JWSS - Journal of Water and Soil Science

---

The main sources of cadmium in soil-plant continuum in amounts that might present a hazard are liquid and solid wastes of sewage sludge, farm manures and fertilizers. In the southwest of Iran (Khuzestan Province) over 50,000 ha of land is under sugarcane (Saccarum officinarum) cultivation and more than 80,000 ha will be under sugarcane by the end of the year 2000. In these sugarcane fields, about 400 kg ha^-1 diamonium phosphate (DAP) and 400 kg ha^-1 urea are applied annually. There is no data available to show the fertilizers impact on soil, water and plant contaminations in Iran with respect to cadmium. The objective of this research was to compare the extractable cadmium of virgin soils with that of soils under sugarcane.

 Four sugarcane growing stations viz. Haft-tapeh, Karoon, Shoeibieh and Ghazali with cultivation histories of 36, 20, 2 and 1 year, respectively, were selected. In each site, along a transect soil samples from 0-30 cm of both furrows and ridges of cultivated soils and of virgin soils were collected. Electrical conductivity (EC), pH, clay and organic carbon contents, CI and Cd of 101 soil samples were measured according to standard methods. Results showed that increasing either EC or CI increased Cd concentration with its maximum in virgin soils and its minimum in furrows.

 Results also indicated a slight decrease in the Cd content of cultivated soils.

---

Electrical conductivity and acidity of soil are the most important chemical factors of soil for agriculture. The nature of soil is in such a way that its change has a continuous form. The method that can take into account this continuity will be able to show a better picture of change in soil characteristics. Objectives of this research are to investigate the relations between measured electrical conductivity and soil acidity of Qom plain, and clustering, compare the clustering methods, determine the optimum numbers of cluster, and to zone the clusters in the study area. Accordingly, two fuzzy clustering methods FCM and GK, were used for data mining and clustering of 465 measured data. For estimating the appropriateness and comparison of two methods, some criteria including Partition Coefficient, Classification Entropy, Partition Index, Separation Index and Xie and Beni's Index were used. Data mining results showed that the optimum number of clusters for FCM and GK method was 15 and 17, respectively. After investigating the results of clustering and based on the criteria of appropriateness, it was indicated that GK was the best clustering method. According to this method, 295 data from 465 measured samples had more than 40 percent of membership function. So, 9 clusters from 17 clusters had more than 20 members. Then salinity-alkalinity zoning based on GK method to show the clusters distribution better in the study area was prepared. This prepared fuzzy map explained that most of Northwest and west belonged to cluster 1 and eastern parts of study area include belonged to cluster 17. Based on this, salinity-alkalinity and the ensuing soil degradation in east of study area is more likely than the west of it.

---

Soil aggregate stability is considered as a key indicator of soil quality and health assessments in rangelands. Many factors and properties such as soil texture, organic carbon, calcium carbonate, sodium adsorption ratio, and electrical conductivity might affect soil aggregate stability. The effects of these factors on aggregate stability of 71 soil samples collected from 4 rangeland sites (2 in semi-arid and 2 in arid lands) in Isfahan province were investigated. Aggregate stability was measured using the wet-sieving method. To optimize the trial conditions for the investigated soils, three shaking times (5, 10 and 15 minutes) were used to impose different hydromechanical stresses on the aggregates of ten soils selected out of the studied soils. The structural stability was assessed using mean weight diameter (MWD) and geometric mean diameter (GMD) of the water-stable aggregates. Significant differences of MWD were observed between the shaking times. The 10-min shaking was selected as best for structural stability assessment in the studied regions because it resulted in better differentiation of soils on the basis of structural stability. Among the intrinsic properties, soil organic carbon content had the most important role in aggregate stability in all zones. However, electrical conductivity (in addition to organic carbon content) had an important role in aggregate stability in the arid rangelands. Log-normal distribution and GMD could represent better the aggregate size distribution when compared with normal distribution and MWD in the studied regions. Overall, wet-sieving method with shaking time of 10 min is suggested to assess the soil structural stability in rangelands of Isfahan province. Therefore, soil aggregate stability and the factors affecting this vital indicator can be used efficiently for assessing and monitoring management effectiveness and rangeland functionality trend.