Effect of organic and conventional farming on soil bacterial diversity of pecan tree (Carya illinoensis K. Kosh) orchard across two phenological stages.

We described the bacterial diversity of walnut grove soils under organic and conventional farming. The bacterial communities of rhizospheric and nonrhizospheric soils of pecan tree (Carya illinoensis K. Koch) were compared considering two phenological stages (sprouting and ripening). Sixteen operational taxonomic units (OTUs) were identified significantly more abundant according to the plant development, only one according to the farming condition, and none according to the soil origin. The OTUs specificaly abundant according to plant development included Actinobateria (2) and Betaproteobacteria (1) related OTUs more abundant at the sprouting stage, while at the fruit ripening (FR) stage the more abundant OTUs were related to Actinobacteria (6), Alphaproteobacteria (6), and unclassified Bacteria (1). The Gaiellaceae OTU18 (Actinobacteria) was more abundant under conventional farming. Thus, our study revealed that the plant development stage was the main factor shaping the bacterial community structure, while less influence was noticed for the farming condition. The bacterial communities exhibited specific metabolic capacities, a large range of carbon sources being used at the FR stage. The identified OTUs specifically more abundant represent indicators providing useful information on soil condition, potential tools for the management of soil bacterial communities.

Growth, yield, and nutrient status of pecans fertilized with biosolids and inoculated with rizosphere fungi.

The application of anaerobically digested biosolids as a nutrient source for pecan, Carya illinoinensis (Wangeh.) K. Koch, cultivar Western, was evaluated. Conventional NPK fertilizers (CF) and biosolids included a treatment with the rhizospheric fungi Pisolithus tinctorius+Scleroderma sp. and Trichoderma sp. After an average of three years, the tree trunks with biosolid treatment grew 9.5% more than with CF; the length of the bearing shoots was 18.1 and 18.3cm and the production of nuts/tree was 9.26 and 8.75kg for pecans with CF and with biosolids, respectively. Western foliar nutrient concentration and nut quality were statistically equal in trees with CF and with biosolids. Soil inoculation with mycorrhizal fungi improved shoot growth by 19.4% when CF was applied, but did not when biosolids were used. Nutrient status and yield did not increase with mycorrhizal fungi. The addition of Trichoderma sp. did not favor any of the variables evaluated with both nutrient sources. Biosolids are efficient fertilizer at promoting the growth, production and nut quality of pecan trees.