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Soil chemistry change on MASTER long term soil liming experiment
MASTER experiment is a long-term agronomic experiment that commenced in 1992. It was designed to develop and demonstrate a sustainable agricultural system that is economically viable and environmentally effective to manage the highly acid soils in the high rainfall region (500–800 mm) of south-eastern Australia. It was designed to run for 6-year cycles (Li et al. 2001). By 2010, we have successfully completed 3 cycles.
Over the past 18 years, subsurface soil acidity has been slowly ameliorated. Results showed that soil pH at 15-20 cm depth increased more than half of a pH unit over 18 years at 0.045 pH units/year whereas the exchangeable Al decreased from 42% in 1992 to below 10% in 2006 at 15-20 cm soil depth by maintaining pH of 5.5 at 0-10 cm. It is estimated that about 180–200 kg/ha/year of lime has been used to neutralise acids added by the system. About 90–100 kg/ha/year has been leached to the subsoil, which has accounted for the increase in pH below 10 cm.
A large amount of soil phosphorus (P) has accumulated on all treatments with 15 kg P/ha applied each year. Results showed that soil Colwell-P at 0-10 cm has been gradually built up, especially on the unlimed treatments. It appeared that limed treatments used more P with better P use efficiency. The site offers a unique opportunity to characterise the soil inorganic and organic P pools and to understand the processes leading to accumulation of organic P in soil and the bioavailability of those organic P pools.
At the MASTER site, soil organic carbon content increased under both perennial and annual pastures. Results from the Roth-C simulation model showed that perennial pastures sequestered slightly more carbon in soil than annual pastures, but the difference is small. It is estimated that perennial pastures sequestered an additional 7.9 t C/ha and annual pastures 6.5 t C/ha over 15 years on the MASTER site, yielding an average 0.57 and 0.46 t C/ha/year for perennial and annual pastures, respectively.
The current changes in redistribution of Mg and K resources from the subsoil to the topsoil is a reversal of the historic weathering of the soil that was associated with soil acidification. The exciting prospect is that we can use the subsurface soil resources of nutrients (K, Ca and Mg) and of alkalinity to partially ameliorate the acidic surface soil. At the same time removal of Mg from the subsurface soil in exchange for acid may have long term benefits for improving subsoil structure and reducing dispersion. In addition, an increase of Mg in soil would increase the Mg content in pastures, hence reducing the risk of a “grass tetany” problem.
This page was last updated on 24/07/2017
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