Final Animal Production and Nutrients Theme

Summary

Highlights

• A minimum protocol was developed which obtained a useful and common set of data across sites and was not too demanding on site resources

• Results from the National Sites highlighted how the more intensive grazing systems based on pasture improvement, higher fertility and higher stocking rates have few environmental problems on some parts of the landscape, but not on others. In many cases the most financially rewarding pasture system also had similar or fewer environmental problems (recharge to groundwater, acidification, erosion risk, loss of nutrients to waterways). There were, however, notable exceptions such as on gradational soils and steep hills.

• Quantities of P and N in runoff waters from sheep pastures were much lower than anticipated at the start of the SGS program, and amount to less than 50c/ha.year of P fertiliser equivalent

• In some environments a high proportion of surface runoff exceeded the healthy stream standard of 0.05 mg P/litre; how much of this reaches the stream is unclear.

• Pasture improvement and fertiliser can in some cases reduce P runoff into waterways (NW Slopes), have little effect (NE Vic sites) or increase the problem (Wagga, Vasey). Reductions in P runoff at the NW Slopes site were associated with increased ground cover causing less erosion. Increases in P runoff occurred where there was already good cover on the low-P control treatment. Why the NE Vic sites behaved differently from Wagga and Vasey has not yet been fully resolved.

• New research leads have been found for how to capture the benefit of fertiliser application while minimising P loss in waterways. This is by intensifying production on areas less likely to contribute to surface runoff.

• N losses on high, medium and low intensity systems were similar, and thus high input systems are no less environmentally acceptable than lower input ones.

• Very little N is lost in surface runoff but substantial concentrations (over the WHO drinking water level of 10 mg N/litre, and well over the stream health figure of 0.5 mg N/litre) can be lost in subsurface flow and deep drainage. Whether this ends up in waterways is unclear but it raises serious political issues about current agricultural systems, particularly those based on annual pastures.

• Nitrogen application has been found to benefit a kikuyu-subclover pasture, but was of little benefit to a phalaris-subclover pasture

• Data sets on plant and soil nutrients have been assembled which will yield a rich wealth of scientific papers and findings during the Harvest Year