What should you pay attention to when irrigation?

Now that it's raining, there's some time to think about watering. Many growers have already spent the necessary hours on this. Boerenbusiness highlights the different aspects of irrigation, from the quality of the irrigation water to the dosage of irrigation.

While there was plenty of watering last year and also this year, it is by no means always clear what this does to the crop and the soil. In addition to the fact that the cold water causes large temperature differences in the crop, the quality of the irrigation water is particularly important.

Salinity matters
The salinity of the water is particularly important here. "The maximum for most crops is 600 milligrams of chlorine per liter and 0,48 to 0,96 grams of salt per liter," says Nelis van der Bok, advisor at Delphy. However, this differs per crop. For example, grains and beets can handle a higher chloride content (up to 1.200 milligrams).

"The salinity is especially important in Zeeland, where without the flushing policy of the Scheldestromen water board, virtually none of the growers in Zeeland would be able to irrigate," says van der Bok. Elsewhere in the Netherlands this is less the case, but growers elsewhere in the country also have to deal with the salt content.

Watch out for yourself
In addition to Friesland, there are also increasing problems with salt seepage water in the Haarlemmermeer. But even if there are no problems with seepage water, according to Van der bok, attention must be paid to the salinity. "If you are above the critical limits, it can cause leaf burn." Provinces keep an eye on the salinity levels, but it may be wise for growers to keep an eye on this themselves.

Well water often has problems with iron. Sources often have to be deferred. There may be a maximum of 2,5 milligrams of iron in the well water to prevent damage to the crop. In case of irrigation with water containing a lot of ionized iron (Fe²⁺) in a sitting position, aeration can offer a solution. The iron then oxidizes during aeration instead of oxidizing on the plant, which can cause burns.

Attack on structure
Although irrigating in dry years can definitely provide a great financial advantage, it is not all positive. "Irrigation is an attack on the structure of the soil," says van der Bok. He mentions acidity as important requirements for the irrigation water. "It must have a minimum pH of 5,5."

The hardness, a measure of the concentration of metal ions (mainly magnesium and calcium), is also important and may be a maximum of 18 degrees German hardness.” If the water has a higher hardness, it can cause limescale deposits in the sprinkler system, which can cause blockages. Other water quality limits below which no damage to crops is to be expected are an ammonium value of 2 milligrams per litre, a sodium value of 115 milligrams per liter and a manganese value of less than 1 milligram per litre.

Given that source and surface water do not always meet the requirements, investing in rainwater storage seems an attractive alternative. Rainwater is generally of much better quality than surface or spring water. However, investing in rainwater is simply too expensive, Van der Bok knows. "You need a lot of volume for a basin."

Dosage is also important
"In addition to the quality of the water, it is also very important how much water is given," says Erikjan van Huet Lindeman, Marketing & Development manager at Eurofins Agro. "The amount of water that the soil can store is important for this. Based on soil research data, we can calculate how much water the soil can store. This is important because if you water too much, you wash away nutrients and you use fuel for nothing."

Eurofins therefore also provides growers with a water retention graph (pF curve) based on the soil survey. This shows the maximum amount that must be irrigated. "We recommend dosing per plot. First check the moisture content with a moisture meter, then make up for the difference with what the soil can absorb," says van Huet Lindeman.

More analysis of irrigation water
With regard to the water quality, he indicates that it is in any case sensible to sample the quality of the water. He also mentions the microbial water quality. "If the crop falls under Global GAP, then analysis of irrigation water for E. coli is mandatory. This bacterium is used by Global GAP as an indicator for microbial water quality." Eurofins Agro has seen an increase in demand for irrigation water analysis since the dry summer of 2018.

Anne-Jan Doorn

Anne Jan Doorn is an arable expert at Boerenbusiness. He writes about the various arable farming markets and also focuses on the land and energy market.

aj.doorn@boerenbusiness. Nl

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