Abstract
Unsustainable agricultural management practices such as non-conservationist tillage and overuse of fertilizers result in soil acidity and, in turn, soil degradation due to reduced carbon (C) concentrations and nutrient availability and increased aluminum toxicity. Application of lime (L) and phosphogypsum (PG) can overcome these constraints and improve soil quality, but the long-term effects of these amendments on both abiotic and biotic soil properties are not known, particularly when applied in combination. Here, we evaluated the effects of L (acidity corrective), PG (soil conditioner), and their combination (LPG) on soil organic matter (SOM) transformations, soil chemical and physical properties, and microbiome assembly in a long-term experiment under a no-till crop rotation system in a tropical soil. The Ca-based soil amendments increased C concentrations (labile and stable fractions), improved soil physicochemical properties, and changed the associations between several bacterial and fungal groups. Contrary to expectations, the acidic soil amended with PG exhibited greater number of significant shifts in the bacterial community than soil amended with L or LPG, as well as higher soil bulk density. By contrast, the fungal community underwent greater shifts in soil amended with L or LPG, which had higher macroporosity. L and LPG amendment shaped the fungal community and rearranged the SOM fractions at similar rates, suggesting an essential role of the altered fungi in SOM transformation. In addition, combining L with PG increased the relevance of many low-abundance microorganisms, especially fungi, compared with the control, indicating an increase in their ecological role in the soil. Finally, by applying general joint attribute modeling and sensitivity analysis, we determined that soil fertility increased most in LPG-amended soil, as the ensuing changes in the bacterial and fungal communities resulted in improved SOM fractions, soil physical characteristics and, ultimately, soil quality.
Highlights
The processes that govern soil acidification are global drivers of soil degradation (von Uexküll and Mutert, 1995; Gibbs and Salmon, 2015; Meng et al, 2019)
The cascade effects of changes in soil pH increased the availability of all soil mac ronutrients; the combined treatment (LPG) was more efficient than L alone in increasing the availability of NO3−, NH4+, Ca2+ and S-SO42
In a long-term no-till intercropping system, amendments that neutralize acidity of the soil play a crucial role in increasing C concentrations and soil physi cochemical attributes, especially considering the synergism between L and PG (LPG amendment)
Summary
The processes that govern soil acidification are global drivers of soil degradation (low productive capacity) (von Uexküll and Mutert, 1995; Gibbs and Salmon, 2015; Meng et al, 2019). Low SOM levels in soils promote leaching of cations, further contributing to soil acidification and severely restricting crop production (Evans et al, 2012; Castellano et al, 2015; Paradelo et al, 2015; Carmeis Filho et al, 2017b). Low soil pH reduces carbon (C) concentrations and nutrient availability and increases the toxicity of certain elements [e.g., aluminum (Al3+) and manganese (Mn)], directly affecting microbial growth (Bowman et al, 2008; Tian et al, 2019). The high concentration of hydrogen (H+) in acidic soils likely reduces microbial biomass and physiology (Meng et al, 2019; Tian et al, 2019)
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