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Villenave-d'Ornon, France

Sierra J.,AINRA | Motisi N.,CIRAD - Agricultural Research for Development
Soil Research | Year: 2012

Several long-term studies on tropical soils have shown that legume residue incorporation increases soil nitrogen (N) sequestration more than that of carbon (C), resulting in a fall in the C/N ratio. This study was designed to assess the short-term effect of legume litter addition on N supply and the long-term effect on soil organic matter (SOM) formation and soil C/N decrease. The long-term effect was evaluated in a 2-year mesocosm experiment with high and frequent organic inputs from two types of legume litter with different C/N ratios, using stable isotope techniques. The short-term effect of litter was analysed using four different litters in 3-month laboratory incubations. A model of litter decomposition was used to describe C and N kinetics in the laboratory experiment and to verify whether the long-term effect of litter may be predicted from short-term incubations. The results of the mesocosm experiment confirmed that legume inputs increased soil organic N (mean +21%) more than organic C (mean +15%) (P≤0.05). Although no differences between litters were observed for C dynamics, N sequestration (14% and 28%) and the final soil C/N (12.0 and 10.8) varied with litter C/N (34.4 and 16.1, respectively). The laboratory experiment and model outputs confirmed these findings and indicated that the higher N sequestration was due to a change in the parameters describing humification of C and N coming from litter. This change depended on litter quality and was greater for litters with low C/NC humification 0.66gCg -1C and N humification 0.76gNg -1N for litter C/N 16.1. Carbon and N sequestration were greater in the laboratory experiment, due to a higher mineralisation of the new SOM derived from litter in the mesocosm experiment32% and 15% for the mesocosm and the laboratory experiments, respectively. Our results indicated that the decrease in soil C/N and the rapid mineralisation of new SOM should be considered in models of litter decomposition to respond correctly to the long-and the short-term effects of legume litter inputs in tropical soils. © CSIRO 2012. Source

In grapevine (Vitis vinifera L.), rootstocks are known to alter scion development by modifying stem weight and yield. The aim of this work was to evaluate the contribution of primary growth to the rootstock effects on scion biomass. The shoot growth of Vitis vinifera cv. Cabernet Sauvignon N autografted and grafted onto Vitis riparia cv. Riparia Gloire de Montpellier and Vitis berlandieriV. rupestris cv. 1103 Paulsen was studied in young plants grown in pots trained to one stem in two experiments. Stem elongation and phytomer emergence were studied from grafting until the end of the growth season. The elongation of the Cabernet Sauvignon N leaves, tendrils and internodes of each phytomer along the stem was fitted using sigmoid curves. The rootstocks studied slightly altered the growth dynamics of the leaves, internodes and tendrils of the scion. This is the first study to examine the effect of rootstocks on shoot growth dynamics in any species. The alterations in primary growth were small, suggesting that rootstocks may alter scion biomass principally by modifying secondary growth. © 2012 CSIRO. Source

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