The short-term cover crops increase soil labile organic carbon in southeastern Australia

Cover crops are usually grown to increase soil fertility. However, little is known about the effects of cover crops on soil labile organic carbon (C), especially in southeastern Australia. In this study, cover crop species, i.e., wheat and Saia oat, were broadcast-seeded in May 2009 and then crop biomass was crimp-rolled onto the soil surface at anthesis in October 2009. Soil and crop residue samples were taken in December 2009 to investigate the short-term effects of cover crops on soil pH, moisture, NH4+-N, NO3--N, soluble organic C and nitrogen (N), total organic C and N, and C mineralization in comparison with a nil-crop control (CK) in southeastern Australia. The soil is a Chromic Luvisol according to the FAO classification with 48.4 ± 2.2% sand, 19.5 ± 2.1% silt and 32.1 ± 2.1% clay. An exponential model fitting was employed to assess soil potentially labile organic C (C0) and easily decomposable organic C for all treatments based on 46-day incubations. Results showed that crop residue biomass significantly decreased over the course of two-month decomposition. The cover crop treatments had significantly higher soil pH, soluble organic C and N, cumulative CO2-C, C0 and easily decomposable organic C, but significantly lower NO3--N than the CK. However, no significant differences were found in soil moisture, NH4+-N, total organic C and N among the treatments. Our results indicated that the short-term cover crops increased soil labile organic C pools, which might have implications for local agricultural ecosystem managements in this region.