Source: Cam Nicholson
Nicon Rural Services, for the Upper Barwon Landcare Network, May 2012
Six paddock scale comparisons were established around Birregurra in April 1999 as part of the Sustainable Grazing Systems (SGS) program. Different rates (at 2 sites) and different supplies of lime (at 3 sites) were applied and compared to a no lime area. A further site had a limed area compared to no lime, but was applied on saline and non saline soil. Rates of solid lime applied varied from 1.5 t/ha to 5 t/ha and was sourced from Kurdeez (K), Lara (L) and Green Valley (GV). Liquid lime was applied at rates from 25 l/ha to 50 l/ha.
Sites were retested in May 2012 to examine the changes in soil pH and soil fertility. One of the sites have been cropped, with three receiving at least one additional application of lime. All other sites have remained in pasture and have not received any additional lime. The period between testing was drier than the long term average, including a drought.
The key findings were:
- Soils have acidified since testing in 1999. Of the two paddocks where no lime has been applied since 1999, the pH (CaCl2) in the top 10 cm has dropped by 0.3 of a pH unit (falling from 4.5 to 4.2) at one site but remained similar at the other site (at ph 4.4). This may appear inconsequential but given the logrithmic scale used to measure pH and the low starting pH values, the change represent highly acid and acidifying soils.
- The pH (CaCl2) of soils limed in 1999 are 0.3 to 0.4 of a unit greater (ie less acid) than the non limed areas. Lime was applied at 2.5 to 3.5 t/ha at these sites and suggests liming has an effect for at least 12 years and possibly more
- There appears to be no obvious difference between the limes types (suppliers) when used at the same rates
- Liquid lime did not change the pH of the soil. The acidity on the liquid lime sites were the same as the Nil treatment, 16 months after application and 12 years later.
- Increased rates of lime reduce the acidity more than lower rates of lime (as expected).
- Liming maintained low levels of available (toxic) aluminium. This means highly sensitive plant species would not be affected, whereas they would be on the non limed areas
- Available phosphorus (Olsen P) was not affected by liming
- Organic carbon increased at two sites by between 0.1% and 0.6 % carbon over 12 years but decreased at one site. Total organic carbon can be highly variable and it is difficult to draw strong conclusions from this data.
- The findings are consistent with responses at eight sites in the Woady Yaloak Catchment.