Effect of different organic matters on time variability of soil aggregate stability at different size fractions

Particle size distribution (PSD) and aggregate stability are dynamic soil properties، which changes with time. This study investigates the effect of different organic matters on PSD variability. The experiment was carried out using factorial method in a randomized complete design with two treatments of organic matter (straw stubble and pistachio residue)، three levels of 0، 1 and 5 %w، three time steps (40، 80 and 120 days) and three replicates. In addition، soil PSD was measured in two manners of dry (DPSD) and wet (WPSD). The results indicated that studied treatments had different influence on the PSD، which depends on type and amounts of added plant residue macro aggregates frequency increased. Also، the control and straw stubble (5%) treatments with median sizes of 0. 228 and 0. 394 mm، resulted in the least and highest effect on DPSD، respectively. The results of DPSD variability showed that for all of the treatments، the frequency of smallest particles (<0. 125 mm) decreased significantly، while the WPSD had no changes with time. In comparison with the DPSD which 0. 125-0. 25 mm particles were the most frequent، for the WPSD this range shifts to the fraction of <0. 125 mm. This finding indicated that the DPSD and WPSD have not the same trend. In addition، Nitrogen utilization led to some changes in DPSD، whilst this effect was insignificant for the WPSD. The findings of this study reveal that following application of any type of organic matter، a range of particles size is most influenced. Taking into account the influence of time in aggregate studies is suggested.