Liming effect of non-legume residues promotes the biological amelioration of soil acidity via nitrate uptake.

Aims: The utilisation of on-farm crop residues to ameliorate soil acidity is thought to be more cost-effective than other organic materials such as animal manures. In addition, using NO3− as the form of N can induce rhizosphere alkalinisation due to the excess uptake of anions over cations by plant roots. Methods: A pot experiment was conducted to evaluate the effectiveness of four commonly-used brown manures, field pea, oats, vetch and wheat in combination with two Ca(NO3)2 levels (64 and 191 mg N kg− 1) in improving wheat growth in two acid soils varying in Al3+ concentration and pH buffer capacity. Results: All amendments increased plant growth and soil pH, and decreased Al concentration in Sodosol (pH buffer capacity, 23 mmolc kg− 1 pH− 1), with legume residues (field pea and vetch) being more effective than cereal residues (oat and wheat). Application of Ca(NO3)2 alone was less effective in ameliorating soil acidity in both Sodosol and Dermosol due to poor root growth and hence lower NO3−-N uptake (< 18 %). However, higher rates of Ca(NO3)2 further increased pH (by 0.12 units) in Sodosol when combined with wheat and oat residues with decreased Al3+, increased root growth and NO3−-N uptake. Conclusions: The capacity of Ca(NO3)2 to ameliorate soil acidity was reduced with legume residues, when it was not the main N source for plant growth. The combined application of Ca(NO3)2 and low-N crop residue (C/N > 52) could act as an alternative to costly lime or off-farm products in ameliorating soil acidity. [ABSTRACT FROM AUTHOR]