Nutrient Management in Soil and Soil-less Culture in the Netherlands: Towards Environmental Goals.

Keywords: Fertilizer, Pollution, Legislation, Target values, Open-systems, Closed-systems, Substrate, Nitrogen, Phosphate, Drainage, Drainage fraction, Irrigation.

Summary:
Glasshouse horticulture could, until recently, be characterised by large fertilizer inputs and low nutrient use efficiencies. The government and growers organizations have reached an agreement aimed at reducing nitrogen (N) and phosphorus (P) losses. Regulations, with crop specific limitations in N and P use, have been implemented recently. In addition, closed growing systems are obligatory for soil-less culture. For crops in soil, re-use of drainage water is obligatory if possible. Basically, closed growing systems offer a good opportunity to reduce nutrient leaching to the environment, given perfect water quality and adequate nutrient management. In practice, a substantial loss of water and minerals still occurs, due to the accumulation of ions and consequently the need for partial flushing, but also due to leakage from the system. With open systems, i.e. substrate with free drainage, high nutrient use efficiency can also be reached by minimising drainage. For soil-grown crops, systems with irrigation and fertilisation strategies based on crop demand have the best potentials for nutrient use efficiency and reaching environmental goals. For all growing systems, further improvements are possible by reducing the N and P target values for the root environment.

Wim Voogt, Applied Plant Research, Business unit Glasshouse Horticulture, PO Box 8, 2670 AA Naaldwijk, the Netherlands.

27 Pages. 6 Figures, 13 Tables, 43 References.


Nutrient Management in Protected Cropping: the Need for Automated Control.

Keywords: Fertilisation, Irrigation, Crop steering, Hydroponics, Sensor, Buffer, Fertilizer unit, Nutrient management.

Abstract:
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 fertilizer 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 fertilizer 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.

Peter Stradiot, Substratus Horticultural Consultancy, POB 1160, 6040 KD Roermond, The Netherlands.

12 Pages, 2 Figures, 5 Tables, 13 References.