Key messages
- Native shrubs could be a potential forage resource as a browse to supplement livestock when pasture metabolizable energy values are low, especially in late summer and/or during winter when pasture growth is poor.
- Low browse protein content means that shrubs will be more suited to maintenance feeding.
About the study site
The trial site is located on a steep south-facing slope on Massey University’s Number 4 dairy Unit. The soil types are a mix of Tokomaru and Ohakea silt loam which are heavy textured soils prone to wetness.
What was trialled
- Seven species were evaluated: Hoheria populnea (Houhere), Pittosporum crassifolium (Karo), Griselinia littoralis (Pāpāuma), Coprosma robusta (Karamū), Coprosma repens (Taupata), Melicytus ramiflorus (Māhoe), Pseudopanax arboreus (Whauwhaupaku) and a shrub willow (Salix schwerinii) (‘Kinuyanagi’).
- Small plot trials (15 plants in each plot with four replicates) were used to assess the establishment and early growth of each species, and the nutritional characteristics of foliage and fine stems (<5 mm diameter).
- Shrubs were planted in rows with 1.5 m spacings between rows and 1.5 m between plants within rows to achieve a plant density of 4,400 plants/ha at 100% survival. Shrubs were planted on slopes of 20-30 degrees.
- All plants were trimmed to 40 cm height prior to planting.
- Weed control was achieved using a herbicide combination of haloxyfop (Gallant) for grass weeds and clopyralid (Versatil) for broadleaf weed control using recommended label rates. Herbicide was spot sprayed using a knapsack sprayer 4 weeks after planting.
- At the end of their 1st summer (2020), shrubs were assessed for survival and growth.
- Height and basal stem diameter were assessed in August 2022.
- Foliage/fine stem samples were collected for analysis of nutritional traits in January and October 2020. Analysis of nutritional traits included metabolizable energy (ME), protein and fibre.
Key findings
- Survival was high (100%) in all species except Whauwhaupaku (90%).
- The Coprosma species (Karamū) had the greatest height and diameter growth increments among the native species at age 1 year.
- Measurement of growth in August 2022 (age 3 years) revealed that Karamū was still performing well but the other species, particularly Houhere, had achieved similar height growth.
- Salix performed better than the native species; mean height of Salix was 2.3 m, significantly greater than all native species.
- Stem diameter growth of Karamū was similar to Salix and significantly greater than all other species assessed.
- Metabolizable energy content of the foliage ranged from 10.5 MJ/kg DM (Salix) to 12.2 MJ/kg DM (Whauwhaupaku). Protein content was generally low (< 10% in all species apart from Houhere).
- Stem ME was lower than that for leaf in all species. Similarly, protein content in the stems was lower than the foliage in all species.