Long-term liming changes pasture mineral profile.

There is limited information on changes of pasture mineral concentrations over the long-term in response to liming. A long-term field experiment was conducted to assess the influence of lime application on (a) changes in pasture mineral composition over time; and (b) key pasture mineral concentrations and ratios important to animal health. Perennial and annual pastures with or without lime application were sampled annually over 12 years and analysed for macro- and micro-minerals. Mineral ratios and indices were calculated to assess the potential impact on animal health. Liming increased the concentrations of calcium, sodium and silicon, but decreased the concentrations of micro-nutrients including copper, zinc and manganese. The same trend was found in both annual and perennial pastures although there were some fluctuations between years. Liming increased the calcium:phosphorus ratio and the dietary cation-anion difference but reduced the tetany index on both annual and perennial pastures. These findings suggest a potential benefit to improve animal health outcomes for some disorders on the limed pastures. However, the reduced concentrations of some trace elements following liming potentially decreases antioxidant capacity and requires further research.

Perennial pastures reduce nitrous oxide emissions in mixed farming systems in a semi-arid environment.

Perennial pastures play a crucial role in mixed farming systems by supplying feed for livestock, restoring soil fertility, reducing deep drainage, providing an opportunity to manage herbicide-resistant weeds and breaking soil-borne disease cycles. However, to our knowledge there is no data on the role of perennial pastures in mitigating N2O emissions from the phased crop rotations in semi-arid environments. Two 4-year field experiments were conducted in a semi-arid environment in southern Australia to (a) evaluate the role of perennial pastures in mitigating N2O emissions in mixed farming systems, and (b) compare the cumulative N2O emissions from different pasture mixes. Results showed that the annual N2O emissions were 31% lower from chicory-based pastures and 12-17% lower from perennial grass-based pastures compared with lucerne-based pastures. During the pasture phase, actively growing pastures kept N2O emissions at a relatively low level (59 g N2O-N ha-1 year-1), but N2O emissions increased significantly upon termination of the pastures. Results showed that the N2O emitted during the summer (December to February) after the pastures were terminated accounted for 70% of the total N2O emissions in the final pasture year. Furthermore, perennial grass and chicory-based pastures were highly productive during favorable conditions, leading to a low N2O emission intensity. It is suggested that emphasis be placed on utilizing highly persistent species to foster a longer and more productive pasture phase, and to manage N-supply in the transition between pasture and crop phases as this is where the greatest risk of N2O emission exists.

Tillage and nitrogen fertilization enhanced belowground carbon allocation and plant nitrogen uptake in a semi-arid canola crop-soil system.

Carbon (C) and nitrogen (N) allocation and assimilation are coupled processes, likely influencing C accumulation, N use efficiency and plant productivity in agro-ecosystems. However, dynamics and responses of these processes to management practices in semi-arid agro-ecosystems are poorly understood. A field-based 13CO2 and urea-15N pulse labelling experiment was conducted to track how C and N allocation and assimilation during canola growth from flowering to maturity were affected by short-term (2-year) tillage (T) and no-till (NT) with or without 100 kg urea-N ha-1 (T-0, T-100, NT-0, NT-100) on a Luvisol in an Australian semi-arid region. The T-100 caused greater (P < 0.05) belowground C allocation and higher (P < 0.05) translocation of soil N to shoots and seeds, compared to other treatments. Microbial N uptake was rapid and greatest in the fertilized (cf. non-fertilized) treatments, followed by a rapid release of microbial immobilized N, thus increasing N availability for plant uptake. In contrast, management practices had insignificant impact on soil C and N stocks, aggregate stability, microbial biomass, and 13C retention in aggregate-size fractions. In conclusion, tillage and N fertilization increased belowground C allocation and crop N uptake and yield, possibly via enhancing root-microbial interactions, with minimal impact on soil properties.