جستجوی مقالات مرتبط با کلیدواژه « vegetation type » در نشریات گروه « آب و خاک »

Slope aspect, vegetation type, and depth of sampling are factors affecting soil chemical properties. These factors affect soil quality by increasing or decreasing organic matter content. However, the simultaneous effects of plant type and aspect on some soil properties have rarely been studied. For this purpose, the effect of aspect, plant type, and depth of sampling on soil chemical properties were studied based on factorial experiment in a completely randomized design with 6 replications, in the Gonbad Paired Watershed Research Station. Soil sampling was done in August 2016 and chemical properties were measured. The soil pH was higher in the southern slopes than in the northern slopes. The pH of the soil under Astragalus parrowianus was significantly lower than that of Bromus tomentellus. In the northern slope, CEC of soil under Astragalus parrowianus was higher compared to that under Bromus tomentellus and inter-plant position, while in the southern slope, soils in the inter-plant position had significantly lower CEC in comparison with those under Bromus tomentellus and Astragalus parrowianus plants. At all plant and inter-plant positions, the CEC and organic matter content were significantly lower in the southern slope than in the northern slope. At the first and second depths of the northern and southern slopes, soil under Astragalus parrowianus plants had significantly higher organic matter and calcium carbonate compared to the Bromus tomentellus and inter-plant position. Also, at the first depth of the northern slope, soil under Bromus tomentellus plants had significantly higher organic matter and calcium carbonate compared to the inter-plant position. Generally, influence of the factors of aspect and vegetation type was more than that of the depth of sampling.

The combined effects of biochemical composition and amount of plant residues returned to soils affect stability of aggregation and the rate of aggregate turnover. To investigate the influence of vegetation type on aggregate size distribution, five vegetation types including rainfed wheat (RW), grasses (G), Astragallus–Bromus (A-B), Astragallus–Lactuca (A-L) and Astragallus–Artemisia (A-A) were studied under similar environmental conditions in terms of parent material and slope aspect in Gonbad watershed, Hamadan. Total organic carbon (TOC), soil carbohydrates (Ch), mean weighted diameter (MWD), size distribution of water-stable aggregates (AS) and aggregate carbon (AC) were measured in surface (0-15 cm) soils. The amounts of TOC, Ch, MWD and AC (present in all aggregate size fractions) were significantly greater in soils under A-B and A-A than the soils of other vegetation covers, while the lowest values were observed in soils under RW and G. The highest AS>2 mm and lowest AS 2 mm were lower in soils under A-L, G and RW compared to other aggregate sizes. A-B and A-A vegetation types had greater canopy, annual production, plant diversity and litter content compared to other vegetation types.Frequent soil ploughing in RW site andlow plant diversity and canopy cover in A-L and G sites contributed to reduced soil aggregation and lower content of coarse aggregates;AS in 0.5-0.053 (mm) fraction in soils of aforementioned vegetation types was greater than other aggregate sizes. It was concluded that Ch and 0.5-0.053 (mm) aggregate size fraction might be reliable soil quality indicators that reflected land use and vegetation type changes.

Soil organic matter is influenced strongly by vegetation cover and management, therefore it is proposed as the main indicator of soil quality and health. The changes in soil organic matter status occur much more rapidly in the labile pools than in organic C. Thus, labile pools can be used as early indicators of changes in total organic matter that will become more obvious in the longer term here. In addition, the labile fraction has a disproportionately large effect on nutrient-supplying capacity and structural stability of soils. Land management as well as soil and environmental conditions lead to the deployment of different plant communities in rangeland ecosystems, which in turn may have different effects on soil quality indicators. The main objective of this research was to investigate the influence of different vegetation covers on the quantity and quality of soil organic carbon fractions in Gonbad experimental watershed, Hamadan. Moreover, the seasonal changes of selected soil carbon fractions were investigated.
Paired Gonbad watershed in Hamedan consists of two sub-basins: in control sub-basin no grazing management is applied, while in protected sub-basin, grazing has been restricted to a very short period in late autumn since 2002. Average annual precipitation and average annual temperature in the area are 304.4 mm and 9.5 °C, respectively (5). The soil cover of the watershed consists of TypicCalcixerepts, TypicHaploxerepts and Lithic Xerorthents (9). Five different vegetation typesof which, grasses (G), Astragalus-Bromus (A-B), Astragalus-Artemisia (A-A), Astragalus-Lactuca (A-L) in protected sub-basin, and Astragalus-Euphorbia (A-E) in control sub-basin, were selected. In addition, a formerly cultivated hilly land outside the watershed, now under rainfed wheat farming (RW) was selected as a non-pasture vegetation type. All of the six vegetation types were similar in terms of soil parent materials and slope aspect.. Soil and plant sampling were conducted in mid-autumn 2012 (a), and late spring 2013 (s). Three plots (1*1 m2) were studied in each vegetation type. Total organic carbon (TOC), carbon stock (CS), carbon stock normalized with sand(CS/Sa), active carbon (AC), normalized active carbon (AC/TOC), soil carbohydrates (Ch), normalized carbohydrates (Ch/TOC), basal respiration (BR) and normalized basal respiration (BR/TOC) were measured in surface soils (0-15 cm). A factorial experimental design with two factors, vegetation type (6 levels) and time (2 levels), was conducted. Prior to statistical analysis, data were normalized, if required.
TOC and CS contentswere significantly different between vegetation types. A-B and A-A had highest canopy cover, litter cover and species diversity. Species diversity in the rangeland ecosystems has direct effect on fodder production and soil organic carbon content. A-E site, despite its low TOC content, hadhigher CS/Sa (51.9 Mg/ha) due to higher amount of clay content, compared to A-A (43.1Mg/ha) with higher TOC content. The amount of AC andAC/TOC in different vegetation types is proportional to the amount of TOC, CS, total canopy, and the canopy and production of herbaceous species. AC content was significantly highest in A-B (711.7 mg/kg), and lowest in RW site(262.6 mg/kg). A-B site is rich in grass species with high amounts of readily decomposable root residues and exudates. The variation of carbohydrate contents in different vegetation types wasvery similar to that of total organic carbon, in that A-B and A-A exhibited the highest (5843 and 5258 mg/kg, respectively) and RW showed the lowest (1937 mg/kg) carbohydrate contents. The woody, not easily decomposible litters in A-A explainedthe high content of Ch/TOC (38.12%) in this site; low rate of humification entails increased soil carbohydrates. Ch/TOC was significantly lower in A-E than other covers. The highest BR andBR/TOC, were observed in A-B and A-A sites, mainly due to the high canopy cover, species richness,and soil organic matter. The lowest BR andBR/TOC were observed in A-E.Thesoil texture in this site was clay.The recirculation of organic matter in fine-textured soils is low because of organic materials protection from microbial decomposition. Total organic matter and labile organic carbon inputs werelower in A-L, A-E and G sites; this may explain the reduction of microbial activity in these vegetation types. Except for AC/TOC, Ch, and BR, seasonal changes of all other indicators were significant. Unlike other indicators, the content of Ch/TOC was significantly higher in autumn than spring.
Vegetation types had significant effects on selected soil quality indicators, so that A-A and A-B sites exhibited the highest soil quality, mainly because of higher vegetation cover, litter, and plant diversity. RW, followed by A-E site, demonstrated the lowest soil quality due to the tillage practices and low plant residue inputs in the first case, and overgrazing of vegetation cover and litter in the second. Total soil organic carbon and active carbon were significantly higher in spring compared to autumn. Seasonal changes of basal microbial respiration and carbohydrates were not statistically significant.