Crop rotation: chance to reduce emissions further

For Dutch greenhouse horticulture, a mandatory purification of residual water-flows will apply from 1 January 2018. "That's a big step, but not all of the emissions to surface water have been addressed," according to Margreet Schoenmakers of LTO Glaskracht Nederland. "We can make further gains during the crop rotation. We try to make growers aware of this. Of course we will provide them with solutions as well."

In the Nefyto magazine, attention is given to crop rotation. Conversations with Margreet Schoenmakers, program manager water at LTO Glaskracht Nederland, and Erik Groen, enforcer at Delfland Water Board are included. The area of this South Holland Water Board has a high concentration of greenhouse horticulture. "As a Water Authority, we choose to work with the sector, as this leads to the best results," says Erik Groen. Margreet Schoenmakers confirms this. "Water administrator and industry both have an interest in clean surface water. The Water Authority is responsible for ensuring that water meets the standards. For the sector it is important to take responsibility for the environment seriously and to retain its package of resources. Repeated standard overruns can ultimately lead to removal of admissions. A narrow resource package makes it difficult to realize Integrated Pest Management."

The crop rotation has two stages: the completion of the old cultivation and the start of the new cultivation. Both phases have their own risks associated with emissions. What can go wrong with a crop change and how to prevent it? "The ending of a cultivation means a big cleaning for the grower. This way the new crop can start fresh," Erik Groen explains. "The old crop is removed, everything is cleaned. This big cleaning involves a lot of water, water to clean the interior of the greenhouses and the dirty water silos, but also drainage water from substrate slabs and percolate water. That is water released by the wasting away of the old crop. All of this water contains residues of plant protection products and those may not end up in surface water." In practice this last thing happens occasionally. "With careful handling this is preventable," says Margreet Schoenmakers. "It is very beneficial when a grower prepares for the crop rotation. When cultivating on substrate, it is advisable to stop the irrigation in time so that the substrate slabs can be pulled dry by the crop as much as possible and can dry out. The water that is still in it after cultivation, has to be discharged into the sewage system, and not on the surface water. Drying out on the ground should not be done. Make sure you can collect leakage water and drain it to the sewage."

Often the dirty water silo is emptied during the crop rotation. This water may contain crop protection products and should therefore not be discharged to surface water, but in the sewer. "This big cleaning gives a peak in sewage discharge," Erik Groen notes. "Surely when neighboring growers are also engaged in crop rotation. Growers should be able to buffer water, which is prescribed by law. However, the prescribed buffer capacity is often not calculated with the peak during a crop rotation. While this is in fact normal business practice. I think this is an focal point." The start of a new cultivation has its own risk factors. "There are also appropriate measures for it," according to Margreet Schoenmakers. "After irrigating the new substrate slabs, draining holes are made to remove excess drainage water. This water must be discharged into the sewer. Traditionally, growers cut all draining holes in one go, releasing a lot of water at the same time with the risk that the buffer capacity is too small. This is easily solved by simply cutting the slabs in a controlled manner: First, smaller openings, that release the excess water less quickly. It is also convenient to start close to the drain discharge point and by not draining all the slabs on the same day." Another ingrained habit at the beginning of the cultivation is discharging the first drainage water. "Growers think that this first drainage water contains substances from the slabs that are harmful to the crop. However, experience has shown that reuse of this first drainage water does not pose additional risks to the young crop. In recent years, greenhouse horticulture is increasingly recycling the water. This means that even more can be gained."

The above-mentioned advice, as well as other advice, have been available for quite some time on the website glastuinbouwwaterproof.nl. "But we want to direct special attention to the crop rotation now," says Margreet Schoenmakers. "This is done by the participating parties within the Framework Afsprakenkader Emissieloze Kas (Agreements Zero Emission Greenhouse). These parties are seven municipalities, two water boards (including Delfland) and the horticulture sector. We hereby offer a crop rotation flyer, which is accompanied by articles and practical tips at glastuinbouwwaterproof.nl. Possibly the purification requirement may have a stimulating effect. This is an opportunity to properly map all water flows in the company and reduce emissions as much as possible, and to make the right choice for the purification method. The final volume of waste water influences the choice of purification method and the required capacity. So it is beneficial to handle water in an economical and responsible manner. In particular also in crop rotation."

What makes this difficult, is that crop rotation is a stressful period for growers, Margreet Schoenmakers notes. "Much needs to be done in a short period of time. And precisely then, great care is required to prevent emissions. Moreover, many growers do not experience the crop rotation as part of their production process. During the whole cultivation season they work painstakingly with regard to the environment. But during crop rotation this seems to receive less attention." Erik Groen agrees. "It would already be a step forward if growers would consider crop rotation as an essential part of their production process."

Crop protection products do not belong in the water. Therefore, Nefyto is committed to contribute to reduce emissions from greenhouse horticulture as much as possible. This is why Nefyto also signed the General Agreement. The admission holders also contributed to synchronize the purification requirement based on admission as much as possible with the obligation from the Activities Decree. Furthermore, Nefyto has actively participated in the further development of the Greenhouse horticulture emission model GEM. Together with the CDG Foundation, the controlled distribution was professionally organized. During crop rotation, Nefyto, together with LTO Glaskracht Nederland, wants to play a role in communication and information. This means that everyone will be informed about the possible risks of emissions to surface water in the different phases of the transition from old to new cultivation.