Abstract
Soil tillage promotes changes in soil structure. The magnitude of the changes varies with the nature of the soil, tillage system and soil water content and decreases over time after tillage. The objective of this study was to evaluate short-term (one year period) and long-term (nine year period) effects of soil tillage and nutrient sources on some physical properties of a very clayey Hapludox. Five tillage systems were evaluated: no-till (NT), chisel plow + one secondary disking (CP), primary + two (secondary) diskings (CT), CT with burning of crop residues (CTb), and CT with removal of crop residues from the field (CTr), in combination with five nutrient sources: control without nutrient application (C); mineral fertilizers, according to technical recommendations for each crop (MF); 5 Mg ha-1 yr-1 of poultry litter (wetmatter) (PL); 60 m³ ha-1 yr-1 of cattle slurry (CS) and; 40 m³ ha-1 yr-1 of swine slurry (SS). Bulk density (BD), total porosity (TP), and parameters related to the water retention curve (macroporosity, mesoporosity and microporosity) were determined after nine years and at five sampling dates during the tenth year of the experiment. Soil physical properties were tillage and time-dependent. Tilled treatments increased total porosity and macroporosity, and reduced bulk density in the surface layer (0.00-0.05 m), but this effect decreased over time after tillage operations due to natural soil reconsolidation, since no external stress was applied in this period. Changes in pore size distribution were more pronounced in larger and medium pore diameter classes. The bulk density was greatest in intermediate layers in all tillage treatments (0.05-0.10 and 0.12-0.17 m) and decreased down to the deepest layer (0.27-0.32 m), indicating a more compacted layer around 0.05-0.20 m. Nutrient sources did not significantly affect soil physical and hydraulic properties studied.
Highlights
Soil physical properties which directly affect plant growth and yield are determined by internal soil properties, conditions above soil surface, as well as by the soil-cropatmosphere relationship (Forsythe, 1967)
The coefficient of variation was below 10 % for most parameters, except for macroporosity, which is affected by the higher variability usually found in larger pores (Souza et al, 2001)
No-till (NT) and chisel plow (CP) treatments resulted in lower bulk density conventional tillage treatments
Summary
Soil physical properties which directly affect plant growth and yield (e.g. temperature, mechanical resistance, water and oxygen availability) are determined by internal soil properties, conditions above soil surface, as well as by the soil-cropatmosphere relationship (Forsythe, 1967). Soil tillage is the major agricultural practice affecting soil physical properties because it promotes changes in soil structure and porosity, which in turn affect soil hydraulic properties and the processes of water infiltration, runoff and storage, soil temperature, and chemical transport (Ahuja et al, 1998). According to these authors, soil tillage generally decreases soil bulk density and increases soil porosity by loosening the soil. The changes in these properties are not permanent and tend to revert asymptotically over time to values close to those of soil before tillage, due to natural reconsolidation during wetting and drying cycles, to slaking and dispersion of soil aggregates enhanced by the raindrop impact on the soil surface, and to external stress application through traffic and/or trampling (Ahuja et al, 1988)
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