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The use of composts appears to be a promising strategy to promote plant growth performance and to enhance soil fertility under field conditions. The objective of the present study was to select the best organic amendment able to enhance garlic growth, yield, physiological and biochemical parameters, as well as to improve soil fertility. The experiment was carried out under field conditions using three treatments: Control (C), Compost 1: horse manure-green waste (C1) and Compost 2: olive pomace-green waste (C2). To evaluate the effects of the application of the two composts on garlic growth, soil fertility and plant physiological, biochemical and nutritional traits were measured. The results showed that C1 decreased soil pH compared to the control, while electrical conductivity increased considerably for C2. In addition, nitrogen (N), phosphorus (P), total organic carbon (TOC) were significantly increased in soil for C1 followed by C2. The increase percentages of shoots dry biomass with C1 and C2 compared to the control were 64.9% and 158%, respectively. Moreover, for bulbs yield, the composts C1 and C2 produced 46.5% and 41.9%, respectively. Besides, physiological and biochemical parameters of garlic were improved by C1 and C2 compared to control plants. Moreover, antioxidant enzymes such as PPO and POX, decreased significantly in treated plants. Furthermore, mineral analyses showed that C1 and C2 significantly improved minerals contents in leaves and bulbs compared to the control. The results demonstrate the potential of horse manure-green waste compost for the improvement and optimization of soil fertility and crop productivity. This organic amendment could be an efficient practice and a potential bio-fertilizer to improve growth and development as well as biological agriculture of garlic production.

The microbial and biological processes in the rhizosphere are important for the plant growth and health. Among beneficial free-living soil microorganisms, some bacteria which have been classified as Plant Growth Promoting Rhizobacteria (PGPR), stimulate plant growth through direct or indirect biological processes. In addition, the majority of terrestrial plant species form symbiotic associations with Arbuscular Mycorrhizal Fungi (AMF). Many studies have shown that both microsymbionts and PGPR improve plant growth and plant resistance to biotic and abiotic stresses. However, there is a lack of knowledge on the biological factors regulating the soil receptivity to mycorrhizal inoculation. Rhizobacteria and mycorrhizal fungi have frequently been considered separately. Now, it is well known that inoculation with both PGPR and AMF is more beneficial to plant growth compared to inoculation with either one of them. The aim of this study was to select some rhizobacteria able to promote the plant growth as well as AMF symbioses. A collection of 203 strains of rhizobacteria was constituted after isolation from rhizosphere of olive trees in an agroforestry system located in the Haouz valley of Morocco. They were characterized in vitro with the following criteria: siderophore production, phosphate solubilization and AIA production. From these assays, we selected 15 strains of rhizobacteria that were identified on their 16S rDNA sequences. They were then used in greenhouse assays to study their effects on plant growth (Brachypodium distachyon and Solanum lycopersicum) and on endomycorrhizal symbiosis (Tagetes patula). (Resume d'auteur)

In Morocco, the use of seed legumes is limited because significant water deficits and the low availability of soil phosphorus (P) limit nitrogen fixation. However, little is known about the ability of faba bean-rhizobium symbiosis to fix nitrogen in P-deficient soils and to transfer fixed nitrogen (N) to intercropped wheat. Arbuscular mycorrhizal fungi (AM) and their extraradical hyphae networks play an important role in the facilitation process by promoting interconnectivity and the transfer of nutrients, such as N and P, between associated plants. The aim of this study was to analyse the impact of AM inoculation on N-2 fixation and the transfer of fixed N from faba bean to intercropped wheat. Germinated faba bean and wheat seeds were transferred into 1-l pots filled with a P-deficient soil that was collected from the Haouz valley near Marrakech (Morocco). Plants from the two species were grown in pots in either pure or mixed stands under greenhouse conditions, and each cropping system was subjected to three mycorrhizal inoculation treatments with a non-inoculated (AM0) and two concentrations of Rhizophagus irregularis inoculants containing 1000 (AM1) or 2000 (AM2) spores pot(-1). The N-15 isotope dilution method was used to determine the amount and proportion of atmospheric N fixed by faba bean (Ndfa%) and the fixed N that was transferred to wheat. Mycorrhizal inoculation had a significantly positive effect on the shoot dry weights and total shoot N in faba bean, but not in wheat. The cropping system had no significant effect on the plant growth and total shoot N in both faba bean and wheat. The Ndfa percentage was very high in all of the treatments, varying from 86 to 91%. The total N fixed by faba bean was 27% significantly higher in the AM2 treatment compared with the AM1 and AM0 treatments for both cropping systems combined. The estimated proportions of fixed N that were transferred from faba bean to wheat were far higher in AM1 (50%) and AM2 (32%) treatments than in AM0 (15%) treatment as well as for the total transferred fixed N. As corroborated by a parallel observation of root mycorrhizal colonization, these results suggest that the development of mycorrhizal networks stimulates the transfer of fixed N from faba bean to wheat, which could significantly contribute to the facilitation process under intercropping conditions.

Phosphorus (P) is a major nutrient limiting plant growth in many soils. To reduce P deficiencies and ensure plant productivity, large quantities of soluble forms of P fertilizers are applied worldwide every year. However up to 80 % of P chemical fertilizer amendments are lost as it is easily precipitated into insoluble forms (CaHPO4, Ca3(PO4)2, FePO4, and AlPO4) and becomes unavailable for plant uptake. Some soil microorganisms are known to be involved in the solubilization of insoluble phosphate by excreting organic acids, phenolic compounds, protons, and siderophores. Among phosphate-solubilizing microorganisms, it has been reported that mycorrhizal fungi have the ability to actively mobilize and translocate nutrients from minerals and soil organic matter, directly to their host plant. Mycorrhizal fungi constitute a key functional group of soil biota that greatly contribute to productivity and sustainability of terrestrial ecosystems. These are ubiquitous components of most of the ecosystems throughout the world and considered key ecological factors in governing the cycles of major plant nutrients and in sustaining the vegetation cover. It has been suggested that the integration of key processes from natural ecosystems (plant-plant facilitation, positive plant soil feedback) in agricultural management systems could resolve increasing agricultural problems. Since these natural processes are frequently connected with arbuscular mycorrhizas, it is necessary to apply mycorrhizal inoculation technologies or to manage native arbuscular mycorrhizal fungus communities to replace or reinforce the mycorrhizal potential in these degraded areas. This chapter aims to describe the influence of some cultural practices (rotation, intercropping, mycorrhizal inoculation) that mimic these natural processes in agrosystems, on soil microbiota (i.e.: soil mycorrhizal infectivity) leading to a sustainable microbial complex with high efficiency against phosphorus mobilization and transferring phosphorus from the soil organic matter or from soil minerals to the host plant.

The aim of this study was to test the impact of Rhizophagus irregularis, an arbuscular mycorrhizal fungus (AMF), on durum wheat growth and soil microbial functionalities in a field inoculation trial conducted in Morocco. The results showed that i) the R. irregularis inoculum effectively improved wheat growth, ii) wheat growth promotion depended on the soil mycorrhizal infectivity and iii) functional abilities of soil microflora depended on AMF inoculation. This study confirms that field AMF inoculation can be proposed as an effective agronomic practice in wheat production and as a sustainable cultural practice to manage soil biofunctioning. To fully promote inoculation practices, a better knowledge of AMF ecology has to be acquired to better adapt AMF inoculation to environmental conditions, and thus warrant better yields and agricultural sustainability.

Plant-plant facilitation is an ecological process occurring in most terrestrial ecosystems. Plant-plant facilitation is considered as a positive interaction between both plant partners in which one plant species promotes the growth, survival or reproduction of the neighbouring plant. Recent studies have underlined the role of mycorrhizal fungi, i.e. arbuscular mycorrhizal fungi (AMF) and particularly extra radical hyphae of AMF, in interconnecting plants and consequently their importance in plant-plant facilitation process. Networks of AMF impact soils both physically and biologically and are considered as an important pathway for the transference of nutrients such as nitrogen and phosphorus. In parallel, AMF increase plant growth and nutrient uptake and decrease the deleterious effects of pathogens and drought. The aims of this chapter are to describe how the AMF are involved in the plant facilitation process and to assess the main mycorrhizal effects on the plant nutrition (P and N) and plant health. Also the contribution of AMF in cropping systems as well as agricultural strategies which improve AM associations in arid agrosystems will be reviewed and illustrated by experimental results from field studies in Mediterranean environment.

Les contraintes majeures qui limitent la productivité des agroécosystèmes en milieu arides sont généralement attribuées aux carences minérales [plus particulièrement en phosphore (P) et en azote (N)], à un déficit en eau, aux processus d’érosion hydrique et éolienne, ainsi qu’à des perturbations dans le biofonctionnement du sol (faible diversité génétique et fonctionnelle de la microflore tellurique, etc.). Lorsque ces milieux ne sont pas soumis à une surexploitation, ils présentent une activité biologique élevée. Il a été ainsi suggéré que leur valorisation via des stratégies culturales adéquates pouvait réactiver les processus écologiques impliqués dans le maintien de la fertilité des sols et ainsi assurer une meilleure productivité de l’agro-écosystème. La plupart des plantes de ces régions arides (espèces sauvages ou cultivées) sont associées à des champignons mycorhiziens à arbuscules (CMA). Ces symbiotes fongiques sont reconnus comme étant des composantes microbiennes majeures dans le déroulement des principaux cycles biogéochimiques des sols (C, P et N) et en conséquence dans le développement des plantes en améliorant leur nutrition minérale mais aussi hydrique et leur état sanitaire. Paradoxalement, leur valorisation au sein d’itinéraires culturaux reste encore très limitée, voire inexistante. Ce chapitre a pour objectifs principaux de décrire le rôle des CMA dans le maintien et l’amélioration de la fertilité des sols et sur le développement des plantes tant au niveau de leur nutrition minérale, de leur résistance au stress hydrique que de l’état sanitaire des sols cultivés (ex. : lutte contre Striga spp.). Des stratégies d’ingénierie écologique seront ensuite proposées afin d’optimiser certaines techniques culturales (ex. : agroforesterie) dans le rôle de maintien du potentiel infectieux mycorhizogène des sols en relation avec une pleine expression des propriétés de la symbiose mycorhizienne sur les plantes cultivées, permettant ainsi d’atteindre des rendements culturaux compatibles avec les besoins des populations locales.