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The processes of N mineralization and immobilization which can occur in agricultural soils during decomposition of plant residues are briefly reviewed in this paper. Results from different incubation studies have indicated that the amounts of N immobilized can be very important and that the intensity and kinetics of N immobilization and subsequent remineralization depend on the nature of plant residues and the type of decomposers associated. However, most of the available literature on these processes refer to incubations where large amounts of mineral N were present in soil.Incubations carried out at low mineral N concentrations have shown that the decomposition rate of plant residues is decreased but not stopped. The immobilization intensity, expressed per unit of mineralized C, is reduced and N remineralization is delayed. Nitrogen availability in soil can therefore strongly modify the MIT kinetics (mineralization-immobilization turnover) by a feed-back effect.The mineralization and immobilization kinetics have been determined in a two-years field experiment in bare soil with or without wheat straw. Mineralization in plots without straw seemed to be realistically predicted by accounting for variations in soil temperature and moisture. Immobilization associated with straw decomposition was clearly shown. It was increased markedly by the addition of mineral N throughout decomposition. It is concluded that mineral N availability is an important factor controlling plant residues decomposition under field conditions. A better prediction of the evolution of mineral N in soil may therefore require description and modelling of the respective localization of both organic matter and mineral N in soil aggregates.

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Polycaprolactone (PCL) was gamma-irradiated at different phases such as solid state at 30 to 55ЊC, molten state, and supercooled state, under vacuum or air atmosphere, to elucidate its crosslinking behavior. Irradiation in the molten state (80ЊC) gave higher gel content compared to room temperature. The resulting gel, however, contains many voids due to the gas evolved during irradiation. Conversely, irradiation of PCL in the supercooled state led to the highest gel content among the three irradiation conditions and it was free of voids. Based on these findings, to evaluate heat resistibility of crosslinked PCL prepared by irradiation in supercooled state, the crosslinked PCL was hot pressed at 200ЊC to form a film. Unirradiated PCL melted at 60ЊC. The film prepared from 160 kGy irradiated PCL (crosslinked sample) under an applied load of 0.667 MPa, at a temperature of 110ЊC did not break even after 3 h. At a temperature of 120ЊC, the film has a tensile strength of 3 MPa. Furthermore, the film extended by hot pressing is transparent and has high heat shrinkability.

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