Adding Intercropping Maize and Faba Bean Root Residues Increases Phosphorus Bioavailability in a Calcareous Soil Due to Organic Phosphorus Mineralization

Background and aims Root residues are an important factor influencing soil phosphorus (P) availability for crop uptake, but how the residues from different species combinations in sole cropping or intercropping systems affect soil P pools remains unclear. Methods Maize and faba bean were planted as either sole crops or intercrops in a P-deficient calcareous soil with and without addition of corresponding previous crop (pre-crop) roots. This was repeated in three cultivations cycles in a greenhouse experiment. Plants sampled in each experiment were analyzed for biomass and P content, and soils sampled from all treatments in the last cultivation were analyzed for soil characteristics. Results Addition of a mixture of intercrop root residues increased biomass, total P content, microbial biomass P concentration and soil acid phosphatase activity, compared with addition of root residues of a single crop. The Hedley soil P fractions from three continuous cultivation cycles differed, depending on root residue source. The sole maize root residue with high C/P ratio caused a considerable depletion of inorganic P (NaHCO3-Pi, NaOH-Pi and 1 M HCl-Pi), and the sole faba bean root residue with lower C/P ratio caused a large depletion in Resin-P and NaHCO3-Po fractions, and the root residue of intercrops with a medium C/P ratio depleted more of the NaHCO3-Po and conc. HCl-Po fractions. However, without root residues, sole faba bean depleted more of the Resin-P, NaHCO3-Pi, NaOH-Pi and NaHCO3-Po fractions than the other two cropping systems did because of its higher P content. Conclusions Adding root residues of mixed species accelerated soil organic P mineralization (NaHCO3-Po and conc. HCl-Po) by increasing microbial biomass P concentrations and acid phosphatase activities, and thus enhanced the intercropping advantage in terms of biomass and P content in a P-deficient soil.

Abscisic acid implicated in differential plant responses of Phaseolus vulgaris during endophytic colonization by Metarhizium and pathogenic colonization by Fusarium

Metarhizium robertsii is an insect pathogen as well as an endophyte, and can antagonize the phytopathogen, Fusarium solani during bean colonization. However, plant immune responses to endophytic colonization by Metarhizium are largely unknown. We applied comprehensive plant hormone analysis, transcriptional expression and stomatal size analysis in order to examine plant immune responses to colonization by Metarhizium and/or Fusarium. The total amount of abscisic acid (ABA) and ABA metabolites decreased significantly in bean leaves by plant roots colonized by M. robertsii and increased significantly with F. solani compared to the un-inoculated control bean plant. Concomitantly, in comparison to the un-inoculated bean, root colonization by Metarhizium resulted in increased stomatal size in leaves and reduced stomatal size with Fusarium. Meanwhile, expression of plant immunity genes was repressed by Metarhizium and, alternately, triggered by Fusarium compared to the un-inoculated plant. Furthermore, exogenous application of ABA resulted in reduction of bean root colonization by Metarhizium but increased colonization by Fusarium compared to the control without ABA application. Our study suggested that ABA plays a central role in differential responses to endophytic colonization by Metarhizium and pathogenic colonization by Fusarium and, we also observed concomitant differences in stomatal size and expression of plant immunity genes.

UTICAJ SORTE I MIKROBIOLOŠKIH PREPARATA NA BROJ I MASU NODULA KOD ORGANSKE PROIZVODNJE PASULJA

Three-year research, in the impact of microbial preparations and Gunatito on bean-root-nodule number and mass in organic production, was published. The highest nodule number and mass was in the year with a more favorable weather conditions, with a higher humidity. The lowest nodule number was in the method with a direct Tiffi application on the pre-sowing seed, whereas the lowest nodule mass was in the control variety. A positive insignificant correlation was determined between nodule number and mass, and yield. Nodulation was variety dependant. EM application 7 days before sowing, and the combination of Guanito before sowing with EM in flowering, showed a positive impact on nodule number and mass.