During the conversion of forest grassland to agriculture in NE Iran, it was found that cultivation decreased organic carbon and nitrogen concentrations. Cultivation also increased bulk density and dispersible clays, indicating the soil had lower structural stability. The authors suggest that farmyard manure or green manure used with conservation tillage practices should help minimize breakdown of soil aggregates and excessive disturbance of soils.
This study examined the conversation of forest grassland soils to agricultural soils in NE Iran, and how this transformation affected various chemical and physical properties of the surface soil. Paired sites, matched for slope, parent material and physical aspect, were used.
As expected, organic carbon and nitrogen concentrations decreased with cultivation. This reflected the reduced return of plant residues (leaf litter). Bulk density and dispersible clays increased in the cultivated soils, indicating lower structural stability. The link between chemical and physical components is that carbon (as organic matter) stabilises soil aggregates against slaking and reduces clay dispersion through binding soil particles.
Retention of soil carbon at high levels is therefore indispensible to the sustainable management of agricultural soils. The authors suggest that farmyard manure or green manure used with conservation tillage practices should help minimize breakdown of soil aggregates and excessive disturbance of soils.
Golchin A & Asgari H (2008) Land use effects on soil quality indicators in north-eastern Iran. Australian Journal of Soil Research 46: 27-36. Read Abstract.