The contribution of crop residues to changes in soil pH under field conditions
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Background and Aims
Crop residues are important for the redistribution of alkalinity within soils. A net increase in pH following residue addition to soil is typically reported. However, effects are inconsistent in the field due to confounding soil processes and agronomic practises.
A column experiment investigated the effects of canola, chickpea and wheat residues, differing in alkalinity content and C:N ratio, on soil pH changes in a Podosol (Podzol; initial pH 4.5) and Tenosol (Cambisol; initial pH 6.2) under field conditions.
Residues (10 g dry matter kg-1 soil; 0–10 cm) increased soil pH, and temporal changes in alkalinity depended on the residue and soil type. Alkalinity was generated via abiotic association reactions between H+ and added organic matter and via ammonification and decarboxylation processes during decomposition. Alkalinity from canola and chickpea residues moved down the soil profile (10–30 cm) and was attributed to nitrate immobilisation and organic anion decomposition by soil microbes.
The application of residues to acid and moderately acid soils increased the pH of both topsoil and subsoils, which persisted over 26 months. Maximal increase of pH observed at 3 months was correlated with the concentration of excess cations in the residues.
KeywordsDecomposition Initial pH Long-term Nitrogen cycle Soluble alkalinity Soil acidification Soil type
We are grateful to Bhawana Bhatta-Kaudal, Fatima Rukshana, Giang Nguyen (Jenny) and Xiaojuan Wang who helped with sampling and analyses throughout the study. We also thank Dr Gary Clark for assistance with instrumentation, particularly ICP-OES. This research was supported by an Australian Research Council Discovery Project fund (DP0877882).
- FAO/ISRIC/ISSS (1998) World reference base for soil resources. FAO, RomeGoogle Scholar
- Helyar KR, Porter WM (1989) Soil acidification, its measurement and the processes involved. In: Robson AD (ed) Soil acidity and plant growth. Academic, Sydney, pp 61–101Google Scholar
- Isbell RF (1996) The Australian soil classification. CSIRO, MelbourneGoogle Scholar
- Reynolds WD, Clarke Topp G (2007) Soil water desorption and imbibition: tension and pressure techniques. In: Carter MR, Gregorich EG (eds) Soil sampling methods and analysis. CRC, Boca RatonGoogle Scholar
- Robson AD, Abbott LK (1989) The effect of soil acidity on microbial activity in soils. In: Robson AD (ed) Soil acidity and plant growth. Academic, Sydney, pp 139–165Google Scholar