Comparison of tillage methods for lime incorporation, Tardun 2016 trial report

Results and discussion

Note; pH discussed as pH (1:5 CaCl₂)

This trial covers three distinct soil types throughout the paddock. The northern section of the paddock is a shallow acid gravel, the middle section a brown sand over gravel of varying depths, the southern section red sandy loam. The results are reported from each of these soil types as each differ in their response to lime and incorporation (Figure 1).

Figure 1 Yield results of lime incorporation trial, Tardun 2016

The inclusion of lime, irrespective of incorporation treatment, has given a significant benefit to yield (Figure 2).

Figure 2 Yield response to lime application (2016)

The addition of lime, 2t/ha or 4t/ha, has increased the surface pH, of the gravel soil in the north of the paddock, from below the target of pH 5.5 to above. Once machine incorporation has been carried out it is shown that 4t/ha lime is required to maintain a higher soil surface pH and increase the mid soil (10-20 cm) pH to a suitable level (Figure 3). The TopDown plough shows a higher subsoil pH below 20cm because one of the three reps has constantly given a high subsoil pH reading each year from the same location. However, this machine would have achieved the deepest lime incorporation and so, even after taking this particular plot result out, it still has the highest subsoil pH after 4t/ha of lime was applied.

Figure 3 Soil pH of north section (acid gravel soil) after harvest 2016, four seasons after lime application and incorporation in 2013

The soil in the centre of the paddock is a loamy sand over gravel. The lime application has increased the topsoil pH but, even after machine incorporation, it has not significantly increased any of the subsoil pH (Figure 4).

Figure 4 Soil pH of mid section (brown loamy sand over gravel soil) after harvest 2016, four seasons after lime application and incorporation in 2013

The incorporation story on the red loamy sand is not as clear because of the inherently high pH. This is because of limestone being present in this area of the paddock which makes it very difficult to draw conclusions from the results (Figure 5).

Figure 5 Soil pH of south section (red loamy sand) after harvest 2016, four seasons after lime application and incorporation in 2013

All sub-surface soils are well above the target of pH 4.8 in the southern area of the paddock. Only two of the topsoil results, involving no lime being applied in the nil and TopDown incorporation treatments, are below the target of pH 5.5 (Figure 5). This shows that it is still worthwhile spreading lime on the surface when required as lime has increased yield in this area (Figure 1).