Procedure For The Application Of Nutrients

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Calculating The Total Fertiliser Requirement

In an orchard situation, a fertilisation program normally indicates the amount of fertiliser that has to be applied per tree. To calculate the total amount of fertiliser required for a specific orchard, the following formula is used:

Total Amount of Fertiliser Required = Fertiliser per Tree (g or ml) x Number of Trees in Orchard:

For field crops, the amount of fertiliser required will be given as a dosage rate per hectare.

Example: Calculating the Total Fertiliser Requirement for an orchard.

The table below represents a typical fertilisation program for a citrus orchard:

The total amount of LAN needed for the July application is calculated as:

Number of Trees in Orchard = Orchard Size in Hectare (ha) x Number of Trees per Ha

= 3.0ha x 316

= 948 trees in the orchard

Total Amount of Fertiliser Required = Fertiliser per Tree g or ml) x Number of Trees in Orchard

= 500g x 948 trees

= 474,000g (/1,000 to convert to kg)

=474kg

This means that 474 kg of LAN is required for the July application of LAN to orchard 10.

Once the total amount of fertiliser required for the orchard has been calculated, the fertiliser can be collected from the store and prepared for application.

In a field crop situation, the fertiliser will be based on leaf and soil analyses. The recommendations will indicate the amount of fertiliser to be applied per m2 or per ha. Before planting, fertiliser containing N, P and K will be broadcasted, while N will be applied as a top-dressed later during the season. The required nitrogen is usually split into smaller amounts, which are then applied at intervals during the growing season.

Collecting Fertiliser From Storage

In line with the standards of Good Agricultural, Practices (GAP) fertilisers must be stored according to their type and packaging. Fertilisers have a fairly long shelf life, provided it is stored in the manner prescribed by the suppliers. However, contamination can occur and bags might lose their labels. If in doubt of the contents or concentration of any fertiliser, take samples and send them for analysis.

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The Description On The Bags Or Containers

To ensure that the correct fertilisers are selected, double-check the following before loading:

The concentration of the active ingredient is specified on the bag or container because some fertilisers are supplied in more than one concentration. Zinc nitrate are supplied in formulations with an active ingredient (Zn) concentration ranging from 5.5% to 16%;

Granular and powdered fertilisers are supplied in 25kg or 50kg bags. LAN is mostly supplied in 50kg bags. In the case such as the example above, ten 50 kg bags, i.e. 500 kg of fertiliser will be collected from the store. Half a bag should be left after the application, and this should be returned to the store and sealed properly for future use. When collecting fertiliser from the store, check that there are no half-used bags that should be used first.

Once the correct fertiliser and its concentration are confirmed, the instruction to load the required number of bags or containers can be executed.

Preparing Fertilisers

Granular and powdered fertilisers seldom need preparation before application. For manual application, fertiliser bags or containers are transported to the orchards and the required number of bags is off-loaded at each orchard.

For fertigation and foliar applications, the fertiliser is merely mixed with the amount of water prescribed in the fertilisation program.

When applied to field crops the fertiliser is either applied through the irrigation system (fertigation) for vegetables and pivot systems, or in granular form by hand or using spreaders.

Measuring Fertilisers

It is important to apply the correct amount of fertiliser, because, apart from the cost implication, over-application can be as harmful to the tree as under-application.

In the case of manual application, the amount of powdered or granular fertiliser that is to be applied is normally stated on the fertilisation program in g/tree. This prescribed mass per tree cannot be weighed for every tree, as this would take a long time and be unproductive. Follow the steps below:

• Carefully weigh the prescribed mass of fertiliser.
• Determine the volume of the mass of fertiliser.
• Make scoops to hold the exact volume of fertiliser that is required, by for instance cutting used oil or canned fruit tins to the correct size. Apply one or two scoops of the specified fertiliser.

In the case of fertigation and foliar applications, the liquid or powdered fertilisers are measured or weighed carefully and added to the prescribed amount of water.

Applying Fertilisers

The feeder roots of an orchard tree are concentrated in the area around the trunk of the tree. This is normally the area, which is wetted during irrigation.

Fertilisers are applied manually in the following manner:

• Irrigate the orchard for about 30minutes before application to demarcate the area in which the feeder roots grow;
• Scoop the required amount of fertiliser from the bag;
• Spread the fertiliser evenly on the wetted area, with little or no fertiliser against the trunk of the tree.