Effect of Chemical Fertilization on the Impacts of Plant Growth-Promoting Rhizobacteria in Maize Crops.

The use of chemical fertilizers strongly promotes productivity in agricultural crops; therefore, large amounts of chemical fertilizers have been used. The use of plant growth-promoting bacteria may be a strategy to reduce the use of chemical fertilizers; however, little is known about the effect of chemical fertilization on the performance of these bacteria through plant-microbe interactions. The present study aimed to verify the performance of Bacillus subtilis, Azospirillum brasilense, B. pumilus, B. amyloliquefaciens, Herbaspirillum seropedicae, Gluconacetobacter diazotrophicus, and the mixtures A. brasilense + B. subtilis, B. pumilus + B. amyloliquefaciens, and H. seropedicae + G. diazotrophicus on parameters such as nitrogen and phosphorus extraction from soil, the concentrations of these nutrients in maize plants, and plant growth in both fertilized and unfertilized soil. The results showed that H. seropedica increased the nitrogen content by 6.6 g kg-1 in leaves and 2.2 g kg-1 in the root when comparing the unfertilized with the fertilized condition. G. diazotrophicus increased the nitrogen content by 3.7 g kg-1 in leaves and 2.4 g kg-1 in the root. B. pumilus increased the phosphorous content by 1.7 g kg-1 in leaves, and B. amyloliquefaciens increased the phosphorous content by 0.61 g kg-1. The present study showed that even though the bacteria presented good performance related to plant growth under fertilized conditions, H. seropedicae, G. diazotrophicus, B. pumilus, and B. amyloliquefaciens could be used in the maize crop with a reduced chemical fertilization dose.

Efficacy of alginate- and clay-encapsulated microorganisms on the growth of Araçá-Boi seedlings (Eugenia stipitata)

The present work aimed to evaluate the effects of encapsulated microorganisms on seedlings of Eugenia stipitata, popularly known as araçá-boi, to evaluate the interaction between the inoculum and encapsulating agents such as clay and alginate. The experiment was carried out in a completely randomized design using a 3×2 factorial scheme. The treatments were control, inoculum, clay without microbial inoculum, clay with microbial inoculum, alginate without microbial inoculum, and alginate with microbial inoculum. The seedlings were grown under nursery conditions over a period of 3 months. No treatment increased the height, stem diameter, shoot dry matter or root dry matter of the araçá-boi seedlings. The use of alginate increased the ammonium content compared to the clay and control treatments. Alginate and clay increased the nitrate content in relation to the control. Alginate increased the total number of bacteria in relation to the clay and control treatments. The application of inoculum combined with alginate increased the nitrate content only in relation to the clay and control treatments. Although the application of inoculum promoted an increase in the nitrate content compared to the uninoculated treatments, there was no effect for the other parameters analyzed. The results suggest that clay and alginate encapsulating agents with the presence or absence of microorganisms may improve some soil parameters.