Soil Acidification and Water Use- Morelamb Environmental Component

Summary

The Morelamb project extended current boundaries of both animal production, and the criteria that define a sustainable pasture system. While for most pastures a 60% perennial grass content is desirable to ensure soil moisture depletion before the end of autumn, and to take up mineral N before it leaches (Kemp et al. 2000), this study has shown that there are situations where much higher legume contents can be sustained for short term special purpose pastures. 
Two years of pure clover do not represent a leaching risk, but in subsequent years the risk gradually increases as N builds up deeper in the soil profile. Of the 2 pure legume pastures tested here, subterranean clover was the easier one to manage, and carried fewer environmental risks. Selective herbicides are available to ensure stand purity, it responds to rain in late summer, and takes up mineral N early in the season. Arrowleaf clover clearly needs a companion plant with winter activity, to take up N and minimise drainage. This would have the added benefit of providing feed in winter, which is the most limiting time of the year. In the last year of the experiment, Arrowleaf clover was oversown into perennial ryegrass, which did not increase the risk of N leaching. However, growth of Arrowleaf suffered through competition from the grass. Other options include a grass that can be sprayed out in spring, or spring sowing of Arrowleaf.