Nutrient management varies within countries or regions. Furthermore there is a division between high and low ‘steering’ levels within the greenhouse and also in the level of knowledge between the different growers. By high and low ‘steering’ is meant the degree of sophistication and precision of control of all factors influencing the growing conditions.
The difference for nutrients between low and high levels shows as less precise control and higher fertiliser costs at low levels of steering, up to 30-40% more (of the variable cost) versus only 3% at the high steering level. A low level steering can be improved quickly with a small investment in control tools and once the production is stable after a number of years, other investments become possible.
The most important risk around the fertiliser unit is the instability of the pH. The bicarbonate buffer is the best guarantee to avoid pH problems. More generally the sensors in the greenhouse are another risk; they may not be present, or are not maintained or are not accurate enough. Over ‘sensoring’ is as risky for the management of the crop as having no sensors and the limits of normal accuracy for sensors are discussed.
Nutrient management of the crop became possible once the Water Content Meter permitted the separation of the control of the salinity from that of the substrate water content. The objective of the producer is to steer the crop based on measurable plant behaviour. Plant behaviour is visualised in a graph with the balance between vegetative and productive (X axis) and the ‘power’ of the plant (Y axis). This allows us to better manage inputs in order to reduce risks and improve the cost price/kg of produce.