Effect of soil physical and chemical properties on aggregate stability in some cultivation systems

Particle size distribution (PSD) and aggregate stability are known as the most important soil physical properties which have important influence on soil behavior. This study investigates the effect of soil physical and chemical properties on aggregate stability in some cultivation systems. The PSD in two statuses of dry (DPSD) and wet (WPSD) was studied in 6 cultivation systems consist of wheat, barley, maize, alfalfa, fallow and tilled land. The results showed that the cultivation systems had significant effects on water stable aggregates larger than 0.25 mm (WSA>0.25mm). Among different cultivation systems, alfalfa and wheat were found to be the best systems in establishing macro aggregates for the DPSD and WPSD, Respectively; however these aggregates for alfalfa were lower stable. The highest amounts of organic carbon were obtained in the wheat and barely cultivation systems (1.09% and 1.04%, respectively), while the other systems, showed no significant differences. All of the physical and some chemical properties (i.e. EC, pH, ESP, organic carbon, exchangeable sodium, and soluble cations) were influenced significantly by the cultivation systems, while this effect was not significant (p>0.05) for other chemical properties such as SAR, CEC, calcium carbonate, exchangeable calcium, magnesium and potassium. In addition, the primary PSD had significant influence on secondary PSD. There was a negative significant relationship between sand fraction and stable aggregates (wet and dry), while this relation was positive for silt. Clay content had no significant influence on macro aggregates. The results also indicated that in comparison to physical properties, chemical properties had less effect on WSA>0.25. In this regard, organic carbon was found as the most prominent factor which can control aggregate stability. The findings of this study reveal that larger aggregates are not always stable particles and based on the PSD, the concept of stability can not be described exactly.