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Does irrigation influence the growth, yield and water use efficiency of the protea hybrid ‘Sylvia' (Protea susannae X Protea eximia)?
P Mortimer, JC Swart, AJ Valentine, G Jacobs, MD Cramer
Abstract
The response of the protea
hybrid ‘Sylvia' (Protea susannae X Protea eximia) to irrigation was
investigated to determine the water requirements of this commercial floriculture
crop. Both field and glasshouse trials were conducted in which plants were
exposed to different irrigation levels. The effects of the irrigation regimes
were determined by measuring the δ13C, δ13N,
gas exchange characteristics, biomass accumulation, yield and root development.
The plants in the glasshouse were exposed to watering regimes maintaining
water at 20%, 40% and 60% of field capacity in sand-filled pots. Higher water
supply resulted in increased growth of the roots in particular, but also
of the shoots, reaching a maximum at 40% of field capacity. There were no
significant changes in the gas exchange characteristics of the plants associated
with this increased growth. In the field trial the intensity of irrigation
(dry-land, normal and double-irrigation) did not influence the vegetative
or reproductive biomass accumulation. Although the water content of the upper
30cm of soil was significantly different between treatments, there were no
differences in δ13C, relative water contents or in elemental
compositions of the leaves. The gas exchange characteristics of the plants
were only slightly influenced by the irrigation intensity maintaining very
similar water use efficiencies between treatments, concurring with δ13C
results. However, the development of cluster roots was strongly increased
by irrigation. Dryland plants had extensive sinker roots penetrating the
deeper (>1m) soil layers. It was concluded that the dimorphic and deep
roots of ‘Sylvia' allow access to water deep in the soil profile once the
root system is established. Although maintenance of cluster roots for nutrient
uptake is important, management practices should take cognisance of the fact
that surface soil water contents only partially determine the availability
of water for these deep-rooted perennial shrubs, if at all.
South African
Journal of Botany 2002, 69(2): 135–143
hybrid ‘Sylvia' (Protea susannae X Protea eximia) to irrigation was
investigated to determine the water requirements of this commercial floriculture
crop. Both field and glasshouse trials were conducted in which plants were
exposed to different irrigation levels. The effects of the irrigation regimes
were determined by measuring the δ13C, δ13N,
gas exchange characteristics, biomass accumulation, yield and root development.
The plants in the glasshouse were exposed to watering regimes maintaining
water at 20%, 40% and 60% of field capacity in sand-filled pots. Higher water
supply resulted in increased growth of the roots in particular, but also
of the shoots, reaching a maximum at 40% of field capacity. There were no
significant changes in the gas exchange characteristics of the plants associated
with this increased growth. In the field trial the intensity of irrigation
(dry-land, normal and double-irrigation) did not influence the vegetative
or reproductive biomass accumulation. Although the water content of the upper
30cm of soil was significantly different between treatments, there were no
differences in δ13C, relative water contents or in elemental
compositions of the leaves. The gas exchange characteristics of the plants
were only slightly influenced by the irrigation intensity maintaining very
similar water use efficiencies between treatments, concurring with δ13C
results. However, the development of cluster roots was strongly increased
by irrigation. Dryland plants had extensive sinker roots penetrating the
deeper (>1m) soil layers. It was concluded that the dimorphic and deep
roots of ‘Sylvia' allow access to water deep in the soil profile once the
root system is established. Although maintenance of cluster roots for nutrient
uptake is important, management practices should take cognisance of the fact
that surface soil water contents only partially determine the availability
of water for these deep-rooted perennial shrubs, if at all.
South African
Journal of Botany 2002, 69(2): 135–143
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South African Journal of Botany. ISSN: 0254-6299