Assessing the long-term effects of zero-tillage on the macroporosity of Brazilian soils using X-ray Computed Tomography

Abstract

Zero-tillage (ZT) is being increasingly adopted globally as a conservationist management system due to the environmental and agronomic benefits it provides. However, there remains little information on the tillage effect on soil pore characteristics such as shape, size and distribution, which in turn affect soil physical, chemical and biological processes. X-ray micro Computed Tomography (μCT) facilitates a non-destructive method to assess soil structural properties in three-dimensions. We used X-ray μCT at a resolution of 70 μm to assess and calculate the shape, size and connectivity of the pore network in undisturbed soil samples collected from a long-term experiment (~30 years) under zero tillage (ZT) and conventional tillage (CT) systems in Botucatu, Southeastern Brazil. In both systems, a single, large pore (>1000 mm 3 ) typically contributed to a large proportion of macroporosity, 91% in CT and 97% in ZT. Macroporosity was higher in ZT (19.7%) compared to CT (14.3%). However the average number of pores was almost twice in CT than ZT. The largest contribution in both treatments was from very complex shaped pores, followed by triaxial and acircular shaped. Pore connectivity analysis indicated that the soil under ZT was more connected that the soil under CT. Soil under CT had larger values of tortuosity than ZT in line with the connectivity results. The results from this study indicate that long-term adoption of ZT leads to higher macroporosity and connectivity of pores which is likely to have positive implications for nutrient cycling, root growth, soil gas fluxes and water dynamics.

The effects of long-term fertilizations on soil hydraulic properties vary with scales

“…This is consistent with work reported by others ( Dal Ferro et al, 2013 , Yang et al, 2018 ). For the woodland, non-tillage is another mechanism underlying the increased core porosity and permeability as non-tillage kept the macropores generated by roots and soil fauna intact ( Borges et al, 2019 , Galdos et al, 2019 ), especially the pores > 1.2 mm ( Fig. 4 A).…”

“…Linking soil hydraulic conductivity to pore geometry obtained from X-ray images is available, but most them integrated the macropores and micropores ( Koestel et al, 2018 , Pohlitz et al, 2019 , Schlüter et al, 2020 , Zhang et al, 2019 ). There are also studies on geometrical change in both intra-aggregate pores and macropores ( Borges et al, 2019 , Galdos et al, 2019 , Koestel and Schlüter, 2019 , Pires et al, 2019 , Schlüter et al, 2018 ), as well as their temporal evolution under different managements ( Lucas et al, 2019 , Schlüter et al, 2011 ). While a change in agronomical practices could lead to an instant change in pore geometries, it might take decades or even century for the pore geometries to reach a new statistically equilibrium state on average across the field following fertilization change or land conversion ( Lohse and Dietrich, 2005 , Lucas et al, 2019 , Neal et al, 2020a ).…”

Soil Quality in Agroecological Production Areas in Southern Brazil: Indicators Based on Farmers' Perception

“…The quantitative analysis shows a lower bulk density (1.23 to 1.38 Mg m -3 ), a higher total porosity (equal or higher 0.43 m 3 m -3 ) and macroporosity (higher than 0.15 m 3 m -3 ) in the agricultural areas (Table 3) probably a reflection of the annual soil tillage carried out for seed crops, according to information from the interviews. Despite the conventional tillage promoting greater soil macroporosity, these are usually agglomerated, more randomly structured, and not connected, whereas in soil under no-tillage the macroporosity can be also higher than conventional tillage, and presented connected pore ramifications, as observed by Galdos et al (2019).…”

Brachiaria species influence nitrate transport in soil by modifying soil structure with their root system

“…smaller pores function predominantly for water storage whereas larger pores contribute to flow processes. The soil pores were also classified according to their shape using the terminology suggested by Bullock et al 35 , described in detail in Galdos et al 36 . The network tortuosity (τ) of the pores and connectivity was calculated using Osteoimage 37,38 .…”