Ms Elizabeth C Coonan1,2, Dr Clive A Kirkby2, Dr John A Kirkegaard2, Mr Martin R Amidy1, Dr Craig L Strong1, Dr Alan E Richardson2
1Fenner School of Environment and Society, Australian National University, Canberra, Australia, 2CSIRO Agriculture & Food, Canberra, Australia
Soil organic matter (SOM) can be lost from the soil following cultivation which may affect agricultural productivity. It has previously been shown that supplementary nutrients (nitrogen (N), phosphorus (P) and sulphur (S)) alongside incorporation of carbon (C) rich wheat residue increased SOM after 5 years of cultivation compared to a control without supplementary nutrients. However, SOM-nutrient interactions have mainly been investigated on annually cropped soils. A key point at which SOM is lost from the soil is during the cultivated transition from a pasture to a crop. It is not clear how initial soil fertility or supplementary nutrient addition may affect SOM dynamics during this transition. We investigated the impact of initial soil fertility on the mineralization of soil C and associated changes in soil nutrients in pasture soils following cultivation of a long-term pasture soil with and without lime. The pasture was managed with 20 years of P fertilization compared to a non-P fertilized control. The high P treatment with greater system productivity was shown to have an increase of 12 Mg C ha-¹ soil C to 60 cm depth. Three treatments were applied during the transition from pasture to crop: a cultivated control, cultivated with lime, and cultivated with lime and along with supplementary nutrient addition. Soil C was assessed in both whole soil and in the more stable <0.4 mm soil fraction. Following the cultivated transition to a crop, loss of C from the <0.4 mm fraction was increased in the limed low fertility soils (12.3% loss) and reduced in the limed high fertility soils (9.6% loss). Addition of nutrients to the limed low fertility soils reduced the loss of C (7.0% loss). Addition of nutrients with lime during pasture to crop transitions can reduce SOM loss in low fertility soils which has implications for management of SOM in cropping systems.
Elizabeth Coonan is a PhD student with the Australian National University Fenner School of Environment and Society and CSIRO Agriculture and Food based in Canberra. Her main research interest is soil organic matter in pasture crop rotation systems with a focus on the impact of liming, nutrient addition, and cultivation on soil organic matter when acid pasture soils are converted to cropping. She has an undergraduate degree in Science and Engineering from the Australian National University.