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March/April 2023 | Muedanyi Ramantswana

Plant quality is key to mechanised planting

Editor's views


Over the past decade the global forest industry has seen the introduction of various new semi and fully mechanised planting machines. The aim of new and existing technologies is to find solutions to increase productivity, reduce costs and deal with labour challenges (costs and availability) to mention a few. With no doubt, there will be improvements on existing machines and new machines will also be coming into the market as various manufacturers aim to fill this gap within the forestry industry. In as much as we have sophisticated planting technologies available it is important to note that their goal is to successfully plant a seedling (plant) that will survive and grow to ultimately meet the landowner’s objectives. Even though a plant may cost very little when bought from the nursery, its value grows exponentially over some years thereby creating an excellent return on investment.

Where it starts
Tree breeders work hard to identify and supply base material to propagate with good genetic material which is suitable for use by various landowners. Once the correct plants that meet the needs and specifications of the user are found, the important plant production process is initiated at the nursery. In this instance, lets look at a high-level typical journey of a eucalyptus plant (note this process and times at different stages may vary depending on the nursery and requirements).
1. Hedges are established, maintained and harvested
2. Trays are filled with growing media and the setting of cuttings is performed
3. Rooting development is initiated in the correct environment
4. After plants are established, they are moved to the growing camp where they reach maturity, thereafter they are assessed if they meet the plant quality index requirements and sorted accordingly.
5. When ready, the plants are dispatched to a temporary holding area at a plantation or directly to the forest where they are planted

Planting quality requirements for mechanised planting
From when the plants leave the nursery until they arrive infield it is important that they are watered, kept in a conducive environment and not damaged in transit. A complete supply chain which considers packing, transport, infield handling and linking up with the mechanical planter in important for mechanised planting (Reinstorf, 2021). In manual direct planting, the plant is predominantly handled carefully by human hand until it is inserted into the prepared soil surface, whilst with / planting tubes the plant is gently deposited down a planting tube. However, in mechanised planting, the plant needs to be packed in a form of carousel in the head of a planting machine. The movement (gravity fed in some cases) of the planting from this point will vary depending on the machine, however the general principle is that the planting has to be dropped or slide from that point until it is planted in the soil.

Some of the plant challenges that maybe experienced include:
• Root damage due to movement and various impacts
• Root plug disintegrates due to various impacts
• Crooked plants get stuck along the planting tube causing blockages
• Overgrown plants get stuck in the tube or planting jaw area (>height or leaves)
• When too young plants are planted, growing shoots may get covered by soil or residues during the planting and firming process
• Too soft plants (inadequate hardening) are broken during the planting process

Possible solutions (Biggs, 2020)
• Root plug consolidation (quality and integrity) by using paper pots which enable the establishment of a robust root system which captures the planting soil area more easily
• Sorting of plants that match the specification of mechanised planting (e.g., no double or multiple leaders)
• Uniform plant height & branching of plants produced from the nursery
• Ensure the timing of releasing plants to field is correct
• Uniform Root collar diameter and sturdiness
• Overall good plant health (no presence of disease or pest damage on growing tip or stem)

Mechanised planting technology development cannot be performed in isolation. Nurseries and machine manufacturers need to be able to communicate their needs. Machine manufacturers need to consider the type of plants available and variability that exists in plants produced from nurseries and innovatively try and cater for what is available. Nurseries also need to adapt and see how best to cater for semi and fully mechanised planting equipment to ensure the plants can survive when planted mechanically. Solutions can be found to ensure a smooth transition from nursery to successful mechanised planting.

Biggs, S. 2020. Paperpots as solution for improved mechanised planting, Ellepot. Nelson Mandela University Silviculture Modernisation Webinar. 21 October 2020
Reinstorf, H. 2021. Integrating new technologies from nursery to field, BCC. Nelson Mandela University Silviculture Modernisation Webinar. 20 October 2021