Literature review: Impact of Chilean needle grass ... - Weeds Australia
Literature review: Impact of Chilean needle grass ... - Weeds Australia
Literature review: Impact of Chilean needle grass ... - Weeds Australia
Create successful ePaper yourself
Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.
Table 8. Typical nutrient levels in <strong>Australia</strong>n <strong>grass</strong>land soils. Source: McIntyre and Lavorel (2007).<br />
Vegetation N P (mg kg -1 ha -1 )<br />
Natural <strong>grass</strong>lands low 1-3 (low)<br />
Native pasture medium 1-3 (low)<br />
Fertilised (improved) pasture high 20 (high)<br />
Sown pasture high 20 (high)<br />
Enriched <strong>grass</strong>land medium medium<br />
Moore (1973) suggested that nitrate levels in the surface soils rarely exceeded a few parts per million at any time <strong>of</strong> year. In<br />
<strong>grass</strong>lands in general a “small active fraction” <strong>of</strong> soil organic matter dominates both C respiration and N mineralisation<br />
(microbial conversion <strong>of</strong> N into the plant-available nitrate and ammonium forms) (Wedin 1999 p. 194). Roberts et al. (2006 p.<br />
148) stated that pasture productivity may be limited when P falls below 25 mg/kg (Colwell), but that “native pastures ... tend to<br />
be more tolerant <strong>of</strong> lower P levels than those dominated by introduced species”.<br />
Weed invasion and nutrient enrichment<br />
Nutrient enrichment by legumes, application <strong>of</strong> fertiliser, run<strong>of</strong>f, deposition <strong>of</strong> atmospheric pollution etc. is a major cause <strong>of</strong><br />
alien <strong>grass</strong> invasion worldwide (Milton 2004) and experimental addition <strong>of</strong> nutrients <strong>of</strong>ten rapidly leads to weed invasion (Carr<br />
1993). Eutrophication, particular with N and P, is a major cause <strong>of</strong> plant diversity decline in terrestrial ecosystems (Hobbs and<br />
Heunneke 1992, Hautier et al. 2009). Grasses tend to be particularly favoured by nutrient inputs, and biodiversity losses are<br />
usually associated with their increasing productivity and dominance (Hobbs and Heunneke 1992).<br />
<strong>Australia</strong>n soils have generally been characterised as nutrient impoverished, particularly in relation to phosphorus, but also in<br />
nitrogen, minor nutrients and organic matter (Leeper 1970). Because most <strong>Australia</strong>n native plants are adapted to these low<br />
nutrient levels, nutrient enrichment favours the establishment <strong>of</strong> exotic weeds that are better adapted to high levels <strong>of</strong> fertility<br />
(Brereton and Backhouse 2003). Cale and Hobbs (1991) found a strong positive correlation <strong>of</strong> nutrient gradients across roadsides<br />
with exotic plant diversity and suggested that nutrient enrichment may increase their competitiveness. Cover <strong>of</strong> exotics increased<br />
from