Selection of pasture species for groundcover suited to shade in mature macadamia orchards in subtropical Australia

Soil erosion is a significant problem in subtropical macadamia orchards in Australia, especially when groundcover vegetation is shaded out under older orchards. The aim of this study was to identify suitable low-growing, perennial groundcovers that would persist in the low light conditions under mature macadamias. Twenty-six legume and grass accessions and 1 herb were evaluated in small plots in a 16-year-old commercial orchard near Lismore, NSW. Plant density, groundcover (%), herbage mass, sward canopy height and groundcover spread were determined in high, medium and low light in the interrow for 2 years (1996–97). Groundcover was also measured for 3 years, on 19 of the accessions in a younger orchard at another site. Dactyloctenium australe provided the best groundcover in both high and low light and met most other specifications for an ideal groundcover for macadamias. Other promising grass species included Paspalum mandiocanum, Panicum laxum and Microlaena stipoides cv. Wakefield. However, Paspalum mandiocanum has been cited as having potential weediness in subtropical Australia, and is not recommended as a groundcover for macadamias. The legumes generally did not perform as well in low light as grass species. However, Arachis pintoi cv. Amarillo and a sterile Arachis pintoi × Arachis repens hybrid provided highest percent groundcover in high and medium light. Further assessment of these species in larger plots to determine their establishment and persistence under heavy orchard traffic and suitability for mechanical harvest operations has commenced

The relationship between orchard crowding, light interception, and productivity in macadamia

Orchard crowding in the macadamia industry is common and there has been concern that it reduces yield and quality. To investigate this we monitored yield, nut quality, tree volume, and light interception in macadamia orchards (Macadamia integrifolia Maiden and Betche) that represented a range in crowding. The predicted rate of change in yield/ha with time remained positive, i.e. yield increased over time, for orchards with crowding levels up to a tree volume of 43 500 m3/ha and light interception of 94%. There was a trend for the rate of yield change to decrease with increasing tree volume/ha. For orchards with tree volume >43 500 m3/ha the rate was negative, indicating a slight decline in yield over time. There was no evidence of a detrimental effect of orchard crowding on percentage kernel recovery, unsound kernel, or grade 1 kernel. It appears that macadamia, unlike many other orchard crops, can maintain yield and quality up to a high level of orchard crowding. The implication of this is that timing of canopy management and optimum canopy dimensions will be dictated by management requirements for machinery access and effective spray coverage before yield decline becomes an issue