The amount of water we need for irrigation at any given moment depends on three factors: the properties of the soil, the weather and the plant being irrigated.

## Weather factors and plants

The soil field capacity and wilting point don’t change, but weather factors do. Temperature, air humidity, and wind determine how much water will evaporate from the soil and the plants. Water loss also depends on the proportion of the ground the plants already cover. At the beginning of growth, a large part of the water evaporates from the soil (evaporation). At the end, when plants already cover a large part of the soil, most of it evaporates from the plants (transpiration).

## How the irrigation advice is calculated

To calculate for irrigation advice, whether it is calculated manually or calculated by an automatic system, the following steps must be performed:

• Measure how much water is currently in the soil
We measure the amount of water that is currently in the ground with the help of automatic or manual sensors. Based on the knowledge of how much water is needed for a certain culture and the selected irrigation strategy, we decide whether irrigation is necessary at all, or whether it is necessary to add water so that the plants can reach it;
• Calculate the amount of water the plants need
Based on the phenophase and the corresponding kc coefficient, predicted air temperatures and the current amount of water in the soil, we can calculate how much water a m2 of field with the selected culture will need in the next period, until we irrigate again;
• We consider the efficiency of the irrigation system
During irrigation, not all of the water reaches the plants. The most effective irrigation system is drip irrigation, where water efficiency is 92%;
• We take into account the amount of predicted precipitation
If we water the crop and it rains soon after, there is double damage: unnecessary use of water and the rainfall will most likely wash nutrients into the groundwater.

When we add water losses and possible precipitation for the next period, we get the amount of water that we need to add to the field. By knowing the irrigation system properties, we can also calculate how long the water has to flow so that the irrigation amount will be correct.

## How the irrigation advice is shown in the application

Irrigation advice is shown for two days - today and tomorrow. It is calculated for the hour determined by the farmer himself, i.e. the hour when he usually irrigates. The advice is given in two units: water quantity and irrigation time. The time is calculated from the amount of water needed and the flow of the irrigation system, so this information is crucial for the correct calculation of the advice.

The calculation time is also indicated, so that the time of the received advice can be easily checked.