Appendix 1 - Greenhouse Technology and Management - page 289

The relative growth rate (RGR) is expressed
in g g −1 (or similar) for the considered
period.
The leaf area ratio (LAR) is the ratio
between the leaf area and the total weight
of the plant, whereas the specific leaf area
(SLA) is the ratio between the leaf area and
the weight of the leaves. The specific leaf
weight (SLW) is the inverse of the specific
leaf area (SLA). The leaf area index (LAI)
is one of the most common parameters.
The leaf area duration (LAD) is the integral
of the LAI through time and is another
parameter used in longer term growth
studies.
The net photosynthesis assimilation
rate (NAR) is the weight of CO 2 fixed per
unit leaf area in a certain time.
The NAR can also be expressed as
weight of dry matter produced (instead of
the CO 2 fixed).
The SLA is an indicator of quality in
leafy vegetables, in which a thinner leaf is
more appreciated, and it is sensitive to cli-
mate parameters, such as radiation
(Giménez et al ., 2002) and CO 2 (Enoch,
1990).

A.5.5 Use of radiation in a typical
greenhouse ecosystem

Table 6.3. Use of solar radiation in a typical
greenhouse ecosystem (adapted from Baille,
1999, according to Warren-Wilson, 1972).

Proportion of energy
available Hypothesis

external global radiation 100%

external PAR (50%) 50% external PAR

Greenhouse
transmissivity (70%)

35% PAR greenhouse

Absorbed PAR (50%) 17.5% PAR absorbed

Dry matter fixed by
photosynthesis (14.3%)

2.5% Gross
photosynthesis

Minus photorespiration
and maintenance (40%)

1.5% Net
photosynthesis

Minus growth respiration
(33.3%)

1.0% Total dry matter
energy

Harvest index (50%) 0.5% Dry matter

energy in fruit

With these hypotheses, the efficiency val-
ues in the use of radiation are of the order of
0.5% of the harvested dry matter with
respect to the external global radiation, or
1% of the total dry matter with respect to
the external global radiation (Baille, 1999).
The energetic equivalence of dry matter is
16 MJ kg −1 dry matter.

A.5.4 Fruit harvest and
biomass indexes

A.6 Chapter 8

Table 6.2. estimated values of the harvest index
(HI, expressed in decimals per unit), dry matter
content of the harvestable product (DMC,
expressed in decimals per unit) and eFF (ratio of
the amount of fresh product formed to total dry
matter produced by the plant: HI/DMC), for
vegetables cultivated in a heated greenhouse.
(Source: Challa and Bakker, 1999.)

A.6.1 Wind effect in natural ventilation

In a multi-tunnel greenhouse with a single
vent or with several vents with the same
ventilation characteristics, half of the venti-
lation area is supposed to act as air inlet and
the other half as air outlet (Papadakis et al .,
1996). According to this simplification the
volumetric flux can be linearly expressed as
a function of the outside wind (Muñoz et al .,
1999; Pérez-Parra et al ., 2003a):

Crop HI DMC eFF

Tomato 0.7 0.06 12.0

Cucumber 0.7 0.035 20.0

Sweet
pepper (red)

0.8 0.085 9.4

S CCU

1
2
w dw

(8.4)

Φ=× × ×

Aubergine 0.8 0.07 11.4

Radish 0.9 0.05 18.0

where:
F w = Air volumetric flux caused by the wind
effect

Lettuce
(butterhead)

0.85 0.05 17.0