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

This study investigated the effect of rate and type of organic matter, and consecutive application of sodium on secondary particle size distribution. At first, a cropland soil was treated with two organic matter (manure and straw stubble) at different rates of 0%, 1% and 5%, with three types 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 with 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 depended on the rate of organic matter. Also, by increasing the SAR values, the frequency of particles in the fractions of 0.25< and 0.125< was increased. At higher levels of SAR, aggregates >1 mm showed more sensitivity against dispersion than those in the 0.25–1 mm fraction. The findings of this study revealed that besides the type and rate of organic matter, the SAR value of irrigation water is effective in particle size distribution. Burning straw stubble after harvesting lead to aggregate instability and increased soil environmental erosion .