Agriculture Reference
In-Depth Information
Tilman
et al.
(1999) investigated the relationship between dandelion (
Taraxacum offici-
nale
) abundance and soil K. Three key pieces of evidence exist:
(a) clear correlation of K and dandelion abundance in the 140-year-old Park Grass Experi-
ment at Rothamsted, UK;
(b) greenhouse trials showing that dandelion had higher K requirements than several common
grasses; and
(c) dandelion abundance was positively correlated with tissue K concentrations.
This research suggests that adjustments in resource supply rates inf luence interspecific
competition where plant species differ in their resource requirements. Such knowledge
provides potential for encouraging beneficial species to competitively control weedy species
(Tilman
et al.
1999).
More generally, Walter
et al.
(2002) tested the spatial cross-correlation between weed
species and several soil properties. Certain weeds were correlated with specific soil chemical
properties (e.g. P, pH); however, other species did not show consistent correlation with soil
types between fields and sampling times, and some were correlated with more than one soil
property. The most consistent relationship was between weed density and clay content. This
result suggests that weeds have different resource requirements and that modifying soil condi-
tions to manage certain weeds may promote others.
Conclusions
Organic crop husbandry relies principally on rotational management, and increasing the
diversity of species in space and time to maximise biological and ecological services. There is a
need for sufficient soil fertility building components in the rotation, such as grass-clover-lays,
for sufficient N accumulation by legumes and for adequate nutrient transfer from preceding to
succeeding crop. In addition to soil fertility maintenance and nutrient management improve-
ment, well-designed crop rotations contribute to the prevention of disease, pest and weed
problems. These aims must be fulfilled under many varying site conditions, requiring aware-
ness of the particular agroecosystem, as well as skilled management. Increasingly, the organic
standards require that farming practices allow for a greater proportion of natural components
to be maintained in the farm design. This diversity can be highly effective in creating a self-
regulatory system, with less reliance on external inputs.
Although organic farming commonly exhibits higher tolerance towards the occurrence of
wild f lora in growing crops, weed regulation is one of the key constraints in organic crop pro-
duction. Depending on farm size and the level of mechanisation, the tools can vary from
hand labour, hand-hoeing tools to a group of mechanical and thermal machines. Intrarow
weeding has traditionally required high labour input due to a lack of adequate implements,
although developments in engineering have improved the suite of tools available to the
organic grower.
Several areas requiring further research in organic crop production include improving
nutrient supply-demand matching, overcoming specific nutrient limitations (e.g. P), investi-
gating the role of landscape elements such as hedges and windbreaks, and developing new tools
and identifying successful strategies for weed management.
References
Abawi, G.S. and Vogel, C. 2000. Evaluation of green manures of marigold against root-knot
nematode on lettuce, 1998-1999. In
Biological and Cultural Tests for Control of Plant
Diseases
. American Phytopathological Society Press, St. Paul.
