Slow movement of alkali from surface-applied lime warrants the introduction of strategic tillage for rapid amelioration of subsurface acidity in south-western Australia

Abstract

Conventional surface-application of agricultural lime takes many years to increase pH deeper in the soil profile, which is a barrier to increased adoption of liming. We conducted a series of experiments to measure the rate of vertical movement of alkali and identify the factors that determine this movement into the subsurface, to evaluate the feasibility of ameliorating acidic subsurface soil using residual (undissolved) lime (CaCO 3) at Wongan Hills (30.858S, 116.748E) and Merredin (31.488S, 118.218E) and to test whether deep tillage and lime incorporation can significantly speed up the amelioration of subsurface soil acidity at Kalannie (30.428S, 117.298E). Multiple applications of lime to the surface of the soil at higher rates (total 6-8.5 Mg ha-1) significantly increased subsurface soil pH but only in the 0.10-0.20 m depth by 0.049 pH units per year over 10-24 years. A large proportion of the surface-applied lime was stratified in the top few centimetres of the soil and incorporation of this undissolved lime with a rotary hoe to a depth of 0.25 m significantly increased soil pH (by 0.63 units) within a year in the Wongan Hills field experiment. Deep incorporation of 6 Mg ha-1 lime to a depth of 0.45 m through excavation and spading with a small rotary hoe also increased soil pH by more than a unit and decreased Al concentration to below the toxic level within two months in the Kalannie experiment, allowing wheat (Triticum aestivum L.) plants to produce root systems up to 0.59 m deep compared with 0.26 m for the control. Our soil column leaching experiment indicated that surface incorporation of lime in higher rainfall regions can be useful to treat subsurface soil acidity but that the rate of improvement in subsurface pH was slow. Therefore, deeper incorporation of lime using cost-effective strategic deep tillage is likely to be necessary.

Short- and Long-Term Effects of Lime and Gypsum Applications on Acid Soils in a Water-Limited Environment: 2. Soil Chemical Properties

“…In the LT, a high rate of L application (4-8 t ha −1 ) increased pH CaCl 2 in the 10-20 cm soil layer while 2 t L ha −1 did not affect subsoil pH CaCl 2 (Figure 2i). This observation is consistent with other studies that have shown L application can be slow or in some cases, ineffective in increasing subsoil pH CaCl 2 [2,35,36].…”

“…Once pH CaCl 2 of the 0-10 cm soil layer has achieved a pH CaCl 2 of 7.1, L will stop dissolving [33,34]. Due to this restriction on L dissolution, the pool of alkalinity available to be leached into the subsoil is insufficient for the L application to have an impact on subsoil pH [2,32,35,36]. In the ST and MT experiments, pH CaCl 2 in the 0-10 cm soil layer was greater than 5.5, and the application of additional L resulted in no impact on subsoil pH CaCl 2 over the sampling period of two years and eight months.…”

Assessing the effectiveness of the TaMATE1B and TaALMT1 genes to enhance the Al3+ tolerance of durum wheat (Triticum turgidum) grown under controlled conditions and in the field

“…In that experiment the soils were well-mixed with the lime and the acid pH was effectively neutralised throughout the profile. Liming is likely to provide the most effective solution to soil acidity in the field if it can be incorporated throughout the soil profile which may take years with repeated applications (Azam and Gazey 2021). Lime application can be costly particularly if it needs to be transported long distances and is typically applied to the surface soil.…”

Dissection of the Contributing Factors to the Variable Response of Crop Yield to Surface Applied Lime in Australia

“…This may explain why lower rates of applied lime failed to generate a yield response. Higher rates of lime and/or deeper incorporation may generate greater pH changes and therefore greater yield responses to applied lime [52].…”