Periods of drought are increasingly leading to shortages of collected rainwater in horticulture. Within the OptiWAIE project, researchers are therefore investigating alternative water sources for irrigation, including treated process water. Trials in tomato cultivation were carried out at Agrotopia in Belgium.
In the tomato crop at Agrotopia, treated process water from the vegetable processing industry was applied at mixing ratios of 10% and 30% of the total irrigation water.
Nutritional analysis crucial
Treated process water from vegetable processing companies is often available year-round, making it a potential alternative during pumping bans or periods of extreme drought when surface water is limited. However, researchers emphasise that process water cannot be directly compared with rainwater or surface water. Its composition varies widely depending on the company, the season, and the purification techniques used. A detailed nutrient analysis is therefore essential to determine whether the water is suitable for a specific crop.
The process water used in the trial had a neutral to slightly alkaline pH. Electrical conductivity (EC) was relatively high, ranging from 2 to 4.5 mS/cm. This elevated EC was mainly caused by salts, particularly sodium and chloride, supplemented by other nutrients such as potassium, calcium, magnesium, and iron.
© Inagro
Low mixing percentages
In the trials, EC management proved to be a key challenge due to the higher salt levels in the treated process water. The presence of salts led to a rapid increase in drain EC, resulting in salt accumulation and deficiency symptoms in the crop.
This also increased the risk of blossom end rot, particularly during periods with EC peaks. To limit these effects, low mixing ratios of 10 to 15% were found to be important, combined with lowering the irrigation EC and avoiding additional salt-containing fertilisers in the crop recipe.
Source: Inagro / Proeftuinnieuws
