Abstract:
The main aim of the research was to contribute means for converting conventional, high-input
production systems to more sustainable ecological systems, thereby improving the sustainability
of macadamia production and ultimately contributing to food security. This was achieved by a)
investigating the potential use of cover crops and compost to enhance soil quality in macadamia
orchards and b) investigating the potential use of use of cover crops and orchard heterogeneity to
control stinkbug pests that target macadamia crops.
Field experiments were conducted in three phases: phase one tested the potential of six cover
crops for crop protection (as trap crops) and simultaneously for soil restoration or fertility
enhancement purposes in macadamia orchards. Phase two repeated the trials of phase one (both
soil restoration and trap crops) but with modifications to both categories. Soil restoration
treatments were conducted with trees which were growing in what appeared to be healthy soils,
and then repeated with trees in the same orchard where the topsoil had been degraded (totally
removed) by agricultural operations. The third phase repeated the trap crop trials only, but this
time on three different study areas (all commercial farms) with the single cover crop which
performed the best as a trap crop during phase two. Trials were modified from the first to the last
phase to overcome practical implementation problems encountered along the way and to adapt to
local conditions experienced in the commercial macadamia farming systems which served as
research sites. Diversity of natural orchard vegetation was enhanced in phase three to improve
conditions for natural predators as part of the trap crop treatments in the last phase and cover
crops were finally first composted and then returned to the root zones of the macadamia trees as
part of the soil quality enhancement treatments in the second phase.
The results from the trap crop trials shows a significant effect of trap crops combined with
increased orchard diversity in reducing unsound kernel percentages caused by stinkbug pests and
demonstrate that trap crops combined with an increase in orchard diversity could be utilized in
macadamia orchards as a more sustainable alternative to inorganic pesticides against the stinkbug
complex.
The most notable changes in the soil that took place with soil quality enhancement treatments
were the significant increases in soil phosphorous content and pH which resulted not in an
improvement in soil quality in terms of these two indicators but revealed an important issue about
the use of compost containing animal manure originating from dairies or feedlots. In summary
however, it was clear that although not all the soil quality indicators that were employed to assess
changes in the soil with compost treatments improved significantly, a holistic consideration of all
indicators portrays an overall improvement which was particularly significant in the degraded soil
plots where the topsoil had been removed by prior agricultural activities.
