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Although entomopathogenic fungi (EPF) are best known for their ability to protect crops against insect pests, they may have other beneficial effects on their host plants. These effects, which include promoting plant growth and conferring resistance against abiotic stresses, have been examined in recent years to acquire a better understanding of them. The primary purposes of the present study were (i) to ascertain in vitro whether three different strains of EPF (viz., Metarhizium, Beauveria and Isaria) would increase the Fe bioavailability in calcareous or non-calcareous media containing various Fe sources (ferrihydrite, hematite and goethite) and (ii) to assess the influence of the EPF inoculation method (seed dressing, soil treatment or leaf spraying) on the extent of the endophytic colonization of sorghum and the improvement in the Fe nutrition of pot-grown sorghum plants on an artificial calcareous substrate. All the EPFs studied were found to increase the Fe availability during the in vitro assay. The most efficient EPF was M. brunneum EAMa 01/58–Su, which lowered the pH of the calcareous medium, suggesting that it used a different strategy (organic acid release) than the other two fungi that raised the pH of the non-calcareous medium. The three methods used to inoculate sorghum plants with B. bassiana and M. brunneum in the pot experiment led to differences in re-isolation from plant tissues and in the plant height. These three inoculation methods increased the leaf chlorophyll content of young leaves when the Fe deficiency symptoms were most apparent in the control plants (without fungal inoculation) as well as the Fe content of the above-ground biomass in the plants at the end of the experiment. The total root lengths and fine roots were also increased in response to fungal applications with the three inoculation methods. However, the soil treatment was the most efficient method; thus, its effect on the leaf chlorophyll content was the most persistent, and the effects on the total root length and fine roots were the most apparent. In conclusion, EPF improved the Fe nutrition of the sorghum plants, but their effects depended on the inoculation method.

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Aims Organic acid exudation by plant roots is thought to promote phosphate (P) solubilisation and bioavailability in soils with poorly available nutrients. Here we describe a new combined experimental (microdialysis) and modelling approach to quantify citrate-enhanced P desorption and its importance for root P uptake. Methods To mimic the rhizosphere, microdialysis probes were placed in soil and perfused with citrate solutions (0.1, 1.0 and 10 mM) and the amount of P recovered from soil used to quantify rhizosphere P availability. Parameters in a mathematical model describing probe P uptake, citrate exudation, P movement and citrate-enhanced desorption were fit to the experimental data. These parameters were Plant Soil

Soil mineralogy and management can have substantial effects on phosphorus (P) diffusion in soil and hence on root morphology. The aim of this study was to assess these effects in soils differing widely in P-sorbing components. Samples of a Rhodic Paleudult (RP), a Rhodic Hapludox (RH), and a Humic Hapludox (HH) under conventional tillage (CT) or no-tillage (NT) were placed in Petri dishes to assess P diffusion. Performance and root morphology in corn grown on soil samples subjected to three different P fertilization treatments (no fertilizer, surface, and deep fertilizer application) were examined. Phosphorus diffusion was slower in the HH than in the other soils by effect of its high P adsorption capacity because of its mineralogy. Soil management had no effect on P diffusion. Fertilization with P only affected plant-related variables in RH: surface fertilization increased root biomass, and deep fertilization shoot biomass and proportion of thick roots. Soil management affected plants growing on HH and RP: the plants grown under NT were taller (RP) and developed more fine roots (HH) than those under CT. Fertilization with P had little effect on plant growth in the goethite-rich soil (HH) or the one with high content in available P (RP). Our results suggest that management system in these soils has therefore greater influence on fertility than fertilization treatment.

Fertiliser nitrogen (N) is essential for maintaining agronomic outputs for our growing population. However, the societal, economic and environmental impacts of excess reactive N from fertiliser is rarely assessed. Here the agronomic, economic and environmental efficacy of three N-fertiliser sources, ammonium-nitrate (AN), urea (U), and inhibited-urea (IU; with NPBT) were evaluated at two grassland sites. Dry matter yield and herbage quality were measured at each silage-cut. Additionally, NH 3-N and N 2 ON losses were measured and used to calculate the effective N source cost and externality costs, which account for associated environmental and societal impacts. We found no effect of different N sources on yield or herbage quality. However, NH 3-N emissions were significantly reduced under the IU treatment, by 48-65%. No significant differences in cumulative N 2 O emissions were observed. Incorporating externality costs increased fertiliser prices by 1.23-2.36, 6.51-16.4, and 3.17-4.17 times the original cost, for AN, U and IU, respectively, transforming U from the cheapest, to the most expensive of the N sources examined. However, with no apparent yield differences between N-fertiliser sources there is no economic incentive for the land-manager to use the more environmentally and socially acceptable option, unless externality costs are incorporated into fertiliser prices at the point of sale.