Increase in organic carbon input by adding organic fertilizers to the soil is used as a way to improve biological, physical and chemical properties of soil and carbon sequestration. Anionic polyacrylamide application as an organic soil conditioner alone or in combination with organic material can change soil quality. The objective of this study was to investigate the influence of some organic soil conditioners on carbon sequestration and retention of different forms of organic carbon in soil. Two heavy and light textured soils were sampled from the top 30-cm layer of two agricultural lands in Hamadan (northwestern Iran) which has a semi-arid climate. The samples were treated with alfalfa and wheat residues (d<2mm at a rate of 50g Kg-1 dry weight basis), and anionic polyacrylamide at the rates of 0, 0.1, 0.2 and 0.4 g kg-1 of soil. Samples were brought to field capacity, and were kept in the dark. Soils sampling was done at different interval times and the data were tested separately for each period. Total organic carbon, organic carbon (OC) in sand and clay + silt size fractions, OC in light and heavy fractions increased with the addition of plant residues (particularly wheat residue) to the soils. Polyacrylamide, in the heavy soil did not improve carbon sequestration. But in the light soil, caused improvements in carbon sequestration. Mean weighted diameter (MWD) of aggregates in the both soils increased significantly with the addition of plant residues, particularly wheat residue. In both the soils without plant residue, the application of polyacrylamide caused an increase in aggregates MWD. But, in the heavy soil treated with wheat and alfalfa straws, the application of polyacrylamide had significantly negative effects on aggregates MWD. However this bad effect on aggregates MWD was not found in the light soil treated with wheat and alfalfa straw.
