Liming with CaCO3 or CaO affects aggregate stability and dissolved reactive phosphorus in a heavy clay subsoil

Gizachew Tarekegn Getahun,Ararso Etana,Lars Juhl Munkholm,Holger Kirchmann

doi:10.1016/j.still.2021.105162

Gizachew Tarekegn Getahun, Ararso Etana + Show 2 more

Open Access

https://doi.org/10.1016/j.still.2021.105162

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Abstract

A 22-month incubation experiment was conducted to study the effect of lime on clay dispersion, wet aggregate stability (WAS) and dissolved reactive phosphorus (DRP), using a heavy clay subsoil with an initial pH of 7.0 and 7.3 g kg−1 of soil organic carbon. Lime was applied to achieve soil pH values of 7.5, 8 and 8.4. Clay dispersion decreased linearly with increased pH (corresponding to an increase in lime amount) for both lime types (R2 = 0.44 for CaO; R2 = 0.53 for CaCO3, P < 0.05), with a decrease of 2–16 % (CaO) and 3–17 % (CaCO3) compared with the control.Both WAS and DRP followed piece-wise linear functions, with an increase and peak around pH 7.5–7.8, and a decline at higher pH (WAS: R2 = 0.73 for CaO, R2 = 0.68 for CaCO3, P < 0.001; DRP: R2 = 0.84 for CaCO3, R2 = 0.33 for CaO, P < 0.001). Wet aggregate stability increased on average by 13 % and 11 % at the lowest and intermediate levels, respectively, compared with the control. At the highest lime application rate, WAS was 6 % (CaO) and 8 % (CaCO3) lower than in the control. These differences were probably caused by changes in electrical charge and in concentrations of soluble calcium and dissolved organic carbon (DOC) as the pH increased. More studies are needed to understand the processes in detail and to draw conclusions that are more robust.

Highlights

Subsoil, commonly below the ploughing depth, often limits root growth due to compaction or poor soil structure
Clay dispersion was significantly negatively correlated with soil pH, for both lime types (R2 = 0.44 for Calcium oxide (CaO); R2 = 0.53 for CaCO3, P < 0.05) (Fig. 1)
Clay dispersion was reduced by on average 3, 10 and 17 %, at the low, intermediate and high rate of CaCO3 and CaO application compared with the control

Summary

Introduction

Commonly below the ploughing depth, often limits root growth due to compaction or poor soil structure. Using available management options, efforts have been made to ameliorate subsoil constraints to limit the negative effects on root growth and crop yield (Gill et al, 2008). One such management option is the application of lime materials to the subsoil. The theory is that addition of lime increases the concentration of calcium ions causing compression of diffuse double layer and flocculation (Ghobadi et al, 2014; Haynes and Naidu, 1998), resulting in the formation of micro-aggregates (Grant et al, 1992; Six et al, 2004)

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