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Abstract: Application of lime and fertilizers might impact soil properties by affecting their physico-chemical parameters. The focus of the Versailles 42-plots experiment that was started in 1929 has always been to determine in fallow conditions the impact of mineral fertilization over time on the physico-chemical properties of a loamy soil. This paper''s aim is to assess the impact of long-term mineral fertilization on mechanical strength and soil stability. Soil samples of similar texture and bulk density were taken from the 42-plots site, with pH ranging from 3.5 to 8.2. Aggregate stability followed the procedure of Le Bissonnais (1996). Compression tests were performed in drained conditions and short loading time (300s). Remolded and saturated soil samples were used to focus on the impact of chemical changes due to repeated fertilization. The pre-compression stress values Pc were derived from compression curves using various model fits according the shape of curve. Chemical discrepancies among soils provided from pH, organic matter and diversity of treatments. The decrease of pH reduced the cationic exchange capacity (CEC) value due to the protonation of variable charges and retention of positively charged hydroxyl-Al polymers. Exchangeable aluminum represented up to 90% of the CEC in acid soils as calcium ions represented from 80 to 98% of CEC with increasing pH of neutral and alkaline soils. Compression curves showed different global shapes according pH values and the contrasted behavior of acid soils when compared to other ones. The Pc values of highly acid soils were much greater than other treatments (greater than 150kPa compared with 30kPa). Nevertheless their Pc values decreased down to 40kPa, when soils were air-dried before compression. Meanwhile the deformation rate decreased when the pH dropped. This lower deformation cannot be explained by kinetic aspects and was not sensitive to drying. So the hypothesis of a set of yield stress avoiding drainage of the water phase and limiting soil compression was proposed. Aggregate stability tests revealed the unstable nature of all plots especially with the highly acid soils. The size distributions of fragment were very similar for all three tests with a narrow distribution in elementary particle class suggesting the predominance of dispersion in fragmentation process. But we found opposite results for this soil by comparing mechanical strength and water stability of aggregates. This contrast raised the question of the crucial role of the air-drying step on aggregate stability measurements. A small increase of aggregate stability was observed in neutral and alkaline soils due to calcium bridges when compared to reference plot. Such effect was not observed in compression behavior of remolded soils. Future studies will require the use of structured soil samples; in particular for neutral and alkaline soils to gather evidence of the effects of calcium bridges on soil stability and mechanical strength. Our results showed the need to consider interfacial processes in the soil stability and compression behavior and the great interest of the 42-plots experiments at INRA Versailles to relate chemical and physical soil properties. [Copyright &y& Elsevier]

We studied the fate of sludge spiked with 14C-labelled diuron, glyphosate and nonylphenol applied to the soil by the way of contaminated sewage sludge in the soil-plant-water system. Here we show that the mineralization of the chemicals in mixture is reduced by 40–80% by comparison with a direct soil contamination. The persistence of the chemicals in soils is increased in the presence of sludge. We showed also that the chemicals present in the sludge are mobile and partly transferred to soil leachates and plant seedlings. These results allow postulating that these compounds may induce an ecotoxicological impact on the soil ecosystem. [ABSTRACT FROM AUTHOR]

Soil is damaged by several threats and, among them, chemical contamination by pesticides and compaction. However, the effect of compaction on the fate of pesticides in soil, and the impact of pesticides on soil biological functioning are unknown. Therefore, we studied the effect of soil compaction on the degradation of the herbicide isoproturon, and the impact of this herbicide on an enzyme activity ( β-glucosidase) involved in the C soil cycle. Undisturbed soil samples were prepared at different bulk densities, treated with isoproturon then incubated at 18°C in darkness for 63 days. The results showed that soil compaction did not modify significantly the degradation of isoproturon, neither the formation rates nor the nature of its metabolites. Moreover, compaction did not modify the impact of isoproturon on β-glucosidase activity. To our knowledge, these are the first results concerning the interactions between soil compaction and the degradation and impact of a pesticide. [ABSTRACT FROM AUTHOR]