JWSS - Journal of Water and Soil Science

---

Due to physiography and weak structure, the pasture soils in Boroojen are potentially degradable. Converting pastures to agricultural land accelerates the degradation processes. A study was conducted in 1999 to show the effects of almost 20 years of farming on originally pasture land on soil physical properties, fertility, and tilth index of pastures in Boroojen region in Chahar Mahal and Bakhtiari Province (central Zagrous). Soil texture, clay content, bulk density, organic matter, saturation moisture percent, cone index, plasticity index, mean weight diameter and aggregate size and distribution, nitrogen, phosphorus, and potassium were measured.

After 20 years of cultivation, bulk density increased about 20% while organic matter decreased by 30%. Cone index was lower in the undisturbed pasture but nitrogen and phosphorus contents were higher compared to the disturbed pasture. The undisturbed pasture contained more larger (> 1 mm) aggregates, while the disturbed pasture had more smaller aggregates. Sustainable use of natural resources will lead to their long term workability, while negligence of conservational practices including appropriate farming management practices will result in the destruction of these resources.

---

The forms and dynamics of soil phosphorus can be greatly affected by land use changes, which often involve changes in vegetation cover, biomass production and nutrient cycling in the ecosystem. Present research evaluates the impact of land use change on the amount of total organic and inorganic P, labile, moderately labile and nonlabile P pools in semiarid soils of central Zagros. Samples were collected from surface soils (0-10 cm) of i) of moderately degraded pasture (20-25% plant cover), ii) highly degraded pasture (5-10 % plant cover), and iii) cultivated field (10 years) in Soolegan sub watershed and i) moderately degraded pasture (25-30 % plant cover) and ii) highly degraded pasture (5-10 % plant cover) in Sadat Abad sub-watershed. Significantly (P<0.05) low amounts of total organic P were found following cultivation (23.9%) and overgrazing (18.2 and 40.8 %) in Soolegan and Sadat Abad, respectively. The largest depletion of labile organic P (NaHCO3-Po) (72.3%) and moderately labile organic P (H2SO4-Po plus NaOH-Pi) (24.3%) were observed in cultivated rainfed land in Soolegan. Overgrazing led to decrease in labile organic P (42.1 and 64.4%), moderately labile organic P (13.9 and 35.7%) and nonlabile organic P (NaOH-Po) including moderately resistant and resistant organic P (12.9 and 44.4%) in Soolegan and Sadat Abad, respectively. Our results showed that degradation of natural plant cover cause to depletion in the soil P pools. Decreasing the amounts of moderately resistant and resistant P pools led to a decline in soil productivity and fertility.