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Aim: This study assessed whether growing cowpea can increase phosphorus (P) availability in the rhizosphere and improve the yield of legume-cereal systems. In alkaline Mediterranean soils with P deficiency, it is assumed that legumes increase inorganic P availability.Methods: A field experiment was conducted at the Staoueli experimental station, in Algiers province, Algeria, to compare the growth, grain yield, P availability, and P uptake by plants with sole-cropped cowpea (Vigna unguiculata L. cv. Moh Ouali) and maize (Zea mays L. cv. ILT), intercropped cowpea-maize, and fallow. Results: P availability in the rhizosphere was increased in both sole cropping and intercropping systems compared with fallow. It was highest in intercropping. The increase in P availability was associated with (i) significant pH changes of the rhizosphere of cowpea in sole cropping and intercropping systems, with the rhizosphere acidification significantly higher in intercropping (−0.73 units) than in sole cropping (−0.42 units); (ii) significant increase in the rhizosphere pH of intercropped maize (+0.49 units) compared to fallow; (iii) increased soil respiration (C-CO2 from microbial and root activity) in intercropping compared with sole cropping and fallow; and (iv) higher efficiency in utilization of the rhizobial symbiosis in intercropping than in sole-cropped cowpea. Conclusion With cowpea-maize intercropping, cowpea increased the P uptake, by increasing the P availability by rhizosphere pH changes in an alkaline soil. Overall, this study showed that intercropping cowpea improved the plant biomass and grain yield of maize in this soil

Soils represent a large carbon pool, approximately 1500 Gt, which is equivalent to almost three times the quantity stored in terrestrial biomass and twice the amount stored in the atmosphere. Any modification of land use or land management can induce variations in soil carbon stocks, even in agricultural systems that are perceived to be in a steady state. Tillage practices often induce soil aerobic conditions that are favourable to microbial activity and may lead to a degradation of soil structure. As a result, mineralisation of soil organic matter increases in the long term. The adoption of no-tillage systems and the maintenance of a permanent vegetation cover using Direct seeding Mulch-based Cropping system or DMC, may increase carbon levels in the topsoil. In Brazil, no-tillage practices (mainly DMC), were introduced approximately 30 years ago in the south in the Paraná state, primarily as a means of reducing erosion. Subsequently, research has begun to study the management of the crop waste products and their effects on soil fertility, either in terms of phosphorus management, as a means of controlling soil acidity, or determining how manures can be applied in a more localised manner. The spread of no-till in Brazil has involved a large amount of extension work. The area under no-tillage is still increasing in the centre and north of the country and currently occupies ca. 20 million hectares, covering a diversity of environmental conditions, cropping systems and management practices. Most studies of Brazilian soils give rates of carbon storage in the top 40 cm of the soil of 0.4 to 1.7 t C ha-1 per year, with the highest rates in the Cerrado region. However, caution must be taken when analysing DMC systems in terms of carbon sequestration. Comparisons should include changes in trace gas fluxes and should not be limited to a consideration of carbon storage in the soil alone if the full implications for global warming are to be assessed. no-tillage / mulch / stocks / fluxes / greenhouse gas / Brazil

The extension of viticulture on hill slopes in the Mediterranean basin might be responsible for a loss of organic carbon from the soil, as a result of increasing runoff and erosion. The loss of C makes soil aggregates less stable, which in turn increases erosion risk. We should use indicators of these risks and so be able to identify the most threatened areas. We first tested four widely used methods for determining aggregate stability for their ability to predict runoff and erosion; all include slaking and give indices such as rates of stable (> 200 mm) macro-aggregates (MA200) or mean weight diameter (MWD). We selected three Mediterranean vineyards characterized by brown calcareous soils and on which we had previously studied the effects of simulated rainfall. The tests were made on the soils from five farming situations, corresponding to 14 simulated rainfalls with an intensity of 60 mm hour ÿ1 . The two indices that best predict erosion are those resulting from the method of Le Bissonnais (MWD in its logarithmic form and MA200). Then, we analysed the relations between aggregate stability and soil properties on 68 soil samples from various locations within the three selected sites. A very significant correlation between the two indices of Le Bissonnais's method and soil organic carbon content was found and we propose a pedotransfer function linking these indices to soil characteristics. The results stress the need for farming practices that preserve the organic C in Mediterranean vineyard soils in order to reduce erosion risks. We believe that our findings might well apply to similar soils elsewhere in the world.Erodibilité des sols de vigre Méditerranéens: Mesure de la stabilité structurale et caractéristiques déterminantes des sols Résumé Le de´veloppement de la viticulture sur les sols en pente du bassin Me´diterrane´en pourrait entraıˆner une diminution de la teneur en C de ces sols et une aggravation du ruissellement et de l'e´rosion. La perte de C rend les agre´gats moins stables, ce qui augmente le risque d'e´rosion. Des indicateurs de ces risques sont ne´cessaires afin d'identifier les surfaces les plus menace´es. Nous avons dans un premier temps compareq uatre me´thodes diffe´rentes, couramment utilise´es pour mesurer la stabilite´structurale des sols afin d'e´valuer leur capacite´a`pre´dire le ruissellement et l'e´rosion; toutes mettent en jeu de l'e´clatement des agre´gats et produisent des indices tels que la proportion de macroagre´gats stables > 200 mm (MA200) ou le diame`tre moyen ponde´re´des agre´gats stables (MWD). Nous avons choisi trois vignobles me´diterrane´ens, caracte´rise´s par des sols bruns calcaires. Les tests de stabilite´structurale ont e´te´re´alise´s sur les sols de cinq sites cultive´s, correspondant a`14 simulations de pluie avec une intensite´de 60 mm heure ÿ1 . Nous avons trouve´des relations significatives entre la stabilite´structurale et le comportement lors d'une pluie simule´e, les deux meilleurs pre´dicteurs de l'e´rosion e´tant les indices MWD logarithmique et MA200 i...