Land use change in a temperate grassland soil: Afforestation effects on chemical properties and their ecological and mineralogical implications

• Published in: The Science of the total environment Vol. 438; pp. 549 - 557
• Main Authors: Céspedes-Payret, Carlos, Piñeiro, Gustavo, Gutiérrez, Ofelia, Panario, Daniel
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier B.V 01.11.2012; Elsevier
• Subjects: acidification; afforestation; Aluminum Silicates; Aluminum Silicates - analysis; analysis; Analysis of Variance; Animal, plant and microbial ecology; Applied ecology; Argiudolls; Biological and medical sciences; cations; clay; clay minerals; crops; Ecosystem; Ecotoxicology, biological effects of pollution; Eucalyptus; Eucalyptus - growth & development; Eucalyptus grandis; Forestry; Forestry - methods; Fundamental and applied biological sciences. Psychology; General aspects; Grassland; grassland soils; grasslands; growth & development; Humic Substances; Humic Substances - analysis; Hydrogen-Ion Concentration; Illite; introduced species; Land use change; methods; nutrients; organic matter; Particle Size; Physicochemical properties; Poaceae; Poaceae - growth & development; potassium; reservoir soils; Soil; Soil - analysis; soil acidification; soil organic matter; South America; Spectrophotometry, Atomic; Statistics, Nonparametric; temperate soils; Uruguay; X-Ray Diffraction; South America; Uruguay; America; Grassland; Eucalyptus; Uruguay; Land use change; Physicochemical properties; Illite; Ecology; Woody plant; Afforestation; Land use; Dicotyledones; Angiospermae; Myrtaceae; Spermatophyta; Chemical properties; Grassland soil
• ISSN: 0048-9697; 1879-1026; 1879-1026
• DOI: 10.1016/j.scitotenv.2012.08.075

The current change in land use of grassland in the temperate region of South America is a process associated with the worldwide expansion of annual crops and afforestation with fast growing exotic species. This last cultivation has particularly been the subject of numerous studies showing its negative effects on soil (acidification, loss of organic matter and base cations, among others). However its effects on the mineral fraction are not yet known, as it is generally considered as one of the slowest responses to changes. This stimulated the present study in order to assess whether the composition of clay minerals could be altered together with some of the physicochemical parameters affected by afforestation. This study compares the mineralogical composition of clays by X-ray diffraction (XRD) in a grassland soil (Argiudolls) under natural coverage and under Eucalyptus grandis cultivation implanted 25years ago in a sector of the same grassland. The tendency of some physicochemical parameters, common to other studies was also compared. XRD results showed, as a most noticeable difference in A11 and A12 subhorizons (~20cm) under eucalyptus, the fall of the 10Å spectrum minerals (illite-like minerals), which are the main reservoir of K in the soil. Meanwhile, the physicochemical parameters showed significant changes (p<0.01) to highly significant ones under eucalyptus, particularly in these subhorizons, where on average soil organic matter decreased by 43%; K+ by 34%; Ca2+ by 44%, while the pH dropped to this level by half a point. Our results show that the exportation of some nutrients is not compensated due to the turnover of organic forestry debris; the process of soil acidification was not directly associated with the redistribution of cations, but with an incipient podzolization process; the loss of potassium together with soil acidification, leads to a drastic change in clay mineralogy, which would be irreversible. [Display omitted] ► Eucalyptus afforestation in a grassland soil causes a loss in fertility. ► Potassium capture by trees irreversibly affects the mineral structure of illites. ► Other physicochemical variables are also affected by these changes associated with the mineralogy. ► The set of processes that occur under afforestation redirects pedogenesis.