The Effect of Land Use Change on Some Physical and Chemical Properties of Soil

Nowadays, land use change increasingly causes environmental problems and usually, in the first step, affects the soil properties and causes a decrease in the quality and an increase in the destruction, and erosion of the soil. Land use is defined as the sum of management and planning activities and inputs that humans do in a specific type of land cover (Ellis, 2021). The improper use and management of land resources, which has led to soil degradation, can have a great impact on the development of sustainable agriculture and is recognized as a serious global challenge for food security and ecosystem sustainability (Ebabu et al., 2020). Changing the use of forest lands and pastures for agriculture purposes has become one of the significant concerns in the world causing environmental degradation and climate change. Studying the effect of land use on soil properties provides the possibility of identifying sustainable management and preventing future soil degradation. The knowledge about the effect of land use change on soil properties, as one of the most essential components in sustainable agriculture in Jiroft, which is considered one of the important agricultural regions of Iran, is very limited. Therefore, this study was carried out to investigate the effect of different land use on some physical and chemical properties of the soil and to prepare distribution maps of these properties in the Konarsandal region of Jiroft.

In this research, the effect of the type of land use was studied in a part of the lands of Jiroft Plain (around the historical hills of Konarandal). For this purpose, by sampling surface soil in four types of land use, including agricultural land, abandoned agricultural land, date garden, and natural forest, some of the physical and chemical properties of soil including the percentage of sand, silt, and clay, electrical conductivity, pH, absorption ratio of sodium, calcium carbonate, organic carbon, bulk density, liquid limit (LL), plastic limit (PL), specific surface area (SSA), cation exchange capacity (CEC) and hygroscopic water content (HWC) were studied, and the spatial distribution maps of some parameters were obtained. In terms of topography, the studied area has a relatively uniform slope and its physiographic unit is in the form of alluvial plains. The dominant forest land cover in this area mainly includes Prosopis and Tamarix aphylla and the dominant vegetation cover of the abandoned agricultural land includes the Salsola soda. Also wheat and melon are mainly cultivated in the agricultural lands. According to the announcement of the residents and owners in the studied area, the history of agricultural lands (date garden and arable land) is more than 20 years and the irrigation system of these lands is in the form of flooding. 26 samples of the surface soil (0 to 20 cm) were taken from each land use (104 sampling points). For statistical analysis of the data, SAS9.1 was used and averages were compared with Duncan’s test (p<0.05). Correlation between the data was done using SPSS16 and Variowin2.2 was used to calculate and draw the Variogram maps.

The results showed that the type of land use changed all the studied parameters. The highest percentage of clay (46%) was observed in the abandoned agricultural land. Changes in the percentage of sand, silt and clay in different land uses could be caused by the type of management conducted on the process of soil particle loss. With changes in soil textural characteristics (sand, silt, and clay), the SSA, LL, PL, HWC, and CEC had also changed. The kriging maps also showed the uniform distribution of these features well. The soil quality in the abandoned agricultural land was not very suitable compared to other land uses. The amounts of EC and organic carbon in this land use were about 2 times more and about 20% less than agricultural lands, respectively. The coefficient of variation of particle size distribution (sand, silt and clay) and the organic carbon among the studied soil variables in the region were relatively high, which could be attributed to the land use changes, differences in plowing, management operations and surface soil erosions.

Differences in the separation of soil particles in different land uses can cause differences in the distribution size of soil particles and even soil texture (Tallen and Yerima, 2018). The result that was also observed in this study. Other properties of the soil such as LL, PL, SSA, CEC and HWC were also different in the studied land uses which could be related by positive and significant correlation (r>0.7**) with clay content. The abandonment of agricultural lands had caused low quality and fertility of soil in this land use; this issue could be due to high evaporation in this area which can increase salinity, and also because of little vegetation in this area which decreased the amount of organic matter of soil. It is suggested that in order to preserve the soil properties of the abandoned agricultural lands, if the conditions in terms of water supplement are available, this land use should be restored as agricultural land, or according to the amount of seasonal precipitation in this region, these lands be cultivated by drought-resistant plants such as Tamarix aphylla.