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

M.V Galdos,L.F Pires,H.V Cooper,J.C Calonego,C.A Rosolem,S.J Mooney

doi:10.1016/j.geoderma.2018.11.031

M.V Galdos, L.F Pires + Show 4 more

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https://doi.org/10.1016/j.geoderma.2018.11.031

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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 mm3) 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.

Highlights

Zero-tillage (ZT), where the seed is sown directly into the soil causing minimal disturbance and retaining surface crop residue, has been widely adopted since the 1940s with 111 million ha managed globally using this approach (Derpsch et al, 2010)
Studies on the effects of ZT on soil properties have previously shown increases in water infiltration rate and storage capacity (Copec et al, 2015; Su et al, 2007), and decreases in surface runoff and erosion compared with conventionally tilled (CT) soils (DeLaune et al, 2013). These differences are ascribed to an increase in aggregate stability, higher numbers of biopores originating from earthworms and root growth and a decrease in the frequency of machinery traffic passing over the soil, which collectively alters soil porosity (Haghighi et al, 2010)
Mangalassery et al (2014) found larger differences between ZT and CT, with CT porosity 47% higher than under ZT soils in the upper 10 cm when assessed by X-ray micro Computed Tomography at a resolution of 64 μm

Summary

Introduction

Zero-tillage (ZT), where the seed is sown directly into the soil causing minimal disturbance and retaining surface crop residue, has been widely adopted since the 1940s with 111 million ha managed globally using this approach (Derpsch et al, 2010). Studies on the effects of ZT on soil properties have previously shown increases in water infiltration rate and storage capacity (Copec et al, 2015; Su et al, 2007), and decreases in surface runoff and erosion compared with conventionally tilled (CT) soils (DeLaune et al, 2013). These differences are ascribed to an increase in aggregate stability, higher numbers of biopores originating from earthworms and root growth and a decrease in the frequency of machinery traffic passing over the soil, which collectively alters soil porosity (Haghighi et al, 2010). An increased number of macropores in CT compared to ZT in the surface but a higher

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