Impacts of Oak Mulch Amendments on Rhizosphere Microbiome of Citrus Trees Grown in Florida Flatwood Soils

Abstract

Rhizosphere interactions are an understudied component of citrus production. This is even more important in Florida flatwood soils, which pose significant challenges in achieving sustainable and effective fruit production due to low natural fertility and organic matter. Citrus growers apply soil amendments, including oak mulch, to ameliorate their soil conditions. Thus, the aim of this research was to evaluate the effects of oak mulch on citrus nutrient uptake, soil characteristics, and rhizosphere composition. The plant material consisted of ‘Valencia’ sweet orange (Citrus × sinensis) trees grafted on ‘US-812’ (C. reticulata × C. trifoliata) rootstock. The experiment consisted of two treatments, which included trees treated with oak mulch (300 kg of mulch per plot) and a control. The soil and leaf nutrient contents, soil pH, cation exchange capacity, moisture, temperature, and rhizosphere bacterial compositions were examined over the course of one year (spring and fall 2021). During the spring samplings, the citrus trees treated with oak mulch resulted in significantly greater soil Zn and Mn contents, greater soil moisture, and greater rhizosphere bacterial diversity compared to the control, while during the fall samplings, only a greater soil moisture content was observed in the treated trees. The soil Zn and Mn content detected during the spring samplings correlated with the significant increases in the diversity of the rhizosphere bacterial community composition. Similarly, the reduced rates of leaching and evaporation (at the soil surface) of oak mulch applied to Florida sandy soils likely played a large role in the significant increase in moisture and nutrient retention.

Evaluation of effects of animal dung composites and Bacillus sp in amended bioremediation of Zn-polluted soil on maize seedlings growth

“…When organic amendments are added to acidic and nutrient-poor soils, they have been especially helpful for microbial productivity and plant growth [1]. According to Santiago et al [20], the pH of rhizosphere soils is frequently lowered by the application of organic amendments such as manures and biosolids. A number of mechanisms are responsible for the acidity of the rhizosphere, including the cation-anion exchange balance, the release of organic acids (such as citric, lactic, malaeic, propanic, oxalic, and butyric acids); the exudation and respiration of roots; and redox-coupled activities involving the consumption or production of H + and modifications in the oxidation state of Mn, Fe, and N [1].…”