In the first part one of this series of articles we have focused on the identification and selection of good quality trees, which in my opinion is one of the most critical steps in macadamia farming. Placing an order for tree should, in all cases, precede the land preparation phase of setting up a new orchard. That being said, imagine that you will receive your top-quality trees in three months’ time, there is a certain amount of soil preparation work that needs to be done, but where do we start? Well seeing that all farms are different, it will depend on a range of factors, but most importantly we will have to take into account what type of soil macadamias like to grow in.
Macadamias like to grow in soils that are:
- Well drained
- Highly aerated ‘
- Well structured
- Rich in organic matter
- Low in plant available Phosphorous
- Slightly acidic in nature
Considering these components, it seems rather logical that we should start our soil preparation practices by doing a thorough examination of the soil chemical and physical properties. In general soil physical properties are assessed by means of in field inspections of the proposed planting area. As a consultant, I typically ask farmers to dig a range of soil profile pits from which we can gather the following information:
- The effective rooting depth or soil depth
- The soil type that we are farming
- The soil texture and structure
- Are there any signs of wetness or a shallow water table?
In most cases, you don’t need to be a consultant to figure these things out, by digging a soil pit you can easily asses the aforementioned points as follows:
Effective rooting depth
Macadamias, require a soil that has an effective rooting depth of at least one meter.
The picture on the left is of a deep red soil, which is uniformly red up to a depth of >1m and is suitable for macadamia production.
The soil on the right has an effective rooting depth of around 35 cm and in most cases, it is not recommended to plant macadamias on these soils without making further adjustments to these soils. When assessing a soil for effective rooting depth, measure the depth of soil that does not have distinct changes in color.
Soil type and texture
Macadamias prefer well drained soils and as a result soils that have a high clay percentage are not recommended. Coarse textured soils are always preferred above fine textured soil in macadamia.
| Determining soil texture (Source:http://www.fao.org/tempref/fi/cdrom/fao_training/fao_training/general/x6706e/x6706e06.htm): | • |
Take a handful of soil, wet it, and work it to the consistency of dough;
Continue to work it between thumb and forefinger and make a mud ball about 3 cm in diameter; • Soil texture can be determined by the way the ball acts when you throw it at a hard surface, such as a wall or a tree. |
• If the soil is good only for splatter shots (C) when either wet or dry, it has a coarse texture; • If there is a “shotgun” pattern (D) when dry and it holds its shape against a medium-range target when wet, it has a moderately coarse texture; • If the ball shatters on impact (E) when dry and clings together when moist but does not stick to the target, it has a medium texture; • If the ball holds its shape for long-range shots (F) when wet and sticks to the target but is fairly easy to remove, it has a moderately fine texture; • If the ball sticks well to the target (G) when wet and becomes a very hard missile when dry, it has a fine texture. |
Signs of wetness
Macadamias absolutely hate it when their roots are standing in water or when the get exposed to extended periods of water logging. Soils that have signs of wetness should therefore be avoided when planting macadamias
When examining the soil pit look for yellow and grey colors in the soil profile. In general, these colors are indicative of soils that have been poorly oxygenated as a result of poor drainage and standing water. When you see red colors, these are usually good signs and the soils are oxygenated and well drained.
Following the soil physical inspection, it is critical to do a soil chemical analysis. These tests might be slightly expensive, but in the long run they are invaluable, seeing that most of the corrections that need to be made to the soil need to be made at the start of the tree’s life cycle. These test can be done at a range of laboratories and you typically need to get the soil analyzed for the following:
– Soil Texture
– Soil pH
– Extractable Phosphorous
– Extractable Potassium
– Organic Matter
– Sodium Content
– Calcium Content
– Zinc Content
– Magnesium Content
– Cation Exchange Capacity
Most of these components will be in a standard soil analysis. Nevertheless, once the soil analysis is received, a grower needs to consult with an agronomist to decide which soil ameliorants and nutrients should be added to the soil. Certain elements need to be added in the soil before the trees are planted, simply because certain nutrients do not move in the soil and if these elements are not added at the start, we will struggle to get the chemical soil balance correct in the future. Mobile and immobile soil elements are summarized in the following table:
Following the physical and chemical examination of the soil, a grower needs to make some decisions regarding the preparation of the soil. Put simply, the grower needs to decide how they want to prepare the soil before planting, in particular should the soil be ripped and should I plant my trees on ridges? Before we get into these details the simple soil preparation process is as follows:
Land Clearing
Deep Ripping
Ridging
Discing
The following needs to be considered when preparing the soil:
Deep Ripping – In general, the soil should be loosened to a depth of at least 800mm using experienced contractors. It is also advised that soil be cross-ripped as this will ensure that no compaction is present when to trees are planted. Remember that you will never have the opportunity to cross rip the orchard again.
Ridging – Ridging is something that needs to be assessed on a case by case basis. When soils are shallow or poorly drained there is no other option as to ridge, as trees need an effective rooting
depth of 1 meter. When soil is deep and well drained ridging should be considered carefully. Ridging has various advantages and disadvantages.
Advantages
- • Soil compaction is confined to the interrow.
- • Creates more room for roots.
- • Creates a favourable water environment for roots.
- • Controls disposal of excess surface water.
Disadvantages
- • Results in increased soil drying.
- • Makes the placement of organic matter on the soil impossible
- • Becomes increasingly difficult to harvest mechanically, especially if ridges were constructed incorrectly.
- • Creates potential erosion problems by channeling rainwater.
Discing – Discing is essential whether you are mounding soils or not. Discing allows the large clots created in the soil preparation process to be broken up and allows for a fine soil bed to be prepared. The finer soil bed creates better contact between the soil and the tree roots and ensures tree success. Furthermore, discing can be used to successfully incorporate pre-plant fertilizers and soil ameliorants into the topsoil.
IIn conclusion, preparing the soil for planting is a critical step in setting up the orchard for success. Using a horticultural consultant to assess your soil before planting could prove to be priceless in the long-term, and an experienced macadamia consultant should be able to provide you with good soil preparation plan.