Effect of organic matter and potassium chloride on soil structure stability indices

Most of the soils in arid and semi-arid regions of Iran contain less than 1 % organic matter, which lead to reduce the quality of some physical properties of the soil, including decreasing the stability of aggregates, destruction the soil structure and reducing saturated hydraulic conductivity. Considering to the importance and role of organic matter and the presence of sodium and potassium in cattle manure and their destructive effects on soil structure, this research was performed to study the effect to investigate the effect cattle manure, sewage sludge and potassium chloride on soil structure stability indices.

In this research, the effects of cattle manure and municipal sewage sludge at three rates (0, 1 and 2 %) and potassium cation (potassium chloride) at three salinity levels (1, 3 and 5 dS/m) and 3 replications as a completely randomized design and factorial arrangement were studied to compare the treatments on soil structure stability indices. Treatments of 1 and 2 % (weight) cattle manure and sewage sludge were applied to soil and treated soil filled in pots (1 kg weight). To saturate the soil, all pots were irrigated with 300 ml of urban water. Then, irrigation was made by KCl solutions and 200 ml of KCl was added to each pot every week for the period of 8 weeks. After then, soil structural stability indices including normalized stability index (NSI), geometric mean diameter of wet aggregates (GMD), and percentage of aggregate destruction (PAD) were measured. The statistical analysis of data was made by JMP8 software and comparison of means based on LSD test at P < 0.001 was performed.

the results of structural stability showed that sewage sludge treatment had a positive effect on aggregate stability, percentage of aggregate destruction and geometric mean diameter of wet aggregates, while manure application due to high concentration of sodium and potassium and their destructive effects on aggregate stability had the negative effect on most structural stability, except for the normalized stability index. In general, geometric mean diameter of wet aggregates in treatment with no organic matter and salinity level of 3 dS/m was the lowest value and it showed the highest value in 1 % of sewage sludge and salinity level of 3 dS/m. Also, amounts of normalized stability index were the highest and lowest values in salinity of 1 dS/m + 1 % of manure, and salinity of 3 dS/m + no organic matter, respectively. Percentage of aggregate destruction significantly decreased at salinity levels less than 3 dS/m when organic matter increased, while it was not significantly changed at salinity of 5 dS/m due to increment of potassium and its destructive effect on soil structure.

Considering the positive effect of organic matter on stability of aggregates in short term, and the cost effectiveness of sewage sludge, it is suggested that the application the sewage sludge on soil structure indices in agricultural lands will be studied during several years.