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Nutrition Management For Mature Trees

No matter whether it is organic, chemical or a blend of both systems the steps used in nutrition management are the same.

First conduct a soil and leaf test – to ensure no major issues such as low pH, deficiency of an element or excess of an element.

If all is in balance, you need to use a crop replacement level, with an allowance for loss. Crop replacement works by putting back what you have taken out in the previous crop – with allowance for loss and tree growth.

It is best to use a constant targeted yield as the basis for calculating replacement rates, rather than changing the rate up and down based on what was harvested. Frequently changing it up and down means you continually chase and can effect your yield pattern. This is because in doing so you are actually fertilising 12 months ahead, which is next season’s crop (which hasn’t appeared when you are applying).

Normal target – 5T/ha
Replacement figures are, allowing for losses:
N – 68kg/ha
P- 6.25kg/ha
K- 55kg/ha

If you let your trees run down by not applying fertiliser, the health of your trees can decline in a short space of time. If they start to decline, it will take at least three years to bring them back to full health. Generally, it is best to work out the rate to apply products by calculating the P and K requirements are as close to balanced as possible.

Typically this means the N application quantity is slightly above the required amount. This generally works well because N is the nutrient required in the highest quantity. N is highly mobile, and easily leached and bound by microbes as it enters the nutrient pathway.

If you apply too much N to young trees you will produce too many large leaves, making the canopies prone to wind damage (larger surface area). This will result in the need for you to have canopy management strategies to overcome this issue.

In Bundaberg high levels of N are being applied to young trees to achieve early production and they are achieving good results. They are managing the canopy carefully as a result of the applications.

Product selection

To determine which product to use, you need to know the elemental analysis of the product.
The elemental analysis is the percentage make-up of the actual elements in the fertiliser, irrespective of its form.

A sample calculation

An example of a fertiliser program produced with the following information: Budget – ensure adequate nutrition, and keep the costs to 10% of total costs, equal to about $600/ha/year). Soil and leaf tests indicate all nutrients and soil chemistry is in balance. Due to limited application equipment, only inorganic fertilisers can be used. There are to be 4 applications made per year. Potassium Sulfate is to be used for K requirements, as it has a lower salt index. The application rate is for a 5T/ha crop.

Getting the balance right

As most blends are not exactly the levels required by macadamias, different products may need to be used. For example, if only North coast mac mix is used and you base your budget on the replacement levels for N, you will deliver substantially more P than required. To avoid this situation, calculate your application rate of NCMM based on the P requirement and then use a suitable product to deliver the remaining K and N requirements. Note this program ensures the level of all three, N:P:K is adequate.

Nitrogen (N) Ammonium Form 14.1% w/w
Phosphorus (P) Water Soluble 3.7% w/w
Phosphorus (P) Citrate Soluble 0.4% w/w
Phosphorus (P) Total 4.1% w/w
Potassium (K) as Chloride 10.8% w/w
Sulfur (S) as Sulfate 12.7% w/w
Boron (S) as Sodium Borate 0.93% w/w

To calculate the kilograms of NCMM needed per hectare: P requirement / P % of fertiliser. 6.25/0.041. 152kg. This will be split into 2 applications.

This fertiliser will deliver:

N – 152 x 14.1% = 21.3kg

The required amount of N is: 68kg

The amount left needed is: 68-21.3 = 46.7kg

K – 152 x 10.8% = 16.4kg

Required amount of K is: 55kg

The amount left needed is: 55-16.4 = 38.6kg

To deliver the left over requirement we will use another product containing N & K fertiliser.

Nitrogen (N) Ammonium Form 10.5% w/w
Nitrogen (N) Nitrate Form 7.4% w/w
Nitrogen (N) Total 17.9% w/w
Potassium (N) as Chloride 15.0% w/w
Sulfur (N) as Sulfate 3.6% w/w
Calcium (N) as Calcium Carbonate 4.4% w/w

Amount of cal-gran applied will be: (Based on meeting N requirements)
46.7/16.9%
=276kg
This will be split into 2 applications

K delivered equals
276 x 14.4%
=39.7

The total delivered and required are:

Nutrient Required Quantity (kg/ha) Delivered Quantity (kg / ha)
N 68 68.0
P 6.25 6.25
K 55 56.2

This program delivers a very balanced requirement of all elements.

Notes:

There are a huge number of products you can use and the choice of product(s) is based on many factors, including your financial resources available to spend on crop nutrition.

As a rule about 10% of your production costs should be spent on crop nutrition (approx $600/ha/year). This can be higher if you have a specific deficiency or issue to address (such as low pH and liming). In general terms the softer the fertilizer on the soil (biology and chemically) the more expensive it is.

Are there any particular deficiencies or excesses in the soil or leaf? If there are particular needs this could change the product you use.

What is the soil type – sandier soils generally do not hold nutrition as well as clay soils or those high in organic matter. Sandy soils with high applications of P applied can run into problems with Phosphorus induced iron deficiency. Red Ferrosols (Krasnozems) fix P readily and so this will affect P cycling and availability.

What equipment do you have for application and handling? Inorganic fertilizers are easily spread through a simple (and generally cheap) fertilizer spreader, while organic products such as broiler litter require specialised machinery. Liquids are also an option that requires a tank, pump and specialised nozzles for application, but this equipment is generally cheap to purchase. Note; trace elements can be applied through an airblast sprayer to the foliage – the uptake from foliars is limited but is adequate for trace elements (some are compatible with insecticides and fungicides, check with manufacturer on compatibility).

How many applications are you going to make? The more the better, as the potential for loss is reduced. Less frequent applications – it may be better to use a slow release product.

Blends or straights? Straights are generally cheaper, but require more application time where as blends are generally dearer but require less application time. It is extremely difficult to blend fertilisers on farm prior to application – it is best to pay the chemical company to do it for you if you have particular needs.

Do you want to do it organically, inorganically or a mix of both? Generally organic based fertilisers require a greater quantity of material to deliver the same amount of nutrients as inorganic products (due to lower elemental analysis), which means specailised application equipment is required.

Excess of any nutrient will impact the uptake into the tree and balance of others in the soil. Keeping nutrients balanced should be the aim of any program.

If you have an unbalanced system (for example very high P) and want to reduce the P level, you need to reduce the P application rate, and not go cold turkey to achieve a balanced system. The reason for this is that the tree has adapted to the levels in the soil and moving away from the levels needs to be done in a staged fashion to not cause other imbalances.

All nutrients are taken up by a tree from the soil solution. Therefore good soil moisture levels are crucial for nutrition uptake. To improve the water holding capacity of your soil, increasing the level of organic matter is the best approach.

Organic matter is very effective at holding water. Research work has shown that soil with organic carbon level of 1% or less, for every 100kg of soil can hold 30kg of water. 100kg of soil with an organic carbon content of 5% can hold 200kg of water. This shows the value of organic matter in retaining soil moisture and ensure adequate nutrient uptake.