The Derwent Catchment Project – Forage Shrub Trial

Summary

The Derwent Catchment Project, with funding from Meat & Livestock Australia, undertook a Producer Demonstration Site (PDS) project that investigated whether forage shrubs could be established at a commercial scale on north-facing slopes in Tasmania. The benefits were two-fold; to add grazing value to marginal areas whilst introducing deep-rooted perennials to stabilise erosion prone north-facing slopes. The trial commenced in winter of 2021 on three 5 ha north facing sites using planted tubestock of Mediterranean saltbush (Atriplex halimus) and also involved direct drilling of 1 ha at the 3 sites. A 5-hectare control was also established at each site.

Pressure from native animals impacted two of the sites to the point that they did not establish. The successful site on a farm near Hamilton was at least 500m away from any remnant native vegetation. The direct seeding failed at all three sites. The project was rescoped to observe, monitor and report on the response of the shrubs at the established site to grazing and to share the learnings with our producer network. Detailed measurements pre and post grazing were taken from the Nareen saltbush site.

The shrubs regrew in the extreme dry of summer, in a drought, delivering green material on a north-facing slope between December and April 2024, when nothing else grew.  Data indicates that post grazing shrub height increased on average by 29% and width by 48%. Growth appears encouraged by the grazing, despite the critical lack of water for the inter-row pasture. The site offers insight into a potentially valuable and durable grazing asset that could, over time, overcome the cost of establishment at ~$2,000 per hectare. The projection of increasing dry spells and drought under climate change could compound its value. 

Objectives

By the 1st of March 2023 the project will:

1. Have demonstrated and assessed the potential of perennial forage shrubs – over a minimum of two grazing seasons - to contribute to useful fodder to address the Winter feed gap on marginal land (North-facing slopes) in Tasmania by:

a. Increasing or maintaining liveweight of lambs (pre and post grazing weight), and
b. Increasing stocking rate (DSE) without associated environmental impact on ground cover
c. Increasing inner row pasture ground cover (kg/DM/ha)
d. Increasing available forage (biomass measured in kg/DM/ha) nutritional value comparison to pasture will be included

2. Have conducted a costed proof of concept for the establishment of forage shrubs on North-facing slopes comparing planting seedlings to direct seeding methods across 3 demonstration sites.

3. Have facilitated a peer learning group of core producers who drive demonstration site design, establishment and monitoring. This peer learning approach will be used to produce a proof of concept to increase uptake by the 11 core producers to incorporate the use of perennial forage shrubs on marginal areas of their grazing systems. This will be measured by evaluation of pre and post knowledge, capacity, skills and confidence of producers.

4. Have conduct workshops and field days and produce a range of supporting resources to showcase the demonstration site results to encourage adoption of key practices by 44 observer producers. Survey of 44 producers will be undertaken to assess changes to the likelihood of adoption.

Key findings

The key findings from our observations collected between December 2023 and April/May 2024:

• The sheep ate every scrap of leaf and a lot of non-woody stem over the 27 days of grazing. They selectively grazed the green shrub biomass after the green pasture was consumed.  Almost no shrub mortality was observed due to the grazing.
• The saltbush regrowth in a drought following a ‘failed spring’, was extremely impressive. Data indicates that post grazing shrub height increased by 29% and width by 48%. Growth appears encouraged by the grazing, despite the critical lack of water for the inter-row pasture.
• The cost of establishment comes to $2,068 per ha/$10,340 across the 5-hectare site. This includes costs for ripping, tube stock, manual planting and some maintenance. The survival rate of the shrubs after planting at the site was approximately 65%.
• The benefit according to our observations support incorporating the shrubs into a grazing cycle of utilisation up to three times a year as the plants respond well to grazing and plant structure benefits. They provide green forage in dry times when the inner row pasture cannot.
• The project learnings have been outlined in a case study short video and producer note sheet which will be circulated through our network (75 producers) and has been communicated more widely through social media posts and a local paper article.
• To see shrubs on north-facing slopes as a viable option, the site needs to be 500 m away from any native remnant vegetation and mechanisation is required to reduce establishment costs.

Benefits to industry

This project observed the response of perennial forage shrubs to sheep grazing. The shrubs regrew over summer, in a drought, providing leafy green forage on a north-facing slope between December and April 2024, when the inner row pasture could not. The shrubs provide deep-rooted perennial plants on erosion prone, marginal grazing land which if not managed carefully can lead to erosion issues.

MLA action

MLA continues to deliver the Producer Demonstration Site (PDS) program, supporting livestock producers working in peer-to-peer groups to pursue new skills, knowledge and management practices applicable to their own commercial livestock production systems.

Future research

Further trials on direct drilling were recommended by the landholder as this would be the cheapest option to establish forage shrubs. The direct drilling trials undertaken in the initial project scope were done on contract by Greening Australia with a purpose build native seed drill however the sites did not successfully establish. There has been successful direct drilling undertaken in the region before with saltbush species. Undertaking further (small scale) trials would be worth investing in.