in the vertical profiles of black soils is accumulative; their highest content is observed in the upper arable horizon, which is determined by the intensity of the nitrification process, as well as-in part-by the introduction of nitrate fertilizers into arable soils (Figure 3). However, even in it, the nitrate content for ordinary black soil corresponds to a low level of security (10-20-mg/kg), and for black soils of southern and dark chestnut soils-very low (< 10 mg/kg). In the arable dark chestnut soil studied in Kamystyn district b (Almanova et al., 2023), a very low level of nitrate nitrogen content was recorded, while its distribution is fairly uniform.

Figure 3
Vertical distribution of nitrates in the profiles of ordinary black soil, southern black soil and dark chestnut soil on agricultural lands of Kostanay region, according to stationary studies (Almanova et al., 2021, 2023; Kenzhegulova et al., 2022).

3.2.2. Spatial variation of nitrate content

Spatial variability of the nitrate content in the arable horizon on certain agricultural lands was studied by employees of the Agricultural Experimental Station "Zarechnoye" in Kostanay and Fedorovsky districts of Kostanay region (Abuova et al., 2019; 2022; Tulkubaeva et al., 2020, 2022). Soils of all the agricultural areas studied showed a very low level of nitrate nitrogen supply (< 10 mg/kg) (Table 2). On one of the fields (#132 "Zarechnoye") the nitrate content in the arable horizon of southern black soil at all sampling points was below the detection limit <2.8 mg/kg. The coefficients of variation in the nitrate content ranged from 7.9 to 42.2%, indicating a low and medium degree of variation in this agrochemical indicator and the absence of pronounced loci of nitrifying or denitrifying microbiota in the studied soils, which can occur with uneven application of arable soils of mineral fertilizers.

Table 2
Statistical characteristics of the variability of nitrate content (mg/kg) in the upper arable horizon of agricultural soils on individual agricultural lands of Kostanay region.

District, soil	Economy, field	Sample size	Average	Minimum	Maximum	Coefficient of variation,%
Fedorovsky, Troyana common black soil	“Trojan”	21	4.8	2.8	8.7	28.5
Kostanay, Lugovoye southern black soils	No. 11704	15	5.9	4.6	9.8	26.3
	“Lugovoye”, No. 14	13	3.0	2.8	3.4	7.9
	“Zarechnoye”, No. 91	39	5.5	2.8	10.5	37.1
	“Zarechnoye”, No. 132	30	<2.8	<2.8	2.8	–
	“Zarechnoye”, No. 133	35	4.3	2.8	10.5	42.2

3.2.3. Nitrate content in arable soils by districts of Kostanay region

Agrochemical studies conducted on agricultural land in various administrative districts of Kostanay region revealed the levels of nitrate content in the arable horizon of the main soil subtypes (Ismuratov et al., 2020). Based on the results of this work, statistical characteristics of this indicator were calculated for all districts of Kostanay region (Figure 4).

Figure 4
Comparison with nitrate nitrogen availability levels (high, medium, low, very low) (Ismuratov et al., 2020). Mean levels (Mean), standard deviation (SD), minimum (Min) and maximum (Max) values of nitrates (_NO3) in the arable horizon of soils in various districts of Kostanay region: (a) on ordinary black soils; (b) on southern black soils; (c) on dark chestnut soils, and their derivatives.

In the subzone of common black soils, the average values of nitrate nitrogen content in the arable horizon of agricultural lands of the Uzof theUzykolsky district refer to a high level of security (>20 mg/kg), Sarykolsky district-to an average level of security (15-20-mg/kg), but in other areas they correspond to a low level of security (10-15-mg/kg) (Figure 4c). The lack of nitrate nitrogen (very low and low level of availability < 15 mg/kg) was detected for common black soils in the Karabalyk district-in 60% of the studied fields, in Mendykarinsky-in 100% of the studied fields, in Sarykolsky-in 50% of the fields, in Uzynkolsky-in 20% of the fields, in Fedorovsky - for 60% of the fields.

In the southern black soil subzone, the average values of nitrate nitrogen content in the arable horizon of agricultural lands of Karasu district relate to the average level of security (15-20-mg/kg), Altynsarinsky and Zhitikarinsky districts – to a low level of security (10-15-mg/kg), in other areas they correspond to a very low level (< 10 mg/kg). The deficit of nitrate nitrogen in the arable horizon with its very low level of supply (< 10 mg/kg) was recorded for southern black soils in Altynsarinsky district – for 30% of the studied fields, in Denisovsky district – for 80% of fields, in Zhitikarinsky-for 40% of fields, in Karasu-for 20% of fields, in Kostanay – on 65% of the fields, Taranovsky – on 80% of the fields (Figure 4b).

In the subzone of dark chestnut soils, the average values of nitrate nitrogen content in the arable horizon of agricultural lands of the Naurzumsky district refer to a low level of security (10-15-mg/kg), and in Kamystynsky and Auliekolsky – to a very low level of security (< 10 mg/kg). The lack of nitrate nitrogen in the arable horizon with its very low level of supply (< 10 mg/kg) was detected on dark chestnut soils in the Auliekolsky district-in 100% of the studied fields, in the Kamystynsky district – in 70% of the fields, in the Naurzumsky district - in 25% of the fields (Figure 4c).

4. Discussion

4.1. Long-term dynamics of humus content in soils of Kostanay region

Based on scientific agrochemical monitoring, changes in the humus content in agricultural soils over the previous 10-50 years were analyzed in stationary test areas of Kostanay region and compared with their virgin counterparts. Most studies have noted a decrease in the humus content in the arable horizon over a long period of time (Abdykhalykov et al., 2004; Dzhalankuzov, 2014, Dzhalankuzov and Nazanova, 2015; Kenzhegulova et al., 2022, 2023; Khusainov, 2016; Kozybaeva et al., 2021; Seidalina, 2009; Zharlygasov and Kalimov, 2017), which the authors explain by increasing oxidative stress in the soil. processes of organic matter during agricultural processing of black soils, as well as the development of erosion phenomena.

When compared with the virgin analogues of the southern black soils of Kostanay region, Dzhalankuzov and Nazanova (2015) noted that as a result of long – term agricultural use, plowed soils lost 26% of the 0-20 cm layer , 23% of the 0-50 cm layer, and 22% of the humus from 0-100 cm, which corresponds to the degradation of the average level. According to earlier data from the U. U. Uspanov Institute of Soil Science, the humus content decreased on average by 20-30% on all arable lands of Northern Kazakhstan (Saparov and Mamyshov, 2008).

Retrospective estimates obtained during long-term agrochemical studies on individual stationary areas, in general, also confirm a decrease in the humus content of arable black soils in the region. Thus, when repeated studies on experimental fields of Kostanay region for 32 years (from 1989 to 2021) of agricultural use of ordinary black soil on one of their lands. Retrospective estimates obtained during long-term agrochemical studies on individual stationary areas do not clearly determine the trund of dehumidificationand arable black soils in the region. Thus, when repeated studies on experimental fields of Kostanay region for 32 years (from 1989 to 2021) of agricultural use of ordinary black soil on one of their lands, the humus content in the upper horizon (0-20 cm) decreased from 4.05 to 3.89%, i.e. by 0.16%, on the other land in the southern black soil decreased from 3.85 to 3.77, i.e. by 0.08% (Kenzhegulova et al., 2022), which cannot be considered a statistically significant change and corresponds to a zero degree of soil degradation (Kenzhegulova et al., 2022).

In another similar monitoring study, the long-term dynamics of humus content in the arable horizon of ordinary black soils of the Karabalyksky district showed multidirectional changes over a 15-year period (from 2006 to 2021). In one of the plots, the humus content decreased from 4.92% to 4.60%, or by 0.32%; in the other, it increased from 4.46% to 4.70%, or by 0.24% in the arable horizon (Kenzhegulova et al., 2023). In an agroecological study on a five-field grain-fallow crop rotation in Kostanay region, a negative humus balance in arable soil was recorded, which amounted to minus 0.8 c/ha during the rotation of the crop rotation (Shepelev and Kadyrova, 2017).

In the study of long-term dynamics (1990-2015) of the organic matter content in ordinary and southern black soils in long-term stationary field experiments in Northern Kazakhstan a number of regularities were noted (Kurishbaev et al., 2016). It is established that as a result of carrying out various waste-free processing methods in arable black soils of the southern regions, the intensity of the decrease in the humus content slows down compared to the previous period of their agricultural use, but the process of dehumidification, including during, flat-cut processing, does not completely stop. The causes of dehumidification of southern black soils are both biochemical (mineralization) and physical (deflation) causes of humus loss. Wind erosion is particularly dangerous in the dry-steppe subzone with arable southern black soils, as a result of which the content of soil organic matter can sharply decrease due to the loss of the inert part of humus that is difficult to replace. At the same time, in the subzone of typical steppes on agricultural lands of the Karabalyk experimental station, protected by forest belts that prevent wind erosion, humus losses in the arable horizon of ordinary black soils were not observed (Kurishbaev et al., 2016).

In a number of field experiments, the influence of agrotechnical methods and the use of fertilizers on soil fertility indicators, including the humus content in arable soils of Kostanay region, was studied. In the study of Dzhalankuzov et al. (2017) in the conditions of "Experimental farm Zarechnoye" LLP of the Kostanay Research Institute of Agriculture on arable land with zero processing, a positive trend in changing the humus balance was noted: its content in the 0-30 cm layer was 4.83%, which is 0.83% higher compared to the traditional treatment option. In a field experiment conducted in 2015-2017 in "Karabalyk Agricultural Experimental Station" LLP on ordinary medium-loamy black soil, was an increase in the total reserves of plant residues on the surface and in the upper layer of the soil (0-10 cm) with zero tillage technology was recorded by 57.5% compared to the traditional one (Popova et al., 2020). Root and crop residues are an important source of organic matter for the preservation and reproduction of soil fertility.

Based on the data of the Ministry of Agriculture of the Republic of Kazakhstan on the agrochemical state of soils of Kostanay region for the period 2019-2022 (Republic of Kazakhstan, 2020, 2021, 2022, 2023a), it is possible to trace the 4-year dynamics of the average humus content and land area with various categories of soil humus content, noted according to the results of periodic agrochemical surveys (Table 3). The weighted average value of humus content in the arable horizon of agricultural lands of Kostanay region varies on the border between low-humus and medium-humus category of soils (4%). In the period 2020-2021, there was a predominance of agricultural areas with a low (2-4%) category of soil humus content, while in 2019 and 2022, the share of arable land with medium-humus content (4-6%)increased, which was most likely due to the characteristics of arable soils in the region included in the sample of the rotational agrochemical survey.

Table 3
Dynamics of humus content and land area with different categories of humus content of arable soils according to agrochemical surveys of Kostanay region for 2019-2022 (Republic of Kazakhstan, 2020, 2021, 2022, 2023a).

Year					2019	2020	2021	2022
Surveyed area, thousand ha					1173.51	804.24	809.16	826.42
Grouping by humus content	low	Group boundaries by content, %	≤ 4.0	thousand ha	528.28	498.12	492.99	401.73
				%	45.0	61.9	60.9	48.6
	average		4.1-6.0	thousand ha	620.38	271.63	316.01	413.21
				%	52.9	33.8	39.1	50.0
	high		≥ 6.0	thousand ha	24.85	34.49	0.16	11.48
				%	2.1	4.3	0	1.4
Weighted average value of humus content,%					4.1	3.8	3.8	4.0

4.2. Long-term dynamics of nitrogen content in soils of Kostanay region

The content of nitrogen forms available to plants is a dynamic indicator. Nitrate nitrogen is quickly absorbed from the soil by plants, so its content is largely related to the agrotechnical conditions and agrochemical measures carried out in the previous few years. The content of easily hydrolyzable nitrogen, which combines nitrate, ammonia and mobile organic nitrogen compounds, is largely interrelated with the content of humus in the soil.

Natural black soils of Northern Kazakhstan contain a significant amount of total and easily hydrolyzable nitrogen, and are characterized by a high nitrification capacity. However, easily hydrolyzable humus and nitrogenous substances are consumed at an accelerated rate in black soils that are in agricultural circulation, the loss of which in old-arable soils reaches 45% of the initial one (Dzhalankuzov and Nazanova, 2015), which corresponds to a high level of degradation of agricultural depletion. As a result, in many arable black soils of ordinary, southern black soils and dark chestnut soils of Kostanay region, there is a shortage of nitrogen nutrition of plants. Studies of the dynamics of the nitrate content in the arable horizon of black soils of the Kostanay district of the Kostanay region have shown that for 32 years from 1989 to 2021, this indicator remains at a very low level of availability (< 10 mg/kg) (Kenzhegulova et al., 2022).

In a number of agrochemical studies in the Kostanay region, however, results were obtained on the positive dynamics of mobile nitrogen forms in the arable soil horizon against the background ofthe use of organic and mineral fertilizers with the inclusion of perennial grasses and green manure in the crop rotation. In these cases, the nitrogen regime of black soils and dark chestnut soils stabilizes and improves (Boldysheva et al., 2020; Saparov et al., 2010; Seitmenbetova and Alibekova. 2012).

In a study on southern black soils conducted by Dzhalankuzov (2014), it was noted that when using agricultural technologies with minimal and zero tillage, the content of available nitrogen forms in arable and sub-arable horizons increases compared to traditional methods of dump plowing. At the same time, other studies have revealed a reduced content of nitrate nitrogen in the soil of variants with wheat crops grown continuously with zero processing, compared with traditional cultivation technology (Bekmagambetov and Kuzhinov, 2018; Boldysheva et al., 2020). A very low degree of nitrate nitrogen supply during the flowering phase of agricultural crops with zero technology is associated with less intensive mineralization of organic substances.

Based on the data of the Ministry of Agriculture of the Republic of Kazakhstan on the agrochemical state of soils of Kostanay region for the period 2019-2022 (Republic of Kazakhstan, 2020, 2021, 2022, 2023a), it is possible to trace the 4-year dynamics of the average content of easily hydrolyzed nitrogen and land area with various categories of this indicator, noted according to the results of periodic agrochemical surveys (Table 4). The weighted average value of the content of easily hydrolyzable nitrogen in the arable horizon of agricultural lands of Kostanay region in 2019 was 49.0 mg / kg, corresponding to the average level of security. In 2020-2022, the weighted average value decreased, and the level of easily hydrolyzable nitrogen supply was low (less than 40 mg / kg). In 2019, there was a predominance of agricultural areas with a high (more than 50 mg/kg) content of easily hydrolyzable nitrogen in the arable horizonof the country's soils, while inthe following 2020-2022, the share of arable land with its low content (less than 40 mg/kg) increases.

Table 4
Dynamics of easily hydrolyzable nitrogen content and land area with different levels of arable soil availability according to agrochemical surveys of Kostanay region for 2019-2022 (Republic of Kazakhstan, 2020, 2021, 2022, 2023a).

Year					2019	2020	2021	2022
Surveyed area, thousand ha					1173.51	804.24	809.16	826.42
Grouping byeasilyhydrolyzed nitrogen	content low	Group boundaries by content, mg/kg of soil	no more than 40 mg / kg	thousand ha	320.45	481.24	486.17	394.45
				%	27.3	59.8	60.1	47.7
	average		41-50 mg/kg	thousand ha	381.52	282.55	308.49	349.65
				%	32.5	35.1	38.1	42.3
	high		more than 50 mg / kg	thousand ha	471.54	40.45	14.50	82.32
				%	40.2	5.0	1.8	10
Weighted average value of easily hydrolyzed nitrogen content, mg / kg					49.0	37.2	37.6	39.9

5. Conclusions

For Kostanay region, a comprehensive analysis of soil health components on agricultural land, including agrochemical properties as well as degradation and pollution processes, is especially important because this region has a pronounced agricultural specialization and remains one of the key farming areas of the Republic of Kazakhstan. The results show that degradation processes are already affecting the productivity of arable land. Common and southern black soils (Calcic Black soils), as well as chestnut soils (Gypsic Kastanozems), which dominate the arable land structure, are characterized by lower humus content compared with their virgin analogues, which allows them to be classified mainly as medium- and low-humus soils. The availability of plant-accessible nitrogen forms in arable soils varies considerably among the administrative districts of Kostanay region; however, many agricultural fields are characterized by a deficiency of mineral nutrients, indicating the development of agricultural depletion processes. Overall, the obtained results confirm the need for regular soil monitoring and for the introduction of scientifically grounded land management practices aimed at preserving soil fertility and maintaining long-term agricultural productivity in the region.

At the same time, this study has several limitations that should be taken into account when interpreting the results. First, the analysis was focused mainly on humus and nitrogen indicators, whereas soil health is a broader concept that also includes physical, biological, and ecotoxicological parameters. Second, the available monitoring data were generalized from different years and districts, which may reduce the comparability of local conditions and management histories. Third, the study relied primarily on agrochemical survey materials and did not include direct yield-based modeling or a detailed assessment of the influence of specific farming technologies, fertilizer systems, and crop rotations on the observed changes.

Future research should therefore expand the set of soil health indicators by incorporating biological activity, soil structure, moisture regime, salinity, and contamination parameters. It would also be useful to establish long-term monitoring sites across the main soil subtypes of Kostanay region in order to track temporal trends under comparable management conditions. In addition, further studies should evaluate the effectiveness of conservation tillage, organic and mineral fertilization, crop rotation diversification, and precision farming approaches for restoring humus reserves and improving nitrogen availability. Such research would provide a stronger scientific basis for developing adaptive land-use strategies for the sustainable management of agricultural soils in Kostanay region.

Acknowledgements

The article was prepared within the framework of the The article was prepared within the framework of the program and target funding of the Ministry of Science and Higher Education of the Republic of Kazakhstan for4-2026 202.4-2026 under the scientific and technical program “Organization and conduct of comprehensive research to ensure sustainable development of the agro-industrial complex of Kostanay region with the creation of a research technology center” (BR24992785).

Data Availability Statement

Data is available from corresponding author upon request.

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Edited by

• Editor:
  Takako Matsumura Tundisi

Publication Dates

• Publication in this collection
  06 July 2026
• Date of issue
  2026

History

• Received
  04 Feb 2026
• Accepted
  23 Apr 2026