JWSS - Journal of Water and Soil Science

Understanding the distribution of different P forms in soil aggregate fractions is important in evaluating the risk of P run-off and leaching in the agricultural soils. The objective of the present research was to determine the effect of aggregate size on soil phosphorus availability and fractionation in 10 calcareous soils. Micro aggregate (< 0.25 mm), macro aggregate (> 0.25 mm) and whole soil were separated by dry sieving. Olsen P, total P, organic P, and inorganic P fractions in micro aggregate, macro aggregate, and whole soil were determined. Soil inorganic P fraction was  determined by a sequential extraction procedure including: dicalcium phosphate (Ca₂-P), octa calcium phosphate (Ca₈-P), apatite (Ca₁₀-P), P absorbed by Al oxide (Al-P), P absorbed by Fe oxide (Fe-P) and P incorporated in to Fe oxide (O-P). The results showed that the amounts of (Olsen P), (Ca2-P), (Ca8-P), (Ca10-P), (Organic P), (Al-P), (Fe-P), (O-P) and (Total P) in 70, 60, 40, 40, 60, 70, 60, 50 and 70 percent of soils, respectively, in the micro aggregates were significantly higher than those of the macro ones. Finally, by increasing the P content, particularly the smaller sized aggregates, it was likely that the eroded material would favor greater P loss.

The present study was conducted to evaluate zinc availability and forms, as well as their relationships with soil properties in some soil samples of Kermanshah and Ilam provinces. Sequential extraction included Mg(NO₃)₂ (soluble + exchangeable), NaOAc pH = 5 (carbonatic fraction), Na-hypochlorite at pH = 8.5 (organic fraction), hydroxylamine hydrochloride at pH 2 (Mn oxides associated Zn), hydroxylamine hydrochloride (amorphous Fe oxides associated Zn), ammonium oxalate (crystalline Fe oxides associated Zn), and HNO₃ (the residual Zn). DTPA-Zn was in the range of 0.34-3.7 mg/kg. The results showed that soluble+ exchangeable, Mn oxides and crystalline Fe oxides associated Zn were not detectable by atomic absorption. Distribution of Zn fractions was in the order of Organic-Zn < Car-Zn < amorphous Fe oxides-Zn < Res-Zn. Organic matter bound Zn and amorphous Fe oxides associated Zn and the residual fractions showed a significant negative correlation with the calcium carbonate equivalent. It seemed s that calcium carbonates were the major factor in controlling the Zn content in the studied soils.

Due to unsuitable soil physical conditions, calcareous soils, and the existence of a huge amount of sulfur in the country, the study of sulfur effects on the soil structure and other soil properties is necessary. Therefore, the effects of different rates of sulfur including: 0, 750, 1500 and 3000 kg/ha, when accompanied by Halothiobacillus neapolitanus bacteria, on the soil properties in the corn-wheat rotation in two years were investigated. Parameters of soil pH, EC, sulphate, organic carbon, soil structure and wheat yield were measured. For the quantification of soil structure and quantity evaluation of sulfur effect on the soil structure, with measuring the aggregate size distribution, the mean weight diameter (MWD) and geometric mean diameter (GMD) of the aggregate indices, and the amounts of fractal dimension were determined. The r results indicated that with the progress of the experiment and further application of sulfur along with thiobacillus bacteria, aggregation and aggregate stability were increased. The effect of sulfur treatments on MWD and GMD was significant; based on quantification indices, it had 28 percent positive effect on the soil structure. Sulfur with 3 percent reduction of fractal dimension had a significantly positive effect on the soil structure. Application of sulfur decreased a small amount of soil pH and increased 12 percent of the soil EC and 40 percent of the soil sulphate. So soil structure improvement and reclamation of soil physical condition can be very effective on the soil conservation and sustainability of the production resources and the conservation of environment.

Due to the importance of nickel (Ni), and the effect of common soil additives on Ni fractions distribution, the present study was conducted to evaluate the effect of zeolite and vermicompost on nickel fractions over time. The experimental design consisted of a factorial combination of two levels of vermicompost (zero and 2% by weight), three levels of zeolite (zero, 4% by weight of Firoozkooh zeolite, and 4% by weight of Semnan zeolite), and two soil texture (clay and sandy loam) in a completely randomized design in triplicates. Treatments were contaminated with 50 and 100 mg nickel/kg soil. Ni fractions were extracted and measured at 20 and 60 days. The results showed that in initial soils, Car-Ni in sandy loam soil was higher than in clay soil, while the content of Fe, Mn- Ox Ni, OM-Ni, and Res-Ni in the clay soil was higher. In sandy loam soil, more nickel was recovered in Exch- and Car-fractions, while nickel recovery was higher in Mn, Fe-Ox Ni, OM-Ni, and Res-Ni in the clay texture. Zeolite addition caused a significant decrease of Exch- and Car-Ni in the clay soil on 60d and 100 mg/kg Ni level. Exch-Ni was reduced due to vermicompost application. Vermicompost application caused the decrease in Fe, Mn Ox-Ni in both studied soils and times, and OM-Ni increased by vermicompost application. Aging generally reduces the Exch-Ni but changes in Car-Ni over time depending on the soil texture. Aging did not affect Mn, Fe-Ox Ni, and Res-Ni, while OM-Ni increased over time in clay soil.