Source: Cam Nicholson
Nicon Rural Services, for the Woady Yaloak Catchment Group, Sep 2011
Executive summary:
Eight paddock scale comparisons were established around Werneth in April 1999 as part of the Sustainable Grazing Systems (SGS) program. Different rates (at 3 sites) and different supplies of lime (at 3 sites) were applied and compared to a no lime area. Two sites only had one limed area compared to no lime. Rates varied from 1.25 t/ha to 5 t/ha. Lime was sourced from Kurdeez (K), Lara (L) and Green Valley.(GV)
Sites were retested in August 2011 to examine the changes in soil pH and soil fertility. Four of the eight sites were in crop and four sites had received further applications of lime, including the areas not limed in 1999. The period between testing was drier than the long term average, including a severe drought.
The key findings were:
- Soils have acidified since testing in 1999. Of the four paddocks where no lime has been applied since 1999, the pH (CaCl2) in the top 10 cm has dropped by 0.2 to 0.3 of a unit (falling from 4.7 to 4.5 or 4.4). This may appear small but given the logrithmic scale used to measure pH, the change represent approximately a doubling of hydrogen in the soil
- The pH (CaCl2) of soils limed in 1999 are 0.2 to 0.5 of a unit greater (ie less acid) than the non limed areas. However because the non limed areas have continued to acidify, a more meaningful comparison is with the pH of the non limed areas in 1999. Three of the four limed sites still remain higher than the pre liming levels when applied at 2.5 t/ha or 3.0 t/ha, suggesting liming has an effect for at least 10 years and possibly more
- There appears to be no obvious difference between the limes types (suppliers) when used at the same rates
- 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 by between 0.15% and 0.32 % carbon over 11 years but cannot be attributed to the lime alone. The accumulation may be a result of additional pasture growth, improve soil biological activity (fungi and bacteria) and farming practices
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