Towards ecologically-based fertilizer recommendations that improve soil quality in high-density apple orchards

View the project final report

• 2014 annual report
• 2015 annual report

Commodities

• Fruits: apples, general tree fruits

Practices

• Crop Production: fertigation, nutrient cycling, organic fertilizers, application rate management, tissue analysis
• Education and Training: on-farm/ranch research, participatory research
• Farm Business Management: agricultural finance
• Natural Resources/Environment: carbon sequestration
• Production Systems: agroecosystems, holistic management
• Soil Management: soil analysis, nutrient mineralization, soil microbiology, soil chemistry, organic matter, soil quality/health

Profitability of high-density orchards is dependent on 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 sustainable soil fertility management practices for Mid-Atlantic and Southern apple growers by applying mulch and compost to apple orchards. 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 based 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 concentration did not increase correspondingly to the soil mineral content. Soil 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 bacterial 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 fertilizer and mulch. The mulch treatment increased the mycorrhizal fungal groups Glomeromycota by 16% and Agaricomycetes by 35%. However, Agaricomycetes also contain some species of decomposers and pathogens. Mycorrhizae would be of particular interest for further study because they're the most likely candidate for playing a growth supportive role for apple trees. The ability to alter the microbial community has important ramifications for the bioavailability of plant nutrients, plant-root bacterial interactions, and therefore orchard sustainability.

Objective 1: Use an interdisciplinary approach to examine the benefits of utilizing carbon-based soil amendments in commercial apple orchard systems so that we can investigate the interaction between soil nutrient source and orchard productivity. Our project will investigate microbial community composition, biomass, and soil biological activity in the soil, particularly in the rhizosphere (the soil-root interface). The research will occur on replicated plots located in three separate regional apple orchards.

• Our research utilizes a research farm trial comparing synthetic fertilizers (calcium nitrate), chicken litter compost, municipal yard waste compost, and treatments that integrate synthetic fertilizers with composts when applied to newly planted high-density apple trees.
• We also developed two replicated on-farm trials with cooperating growers.
• Among the three farm sites outlined in this objective, this research project spans 200 miles and puts growers throughout the Mid-Atlantic in close proximity to the test sites, which will encourage faster adoption of the most effective treatments.

Objective 2: Educate stakeholders in orchard nutrition management. Develop printed materials to support educational activities.