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Abstract: Laboratory decomposition experiments measuring the mineralization of C from plant residue are increasingly used to test the effects of different litter sources and soil conditions. To date, the most widely used methods are infra-red gas analysis (IRGA) and gas chromatography, which are time-consuming, and relatively expensive and complex to operate. The aim of this study was to devise a simple and rapid laboratory method to assess litter decomposition rates at frequent time intervals. We modified the MicroResp™ system to measure the amount of CO2 produced by two soils supporting contrasting microbial communities and containing the litter of eight crop species. The method was sensitive enough to differentiate both soil microbial communities and litter qualities. The method combines the accuracy of gas chromatography with the speed of absorbance measurements obtained via microplate readers. This technique provides an effective means for devising complex litter decomposition experiments capable of addressing the joint influence of multiple species, soil communities, environmental conditions, and their multiple interactions. [Copyright &y& Elsevier]

Abstract: Residue quality has been shown to influence soil water-stable aggregation (WSA) during crop residue decomposition, but there is still little information about its interactive effect with soil mineral N availability. The aim of this study was to determine the effect of soil mineral N on WSA during the decomposition of two high-C/N crop residues (wheat straw with C/N = 125.6 and miscanthus straw with C/N = 311.3). The two crop residues were combined with three mineral N addition rates (0, 60, and 120 mg N kg−1 dry soil). Respiration, soil mineral N content, and WSA (expressed as mean-weight diameter, MWD) were measured on several dates during a 56-d incubation. The effect of decomposing crop residues on WSA followed two phases. (i) Between 0 and 7 d, the increase in WSA was related to intrinsic residue quality with higher decomposability of the wheat straw resulting in higher WSA. (ii) Thereafter, and until the end of the experiment, mineral N addition rates had a predominant but negative influence on WSA. In this second phase, the average MWD of residue-treated soils was 0.92, 0.55, and 0.44 mm for the 0, 60 and 120 mg N kg−1 dry soil addition rates, respectively. Mineral N addition which did result in higher crop residue decomposition did not lead to higher WSA. WSA during crop residue decomposition is therefore not simply positively related to the induced microbial activity, and changes in microbial community composition with differential effects on WSA must be involved. The impact of high-C/N crop residues inputs on WSA, initially assumed to be low, could actually be strong and long-lasting in situations with low soil mineral N content. [Copyright &y& Elsevier]