NUTRIENT MANAGEMENT IN PROTECTED CROPPING: THE NEED FOR AUTOMATED CONTROL

The nutrient management is not homogeneous within countries or regions. Hence the split up in high and low steering level of the greenhouse and high and low knowledge level suits better to evaluate the management of the different growers. The difference in nutrient management of the low and high level is noticed by a lower security systems and a higher fertiliser cost in the low levels. Up to 30-40% more (of the variable cost) versus only 3% in the high steering level. The low steering level can improve quickly with a small investment in safety tools. Once the production is stable over the years, the other investments become possible. The most important risk around the fertiliser unit is the unstability of the pH. The bicarbonate buffer is the best guarantee to avoid the pH problems. More in general the sensors in the greenhouses are another risk; they are not present, are not maintained or are not accurate enough. Over ‘sensoring’ is as risky for the management of the crop as having no sensors. The limits of normal accuracy are given in the table. Nutrient management of the crop became more achievable since the Water Content Meter helps to steer the EC separately from the substrate water content. The perspective of the management is the steering of the crop based on measurable plant behaviour. The plant behaviour is visualised in a graph with the balance between vegetative and generative (X axis) and the power of the plant (Y axis). This allows us to manage better the input in order to reduce the risks and improve the cost price/kg.