Consecutive Application of Organic Matter and Sodicity on Secondary Particle Size Distribution

This study investigates the effect of rate and type of organic matter and also consecutive application of sodium on secondary particle size distribution. At first step، a cropland soil was treated with two organic matter types (manure and straw stubble)، at different rates of 0، 1 and 5%، with three replicates during 4 months. Subsequently، four levels of SAR (0، 1، 10 and 30) were added to the pretreated samples through irrigation water. The results indicated that among different treatments، straw stubble 5% led to the most frequency of aggregates >1 mm and 0. 25-1 mm. It was found that increasing organic matter rate، the size and stability of aggregates increased. Aggregates >0. 25 mm were decreased with increasing the irrigation water SAR value، while this reduction was lower for higher rates of organic matter. This indicates that the effect of sodium on aggregate dispersion depends on the rate of organic matter. Also، increasing the SAR values، the frequency of particles in the fractions of 0. 25< and 0. 125< was increased. At the higher levels of SAR، aggregates >1 mm showed more sensitivity against dispersion than those in 0. 25–1 mm fraction. The findings of this study reveal that besides of type and rate of organic matter، the SAR value of irrigation water is effective in particles size distribution. Burning straw stubble after harvesting will lead to aggregate instability and soil environmental erosion increasing.