2018 ASHS Annual Conference

The profitability of high-density apple (Malusxdomestica) orchards is dependent upon obtaining sufficient vegetative growth and high fruit yields during the first three years after planting, a goal typically achieved through applying high rates of synthetically derived nitrogen fertilizer. The purpose of this project was to test the use of mulch and composts as alternative soil fertility management practices for Mid-Atlantic and Southern apple growers. Over three years, we sampled from study sites at Virginia Tech’s Alson H. Smith, Jr. Agricultural Research and Extension Center (AREC), and at the orchards of grower cooperators in Virginia and Maryland. By the third year, the mulch treatments increased tree growth at all three sites. However, using compost either alone or in conjunction with calcium nitrate did not further increase tree growth at any of the sites. Additionally, the compost applications increased plant-available soil phosphorus at the AREC site and potassium at the Maryland site, but leaf tissue mineral concentration did not increase correspondingly to the soil mineral content. Soil microbiotic communities were analyzed using the Quantitative Insights Into Microbial Ecology software. Quality checking of the more than 1.5 million bacterial sequence reads and 0.25 million fungal reads showed that the greatest effect was due to location. The dominant Operational Taxonomic Units were most closely related to Proteobacteria, Acidobacteria, and Actinobacteria. Bacterial community changes that were consistent across locations were strongly associated with root-zone Proteobacteria, increasing by 26% due to the mulch application. Evidence for fertilizer-induced changes in the relative abundance of ammonia-oxidizing bacterial family were also apparent and suggest that there are functional differences in nitrogen cycling resulting from both the mulch and fertilizer treatments. The ability to alter the bacterial community has important ramifications for the bioavailability of plant nutrients, plant-root bacterial interactions, and overall orchard sustainability.