Effects of Sewage Sludges and Composts on Soil Porosity and Aggregation

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Abstract
Modifications induced in soil porosity and in stability of soil aggregates were studied for 2 years on an Italian sandy loam soil. Aerobic and anaerobic sludges and their composted mixtures with the organic fraction of urban refuse were used and compared with manure. Addition rates were equivalent to 50 and 150 metric tons/ha of manure on the organic carbon basis. A control plot was also present. Porosity and pore size distribution were measured on thin sections prepared from undisturbed soil samples by using electro‐optical image‐analysis equipment. The stability of soil aggregates was determined by a wet‐sieving method.All organic materials increased the total porosity significantly at all sampling times. Differences between the two application rates were generally not significant. The improvement of total porosity caused by sludges and composts was comparable to that of manure. Modifications of pore size distribution were also observed. Stability of soil aggregates increased slightly in treated samples. The best stabilizing effect was shown by the anaerobic sludge.