Soil Hydrological Properties’ Response to Long-Term Grazing on a Desert Steppe in Inner Mongolia

: Soil hydrological properties play an important role in maintaining ecosystem functions. It is critical to understand how those properties respond to human disturbance especially in semi-arid areas. In the present study, we investigated the effects of different long-term grazing intensities (no grazing, light grazing, moderate grazing, and heavy grazing) on eight parameters that related to soil hydrological properties in different soil depths based on a grazing platform that was established in 2004 on a desert steppe in Inner Mongolia. The relationships among different parameters and between hydrological and chemical properties were also analyzed. The results show that grazing intensity, soil depth, and their interaction all have signiﬁcant effects on soil moisture content, saturation capacity, ﬁeld capacity, and bulk density. At different soil depths (0–10, 10–20, and 20–30 cm), soil bulk density was negatively correlated with saturation capacity, capillary capacity, and non-capillary porosity but positively correlated with ﬁeld capacity. Furthermore, we found that ﬁeld capacity and soil moisture content were positively correlated but non-capillary soil porosity was negatively correlated with most soil nutrients. Our results indicate that overgrazing has detrimental effects on soil hydrological properties which may further negatively affect soil nutrient content. Light grazing may be an optimal grazing intensity on this semi-arid steppe with respect to soil hydrological properties.


Introduction
Soil water is the primary water source that vegetation can directly access during its growth.Through permeability and storage, soil water serves as a conduit connecting surface water and groundwater.It is also a critical link in the transformation of meteoric water, surface water, soil water, and groundwater [1].In most studies, soil hydrological properties primarily include bulk density (BD), porosity, field capacity (FC), wilting point (WP), saturation capacity (SC), soil water characteristic curve, and other parameters.Soil water-holding capacity is mainly influenced by soil BD and porosity, with FC being the most closely related index to soil hydrological properties that affect plant growth.As carriers of nutrient elements and energy circulation in the soil, these parameters impact soil water evaporation and permeability, which in turn have a significant influence on soil properties, vegetation growth, and the functions of ecosystems [2][3][4].Grassland is a crucial terrestrial ecosystem, and the prevalent grazing disturbance on grasslands directly affects soil properties, especially its hydrological characteristics.Thus, it is essential to study the impact of grazing on soil hydrological properties in grassland ecosystems.
In arid and semi-arid regions, soil moisture is a key element in establishing and maintaining regional ecosystems and controlling the number and size of perennial plant species [5][6][7].Previous studies have found that soil moisture content (SMC) is affected by land use type and grassland management, which in turn control plant canopy cover, leaf area, plant evaporation, and community composition [8,9].For example, based on an 11-year grazing experiment, Wang et al. (2008) found that SMC and carbon storage increased significantly with the elongation of grazing cessation.They attributed the increase of SMC primarily to the enhance of below-ground biomass [6].At the same time, they found that grazing significantly increased soil BD in the 30-50 cm soil layer but inhibited the accumulation of below-ground biomass [6].Through monitoring soil moisture and temperature on natural grassland, winter-grazed grassland, and heavily grazed grassland, Zhao et al. (2011) concluded that soil moisture was lower in grazed grassland than in natural grassland, especially in the 30-50 cm soil layer [10].Seasonal variations in soil moisture were most pronounced in the surface layer (0-10 cm) and less so in deeper soil layers due to changes in precipitation and atmospheric demand.Therefore, soil depth may play an important role in regulating the response of soil hydrological properties to grazing.
The effect of grazing intensities on soil moisture is significant in different seasons, whereas its effect on soil temperature is less pronounced.Soil moisture storage decreases significantly with increasing grazing intensity.Grazing significantly alters the physical properties of soils in grassland ecosystems [11].On grazed grasslands, when the pressure on the soil is lower than its pre-compression stress, the soil can withstand livestock trampling without severe adverse effects on soil physical properties [12].Through structural resilience mechanisms, such as plant and root growth, decomposition, soil microbial activities, and meiofaunal activities, soils can be restored to their original state at low grazing intensities [13].However, if the applied pressure exceeds the soil's pre-compression stress, frequent disturbances may surpass the soil's natural resilience, leading to deterioration and consolidation of soil structure.This, in turn, negatively affects soil porosity and essential physical properties [14].As grazing intensity increases, soil porosity, permeability, and electrical conductivity decrease, and BD increases, resulting in a reduction of soil functions [15].A study by Zhang et al. (2019) indicated that the average BD increased from 0.52 g m −3 to 0.92 g m −3 , and soil porosity decreased from 0.78% to 0.64% with increasing grazing intensity [13].Consequently, overgrazing initially enhanced soil compaction, BD, and other indices but reduced the stability of soil aggregates, sharply decreasing soil infiltration, leading to continuous soil erosion.As a result, many grasslands experience severe soil erosion and reduced productivity.This has given rise to various grassland degradation issues, such as soil bareness in severely degraded areas, reduced grassland vegetation coverage, decreased soil fertility, and diminished ecological productivity [16][17][18].
China has a vast grassland area of up to 400 million hectares, accounting for 41.7% of the national land area.This is 3.3 times greater than the area of arable land and three times larger than that of forests, making it crucial for China's food and ecological security [19][20][21][22].The desert steppe, a transition zone from typical steppe to desert, is one of the most arid ecosystem types on the Eurasian Steppe and has a long history of sheep grazing [23].Maintaining the function of the desert steppe is vital for regional and global ecosystem balance.However, the vegetation productivity, soil fertility, and ecosystem stability of the desert steppe are generally lower than those of other semi-arid grasslands [24].Consequently, the desert steppe is considered a fragile grassland ecosystem highly sensitive to grazing disturbance.In recent years, due to grazing activities, ecological problems have emerged in some areas with severe overgrazing.These issues include vegetation degradation, reduced species diversity, decreased vegetation coverage, and severe soil wind and water erosion.This has garnered the attention of local governments, leading to the introduction of management measures to encourage herders to practice standardized grazing [25][26][27].However, there is a lack of quantitative indices, and many management measures are based on observable changes in vegetation, while the impact of grazing activities on grasslands is often delayed, persistent, and widespread.Driven by economic interests, many herders continue to engage in overgrazing.As a result, the ecological environment of grasslands has not seen effective improvement.Based on this background, this study investigates the influence of different grazing intensities on the soil hydrological properties of the Inner Mongolian desert steppe, and examines the changes in the soil hydrological cycle and its ecological effects on other soil properties (such as soil chemical properties) under varied grazing intensities and soil depth.This research aims to provide a theoretical foundation for establishing reasonable grazing intensities on the Inner Mongolian desert steppe.

Site Description
The experimental area was located in a desert steppe ecosystem in the Inner Mongolia Autonomous Region in China (41 • 47 N, 111 • 53 E, 1456 m a. s. l).The region has a midtemperate continental climate.Over the past 50 years, the average temperature was 3.7 • C, peaking in July.In most years, the annual temperature ranged from −25 • C to 33 • C. The average precipitation was 280 mm, predominantly occurring from July to September.The grassland in this area is categorized as a desert steppe.The constructive species in this area is Stipa breviflora Griseb., while the dominant species include Artemisia frigida Willd.and Cleistogenes songorica Ohwi.The main companion species are Convolvulus ammannii Desr., Neopallasia pectinate Poljakov, and Bassia prostrata Beck.The soil at the study site has a sandy loam texture and is classified as Haplic Calcisols based on the FAO (Food and Agriculture Organization of the United Nations) soil classification system.

Experimental Design and Sampling Method
The long-term grazing experiment was established in 2004.The experimental area spanned 50 ha and was primarily utilized for free grazing before the creation of the experimental platform.The study was executed using a completely randomized block design consisting of three blocks (replicates), with each block encompassing approximately 4.4 ha.The three grazing treatments had stocking rates of 0.91, 1.82, and 2.71 sheepunits/ha/half year, which classified the grazing intensities as light grazing (LG), moderate grazing (MG), and heavy grazing (HG), respectively.
Soil samples were taken in August 2021, the peak period of the growing season.For each plot, nine soil samples were indiscriminately taken from depths of 0-10 cm, 10-20 cm, and 20-30 cm using a ring cutter (100 cm 3 , 5 cm height, 5.05 cm diameter).In total, 108 soil samples were evaluated for indices associated with soil moisture including: soil moisture content (SMC), soil saturated capacity (SC), capillary capacity (CC), and field capacity (FC); and indices associated with compaction including capillary porosity (CP), non-capillary porosity (NCP), total porosity (TP), and BD.

Soil Sample Analysis
Indices linked to soil moisture (including SC, CC, FC, and SMC) were measured using the constant head method at a steady temperature.The procedure went as follows: initially, the top cover of the ring cutter was detached, keeping only the bottom cover equipped with a mesh lid lined with filter paper.This setup was weighed and noted as "A".It was then placed in a flat-bottomed basin filled with water up to its top edge and left to stand for 12 h, allowing the soil samples inside to become saturated.After this period, the ring cutter's weight was noted as "B".The ring cutter was then positioned on a flat plate filled with dry sand for another 12 h, after which its weight was recorded as "C".This procedure was repeated, and the subsequent weight was noted as "D".Following this, the ring cutter was dried until it reached its dry weight, which was marked as "E".After emptying the soil from the ring cutter, its weight was recorded as "F".The specific formulae for each moisture content index are as follows: The soil BD (g•cm −3 ) was calculated according to the following formula: where V is the ring cutter sample volume (cm 3 ).The CP, TP, and NCP were calculated according to the following formula: where V denotes the ring cutter sample volume (cm 3 ).The SMC (%) was calculated according to the following formula: Finally, we analyzed the soil nutrient content only in surface soil (0-10 cm).Soil organic carbon (SOC) and dissolved organic carbon (DOC) were determined by the dichromate oxidation method, and soil total nitrogen (STN) and available nitrogen (SAN) were determined using the Kjeldahl method.We measured the total phosphorus colorimetrically using an ultraviolet spectrophotometer (UV-1800, Mapada, Shanghai, China) after wet digestion with H 2 SO 4 and HClO 4 .We measured the available phosphorus using the Olsen method.

Statistical Analysis
For each response variable, we compared the effects of the grazing intensities and different soil depths using two-way analysis of variation (ANOVA) followed by a least significant difference (LSD) multiple comparison (p < 0.05), using SPSS version 25.0 (SPSS, Inc., Chicago, IL, USA).In the repeated measures analysis, various types of covariance structures (e.g., UN, AR (1), and CS) were fitted and the one with the lowest AIC value was selected for the analysis.For soil nutrient indicators, we only compared 0-10 cm among four grazing intensities using one-way analysis of variation (ANOVA).Analyses were conducted using SPSS 19.0 (IBM Corp., Armonk, NY, USA) and all figures were made in Origin 2021 (Origin Lab Corporation, Northampton, MA, USA) and Canoco 4.5 (Plant Research International, Wageningen, The Netherlands).

Effects of Grazing Intensities and Soil Depth on Soil Hydrological Properties
The results of the two-way analysis of variance (ANOVA) indicated that grazing, soil depth, and their interaction had significant effects on soil moisture content, saturation capacity, and field capacity (p < 0.001, Figure 1).In contrast with CK, grazing significantly decreased the soil moisture content and soil field capacity independent of grazing intensity and soil depth.Meanwhile, for saturation capacity, only light grazing was significantly lower than that of CK at the 0-10 cm soil depth.At the 20-30 cm depth, three grazing intensities enhanced saturation capacity (p < 0.001, Figure 1).Interestingly, grazing and soil depth had no significant effects on soil capillary capacity (p > 0.05); only their interaction was significantly affected.and soil depth had no significant effects on soil capillary capacity (p > 0.05); on interaction was significantly affected.Soil bulk density responded significantly to grazing, soil depth, and their int (p < 0.001).As shown in Figure 2a, grazing increased bulk density in all the soi This may have arisen mainly from soil compaction.Furthermore, soil bulk den creased with soil depth only in CK but not in other treatments.Soil porosity in capillary porosity, non-capillary porosity, and total porosity only responded signi to grazing but not to soil depth and its interaction with grazing (Figure 2b-d).In lar, grazing decreased capillary soil porosity and non-capillary soil porosity, and induced a sharp decrease in total soil porosity.Soil bulk density responded significantly to grazing, soil depth, and their interaction (p < 0.001).As shown in Figure 2a, grazing increased bulk density in all the soil layers.This may have arisen mainly from soil compaction.Furthermore, soil bulk density increased with soil depth only in CK but not in other treatments.Soil porosity including capillary porosity, non-capillary porosity, and total porosity only responded significantly to grazing but not to soil depth and its interaction with grazing (Figure 2b-d).In particular, grazing decreased capillary soil porosity and non-capillary soil porosity, and finally induced a sharp decrease in total soil porosity.

Correlation of Soil Hydrological Properties at Different Soil Depths
In the surface soil, SC and CC showed significant positive correlations with TP but a significant negative correlation with BD.FC and SMC showed significant positive correlations with CP and BD but significant negative correlations with NCP (Figure 3a).In the 10-20 cm soil layer, SC showed a significant positive correlation with NCP, whereas CC and FC showed significant negative correlations with SMC (Figure 3b).In the 20-30 cm soil layer, SC showed a significant positive correlation with CP, whereas CC and FC showed significant negative correlations with SMC (Figure 3c).Those results indicate that different soil hydrological properties may affect each other.

Correlation of Soil Hydrological Properties at Different Soil Depths
In the surface soil, SC and CC showed significant positive correlations with TP b significant negative correlation with BD.FC and SMC showed significant positive co lations with CP and BD but significant negative correlations with NCP (Figure 3a).In 10-20 cm soil layer, SC showed a significant positive correlation with NCP, whereas and FC showed significant negative correlations with SMC (Figure 3b).In the 20-30 soil layer, SC showed a significant positive correlation with CP, whereas CC and showed significant negative correlations with SMC (Figure 3c).Those results indicate different soil hydrological properties may affect each other.

Correlation of Soil Hydrological Properties at Different Soil Depths
In the surface soil, SC and CC showed significant positive correlations with TP but a significant negative correlation with BD.FC and SMC showed significant positive correlations with CP and BD but significant negative correlations with NCP (Figure 3a).In the 10-20 cm soil layer, SC showed a significant positive correlation with NCP, whereas CC and FC showed significant negative correlations with SMC (Figure 3b).In the 20-30 cm soil layer, SC showed a significant positive correlation with CP, whereas CC and FC showed significant negative correlations with SMC (Figure 3c).Those results indicate that different soil hydrological properties may affect each other.

Soil Nutrients' Response to Grazing Intensity and Their Relationship with Hydrological Properties
In the present study, we only analyzed the content of surface soil nutrients (0-10 cm).The results of one-way ANOVA show that SOC changed from 16.13 g kg −1 to 15.29 g kg −1 when the grazing intensity changed from CK to heavy grazing.Relative to CK, only moderate and heavy grazing decreased SOC significantly (Table 1).STN showed pronounced decreasing trends only in heavy grazing.With the increase of grazing intensities, STP, DOC, SAN, and SAP also showed decreasing trends.Finally, a correlation between soil hydrological and soil nutrients was made (Figure 4).The results show that SC was negatively correlated with STP and SOC, while FC was positive correlated with SOC, STN, DOC, SAN, and SAP.CP and SMC were positively correlated with STN, STP, DOC, SAN, and SAP.At the same time, we found that CNP was negatively correlated with STN, STP, DOC, SAN and SAP.Those results suggest that soil hydrological properties are closely related to soil chemical properties, indicating that grazing-induced changes in soil hydrological properties may have important effects on soil nutrient content.

Soil Nutrients' Response to Grazing Intensity and Their Relationship with Hydrological Properties
In the present study, we only analyzed the content of surface soil nutrients (0-10 cm).The results of one-way ANOVA show that SOC changed from 16.13 g kg −1 to 15.29 g kg −1 when the grazing intensity changed from CK to heavy grazing.Relative to CK, only moderate and heavy grazing decreased SOC significantly (Table 1).STN showed pronounced decreasing trends only in heavy grazing.With the increase of grazing intensities, STP, DOC, SAN, and SAP also showed decreasing trends.Finally, a correlation between soil hydrological properties and soil nutrients was made (Figure 4).The results show that SC was negatively correlated with STP and SOC, while FC was positive correlated with SOC, STN, DOC, SAN, and SAP.CP and SMC were positively correlated with STN, STP, DOC, SAN, and SAP.At the same time, we found that CNP was negatively correlated with STN, STP, DOC, SAN and SAP.Those results suggest that soil hydrological properties are closely related to soil chemical properties, indicating that grazing-induced changes in soil hydrological properties may have important effects on soil nutrient content.

Effects of Grazing Intensities on Soil Hydrological Properties
Grazing represents a primary method of natural grasslands use, which can amplify habitats' heterogeneity as well as affect plant growth and development through herbivores' trampling and excretion.These alterations then impact nutrient cycling, which, in turn, modifies the physical construction of grassland soils [11].Specifically, livestock trampling first changes soil compaction, subsequently influencing other physico-chemical properties.As shown in our study, soil bulk density was significantly increased by grazing.This is consistent with many other studies, and some research pointed out that grazing-induced compaction is heightened through repeated trampling, especially post-rainfall when soil moisture peaks, exacerbating the soil compaction effects [13].Grazing also impacts other hydrological properties like SMC, soil porosity, and soil water retention capacity.The reason may be attributed to changes in permeability and residue from livestock manure.
Our findings revealed an increase in SC under LG conditions, while both SC and CC showed a marked decline under MG and HG conditions.LG appears beneficial for enhancing the water-holding capacity which suggests that more soil water can be used by plants in LG treatment.In contrast, under overgrazing conditions, the increase of livestock feed intake leads to a decrease in the aboveground biomass and less vegetation coverage, which may increase the evaporation of soil moisture.The mineralization of organic matter is strengthened under dry conditions.The decrease of organic matter leads to soil compaction, an increase of soil bulk density, and finally a decrease in porosity and soil water holding capacity [28].This implies that grazing can deplete organic soil matter and alter aggregate soil structure, undermining the soil's water retention capacity [29].Previous research has indicated that surface SMC alterations were raised predominantly from grazing.As stocking rates increase, surface SMC initially increases for the early grazing period but decrease sharply during the latter stages [11].Our study also found that, as the grazing intensity changed from LG to HG, CC showed a decreasing trend.A probable cause is the more frequent trampling of the surface soil by livestock with rising stocking rates, leading to intensified soil surface compaction.Reduced soil porosity and CC, coupled with diminished vegetation cover because of greater feed consumption, result in escalated soil surface moisture evaporation and reduced water retention [30].
Bulk density acts as an indicator of soil compaction, mirroring the state of soil particles and porosity.It is intrinsically tied to soil permeability and can serve as a degradation metric for grasslands.It is generally believed that with the continuous increase of grazing intensity, the soil pressure and bulk density will increase but the porosity will decrease, which may lead to hardened soil with poor ventilation.For example, an investigation on a Canadian semi-arid steppe revealed that grazing significantly amplified BD in surface soil but not deep soil [31].Other studies from diverse grassland ecosystems [13,32] corroborate that increasing stocking rates boosts BD, a conclusion this paper also reaches.One plausible explanation is that, under MG conditions, livestock trampling integrates vegetation litter with the surface soil.However, in HG scenarios, the topsoil structure suffers, presenting fewer granules and aggregates, leading to BD reduction [12].Beyond the direct effects of trampling, diminishing litter and plant cover indirectly influence BD.Vegetation, as a protective barrier, can mitigate livestock pressure, preserving soil integrity, while litter helps distribute trampling stress [13].
Soil porosity is one of the most important places for material and energy exchange in both grazing and natural grassland, and plays a crucial role in regulating soil water dynamics and plant water use efficiency.This is critical for the growth of plants, especially in water-limited ecosystems [33].Our findings indicate that grazing significantly reduced total soil porosity and led to the compression of macropores but increased the amount of micropores.This result was consistent with many other studies.For instance, Valani et al. (2022) evaluated soil physical properties across different grazing systems in Brazil and highlighted that total porosity was decreased by cattle trampling [34].Similarly, Chen et al. (2022) found that enclosure (grazing cessation) significantly increased total capillary and non-capillary soil porosity compared with continuous grazing in dry-hot savanna [33].In addition, some studies demonstrated that high-intensity grazing exerts a more substantial influence on soil porosity in arid and semi-arid ecoregions [12].Light grazing increased soil porosity, either because (1) light grazing benefits the growth of plants especially for belowground biomass which may favor the maintenance of soil structure; or because (2) animal trampling may accelerate the decomposition of dead litter, and hence increase the content of soil organic carbon [13,35].In contrast, HG results show a decline in soil porosity, likely due to the compression of macroporosity and the collapse of sizeable mesopores because of soil compaction [36].

The Relationships among Different Hydrological Indicators and Their Effects on Grassland Functions
Given that BD and porosity serve as measures of soil compaction, they can indicate the degree of compactness.Some research has suggested that a TP below 40% is the minimum threshold necessary for maintaining an ideal balance between air and water in the soil.This is equivalent to a soil BD exceeding 1.7 g m −3 .Below this value, the soil is typically seen as too compact to permit adequate root movement within the soil matrix [37,38].When soils experience compaction from animal trampling, the volume and effectiveness of macropores decrease, thus diminishing the air and water permeability of the soil.As Drewry et al. (2021) have emphasized, the macroporosity value might be an incredibly sensitive indicator for evaluating soil physical conditions [15].For instance, soils with macroporosity values below 10% are deemed excessively compact, potentially leading to diminished pasture yields.The optimal macroporosity value for the maximum pasture yield may differ based on factors like soil type, organic carbon, texture, mineralogy, etc., and thresholds can vary across soil types [15].
A negative correlation exists between soil moisture and compaction.As evidenced in this study, there were significant correlations between soil BD, porosity, and SMC.In more compact soils, the diminished soil porosity results in a decreased water diffusion rate, leading to a drop in saturated hydraulic conductivity [39].Furthermore, the heightened runoff, due to decreased permeability, can cause increased erosion, leading to organic matter loss and diminished water availability for plants.Organic matter content and composition greatly influence soil physical properties.Grazing-induced reductions in surface litter mean that fewer residues (primary sources of organic matter) are incorporated into the soil [28].This eventually causes an increase in bare soil proportion, leading to amplified evaporation rates of soil moisture [40].Moreover, severe soil degradation results in sharp drops in SC, CC, and FC on grasslands [29].Odriozola et al. (2014) suggested that the soil moisture response to grazing correlates with environmental factors and soil properties [30].In conclusion, our study posits that soil hydrological attributes are significantly impacted by grazing intensity.While light grazing may preserve optimal soil moisture characteristics, excessive grazing might undermine soil water retention capacity, potentially jeopardizing soil ecological processes.

Conclusions
Grazing represents a primary method of natural grassland use.Based on a long-term platform for different grazing intensities that was established in 2004 on the desert steppe in Inner Mongolia, the present study analyzed the responses of soil hydrological properties to four grazing intensities.Our results show that soil moisture content, saturation capacity, field capacity, and bulk density responded significantly to grazing intensity and soil depth, as well as their interaction.Soil bulk density was negatively correlated with saturation capacity, capillary capacity, and non-capillary porosity but positively correlated with field capacity.In addition, we found that soil hydrological properties have an important role in regulating the content of soil nutrients.Therefore, it is necessary to incorporate those parameters into the frame of soil health or soil quality assessment.

Figure 1 .
Figure 1.The effects of grazing intensity, soil depth, and their interaction on soil moisture (a), soil saturation capacity (b), soil capillary capacity (c), and soil field capacity (d).Note grazing; LG: light grazing; MG: moderate grazing; HG: heavy grazing.Various capital lett cate significant differences in different grazing intensities at the same soil depth at p = 0 lowercase letters indicate significant differences in different soil depths at the same grazing at p = 0.05 level.

Figure 1 .
Figure 1.The effects of grazing intensity, soil depth, and their interaction on soil moisture content (a), soil saturation capacity (b), soil capillary capacity (c), and soil field capacity (d).Note: CK: no grazing; LG: light grazing; MG: moderate grazing; HG: heavy grazing.Various capital letters indicate significant differences in different grazing intensities at the same soil depth at p = 0.05 level; lowercase letters indicate significant differences in different soil depths at the same grazing intensity at p = 0.05 level.

Figure 2 .
Figure 2. The effects of grazing intensity, soil depth, and their interaction on soil bulk density capillary soil porosity (b), non-capillary soil porosity (c) and total porosity (d).Note: CK: no graz LG: light grazing; MG: moderate grazing; HG: heavy grazing.Various capital letters indicate sig icant differences in different grazing intensities at the same soil depth at p = 0.05 level; lower letters indicate significant differences in different soil depths at the same grazing intensity at p = level.

Figure 2 .
Figure 2. The effects of grazing intensity, soil depth, and their interaction on soil bulk density (a), capillary soil porosity (b), non-capillary soil porosity (c) and total porosity (d).Note: CK: no grazing; LG: light grazing; MG: moderate grazing; HG: heavy grazing.Various capital letters indicate significant differences in different grazing intensities at the same soil depth at p = 0.05 level; lowercase letters indicate significant differences in different soil depths at the same grazing intensity at p = 0.05 level.

Figure 2 .
Figure 2. The effects of grazing intensity, soil depth, and their interaction on soil bulk density (a), capillary soil porosity (b), non-capillary soil porosity (c) and total porosity (d).Note: CK: no grazing; LG: light grazing; MG: moderate grazing; HG: heavy grazing.Various capital letters indicate significant differences in different grazing intensities at the same soil depth at p = 0.05 level; lowercase letters indicate significant differences in different soil depths at the same grazing intensity at p = 0.05 level.

Figure 4 .
Figure 4. Relationship between soil hydrological properties and soil nutrients under long-term grazing.* represents significant correlation at p < 0.05 level; ** represents significant correlation at p < 0.01 level.

Table 1 .
Effect of grazing intensity on soil nutrients.

Table 1 .
Effect of grazing intensity on soil nutrients.Lowercase letters indicate significant differences among the four treatments at p = 0.05 level.Abbreviations: SOC: soil organic carbon; STN: soil total nitrogen; STP: soil total phosphorus; DOC: dissolved organic carbon; SAN: soil available nitrogen; SAP: soil available phosphorus.