1- Sari Agricultural Sciences and Natural Resources University
2- Tarbiat Modares University
2- Tarbiat Modares University
Abstract: (43 Views)
Introduction: Many studies indicated that the land use change through the change in the structure and function of the ecosystem, as well as the effect on the biochemical cycle, and the change in the properties of the soil causes the change in the soil quality over time and space. In Iran, especially in the north of the country, which is considered an agricultural pole due to the climatic and soil conditions, types of land use change have always been one of the human problems. In Kiasar region, it can be seen that the conversion of rangelands to various types of cultivation and the abandonment of agricultural lands after decrease of yield. Therefore, for the principled management of these lands should be known the history of conversion and its comprehensive effects on the environment, so this study was carried out to investigate temporal dynamics of soil quality characteristics after land use change in Kiasar city, Mazandaran province.
Materials and methods: For this study, the following sites were selected: in the village of Era – a barley cultivation area (<10 years old) and a control rangeland; two garden land uses (<10 and >30 years old); in the village of Vauser – a barley cultivation area (>20 years old), a control rangeland, and a garden land use (>30 years old); and in Orost village – a barley cultivation area (>30 years old) and a control rangeland. To investigate and compare land use change on the soil properties of the region, the land uses were selected in such a way that they have similar conditions in terms of physiography, especially the slope to can keep all the conditions constant. In each of these land uses, soil samples were taken from two depths of 0-15 and 15-30 cm with five repetitions and a total of 90 soil samples were taken from all land uses. Then, the percentage of clay, sand and silt, bulk density, specific density, aggregate stability, soil porosity percentage, organic carbon percentage, carbon sequestration, nitrogen percentage, nitrogen sequestration, absorbable phosphorus, particulate organic carbon and particulate nitrogen were determined. In order to investigate the effect of land use change on soil quality characteristics, the three-way factorial test with 5 replications was used. Also, comparison of means was done using Duncan's test at one and five percent probability level. All statistical tests were performed using SPSS software version 22.
Findings: The results of variance analysis for soil physical properties showed that land use type (garden, barley, and rangeland) and soil depth (first and second layers) had significant effects on all studied physical properties (P < 0.01). However, the time since land use change did not significantly affect bulk density, specific density, or porosity, though it did influence clay, silt, and sand percentages, as well as aggregate stability. The interaction effects between land use type and age were non-significant for all properties except aggregate stability. While none of the interaction effects were significant for specific density, all were significant for aggregate stability. The highest soil aggregate stability (mean = 55) was observed in the first depth of gardens >20 years after land use change, whereas the lowest value (mean = 16.8) occurred in the second depth of 20-year-old barley cultivation. Regarding soil chemical properties, land use type, age, and depth significantly affected all variables (P < 0.01 and P < 0.05). The land use × depth interaction was non-significant only for phosphorus, whereas the land use × age interaction was significant for all chemical variables. All interaction effects were significant for organic carbon, sequestered carbon, particulate organic carbon, and particulate nitrogen. In the first soil depth, the highest values were recorded in >30-year-old gardens: carbon sequestration (24.5 mg/kg), particulate organic carbon (0.33%), nitrogen sequestration (5.24 mg/kg), and particulate nitrogen (0.02%). Conversely, in the second depth, the lowest values were found in 30-year-old control rangelands: organic carbon (0.06%), nitrogen (0.02%), and phosphorus (mean = 16.2 mg/kg in 20-year-old rangelands)
Conclusion: In this study, the land use change improved the stability of soil in land uses of more than 20 and 30 years old. The amount of soil organic matter was the highest in garden use, therefore, the increase of total organic matter improves the soil structure, because organic matter is a humic binding factor in the formation of soil particles. The garden use with an age of more than 30 years had more carbon and nitrogen storage and sequestration than other uses. Also, particulate organic carbon, as an unstable part of soil organic carbon, reacted faster than characteristic organic carbon to management and land use change. In general, the results of this research showed that most of the physical and chemical characteristics of the soil improved over time in garden uses after the land use change, and this shows that the qualitative characteristics of the soil depending on the change in caused environmental conditions by the land use change are not independent of time. Therefore, it is suggested that along with a better understanding of the reaction of soil factors to management methods, the length of time should be taken into account in the best possible management strategy of these soil characteristics.
Materials and methods: For this study, the following sites were selected: in the village of Era – a barley cultivation area (<10 years old) and a control rangeland; two garden land uses (<10 and >30 years old); in the village of Vauser – a barley cultivation area (>20 years old), a control rangeland, and a garden land use (>30 years old); and in Orost village – a barley cultivation area (>30 years old) and a control rangeland. To investigate and compare land use change on the soil properties of the region, the land uses were selected in such a way that they have similar conditions in terms of physiography, especially the slope to can keep all the conditions constant. In each of these land uses, soil samples were taken from two depths of 0-15 and 15-30 cm with five repetitions and a total of 90 soil samples were taken from all land uses. Then, the percentage of clay, sand and silt, bulk density, specific density, aggregate stability, soil porosity percentage, organic carbon percentage, carbon sequestration, nitrogen percentage, nitrogen sequestration, absorbable phosphorus, particulate organic carbon and particulate nitrogen were determined. In order to investigate the effect of land use change on soil quality characteristics, the three-way factorial test with 5 replications was used. Also, comparison of means was done using Duncan's test at one and five percent probability level. All statistical tests were performed using SPSS software version 22.
Findings: The results of variance analysis for soil physical properties showed that land use type (garden, barley, and rangeland) and soil depth (first and second layers) had significant effects on all studied physical properties (P < 0.01). However, the time since land use change did not significantly affect bulk density, specific density, or porosity, though it did influence clay, silt, and sand percentages, as well as aggregate stability. The interaction effects between land use type and age were non-significant for all properties except aggregate stability. While none of the interaction effects were significant for specific density, all were significant for aggregate stability. The highest soil aggregate stability (mean = 55) was observed in the first depth of gardens >20 years after land use change, whereas the lowest value (mean = 16.8) occurred in the second depth of 20-year-old barley cultivation. Regarding soil chemical properties, land use type, age, and depth significantly affected all variables (P < 0.01 and P < 0.05). The land use × depth interaction was non-significant only for phosphorus, whereas the land use × age interaction was significant for all chemical variables. All interaction effects were significant for organic carbon, sequestered carbon, particulate organic carbon, and particulate nitrogen. In the first soil depth, the highest values were recorded in >30-year-old gardens: carbon sequestration (24.5 mg/kg), particulate organic carbon (0.33%), nitrogen sequestration (5.24 mg/kg), and particulate nitrogen (0.02%). Conversely, in the second depth, the lowest values were found in 30-year-old control rangelands: organic carbon (0.06%), nitrogen (0.02%), and phosphorus (mean = 16.2 mg/kg in 20-year-old rangelands)
Conclusion: In this study, the land use change improved the stability of soil in land uses of more than 20 and 30 years old. The amount of soil organic matter was the highest in garden use, therefore, the increase of total organic matter improves the soil structure, because organic matter is a humic binding factor in the formation of soil particles. The garden use with an age of more than 30 years had more carbon and nitrogen storage and sequestration than other uses. Also, particulate organic carbon, as an unstable part of soil organic carbon, reacted faster than characteristic organic carbon to management and land use change. In general, the results of this research showed that most of the physical and chemical characteristics of the soil improved over time in garden uses after the land use change, and this shows that the qualitative characteristics of the soil depending on the change in caused environmental conditions by the land use change are not independent of time. Therefore, it is suggested that along with a better understanding of the reaction of soil factors to management methods, the length of time should be taken into account in the best possible management strategy of these soil characteristics.
Keywords: carbon sequestration, particulate nitrogen, particulate organic carbon, temporal dynamics, soil particle stability.
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