Emilia Urbanek

Why are aggregates destroyed in low intensity fire

Soil structure is often severely affected during high intensity burning, while low intensity prescribed burning has often been thought to have a low or neutral effect on soil aggregation. In this issue of Plant and Soil, (Albalasmeh et al. 2012) report a novel mechanism of aggregate disruption during low intensity burning that may explain some contradictory results reported in previous studies. Albalasmeh et al. (2012) suggest that during rapid heating of moist soil aggregates, intra-aggregate water is vaporized and the increased pressure causes rupture of the internal bonds and leads to aggregate breakdown. This mechanism can be compared to the aggregate breakdown due to slaking, when dry aggregates are suddenly wetted or submerged in water. Identification of the reasons for the aggregate disruption at low temperatures is important for choosing optimal soil and weather conditions for prescribed fires.

Effect of Long Storage and Soil Type on the Actual Denitrification and Denitrification Capacity to N2O Formation

Abstract The actual denitrification to N2O and denitri-fication capacity to N2O after flooding of different soil samples stored for over 25 years in air-dry conditions and fresh, air dried samples were compared in our study. Zero N2O release was observed from the stored soils but the fresh soil samples had very low actual denitrification to N2O. NO3- addition significantly increased the amount of N2O (denitrification capacity to N2O) released after flooding, which depended on the length of storage and type of soils and was much higher in stored soils. Prolonged exposure of the soils to drought conditions caused a greater decrease in the Eh value compared with the fresh soil. The total cumulative release of N2O from the stored and fresh soils was correlated with the reduced NO3- and organic C content in soils enriched with NO3-. Some soils showed the capability of N2O consumption. CO2 release depended on the length of storage and type of soils under flooding after pro-longed drought. On average, CO2 release was higher from the stored rather than fresh soils. The organic C content in the stored soils was generally lower than in the fresh soils, probably due to the storage effect. The cumulative CO2 release from the stored soils was well correlated with the organic C while no correlation was observed for the fresh soil samples.

Tensile and erosive strength of soil macro-aggregates from soils under different management system

Abstract Reduced soil tillage practices are claimed to improve soil health, fertility and productivity through improved soil structure and higher soil organic matter contents. This study compares soil structure stability of soil aggregates under three different tillage practices: conventional, reduced and no tillage. The erosive strength of soil aggregates has been determined using the abrasion technique with the soil aggregate erosion chambers (SAE). During abrasion soil aggregates have been separated into the exterior, transitional and interior regions. The forces needed to remove the material from the aggregate were calculated as erosive strength and compared with the tensile strength of the aggregates derived from crushing tests. The relationship between aggregate strength and other soil properties such as organic carbon and hydrophobic groups’ content has also been identified. The results show that erosive and tensile strength of soil aggregates is very low in topsoil under conventional and reduced tillage comparing with the subsoil horizons. Negative correlation was found between the content of organic carbon, hydrophobic compounds and erosive aggregate strength which suggests that the stabilising effect of soils organic carbon may be lost with drying. The positive relationship between the tensile strength and erosive strength for aggregates of 8-5 mm size suggests that the total strength of these aggregates is controlled by the sum of strength of all concentric layers