Recovery liming
Applying agricultural lime is the most cost-effective way of treating soil acidity. The amount of lime required will depend on the current pH profile, soil type, rainfall, farming system and lime quality. To avoid wasting resources, always apply sufficient lime. Target specific areas if you can’t do it all.
Estimating the amount of lime required to recover acidic soil to recommended pH targets is complicated. Enough lime needs to be applied to treat ongoing acidification as well as the already acidified soil (Figure 1).
The rule-of-thumb guide (Table 3) indicates of the amount of lime that may be required on sandy soils over five years to achieve pHCa above 5.5 in the topsoil and 4.8 in the subsurface after 10 years. Where more information is known about the farm and farming system, a 10-year liming plan can be developed. Increases in pH will depend on soil type, rainfall, lime quality and quantity applied and other farming practices as well as the soil pH profile. Expert advice should be sought for individual recommendations.
| Soil depth (cm) | pHCa | Lime amount over five years (tonnes per hectare) |
|---|---|---|
| 0-10 | <5 | 2t/ha |
| 0-10 | <5.5 | 1t/ha |
| 10-20 | <4.5 | 2t/ha |
| 10-20 | <4.8 | 1t/ha |
| 20-30 | <4.5 | 1t/ha |
| 20-30 | <4.8 | measure pH in three years |
Monitoring the topsoil and subsurface soil about every three years is very important when liming to recover acidic subsurface soil. This will allow adjustment of the liming schedule as the soil pH increases or if it does not respond as expected. It is essential to maintain the topsoil pHCa above 5.5 for alkalinity to move down to treat acidity in the subsurface soil.