European Journal of Agronomy 11 1999 207–215 www.elsevier.comlocateeja
Productivity and water use efficiency of sweet sorghum as affected by soil water deficit occurring at different vegetative
growth stages
Marcello Mastrorilli a,, Nader Katerji b, Gianfranco Rana a
a Istituto Sperimentale Agronomico, Via Ulpiani 5, I-70125 Bari, Italy b INRA-Unite´ de Bioclimatologie, F-78850 Thiverval-Grignon, France
Accepted 10 May 1999
Abstract
The growth and production of sweet sorghum [Sorghum bicolor L. Moench] crops under semi-arid conditions in the Mediterranean environment of southern Italy are constrained by water stress. The effects of temporary water
stress on growth and productivity of sweet sorghum were studied during three seasons at Rutigliano Bari, Italy. The aim of this research was to evaluate the sensitivity of phenological stages subjected to the same water deficit. In
a preliminary study it was observed that stomata closed when pre-dawn leaf water potential Y b
became lower than −
0.4 MPa. This criterion was used in monitoring plant water status in three different plots: one never stressed and two stressed at different phenological stages ‘leaf ’ and ‘stem’ when mainly leaves or stems were growing, respectively.
An evaluation of the sensitivity of phenological stages subjected to identical water stress was obtained by comparing the above-ground biomass and WUE of drought crops with those of the well-irrigated crop up to 32.5 t ha−1 of dry
matter and 5.7 g kg−1. The sensitivity was greatest at the early stage ‘leaf ’, when a temporary soil water stress reduced the biomass production by up to 30
with respect to the control and WUE was 4.8 g kg−1 average of three seasons. These results help quantify the effects of water constraints on sweet sorghum productivity. An irrigation
strategy based on phenological stage sensitivity is suggested. © 1999 Elsevier Science B.V. All rights reserved.
Keywords: Biomass; Drought stress; Irrigation; Plant water relationships; Sweet sorghum
1. Introduction studies on sweet sorghum have been conducted to
assess its potential productivity and water require- In addition to being highly productive in terms
ment under non-limiting conditions Mastrorilli of biomass, sweet sorghum is also known to show
et al., 1995a, 1996. However, since water resources high drought and waterlogging resistance and
in the Mediterranean region are limited, the success salinity tolerance. For these reasons, among the
of sweet sorghum in this area depends upon the biomass energy crops, it is considered as the ‘camel’
optimisation of water supplied by irrigation. To Li, 1997. In the Mediterranean regions, previous
devise a strategy for optimising the amount of water provided to sweet sorghum, we had to first
answer the question: what is the sensitivity of each
Corresponding author. Tel.: +39-080-5475014;
growth stage to soil water depletion? To this end,
fax: +39-080-5475023. E-mail address: agrobariinterbusiness.it M. Mastrorilli
we analysed the consequences for final yield of a
1161-030199 – see front matter © 1999 Elsevier Science B.V. All rights reserved. PII: S 1 1 6 1 -0 3 0 1 9 9 0 0 03 2 - 5
208 M. Mastrorilli et al. European Journal of Agronomy 11 1999 207–215
temporary stress occurring during the growth 1990 to 1993 at a density of 11.5 plants m−2. In
1991 violent storms reduced cycle length, and only cycle. From the results, we suggest how to optimise
the use of a limited water supply in the manage- the results from the other three years are given
here. Sowing dates were: 14 May 1990 Julian day ment of the crop.
We adopted a method previously used success- 135, 29 April 1992 120, and 25 May 1993 145.
Harvest dates were: 9 October 1990 Julian day fully both in the glasshouse Katerji et al., 1993
and in the open field Mastrorilli et al., 1995b. 282, 5 October 1992 279, and 18 October 1993
291. The method consisted of stopping watering during
a given stage and monitoring directly the plant Irrigation water was uniformly distributed all
over the field by means of a drip irrigation system. water status by measurements of leaf water poten-
tial Y . Watering was resumed when Y attained Each year the same experimental design covering
a field area of 2 ha was repeated in different a certain threshold value, which was the same for
all stages. As the water deficit provoked the same positions within the farm.
degree of stress Katerji et al., 1991 it was possible to compare the consequences for yield of a given
2.1. Calibration stress occurring during a particular growth stage.
This study was carried out in two stages: first, To characterise the reaction of crop water status
to soil water depletion, leaf water potential Y calibration of the method for detecting the occur-
rence of water stress; and second, evaluation and stomatal conductance g
s were measured
hourly, under conditions of different evaporative during the vegetative phase of the sensitivity of
two stages to a water stress of the same intensity. demand. In practice both Y and g
s were measured
on a sample of 10 well-developed mature leaves Sensitivity was expressed in terms of yield and
water use efficiency. Our analysis is limited to the from the top of the canopy. Measurements were
performed by means of a pressure chamber vegetative phase because it represents the relevant
part of the life cycle, as the stalks, harvested before Scholander et al., 1966 and a steady state poro-
meter Li-Cor 1600 respectively. The objective of grain maturity, constitute the commercial product
of this crop. this eco-physiological characterisation was to find
a Y threshold value for scheduling irrigation and managing water stress. When the water status was
higher than the Y threshold, the crop was consid-
2. Materials and methods
