Soil chemical management drives structural degradation of Oxisols under a no-till cropping system

Abstract

Physical degradation of the subsurface layer of soils reduces the effectiveness of no-till (NT) as a sustainable soil management approach in crop production. Chemical factors may reduce the structural stability of Oxisols and thereby exacerbate compaction from machinery traffic. We studied the relationship between chemical management and structural degradation in Oxisols cultivated under NT at three sites in southern Brazil. The surface and subsurface layers of the soils were characterised chemically and mineralogically and three physical attributes related to soil structural stability (readily dispersible clay in water, mechanically dispersible clay in water, and water percolation) were quantified for each layer. The same characterisations were performed on Oxisols collected from adjacent non-cultivated areas, to provide reference data for non-degraded soil. The levels of dispersed clay in the cultivated soil from the surface layer matched those of the non-cultivated soil, but for the subsurface layer higher dispersed clay levels in the cultivated soil showed that it was physically degraded relative to the non-cultivated soil. Water percolation was found to be slower through the Oxisols cultivated under NT, irrespective of the soil layer. The relationships between the three indicators of soil structural stability and the measured chemical and mineralogical variables of the soils were explored through an analysis of canonical correlation. The principal variables associated with the lower stability of the cultivated vs non-cultivated Oxisols were the lower concentrations of organic carbon and exchangeable aluminium and, for the surface layer, the higher pH. It is argued that structural degradation of Oxisols cultivated under NT, observed predominantly in the subsurface layer, has been aggravated by the accumulation of amendments and fertilisers in the surface soil and reduced levels of organic matter, especially in the subsurface layer.

Lime movement through highly weathered soil profiles

“…Since lime is relatively insoluble, surface application may not be effective for ameliorating subsoil acidity (Shainberg et al 1989) and neutralizing Al toxicity (Ernani et al 2004, Godsey et al 2007, Kirkegaard et al 2014, Santos et al 2018, Barth et al 2018 in NT fields. If lime does not move downward into the soil profile under NT, continued surface applications can cause significant increases in pH and nutrient concentrations in the nearsurface layer (i.e., 0 to 3 cm) over time (Kirkegaard et al 2014, Bortolanza and Klein 2016, Nunes et al 2017a, Barth et al 2018. Excessive accumulation of lime within the topsoil can promote chemical stratification, increase surface soil pH, and decrease availability of cationic micronutrients such as Cu, Mn, and Zn (Tahervand and Jalali 2017) within the soil profile.…”

Methodological aspects of the quantification of dispersible clay and their relations with soil properties along a catena under no-till system

“…Cropping system management plays an important role in the construction and modification of the geomorphology and soil structure of sloping agricultural landscapes (De Alba et al, 2004;Arnáez et al, 2015). Inadequate conservation practices can promote a continuous degradation of soil structure (Nunes et al, 2017), resulting in the dispersion of particles as a result of the presence of unstable aggregates, impeding the retention of rainwater and favouring the displacement of these particles, thereby facilitating erosion (Beutler et al, 2001;Farahani et al, 2018a).…”

“…Reichert et al, 2009;Giarola et al, 2013;Silva et al, 2014;Nunes et al, 2015;Tormena et al, 2017). Nunes et al (2017) explains that soil management practices can induce high concentrations of mono-(e.g. K + ) and bivalent salts (e.g.…”

“…erosion) (Arnáez et al, 2015;Rosemary et al, 2017). The indicators of structural stability can be used to contribute to the monitoring of possible modifications, indicating improvements or deteriorations in the structure of the soil (Arshad and Martin, 2002;Nunes et al, 2017). Dispersible clay represents the portion of the total clay which has the ability to disperse easily in the presence of water (Dexter and Czyż, 2000;Dexter et al, 2011); it is an important indicator of structural stability (Igwe and Udegbunam, 2008;Nunes et al, 2017) in catena soils which have been influenced by intensive fertilization, constant soil tillage and the absence of organic carbon (Azevedo and Bonumá, 2004;Dexter et al, 2011;Czyż and Dexter, 2015).…”

“…Clay dispersion has a significant impact on the environment (Azevedo and Bonumá, 2004) and is influenced by a wide range of soil attributes (e.g. see Igwe and Udegbunam, 2008;Nunes et al, 2017). Clay content, water dynamics in soil and organic matter, cation exchange and mineralogical composition (e.g.…”