Browsing by Author "Thompson, Ashley A."

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    Compost applications increase bacterial community diversity in the apple rhizosphere
    Sharaf, Hazem; Thompson, Ashley A.; Williams, Mark A.; Peck, Gregory M. (2021-03-24)
    Sustainable practices are key to the improvement of soil fertility and quality in apple (Malus x domestica Borkh.) orchards. Rootstock genotype and fertilizer inputs can alter soil biology, as well as aboveground traits including nutrient acquisition. In this study, a factorial design was used to assess the interaction between two apple rootstocks, 'Geneva 41' ('G.41') and 'Malling 9' ('M.9') with four fertilizer treatments [chicken-litter compost, yardwaste compost, fertigation using Ca(NO3)(2), and an unamended control]. The bacterial community in the rhizosphere was assessed for its impact on both plant and soil properties for each rootstock x fertilizer treatment combination. The bacterial community was dominated by Acidobacteria, Proteobacteria, and Planctomycetes, but Verrucomicrobia and Chloroflexi were the most responsive to the fertilizer treatments. The chicken litter and yardwaste treatments had a greater effect on bacterial community structure than the control. Yardwaste, in particular, was associated with increased relative abundance of Chloroflexi, which was correlated with soil nutrient concentrations. Malling 9 had a greater bacterial diversity than G.41, but the rootstock treatment had no independent effect on the rhizosphere community structure. There was, however, a strong interaction between the rootstock and fertilizer treatments. Carbon cycling was the most prominent functional change associated with the soil bacterial community. These results suggest that compost amendments have a more positive effect on soil bacterial activity and nutrient availability than Ca(NO3)(2). Our work shows that waste-stream amendments can lead to multiple positive responses, such as increasing aboveground tree biomass, thus potentially improving orchard productivity.
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    The Effects of Rootstock Selection and Carbon-based Fertility Amendments on Apple Orchard Productivity and Soil Community Ecology
    Thompson, Ashley A. (Virginia Tech, 2016-12-08)
    In apple (Malus domestica Borkh.) orchards, rootstock genotype, and soil fertility management practices impact soil fertility, plant associated soil microbial communities, and orchard productivity. Apple growers select rootstocks to confer beneficial traits, including size control, precocity, and pest and disease resistance. Rootstock genotype may also influence microbial communities, resulting in changes that affect tree health and productivity. Many apple growers apply synthetic nitrogen fertilizers to improve fruit yield and quality. In excess of tree requirements, nitrogen fertilizers may reduce crop yield and quality, as well as contribute to water pollution. The addition of carbon-based amendments, such as yardwaste, chicken litter composts, and biochar, may potentially reduce nitrogen and water loss, while improving soil structure and mineral nutrient availability. Orchard and pot-in-pot experiments were designed to study the following objectives: 1) determine the effects of integrated carbon-based fertilizer amendments on tree growth, productivity, and orchard soil fertility, 2) assess the effects of biochar on tree growth, leaf mineral nutrition, soil physiochemistry, and microbial community structure and activity, and 3) understand how rootstocks and fertilizers alter soil microbial communities. Applications of composts, integrated compost-calcium nitrate fertilizers, and biochar increased soil carbon, organic matter, cation exchange capacity and microbial respiration. In the orchard study, nitrogen fertilizer application did not increase tree growth, fruit quality, or leaf nitrogen concentration. Biochar applied at high rates with nitrogen fertigation increased tree growth and leaf nitrogen concentration similar to nitrogen fertigation. In the pot-in-pot compost study, chicken litter compost increased tree growth, and integrated compost-calcium nitrate fertilizer applications increased leaf N concentration. Analysis of the microbial community structure of bulk soil samples from the biochar and compost pot-in-pot experiments determined that the community structure was similar for all treatments during the three-year study. Metagenomic sequencing of the rhizosphere bacterial community indicated that compost applications altered community diversity and evenness, and that compost treatments were more similar to each other than to the calcium nitrate treatment. Data from my dissertation research suggests that compost can be used to increase orchard soil fertility, tree growth, and leaf nutrition, and that compost applications increase soil microbial community diversity and activity.