Calculation of water and fertilizer needs in fruit trees

Calculating the irrigation needs of any plant is not an easy task. Once the methodology is learned, it is no longer so complex to carry out the calculations, however, a multitude of factors intervene that must be adequately considered to achieve maximum success in the results. In this article we will name all the parameters to consider in calculating the needs of water and fertilizers in fruit trees.

General data

In this section and despite not intervening in the calculation process or in the results, we must always take the farm name and of the owner in order to know later who the data belongs to and to whom to deliver the recommendation.

The ubication of the plantation is extremely important. He will inform us of the weather characteristics. We can look for information from a weather station near the farm.

An Agroclimatic Station is a set of devices that can perform various meteorological measurements, such as Temperature, Air Humidity, Wind Direction and Speed, ETo (reference evapotranspiration), etc. All these parameters are extremely important in calculating water needs. Of all of them, the most important is ETo.

Calculation of water and fertilizer needs in fruit trees: header data

Fertigation is a system used in RLAF (localized high frequency irrigation) and there is generally an irrigation head that is where the water leaves for all sectors of the farm. The irrigation head is the set of elements intended to filter, treat, measure and supply water through the pipe distribution network.

In the case of large farms there may be two or more heads. The data to consider are: head number and the CE (electrical conductivity) of the water. Although the quality of irrigation water is defined by its physical, chemical and biological characteristics, the only factor that will intervene in the amount of water to apply will be the salinity parameter and we can obtain it through the value of the EC.

To measure EC we need a device called a conductivity meter. The value of the EC intervenes in the calculation of the FL (fraction of leaching). The higher the EC of the water, the higher the FL will be and therefore a greater amount of water will have to be provided in irrigation to avoid salinization of the soil.

Industry data

Each irrigation head can supply water to one or several sectors. They are called sectors since it is the result of sectorizing (dividing into sectors) the head. Each of these sectors will have specific characteristics, as well as being individual irrigation units (which can be irrigated individually). The data that we should know about the sector are:

The sector number:

Each sector will be identified by a number so that there is no confusion with the other sectors of the farm.

the crop is another essential piece of information. Each crop has some parameters: crop coefficients (Kc), fertilization percentages,…, characteristics that must be considered when calculating irrigation and fertilizer needs.

the rootstock:

This data does not have much influence in terms of water needs, although it is advisable to have this data for two reasons: Firstly, because there are rootstocks that have little tolerance to root suffocation and/or excess irrigation and secondly because when interpreting a foliar analysis, this data has a significant influence. After numerous investigations, we have concluded that the rootstock exerts a highly significant influence on the nutritional values ​​of its organs (usually leaves).


In the cultivation section we have shown that each one has some general characteristics. In the case of the varieties, they also present differences from each other. This is mainly due to the fact that each variety has different harvest dates from the rest, different yields and many other determining factors.

Number of trees:

It is essential to know how many trees the sector has. Depending on the number, more or less water and fertilizers will be provided.

More about calculation of water and fertilizer needs in fruit trees

Tree crown diameter:

There are different ways of calculating fertigation needs. The research groups in which I have participated have always been of the opinion that the most objective and real data is the size of the trees and consequently their crown diameter. There are still professionals who prefer to use the years of the plantation or the trees per hectare instead of this parameter.

Considering the number of years of the plantation is not correct. I will give you an example: A lemon tree crop of the fino variety whose rootstock is Citrus macrophillacould reach (with good crop management) full production between 5 and 7 years after planting.

This rapid growth is due to the fact that the rootstock Citrus macrophilla induces a lot of vigor to the variety. However, if the rootstock used is Citrange troyer, Citrange reed or Mandarin cleopatra; under the same conditions, to reach full production it could take between 7 and 9 years. With this example it is sufficiently clarified that it is much better to use the data of the crown diameter than with the years of the plantation.

Plantation frame (Mp):

If we multiply the number of trees by the plantation frame, we will obtain the total area of ​​the sector. The Mp is the distance between the trees and between rows. A typical orange plantation frame is 6×4, which means that the distance between trees is 4 meters and 6 meters between rows.

Number of drippers per tree:

The water flow (Q) received by each tree results from multiplying the number of drippers by their flow.

calculation of water and fertilizer needs in fruit trees

Dripper flow rate (Q):

In order to calculate the irrigation hours we need to know the water that each tree receives per unit of time (usually per hour). This data is expressed in litres/hour.


This parameter is very important since depending on the type of soil, it will have a greater or lesser capacity to retain water. This characteristic gives us an idea of ​​the amount of water available in the soil available to the crop. On the other hand, it is also important to consider that a soil with a high clay content and irrigated with excessive water can cause root suffocation in the crop (due to anoxia).

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