Abstract
Relationship between macroscopic and microscopic behavior of soils is a difficult issue, especially when dealing with complex properties such as structure or carbon sequestration, but it is necessary for a suitable understanding of the agricultural soil quality. In this work, we used the extended-DLVO theory to compute total energy of interaction between particles (kT), of three soils over granodiorites. This parameter allows predicting the tendency to aggregate formation at the colloidal scale, being the basis of soil structure. Furthermore, we characterized the mechanism and adsorption capacity of humic molecules on mineral surfaces, and its influence in the interaction energy, by means of the adsorption isotherms. The aim was to compare first the effects of organic farming on conventionally managed soils and, second, to compare these with a non-cultivated forest soil under Mediterranean climate. When total energies are negative (particle attraction), or positive (particle repulsion) but near 0 kT (<100 kT), then particle flocculation occurs and the structure at colloidal scale can be developed. Total energy was less in the forest sample and greater in the soil of conventional groves, with intermediate values in organic farming soil. This indicates a tendency toward particle flocculation and more stability of the structure at colloidal scale in less disturbed soils, agreeing with other soil physical properties such as the total porosity (50, 41 and 37% in forest, organic and conventional plots, respectively) or the aggregate stability index (0.94, 0.73 and 0.66, respectively), which followed the same trend. Of the three components of the total energy of interaction, the acid-base force was a key factor. This component, related with the electron-donor component of surface free energy, γ−, yielded a strong attractive force (−150 kT at 3 nm) when calcium solutions were analyzed for the forest soil. This indicates a clear hydrophobic character of this sample. Because the mineralogical composition of the samples is quite similar, hydrophobicity should be attributed to the organic carbon content of the forest soil, which is much higher than that of the cultivated ones (12.03 vs. 1.44% and 0.88% in organic and conventional farms, respectively), proving to be an essential element for the development of the structure at the colloidal level.
Highlights
Soil structure consists of the spatial arrangement of soil particles and aggregates through aggregation processes that operate at several scales, resulting in a complex network of pores of multiple sizes and shapes (Peng et al, 2015)
The soil mineralogy matched the granodiorite parent rock, formed mainly by quartz and phyllosilicates, showing a clay fraction dominated by 2:1 phyllosilicates as illite, vermiculite, hydroxyl-interlayered vermiculite (HIV) and their intergrades, with little differences between soils. ζ curves of the fine earth fraction (
Structure behavior of the soil samples at colloidal scale where characterized by total interaction energies, calculated according the extended DLVO model
Summary
Soil structure consists of the spatial arrangement of soil particles and aggregates through aggregation processes that operate at several scales, resulting in a complex network of pores of multiple sizes and shapes (Peng et al, 2015). Because it determines porosity, the structure is a fundamental property that largely determines all soil functions, such as CO2 sequestration or water quality. The structure deteriorates during conventional tillage, because of physical stress caused by the tillage itself and loss of organic matter from surface layers (Gomez et al, 2003, Gomez et al, 2009). Karlen et al (1997) indicated a close relationship between the loss of soil organic matter (SOM) and deterioration of the structure. Normative frameworks of the European Union (EC, 2005; EC, 2011) reflect a change of management recommendations from conventional agriculture to conservation and organic farming, based on the adoption of practices aimed at increasing soil organic matter, care of the structure, and erosion control
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
