Effect of Water Stress during the Spike Growth Period on Wheat Yield in Contrasting Weather
Abstract
The ef fect of water deficit on spring wheat yield (Triticum aestivum L.) was analyzed focusing on crop growth and dry weight partitioning during the spike growth period (SGP). Two levels of water availability (rainfed and irrigated) were tested in two locations (Córdoba and Balcarce, Argentina). The degree of source limitation for grain filling was greater under rainfed conditions (12%) than under irrigation (5%); however, water stress affected yield by 40% (mean of all experiments), mainly through grain number m-2 (GN) rather than by differences in weight per grain. The decrease in GN due to water stress was associated with spikes dry weight (SDW = total spikes weight – grain weight) measured 7 days after anthesis, but some additional experiment effect was detect ed on GN. Analysis of different weather variables showed the vapor pressure deficit ( VPDX ) as the one that best explained GN deviations. A model for GN estimation with or without water stress, was developed including the effect of water stress on SDW reduction ( ΔSDW ), where H represents no water stress:
GN = 4878 + 51.SDWH - max(-10 + 91.VPDX,51) ΔSDW (R^2=0.93).
The SDW was analyzed as the product between spike growth rate (SGR) and the spike growth period (SGP) duration. SGP duration was not affected by water level, but anthesis date was up to 9 days earlier under water stress in Córdoba. SGR was more associated with crop growth rate (CGR) than with assimilates partition to spikes, and this effect increased when CGR was reduced. CGR was associated with the amount o f intercepted photosynthetic active radiation during the SGP but not with the radiation use efficiency. Thus, GN was affected for both water stress reducing the availability of assimilates for spike growth and VPDX of each environment.
Keywords
Download Options
Introduction
Increases in world population will lead to sustained increases in food demand for incoming years (FAO, 2009). Possibilities of supplying food to increasing population will come mainly from an increase in yield per unit area (Andrade, 2011). However, food security is at serious risk in the long term (Fischer et al., 2014). Indeed, climate change has been associated with the occurrence of extreme meteorological episodes, including an increase in the frequency of droughts, which may have strong impact on agricultural production (FAO, 2009).
In Argentina, wheat production is mostly concentrated in greats plains with reduced rainfall from east to west regions, where water availability is the main limiting factor.
The crop-physiological approach proposed by Fischer (1984) considers that in wheat, grain number per unit area (GN) is the component most highly associated with yield, and this variable can be analyzed as the product between: (i) the duration of the rapid spike growth period previous grain filling (SGP), (ii) crop growth rate during this phase (CGR), (iii) dry weight partitioning to spikes (PE), and (iv) number of grains g-1 of spike produced, which is an indicator of spike fertility (SF). This approach has been previously used to examine the effects of solar radiation (Fischer, 1985; Abbate et al., 1997), cultivar (Slafer et al., 1991; Abbate et al., 1998), nitrogen (Thorne and Wood, 1987; Fischer et al., 1993; Abbate et al., 1995), phosphorus (Lázaro et al., 2010) and water (Robertson and Giunta, 1994) on wheat. A change in any of these ecophysiological components may cause variations in GN. The first three components define the spike dry weight per unit area at the start of grain filling (SDW) which reflects the amount of assimilates used by the crop for the formation and growth of reproductive organs, i.e. the survival of differentiated flowers, and therefore the GN. Several studies have shown that GN and SDW are positively related in the absence of water and nutritional deficiencies, i.e. across changes in intercepted radiation and temperature (Fischer, 1985; Thorne and Wood, 1987; Abbate et al., 1995; Abbate et al., 1997; Lázaro and Abbate, 2012). At the same time, SDW was directly associated with variations in crop growth during SGP (Fischer, 1984; Fischer, 1985; Abbate et al., 1995; Abbate et al., 1997; Lázaro et al., 2010; Fischer, 2011). In the absence of water andnutritional limitations, crop growth and GN are lineal function of the amount of intercepted radiation during the SGP (Fischer, 1985; Abbate et al., 1997; Lázaro and Abbate, 2012).
Water stress reduces crop growth by decreasing the amount of intercepted radiation (Gallagher and Biscoe, 1978; Robertson and Giunta, 1994) through a reduction in leaf expansion, less exposure of leaf surface (e.g. leaf curling) or leaf death. In addition, water stress can also reduce crop growth due to a decrease in photosynthesis (Subrahmanyam et al., 2006) and in radiation use efficiency (RUE; Gallagher and Biscoe, 1978; Robertson and Giunta, 1994). Therefore, water stress during SGP could reduce GN mainly due to a lower crop growth. However, it has been indicated that although water stress operates mainly through a reduction in the assimilates supply to the spikes during SGP (Fischer, 1984; Fischer, 2011), an additional reduction in GN per spike (Fischer, 2011) has been observed due to male sterility (Fischer, 1973). The existence of GN reduction due to N deficiencies during SGP has been previously shown by Abbate et al. (1995). Similar effect was not found by early P deficiencies (Lázaro et al., 2010). However, additional effects (i.e. supplementary GN decreases as a function of SDW reduction) of water stress over yield and GN in wheat has not yet been clearly analyzed or quantified under field conditions.
The aim of this work was to compare wheat the yield obtained under natural water stress scenarios with that achieved under non-limiting water conditions in two contrasting environments of Argentina and obtain GN estimations under both conditions.
