Protected Crops - Horticulture: Plants for People and Places - page 369

Plant Nutrition, Nutrient Management and their Effect
on Plant Growth and Development in Soilless Culture
General
Correct crop nutrition is essential for successful plant production (Bailey and Nelson
2012 ) and even more for protected crops. The nutrient uptake of the protected plants
is generally higher compared with field cultivation, because of high production in-
tensity and potentially higher yields. For instance, yields of more than 500 t ha −1 a −1
are not an exception for tomatoes and cucumbers produced in High-Tech green-
houses. Since harvest residues are totally removed from the greenhouse the nutri-
ents used for biomass production of follow-up crops have to be fully compensated
by the fertilizer and if high temperatures are encountered, the mineralization rate
of organic matter in the greenhouses is higher than in the open field. Similarly, the
movement of nutrients in soil is high particularly potassium and nitrogen levels, and
leaching losses are often high, due to frequent watering and the attempt to keep up
soil moisture. Special attention needs to be paid to the control of nutrient and salt
contents in soil and soilless culture systems in protected cultivation. Appropriate
fertilization (especially with nitrogen) requires more frequent analyses in shorter
intervals, e.g. once in every 4 weeks. A combination of both ferti lization and irri-
gation is sometimes used. This combination process is known as “ fertigation ” and
such systems are “ fertigation systems ”. If fertigation systems are used, soil analysis
has to be limited to the wetted root zone. Particularly important is the nutrient con-
trol in soilless culture, because their restrictive root volume and a very low buffer
capacity. Here, at least daily analyses of EC- and pH-values of the nutrient solution
are required. Since fertigation management in such systems is usually carried out by
computer programs these two characteristics are however continuously controlled:
some equipment allows separate management for each element. In all cases nutri-
ent solution has to be tested periodically. Another way to control the nutrients is to
analyze crop leaves where young leaves from the same age are used (Drews and
Fischer 1992 ).
In soil culture, preplant and post-planting fertilization have to be differenti-
ated (Bailey and Nelson 2012 ), however, in soilless culture only a post-planting
fertilization or an accompanied fertigation with a nutrient solution is provided.
Dolomitic limestone is often added to raise the pH of peat and other acid substrates
(Jackson et al. 2009 ).
Soilless Culture
The term “soilless culture” is defined as the cultivation of plants in systems without
soil “ in situ ” and this method is the most intensive and effective in today's horti-
cultural industry. In recent years, a multitude of innovative cultivation procedures
using bags, mats, and containers, in addition to nutrient solutions, have been devel-