Over the last few years the south-west of the Netherlands, and thus also the Rusthoeve Experimental Farm, have experienced periods of heavy rainfall and dry periods. This was the case in the spring of 2018, followed by a lengthy drought in the summer. The drought, combined with very high air temperatures, produced a disastrous situation, particularly in the aftermath of the heavy spring rainfall. Previous years had also experienced dry, hot periods, but no irrigation took place at Rusthoeve. Long dry and hot periods again occurred in 2019. One of the measures that we want to study and test at the Rusthoeve Experimental Farm – as a test location in the Province of Zeeland – is subirrigation by means of controlled drainage.
Good water supply and water management in times of drought
In times of both dry and wet weather extremes, it is important to be able to anticipate such events. This involves a key role for good water supply and water management, for the purpose of maximising the buffering and retention of water, as well as discharging it in a timely manner. Moreover, the available freshwater sources also need to be used efficiently. At the Rusthoeve Experimental Farm we will therefore carry out practical research into how to deal with long dry periods, with a view to offering options to growers in areas where sprinkler irrigation is not possible. Since freshwater supplies are always very location-specific, the work will not produce a generic solution: any solution is, and will always be, a tailored one.
Subirrigation via controlled drainage
A number of years ago a controlled drainage system was installed at the Rusthoeve Experimental Farm. Since controlled drainage is an interconnected system, the drainage level – which can be set at different heights – can be actively controlled through wells. With this controlled drainage we can therefore retain any available water and buffer it in the ground. But the system can also be used to actively replenish the groundwater: subirrigation (‘the delivery of water below the surface by means of a ditch or pipe system’).
The delivered water which replenishes the groundwater through the drains is intended to raise the watertable to the point where, via capillary rise, it becomes available to the plant roots. This makes for an efficient use of water because no water disappears from the soil system, other than through crop transpiration.
The project should provide an answer to the question of whether and, if so, to what extent, the controlled drainage system can actually be used to supply freshwater to the Rusthoeve and the surrounding area. The effects of subirrigation must be noticeable and measurable in the dry matter yield of the cultivated crops.