Effects of land-use change on soil physical characteristics and nutrients in northern Khuzestan

Land-use changes may influence various natural and ecological processes, including soil nutrients, soil moisture, soil erosion, land productivity and biodiversity. Compact cropping and lack of suitable management approaches in agricultural fields all over the world have affected soil properties in vast areas and led to changes in soil quality. The cultivation of sugarcane in the south of Iran started 60 years ago. The cultivation of sugarcane was mechanized in the southwest of Iran in the late 1950s. Over the past 40 years, the sugarcane yield has been declined from 110 to 50 tons per hectare over the same period. The long-term cultivation period (6 to 7 months), high water consumption (30,000 cubic meters per hectare at 25 to 30 turns irrigation), extensive heavy machinery uses in the planting stage, and sugarcane harvesting may change soil properties. In order to determine how these changes are taking place, it is necessary to examine the land qualitatively and quantitatively to prevent further destruction of this vast God-given source. Due to the fact that few types of research have so far been conducted on the long-term effects of cultivation on the physical and chemical properties of soil, this study aimed to investigate the effect of long-term sugarcane cultivation on some chemical and physical properties of soil in the Karoun Agro-industry Unit in Shoushtar city, Iran.

 This research was carried out to investigate the effect of long-term sugarcane cultivation on soil chemical and physical properties in Karoun Agro-industry Unit in Dimcheh with the geographical coordinates Latitude: 32° 02' 60.00" N Longitude: 48° 50' 59.99" E and 68 meters above mean sea level located at 12 kilometres to the west of Shoushtar city in Khuzestan province of Iran. The total area of the land is 45,000 hectares. This area has warm and dry climate conditions. The dominant soils of the area are classified in the large Calcic Haplousteps group. This study was carried out as a factorial experiment based on a complete randomized design with two factors, including fields in seven levels and depth in three levels (0-30, 30-60 and 60-90 cm) and three replications. Soil samples were collected from three depths in six fields with long-term sugarcane cultivation and adjoining uncultivated land. Then, some chemical properties were measured by standard methods Soil texture by hydrometric method, soil organic matter content by wet oxidation method, the soil sodium bicarbonate extractable phosphorus by Olsen method and available K using 1 N NH4OAc were measured. Also, total porosity and mean weight diameter were calculated based on conventional equations. Statistical analysis of data was performed by SAS 9.2 software, and the comparison of means was made using Duncan's multidomain test at a 1% probability level. Figures were also drawn using Microsoft Excel software.

 Results indicated that land-use changes and long-term sugarcane cultivation result in soil chemical properties changes. By land-use changes, the amount of sand decreased from 22.55% in virgin soil to 6.67% in sugarcane fields. The apparent density and the mean weight diameter by changing the use of virgin soil to sugarcane farms increased by 16% and 67%, respectively, though this result was opposite for the total porosity. Also, land-use changes from virgin soil to sugarcane fields increased organic matter and absorbable phosphorus and reduced potassium absorbable and carbon-to-nitrogen ratio. Overall, changes in chemical properties in surface soil (0-30) were more than other depths (30-60 and 60-90). Also, estimating the correlation coefficients between different traits under the studied treatments showed that sand was correlated with all traits except clay and organic matter. In contrast, the clay had a positive and significant relationship with the mean weight diameter of soil aggregates.

 This research showed that the soil chemical properties of different sugarcane fields significantly changed by the land-use changes of long-term sugarcane cultivation. Thus, the land-use changes, abundant irrigation and leaching increased the organic matter, the mean weight of the diameter of aggregates and the apparent density of the soil. Also, the amount of phosphorus absorbed by sugarcane and fertilization increased, while the amount of organic matter of C/N and soil absorption potassium decreased in cultivated land. Potassium is essential for sugarcane growth, and the reduction of potassium absorbable can cause limitations in its growth and performance. On the other hand, concerns about soil density and change in the optimal plant growth conditions due to heavy agricultural machinery are clear and severe. Therefore, creating a cultivated system with minimal density is essential. Also, soil chemical properties monitoring and maintaining the quality of the studied soils must be considered in land management approaches.