Fertigation: What and how much to apply?

The fertigation is a tool we have at our fingertips to better manage our sports surfaces. The technology allows us to monitor how the injection systems work from a distance, through a PC or smartphone, especially useful in these times of "Teleworking". The monitoring can be done automatically through the reading of the electrical conductivity, pH, etc.. We can also take readings of the concentrations of the different nutrients in the new "fertilised" irrigation water.

Fertigation allows nutrient dosing at very low doses, making it a very sustainable management method that minimises losses through leaching, volatilisation and over-fertilisation. It will always be necessary that the irrigation system works efficiently and is well calibrated. In fact, if the hydraulic systems have a double circuit, in order to use two qualities of irrigation water for different areas, it would be very interesting to have two different injections. In this way we can have different fertilisation plans depending on each zone, distinguishing for example between greens and the rest of the course.

Let's imagine that our irrigation water has a salinity of 1760 ppm and that of that salinity, 15.2 ppm correspond to Nitrates. If we activate our fertigation system, in particular by injecting calcium nitrate and increase the nitrate concentration by a factor of 10, up to 152 ppm (152 ppm NO3), as the Nitric Nitrogen turns out to be 22% by weight, we will have to multiply by 0.22 to know the amount of nitric nitrogen in the water. I.e. 152 ppm x 0.22 = 33.44 ppm of Nitric Nitrogen. If we apply a daily irrigation (let's imagine according to the Evapotranspiration of 1 mm), of 1 l/m2, we will be providing 33.44 mg of Nitric Nitrogen (N-NO3) for each m2 and day. If we multiply it by 30 days to know the monthly contribution, we will have a contribution of 1003 mg N-NO3 for each m2 and month, that is to say, we will have applied 1 gram of Nitrogen/m2, sufficient quantity to fertilize a few greens of agrostis in Madrid in April, according to the potential for growth of the area of this example.

In the same way we would proceed with the rest of the fertilisers according to the % in the leaf tissues. If the % of Potassium in the leaf tissue is approximately half that of Nitrogen for our greens or football fields, then we should provide approximately half as much Potassium as Nitrogen in the irrigation water, i.e. 33.44 ppm /2 = 16.72 ppm of Potassium. Similarly, if the leaf content of Phosphorus in optimal conditions of our lawn is 0.5%, while that of Nitrogen is 5%, this indicates that the phosphorus needs will be one tenth of the Nitric Nitrogen, i.e. 33.44 / 10 = 3.3 ppm Phosphorus in our irrigation water. The same applies to any other nutrient, and we advise you to be careful not to mix incompatible fertilisers together, which could lead to precipitation in the tank.

It is therefore recommended to have several tanks, one for each fertiliser, and in the worst case to mix in test tubes before any mixing in the tanks. In this way, phosphorus can react with magnesium sulphate or calcium sulphate to form precipitates.

In this specific example we cover the nutritional needs of the greens or football pitches through fertigation, providing exactly the nutritional needs based exclusively on the growth of the grass. For each litre of extra irrigation provided, we incorporate 1 gram of nitrogen, 0.5 grams of potassium and 0.1 grams of phosphorus per square metre. at the end of the month.

The application of wetting agents through fertigation by mixing them with fertilisers. The use of surfactants on sports surfaces is ideal and there are many success stories that you can see here: https://www.tiloom.com/agentes-tensoactivos-iii-casos-de-exito/ .

The application of micronutrients is recommended in chelated form to avoid precipitation problems.