Long term trials have shown continuous cropping under a cereal legume rotation with district practice application of fertiliser N and retention of stubble caused a decrease in soil pH of up to 1.6 units over 14 years. Reduced N inputs can lessen this impact (as can stubble removal) but also decreases yield. At Wagga, the application of lime in combination with phosphorous (P) increased grain yields by almost 100%, whilst stocking rates increased by 25% after six years. Soil pH initially increased from pH 4.0 to 5.5 after application of 3.7 t/ha lime, but subsequently decreased back to 5.0 over the next six years.
- High initial lime rates will improve soil pH more rapidly and allow excess lime to move deeper into the profile addressing subsoil acidification.
- Maintenance lime is required to maintain changes in soil pH.
- Liming may increase N leaching.
- P application is more efficient.
- Excessive N application and leaching of nitrate is likely to accelerate the decline in soil pH.