Soilless cultivation offers new opportunities for growing apples on sandy soils. For example, soilless cultivation in trenches is a potential solution to soil degradation. Meanwhile, the current system of chemical pest control is under pressure. The permitted dose of metam sodium for chemical soil disinfection was reduced by 40% in 2015.
Soilless cultivation also makes it possible to guarantee optimum fruit sizes for harvesting. Furthermore, this new cultivation system enables the regulation of shoot growth using controlled water stress. It also improves yields and harvest quality and ensures a more homogenous crop, while strongly reducing the pollution caused by fertilisers and herbicides.
This research project started testing three systems at the experimental orchard in Randwijk, situated in the heart of the Dutch fruit-growing region. One system has been discontinued.
Cultivation in 30 cm wide trenches filled with nematode-free fine black sand with growth regulation through controlled watering
This system offers the best prospects and is the focus of further development. Application of controlled water stress in July 2012 and 2013 led to 8% higher yields in 2013 and 2014 in comparison with the methods that involved maximising growth. In the third year of growth (2013), the trial cultivar Junami yielded some 50 tonnes/ha of good-sized apples (average of 75-80 mm).
This system is also being used to experiment on methods for improving the biological health of ‘Brabant sand’ using Plant Health Cure (PHC) products. More than one year after planting, the nematode Pratylenchus penetrans had not yet started to develop, while this pest was already present in the reference plot. The trees treated with PHC products had higher total nematode counts, which indicates healthy development of soil life. The trench system is being further tested with the same fine black sand in two trial plots in North Limburg. A P. penetrans infestation was identified in one of the plots (36 nematodes/100 ml) and controlled by means of inundation (the sand in the trench was completely submerged). Planting the trees immediately after inundation produced poor results, while planting after a break during the winter of 2014/2015 helped the trees off to a good start. This break was still insufficient on the other trial plot, probably due to water damage that occurred because the trenches could not be watered individually.
The trial in Randwijk used a clayey soil as alternative substrate. After a few years, the researchers saw that the growth and yields in trenches filled with sandy clay (12% lutum content) were lower than those of fine black sand. The clay probably develops a poor soil structure due to the intensive fertigation of the entire surface of the trench. The sandy soils are probably sufficiently oxygenated due to the excellent drainage properties of the sand.
The system could also be applied in situations where other problems than soil degradation play a role, such as waterlogging in heavy soils with shallow groundwater. Fruit growers Gert and Christian van Os started a trial plot using the system in Benschop in 2014. Root development was much better with this system due to the good drainage. A point for attention is the trench substrate. Filling the trench with the same heavy soil eventually retards the growth of the plants due to lack of oxygen (caused by soil subsidence).
Two other methods were also tested.
Cultivation in trenches filled with 0.5 mm white sand and EC growth regulation through fertigation with permanent over-drain
The trenches are covered. This trial is focusing on developing fertigation timetables for this new cultivation method. From 2014, the yields with this system were equal to those of the open trench system.
Cultivation in containers (RocketpotTMPot) with 50 litres of nematode-free black Brabant sand as substrate
The results of the first trial year (2010) revealed that apples grow extremely well in containers with sandy soil as a growing substrate. A major trial plot that was planted in June 2011 died off during the harsh and unsettled winter of 2011/2012, when the roots of the trees in the containers all froze. Due to these results, the container cultivation trial with apples was discontinued.