The Response of Topsoil Properties and Nitrogen Transformation to Land Cover in a Semi-arid Rangeland (Case Study: Kojur Rangeland in Mazandaran Province, Iran)

Nastaran Armat ¹ ( Tarbiat Modares University, Iran )
Ghasem Ali Dianati Tilaki ² ( Tarbiat modares University, Iran )
Yahya Kooch ³ ( Tarbiat Modares University, Iran )

تاریخ ارسال : 1401/01/07 تاریخ تایید : 1402/02/22

کلید واژه: Grazing exclusion, Grazed rangeland, Rainfed agriculture, Nitrogen Mineralization,

چکیده مقاله :

The role of different plant covers (i.e. Artemisia aucheri Boiss, Cousinia commutate Bunge and Agropyron longiaristatum Boiss) in topsoil properties and Nitrogen transformation is less known under semi-arid mountains. The main objective of this research was to study the effect of land covers on topsoil properties and nitrogen transformation. The study was carried out for investigating the soil properties of Grazing Exclusion (GE), Grazed Rangeland (GR) and Rainfed Agriculture (RA) in Kojur, Mazandaran province, Iran. Thirty-six 1m2 plots were set at three treatments to sample the dominant plant species. Soil samples were then taken from the central part of each plot sample in an area of 20×20 cm and depth of 20 cm. Our findings demonstrated that the carbon (C) content of plant materials did not differ for studied land covers whereas GR and RA had higher N content (1.48 and 1.41%, respectively) and lower C/N ratio (13.33 and 14.45%, respectively). In the GE, N concentration of soil (with 0.34%) was 1.5 times more than that in GR and RA (0.20 and 0.21%, respectively). Soil nitrification and N mineralization rates were significantly higher in the GE (0.33 and 0.28 mg kg−1d−1 respectively) as compared to the RA (0.15 and 0.08 mg kg−1d−1 respectively) and GR (0.01 and 0.04 mg kg−1d−1 respectively). There were no significant differences among land covers for bulk density, available K, microbial respiration, and ammonification rates. According to the results, grazing exclusion with presence of grass species increases the organic C contents, total N, and eventually, N mineralization which totally leads to improved soil quality in these regions.

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The Response of Topsoil Properties and Nitrogen Transformation to Land Cover in a Semi-arid Rangeland (Case Study: Kojur Rangeland in Mazandaran Province, Iran)

 

Nastaran ArmatA, Ghasem Ali Dianati TilakiB*, Yahya KoochC

A M.Sc. graduated, Department of Natural Resources and Marine Sciences, Tarbiat Modares University, Noor, Mazandaran, Iran 

B Associate Prof., Faculty Member, College of Natural Resources and Marine Sciences, Tarbiat Modares University, Noor, Mazandaran, Iran, * (Corresponding author), E-mail: [e-mail]  

C Associate Prof., Faculty Member, College of Natural Resources and Marine Sciences, Tarbiat Modares University, Noor, Mazandaran, Iran

 

Abstract. The role of different plant covers (i.e. Artemisia aucheri Boiss, Cousinia commutate Bunge and Agropyron longiaristatum Boiss) in topsoil properties and Nitrogen transformation is less known under semi-arid mountains. The main objective of this research was to study the effect of land covers on topsoil properties and nitrogen transformation. The study was carried out for investigating the soil properties of Grazing Exclusion (GE), Grazed Rangeland (GR) and Rainfed Agriculture (RA) in Kojur, Mazandaran province, Iran. Thirty-six 1m2 plots were set at three treatments to sample the dominant plant species. Soil samples were then taken from the central part of each plot sample in an area of 20×20 cm and depth of 20 cm. Our findings demonstrated that the carbon (C) content of plant materials did not differ for studied land covers whereas GR and RA had higher N content (1.48 and 1.41%, respectively) and lower C/N ratio (13.33 and 14.45%, respectively). In the GE, N concentration of soil (with 0.34%) was 1.5 times more than that in GR and RA (0.20 and 0.21%, respectively). Soil nitrification and N mineralization rates were significantly higher in the GE (0.33 and 0.28 mg kg−1d−1 respectively) as compared to the RA (0.15 and 0.08 mg kg−1d−1 respectively) and GR (0.01 and 0.04 mg kg−1d−1 respectively). There were no significant differences among land covers for bulk density, available K, microbial respiration, and ammonification rates. According to the results, grazing exclusion with presence of grass species increases the organic C contents, total N, and eventually, N mineralization which totally leads to improved soil quality in these regions.

 

Key words: Grazing exclusion, Grazed rangeland, Rainfed agriculture, Nitrogen Mineralization

 

 

Introduction

The world's human population has grown fourfold only in the last century. This increase in population, due to improving agricultural and industrial techniques, has created increasing pressure on food production for feeding the growing numbers. Soil degradation as a result of human activity is an environmental problem that has been identified in many areas (Turmel et al., 2015). Lack of proper land management, clear-cutting the forest, biomass burning, conversion of natural ecosystems to agriculture and changing crop types, accelerating organic matter decomposition and aerobic respiration in the soil and help to mineralize and oxidize humus cause emits organic carbon in the form of carbon dioxide from the soil into the atmosphere (Sheydai Karkaj et al., 2017). The severity of food production over the years has caused damage to the health and quality of ecosystems soil (FAO, 2011). Animal grazing as a common type of rangeland management has an influence on regulating feeding cycles and energy flow (Sun et al., 2017). Research on the effect of herbivores on the regulation of organic carbon (C) and nitrogen (N) is important to evaluate the contribution of grassland ecosystems to global flows C and N (Gao et al., 2009; Sitters et al., 2020). One of the remarkable effects of soil properties on ecosystem global changes is the change in the plant species distribution and also the plant community structure (Orwin et al., 2010). At the plant community level, it is clear that plant diversity and the structure of plant communities can affect the density and function of soil microorganisms as well as the quality of soil input sources (De Deyn et al., 2011; Fahey et al., 2020). Animal grazing is one of the major factors in increasing the non-palatable plants and reducing vegetation cover, biomass and species diversity (Zhu et al., 2016). Changing the composition of plant species in rangelands depends on the intensity of livestock grazing. Wei et al. (2011) showed that animal grazing activities can change the soil C and N cycle in grassland ecosystems. Zhong et al. (2014) found that heavy grazing pressures reduce soil C and N. Mofidi et al. (2012) and Liang et al. (2018) showed that herbivores can influence the rate of N mineralization by affecting the rate of organic matter decomposition  via dung and urine decomposition that can influence soil pH and electrical conductivity, and increase CO2 exchange rates in the grazing land. The grazed lands increase the amount of organic matter than agricultural land soils because of more root biomass, the return of plant residues and organic matter cycles (Rumpel et al., 2015). Wright et al. (2004) showed that grazing pressures and the combination of forage species could have an interacting effect on C dynamics and N mineralization. The findings Pineiro et al. (2010) and Hao and He (2019) on the effects of animal grazing on soil and vegetation structure revealed no significant relationship between species composition, root biomass and also C and N. These findings show the complexity of interactions in grassland ecosystems (Mikhailova et al., 2000). In general, maintaining the content of soil organic matter is an important goal for any sustainable agricultural system (Blanchet et al., 2016). Reduction of soil organic matter can have adverse effects on some soil physico-chemical and biological properties (Wang and Wesche, 2016). The conversion of native meadows to the farmlands without sufficient fertility usually results in damage to soil characters (Raiesi, 2017). Feng et al. (2015) reported that soil N mineralization and total N are considered as two striking indices of N availability since they are able to straightly control the concentration of ammonium and nitrate in the soil and provide mineral N for plants. Nitrogen is one of the important elements and its lack of plant growth limitation in temperate rangeland ecosystems (Kahmen et al., 2008). Accoe et al. (2004) indicated that the N dynamics such as the N mineralization determine many shapes and roles of rangeland ecosystems. Zhou et al. (2017) proved that grazing stimulates N mineralization while Qasim et al. (2017) showed that grazing reduces N mineralization.

This study aimed to investigate: 1) if various land covers affect the plant quality (the N content of plant materials) and soil physical, chemical, biochemical features and 2) to examine possible regulating factors for N transformation rates by analyzing the relationships between N transformation rates and several soil variables in the rangelands (GE: Grazing Exclusion -and GR: Grazed Rangeland), and Rainfed Agriculture (RA) systems under the semi-arid mountains of northern Iran.

 

Materials and Methods

Study area

The study was conducted in three rangelands, in Kuhpar experiment station (36 ̊ 31ʹ 57ʹʹ N and 51 ̊ 14ʹ 8ʹʹ E), in the western Mazandaran province of the Kojur Nowshahr, Iran. The areas include grazing exclusion (enclosed 30 years ago) with 30 ha and grazed rangeland (continual grazed) with 50 ha. Rainfed agriculture area (50 ha) was rangelands 30 years ago; they were cultivated with wheat and barley crops (Fig. 1) and now abandoned as rainfed fields (Mohebbi et al., 2016). The study areas with a semi-arid mountain climate are located at an altitude of 1,600 m above sea level, and there was a flat territory with a low slope (<10%). Based on 30-year meteorological data from the area under study, the annual mean precipitation is 319 mm, the most rain occurs in November and its least is in July. The mean annual temperature was 10.4°C and the maximum and minimum average monthly temperatures were 22 °C in August and 4 °C in January (Fig. 2) (Mohebbi et al., 2016).  According to the USDA Soil Taxonomy, soil is classified as Alfisols, developed on dolomitic limestone belonging to the upper Jurassic and lower Cretaceous period and has loam-clay loam texture (Ghelichnia, 2006). In the grazed rangeland, animal unit month per hectare is 2.22. While livestock grazing is done 7 times more than the capacity of the rangeland. Vegetation cover of the area is often Artemisia aucheri Boiss (Mohebbi et al., 2016). 

 

 

 

Fig. 1. Site locations of the study area in Mazandaran province, north of Iran

a)       Grazing exclusion, b)   Grazed rangeland, c)   Rainfed agriculture

 

 

 

 

 

 

 

 

 

 

Fig. 2. Mean monthly temperature and precipitation in the study area

 

Data collection and soil analysis

Three sample plots (1m2) were set at 25 m intervals along each 50 m sampling transect, resulting in 12 samples at each land cover. Before soil sampling, for each sample unit, sampling of vegetation was performed to determine the coverage percent and the number of individuals of plant species. Then, the above-ground and underground organs of dominant plant species were extracted. Soil sampling was conducted in June 2016. In each land cover, 12 soil cores (20×20×20 cm) were taken at a randomized-systematic method and then to better soil uniformity, they were sifted (<2 mm) of stones and roots. The collected soils were eventually split into two subsamples: one of subsample was kept at 4 °C for incubation research and the other was air-dried for soil physico-chemical properties investigation. The total C and N contents of plant samples were determined in quadruplicate using dry combustion with an elemental analyzer (Fisons EA1108, Milan, Italy) calibrated using the BBOT [2, 5-bis-(5-tert-butyl-benzoxazol-2-yl)- thiophen] standard (Ther moQuest Italia s.p.a.). The obtained data were corrected for moisture content (Allison, 1975).

          Soil bulk density was measured by Plaster's, (1985) clod method. Soil texture was determined by the Bouyoucos hydrometer method (Bouyoucos, 1962). Soil water content was measured by drying soil samples at 105°C for 24 h. Soil pH and EC were measured in H2O using a 1:5 soil to solution ratio after the soil suspension had been equilibrated for 1 h on a shaker. Soil organic C was determined using the Walkey-Black technique (Allison, 1975) and the total N content was assayed using the Kjeldahl method (Bremner, 1960). Available P was determined with a spectrophotometer using the Olsen method Homer and Pratt) 1961), and available K, Ca (by ammonium acetate extraction at pH) were determined with an atomic absorption spectrophotometer )Bower et al., 1952) and microbial respiration was determined by measuring the CO2 evolved in a 3-day incubation experiment at 25°C (Alef, 1995). The buried-bag technique Wang et al. (2010) was used to estimate soil N mineralization, nitrification, and ammonification rates. Two samples were taken: the first in June and the second in July 2016. One from each pair of samples was used to determine the initial concentrations of extractable NH4+ and NO3−, and the other was placed in a polyethylene bag and buried (in a 20 cm depth) in land cover. The incubation period was 30 days (Duran et al., 2009). Soil NH4+ and NO3− were extracted with a 2 M KCl solution (soil: solution, 1:5) and then filtered through a 0.45 μm filter. The extracted solutions were measured via colorimetric techniques at 645 and 420 nm to determine NH4+ and NO3− concentrations, respectively (Li et al., 2014). N mineralization was defined as the increase in NO3− and NH4+ over the incubation interval, and the increase in NO3− and NH4+ was used to indicate nitrification and ammonification rates, respectively (Asadiyan et al., 2013).

 

Data analysis

The normality of the variables was checked by the Kolmogorov -Smirnov test and Levene's test was used to examine the equality of the variances. One-way analysis of variance (ANOVA) was used to compare plant cover and soil properties data among the land covers. Duncan's multiple comparison test was further employed to test for differences at the 5% probability level. All statistical analyses were conducted using the SPSS v. 19.0 statistical software package. Factor analysis which includes principal component analysis (PCA) was used to determine relationships between plant cover and soil property under different land covers (Mc Cune and Mefford, 1999).

 

Results

a)       Vegetation, plant cover and soil properties

According to the floristic list, in GR, GE and RA, the dominant species of areas were Artemisia aucheri Boiss, Agropyron longiaristatum Boiss, and Cousinia commutate Bunge, respectively (Table 1). Obtained data indicate that the C content of plant materials was not remarkably different among the three studied land covers (Fig. 3a). However, GR and RA had significantly higher N content of plant materials than GE (Fig. 3b). There was higher C/N ratio of plant materials in the GE and decreasing ratio for GR and RA (Fig. 3c). Total N was the highest quantity in GE compared to other studied lands whereas the greater concentrations of the C/N ratio and available nutrients (P and Ca) were detected in the RA. GE had dramatically higher sand content than GR and RA whereas the greatest amounts of silt, clay and water content were found under RA. Soil pH under GE, EC, and organic C under GR were the lowest compared to other land covers. There were no differences in bulk density, available K, and soil microbial respiration between land covers (Table 2).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Table 1. Mean cover (%) of plant species in three land covers

Species	Family	GR (%)	GE (%)	RA (%)
Agropyron longiaristatum (Boiss)	Gramineae	0.33	34.44	0.44
Artemisia aucheri Boiss.	Asteraceae	36.66	3.33	0
Cousinia commutate Bunge.	Asteraceae	0.54	0.22	38.50
Festuca ovina L.	Gramineae	3.10	7.8	2.33
Phleum paniculatum Huds..	Gramineae	3.21	0	1.88
Stachys laxa Boiss. & Buhse.	Lamiaceae	9.37	5.44	2.94
Medicago sativa L.	Leguminosae	0	7.66	0
Bromus tomentellus	Gramineae	0	1.66	0
Dactylis glomerata L.	Gramineae	0	3.33	1.10
Bromus tectorum L.	Gramineae	0	1.11	4
Eryngium planum L.	Apiaceae	0.21	0.66	7.10
Traxacum montanum	Asteraceae	0	0.33	0.54
Coronilla varia (L.) Lassen	Leguminosae	0	0.33	0
Phlomis olivieri	Lamiaceae	1.66	0.33	0
Teucrium polium L.	Lamiaceae	1.10	0	0
Stachys byzantine K. Koch.	Lamiaceae	1.21	0	0.28
Astragalus gossypinus	Leguminosae	0.88	0	0
Plantago lanceolata L.	Plantaginaceae	0.54	0	0.28
Poterium sanguisorba L.	Rosaceae	0.21	0	0.16
Alyssum bracteatum Boiss. & Buhse	Brassicaceae	0.21	0	1.46
Poa bulbosa L.	Gramineae	0.88	0	0
Bromus briziformis Fisch. & C. A. Mey.	Gramineae	0.44	0	0
Astragalus mollis	Leguminosae	0.21	0	0
Salvia virygata	Lamiaceae	0	0	0.72
Hordeum fragile	Gramineae	0	0	1.33
Teucrium polium L.	Lamiaceae	0	0	2.21
Astragalus lentiginosus Dougl. ex Hook	Leguminosae	0	0	0.54
Geranium tuberosum L.	Geraniaceae	0	0	0.33
Gallium aparine L.	Rubiaceae	0	0	0.54

The studied different land covers were Grazed Rangeland (GR), Grazing Exclusion (GE), Rainfed Agriculture (RA).

 

 

 

 

 

 

 

 

 

 

 

 

Fig. 3. Mean of plant carbon (a), nitrogen (b) and organic C to nitrogen ratio (c) under different land covers. The studied different land covers were Grazed Rangeland (GR), Grazing Exclusion (GE) and Rainfed Agriculture (RA).

 

 Table 2. Mean values and standard error (SE; n = 12) of the soil variable analyzed

Soil features	GR	GE	RA	F test	p value
	Mean±SE	Mean±SE	Mean±SE
Bulk density (g cm−3)	1.53±0.15 a	1.51±0.18a	1.42±0.16a	1.39	0.20
Sand (%)	40.41±4.73 b	48.16±5.33a	26.08±6.61c	47.70	0.00
Silt (%)	33.30±4.69 b	30.16±5.55 b	43±5.49a	19.35	0.00
Clay (%)	26.36±3.24 b	21.50±2.84c	30.58±2.96a	27.09	0.00
Water content (%)	3.50±0.00 b	3.50±0.00b	4.60±0.01a	7.92	0.00
pH (1:2.5 H2O)	8.05±0.05a	7.90±0.07b	8.06±0.06a	25.71	0.00
EC (ds/m)	0.16±0.01 b	0.19±0.02a	0.18±0.01a	7.57	0.00
Organic C (%)	1.22±0.16 b	2.13±0.38a	1.93±0.33a	30.71	0.00
Total N (%)	0.21±0.05 b	0.34±0.08a	0.20±0.08b	13.46	0.00
C/N ratio	5.97±1.71 b	6.56±2.42b	10.43±3.32a	9.90	0.00
Available P (mg kg-1)	9.80±4.28 b	9.83±2.03b	12.91±2.67a	3.88	0.03
Available K (mg kg-1)	189.33±17.56a	191.83±12.03a	200.75±8.71a	2.44	0.10
Available Ca (mg kg-1)	329.55±4.16 b	328.10±5.48b	341.01±3.19a	30.78	0.00
Microbial respiration  (mg CO2-C g-1soilday-1)	0.04±0.03a	0.04±0.03a	0.06±0.04a	1.73	0.19

Different letters in each row indicate significant differences (p < 0.05 by Duncan test) under different land covers. The studied different land covers were Grazed Rangeland (GR), Grazing Exclusion (GE), Rainfed Agriculture (RA). 

 

b) Soil nitrogen transformation

The RA had higher NH4+ concentration in June whereas greater concentrations were detected under GE when compared with GR and RA in July (Fig. 4a). The soil nitrification and N mineralization rates under GE demonstrated higher values when compared with the other studied land covers (Fig. 4d, e). The concentration of NO3− and ammonification were not significantly different among land covers (Fig. 4b, c).

From the PCA output, the first PC was described more than 65% variance in plant cover and soil properties under the studied land covers (Fig. 5). The left PC1 illustrates the status with good water content, the most alkaline soil, collection of nutrients element, and low N mineralization rate that can be attributed to the RA while the right PC1 offered circumstances with less alkaline soil, low components nutrients and more N mineralization rate related to the GE (Fig. 5). GR was situated at the positive sector of PC2 (explained variance less than 40%), and is related to good quality of plant cover (Fig. 5).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Fig. 4. Mean of NH4+−N concentration (a), NO3−−N concentration (b), net ammonification rate (c), net nitrification rate (d) and net N mineralization rate (e) in the top mineral soil under different land covers. The studied different land covers were Grazed Rangeland (GR), Grazing Exclusion (GE) and Rainfed Agriculture (RA).

 

 

 

Fig. 5. PCA based on the correlation matrix of the, land covers, soil physico-chemical and biochemical features. NH+4 a= ammonium (sampling in June), NH+4 b= ammonium (sampling in July (, NO-3 a= nitrate) sampling in June), NO-3 b= nitrate) sampling in July), NAR= net ammonification rate, NNR= net nitrification rate, NNMR= net N mineralization rate from the Grazed Rangeland (GR), Grazing Exclusion (GE), Rainfed Agriculture (RA).

 

Discussion

a)       Plant quality and soil properties

Good qualities (higher concentration of N with lower levels of C/N ratio) of plant cover were observed in GR and RA while GE displayed few plant cover qualities (lower aggregation of N with superior levels of C/N ratio). The grazing severity increases the toxicity of plants. The presence of nitrate in the secondary compounds of toxic plants (Artemisia aucheri ) and also, promotion of fast growing species through grazing increases the N content and quality of plants (Arzani et al., 2006; Schrama et al., 2013). Although in many cases, grazing leads to soil compression, reducing soil porosity, enhancing soil bulk density (Wang and Wesche, 2016; Oduor et al., 2018), a notable difference was not seen in bulk density of soil in our study. In parallel to decreasing soil pH in GE, it could be pointed out that the density of organic matter is a construction that can lead to soil acidification under this land cover (Pei et al., 2008). Related to increase of EC in the GE, it can be known as leaching loss due to low grazing, increased organic matter, land cover (which is the relative area covered by physical materials of plant species in a plot) and infiltration (Aghajantabar et al., 2015). According to the results of Mehrani et al. (2014) and Raiesi (2017), the highest soil pH and EC content was observed in the RA; it may be due to the specific biological properties of the soils of the study area. Generically, it can be mentioned that plant pH has an effect on soil pH (Kooch et al., 2012), so the soil pH and EC changes under different land covers may be caused by different plant species, properties and quality (Khajehzadeh et al., 2014; Ruwanza and Shackleton, 2016). According to our outcomes, the largest soil organic C amount belonged to GE and RA. Generally, the effect of the GE with more grass species on soil organic C was predominantly detected in the top 20 cm soil surface where nutrient and soil organic matter aggregation result from complex interchange between plant and soil biotic processes (Fahey et al., 2020; De Araujo Pereira et al., 2021;). In addition to other reasons of increased soil organic C in the GE, plants have major production more than the time of breathing which contributory assemble soil organic C. The presence of most of the gramineous species in the GE enhances the organic matter of soil above ground and below ground due to lack of continuous woody structures and the overall higher decomposability (Deng et al., 2013). The soil organic C stock of the RA may be higher than the GR, due to organic manure and organic fertilizers applications and the effect of crop residues (Zhang et al., 2012; Conant et al., 2017). The elimination photosynthetic tissue and fallowing respiration of assimilated C by the grazing animals lead to a very few quantity of soil organic C in GR since potential C inputs to soil organic matter have decreased (Wang et al., 2014; Bagchi et al., 2017).

          The accumulation of nitrous oxide in the enclosed lands can be instantly linked to the enhancement of surface and underground biomass, the aggregation of organic matter as litter on the surface of the earth, and the increase in the entry of nitrogen into the soil by litter and roots (Ley et al., 2018). The rise of above and below ground biomass, the collection of remaining grass as litter on the ground, and the increased input of N into soils by litter and roots have straightly resulted in the accumulation of total N in GE grassland (Qiu et al., 2013; Yusuf et al., 2015) which confirms our findings of soil under GE compared with the other land covers. It has been proved that the reduction of the rate of N mineralization and N supply in RA lead to increasing the C/N ratio in the area (Pringle et al., 2014; Noghreh and Kooch, 2019).  The organic manure applications under RA can be contributory to increase available P and Ca in this land cover. Moreover, existence of more silt and clay fractions due to their greater capacity for holding cations is another reason to increase these elements in the RA (Lu et al., 2015). Soil microbial respiration is primarily controlled by climatic factors while plant coverings have a secondary effect on it. Thus, the rate of soil microbial respiration is controlled primarily by climatic factors and substrate factors while vegetation has a secondary effect on it (Raich and Tufekcioglu, 2000); in our study areas, there were no significant differences in soil microbial respiration. It might be related to the carbon of plants in three land covers.

 

b)       Soil nitrogen transformation

In general, the accumulation of NH4+ was lower in July than in June while NO3− concentrations were mainly lower in June than in July. According to the report by Vymazal (2007), NH4+ can be reduced by processes such as adsorption, plant uptake and volatilization. Higher NH4+ contents from RA may occur as a result of a lack of rainfall in that period and lower volatilization due to more clay fractions in the land cover. In contrast, most NH4+ contents from GE may occur as a result of increases in plant biomass because NH4+ leaching under GR and RA is high due to the rainfall. Whereas animal grazing leads to decrease total nitrogen content, the accumulation of annual nitrification would decline (Shan et al., 2011). It is said that enhancing the nitrification resulted from increasing NH4+−N concentration, since the nitrification is independent of organic matter, plant and litter quality, and there is no competition between them and ammonification (Jalali et al., 2014). Wang et al. (2022) indicated that grazing horse induced significant increases in soil moisture and NO3− in desert grassland. According to the dataset of this study, the RA had a higher C/N ratio in comparison to both GR and GE. When soil C/N ratios are high, microbes have C; however, N is limited as a multiplier factor in the C/N ratio and consequently, decreases the N mineralization rate and N supply to the rangeland (Magdoff and Weil, 2004), thereby decreasing rangeland productivity. Many studies have suggested that the quantity of soil organic matter may be an important determinant of N mineralization (Cai et al., 2016); however, our data do not show this. The reason is seasonal variation in allelopathic potential and antimicrobial activity of toxic plants such as Artemisia genus (Mahboobi and Ghazian, 2009; Kegode et al., 2012) indicating that the mineralization of nitrogen in soil was influenced by the quality of plants. Seasonal variation in allelopathic potential has been reported for Artemisia aucheri and Artemisia genus; so, GR showed lower soil microbial activities. Based on principal component analyses (PCA), the outcomes of this study detected that there is a positive correlation between the amount of soil N mineralization and N, ammonium and nitrate concentration that agreed with previous findings (Magdoff and Weil, 2004; Dong et al., 2021). Animal grazing could have induced shifts in plant and soil microbial community composition, resulting in dissimilarities in net N mineralization contents, with the peak value of net N immobilization appearing (Zheng et al., 2011; Leptin et al., 2021). Extremely grazing may decrease the root exudates generation due to over-defoliation, and hence, result in a reduced N mineralization (Xu et al., 2007; Sun et al., 2017). Schrama et al. (2013) hypothesize that soil compaction by herbivores reduces oxygen availability in wet soils such as those in the present study, resulting in a reduction in N mineralization. Zhao et al. (2010) found since various plant species show different growth rates, root functioning capable have a diverse effect on microbial processes such as nitrogen mineralization and nitrification.

 

Conclusion

Based on finding of this study, land covers have diverse influence on plant quality and also, the topsoil physical, chemical and biochemical features. Grazing exclusion plays a positive role in adjusting soil N content and increasing N mineralization. This research recommends a temporal grazing exclusion with the presence of annual and perennial grasses abundance that can help better performance than other land covers techniques in betterment soil quality, particularly the N content and the net N mineralization rate.

 

Acknowledgment

 Many thank Mr. Sadegh Boor for his tireless assistance with Laboratory analysis. This research was done by financial supports of Tarbiat Modares University, Tehran, Iran.

 

 

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واکنش مشخصه های خاک سطحی و تغییر شکل نیتروژن نسبت به پوشش اراضی در مراتع نیمه خشک (مطالعه موردی: مراتع کجور مازندران) 

نسترن آرماتالف، قاسمعلی دیانتی تیلکیب*، یحیی کوچج

الفدانش آموخته کارشناسی ارشد دانشکده منابع طبیعی و علوم دریایی،، دانشگاه تربیت مدرس، نور، مازندران، ایران

ب عضوهیئت علمی دانشکده منابع طبیعی و علوم دریایی،، دانشگاه تربیت مدرس، نور، مازندران، ایران

*(نگارنده مسئول)، پست الکترونیک: [e-mail]

ج عضوهیئت علمی دانشکده منابع طبیعی و علوم دریایی،، دانشگاه تربیت مدرس، نور، مازندران، ایران

چکیده. نقش پوشش گونه های گیاهی مختلف از قبیل Artemisia aucheri Boiss, Cousinia 

commutate Bunge, Agropyron longiaristatum Boiss بر ویژگی های خاک سطحی و تغییر شکل نیتروژن در مناطق کوهستانی نیمه خشک، کمتر شناخته شده است.  هدف از این تحقیق تأثیر پوشش گیاهی بر ویژگی های خاک و تغییر شکل نیتروژن در اراضی قرق، چرا شده و دیم زار رها شده در استان مازندران می باشد. به منظور نمونه برداری از گونه های گیاهی غالب موجود در سه منطقه مورد مطالعه 36 عدد پلات یک مترمربعی مستقر شد. نمونه های خاک نیز از مرکز هر پلات به مساحت 20×20 و به عمق 20 سانتیمتر برداشت شده است. یافته های ما نشان داد که بین مقدار کربن گیاهی در این سه اراضی تفاوت معنی داری وجود نداشت، در حالیکه اراضی چرا شده و دیم زار رها شده مقدار نیتروژن بیشتری (1.48 و 1.41% به ترتیب) و نسبت کربن به نیتروژن کمتری (13.33 و 14.45 % به ترتیب) داشتند. در منطقه قرق شده غلظت نیتروژن خاک (با 0.34%) 5/1 برابر غلظت نیتروژن موجود در اراضی چرا شده و دیم زار رها شده (0.21 و 0.20 % به ترتیب) بوده است. میزان نیتریفیکاسیون خاک و معدنی شدن نیتروژن در مدیریت قرق (33/0و 28/0 میلی گرم بر کیلوگرم وزن خشک، به ترتیب) بطور معنی داری بیشتر از دیم زار رها شده (15/0 و 08/0میلی گرم بر کیلوگرم وزن خشک ، به ترتیب) و منطقه چرا شده (01/0 و 04/0- میلی گرم بر کیلوگرم وزن خشک، به ترتیب) بودند. در میزان جرم مخصوص ظاهری، پتاسیم، تنفس میکروبی و میزان آمونیفیکاسیون خاک در بین پوشش های مختلف اراضی تفاوت معنی داری مشاهده نشد. مطابق با نتایج، منطقه قرق شده با حضور گونه های علفی منجر به افزایش مقدار کربن آلی، نیتروژن کل و در نهایت معدنی شدن نیتروژن شده که در مجموع منجر به بهبود کیفیت خاک در این اراضی شده است.

کلمات کلیدی: مرتع قرق شده، مرتع چرا شده، دیم زار رها شده، معدنی شدن نیتروژن