Cause and management of soil acidification
Subsoil acidity is widespread and its amelioration is costly and often impractical. Our research suggests that the development of subsoil acidity depends largely on acid production by plant roots due to excess cation uptake, particularly under legume-based agriculture. The deposition and decomposition of plant residues do not cause subsoil acidification but contribute to the development of subsoil acidity profiles through their liming effect on the topsoil.
Nitrification from ammonium-based fertilizers or from organic N in plant residues, and subsequent leaching of nitrate, contribute mainly to topsoil acidification. In contrast, the uptake of leached nitrate and denitrification in deeper layers may decrease subsoil acidity.
Biological amelioration through managing excess anion (nitrate) uptake has been tested in the field and is a promising method to ameliorate subsoil acidity. The major challenge for the biological amelioration method is to synchronise nitrate movement and root capture in the subsoil for maximal alkalization and minimal nitrate leaching loss.
Our recent research showed that the addition of organic acids stimulated microbial NO3 uptake and ammonification and decomposition of indigenous soil organic matter resulting in a priming effect on alkalinity release, and that the degree of the alkalinity priming is influenced by type of organic acid, native soil organic matter and initial soil pH.
Future work will focus on understanding the relationship between soil acidification and soil C under different farming systems, to determine the effect of soil acidity and liming history on changes in the quantity and composition of soil C.
Contributors: Dr Xiaojuan Wang, Dr Clayton Butterly, Fatima Rukshana, Professor Caixian Tang.
Collaborators: Dr Jeff Baldock (CSIRO Land and Water), Drs Mark Conyers and Deli Liu (DPI NSW), Professor Jianming Xu (Zhejiang University).
- Linking soil acidification with carbon dynamics in Australian agroecosystems (Funded by ARC)
- Role of organic matter in soil pH change in agroecosystems (ARC)
- Combating subsoil acidity for sustainable production through managing plant cation-anion uptake (ARC)