In the experiments reported below, sweet pepper plants were grown in polythene greenhouses in Murcia, Spain.
Three substrates were tested, namely coir dust, rice hulls mixed with polyacrylamide crystals to improve water retention, and a urea formaldehyde foam consisting of "a plastic made from amino compounds". The latter compound was inert and was believed to be broken down by the ultra-violet radiation in sunlight.
The substrates were contained in 40-litre plastic bags and the quantity of nutrient solution to be applied each day was increased as the plants grew.
Irrigation applications were scheduled by accumulated radiation and adjusted to deliver between 30 and 40 per cent more than the plants actually needed.
Plants growing on the rice hulls performed badly in all years while those on coir dust usually gave the highest marketable yields as well as a higher proportion of fruit in the top grades.
With the urea formaldehyde foam, it appeared that irrigation needed to be applied in small doses and more frequently for it to be continuously available to the plants.
Agronomical Response and Water Use Efficiency of Sweet Pepper Plants Grown in Different Greenhouse Substrates by del Amor and Gomez-Lopez (2009). HortScience 44 (3): 810-814. Members of ISHS can view HortScience from the website www.ishs.org.