Selected wheat and barley varieties were assessed for their tolerance to waterlogging and susceptible varieties were used to investigate how controlled-release fertiliser (CRF) compares with conventional split-applied urea in improving plant growth under
waterlogged conditions. The varieties were subjected to prolonged waterlogging instigated at the two leaf stage for 70 days. Different attributes for shoot vigour namely: tiller
number, number of green leaves, leaf chlorophyll content and number of dead leaves were recorded fortnightly. The above-ground dry matter (AGDM) was determined after
waterlogging. In the subsequent experiment, leaf chlorophyll content and chlorophyll fluorescence were recorded weekly and tiller number, green leaf area, AGDM and root DM were determined after waterlogging and recovery. The results showed significant variations between wheat and barley varieties (P < 0.05). Tiller number and the number of green leaves were markedly reduced by waterlogging particularly in wheat. Mackellar was the most affected with an 86% reduction in tiller number compared with other wheat varieties. Barley varieties, TX9425 and Naso Nijo had relatively similar number of tillers and green leaves for both the control and waterlogged. Leaf chlorophyll content and AGDM of both wheat and barley varieties were significantly affected by waterlogging (P
< 0.05). Mackellar and Naso Nijo had the lowest amount of leaf chlorophyll content and AGDM for both wheat and barley, respectively. In the second experiment, N fertiliser application improved leaf chlorophyll content, tiller number, green leaf area, AGDM and
evident for most of the parameters measured. After waterlogging, the CRF had the highest amount of AGDM for both Mackellar and Naso Nijo. It sustained N supply throughout the duration of the experiment. Conventional urea on the other hand, improved Mackellar and Naso Nijo’s growth at the start of waterlogging and significantly during recovery as the remaining urea was top-dressed.
Key words:duplex soils; enhanced-efficiency fertilisers; Hordeum vulgare L.; Triticum aestivum L.; waterlogging; waterlogging tolerance
3.2 Introduction
Waterlogging of duplex soils is a major abiotic constraint to cereal production in the high rainfall zones of Australia (Acuña et al. 2011). It is estimated to cause yield losses of ca. 30-50% (Zhou 2010). In Tasmania, waterlogging occurs especially during winter due to rainfall exceeding evapotranspiration (Bakker et al. 2007; Hardie et al. 2012). This is exacerbated by the duplex nature of Tasmanian soils occupying 23% of the total land mass (Cotching et al. 2009). Waterlogging can be transient, intermittent, prolonged or
permanent (Ashraf 2012). Transient waterlogging is widespread on duplex soils (Condon & Giunta 2003; Setter et al. 1999; Yaduvanshi et al. 2012). It is highly variable and depends on several factors including: the frequency and intensity of rainfall events, soil type, depth of the A-horizon and slope of the land (Condon & Giunta 2003).
Waterlogging adversely affects plant growth and development (Pang et al. 2004). It reduces the availability and uptake of essential nutrients (Pang et al. 2007; Pang et al. 2004), leaving plants with marked nutritional deficiency symptoms (Huang et al. 1994b; Trought & Drew 1980) that lead to yield losses (Collaku & Harrison 2005). Plants can modify their root architecture to maximize resource capture (Bailey-Serres & Voesenek 2008). Such modifications include: aerenchyma formation to facilitate long-distance gas
transport between the aerobic shoot and the anaerobic root(Wenger 2010), development of numerous adventitious roots at the shoot base (Colmer et al. 2001; Pang et al. 2007; Pang et al. 2004; Sairam et al. 2008) and elongation of internodes as an escape strategy (Bailey- Serres & Voesenek 2008; Parelle et al. 2010; Vartapetian & Jackson 1997). These
mechanisms vary depending on the crop, growth habit of the cultivar and duration of waterlogging (Setter et al. 1999). Wheat (Condon & Giunta 2003)and barley (Pang et al. 2007; Pang et al. 2004) are sensitive to waterlogging; however, genetic diversity in
waterlogging tolerance exists within both species (Setter et al. 1999; Thomson et al. 1992).
Agronomic management strategies to mitigate the adverse effects of waterlogging
particularly reduced nitrogen (N) loss are also viable options. Nitrogen loss can be reduced through appropriate timing of N fertiliser application and use of enhanced-efficiency N fertilisers such as controlled-release fertilisers (CRFs) (Dinnes et al. 2002). Controlled- release fertilisers release N over an extended period of time during crop growth
(Lubkowski & Grzmil 2007; Shaviv & Mikkelsen 1993; Trenkel 2010) and maximize nitrogen-use efficiency (NUE) by synchronizing N release with crop demand (Shaviv & Mikkelsen 1993; Trenkel 2010).
The application of N fertilisers plays a significant role in improving plant growth and development under waterlogged conditions (Pang et al. 2007; Swarup & Sharma 1993). For example, foliar applied N improved leaf chlorophyll content, net CO2 assimilation,
shoot and root growth and increased the production of adventitious roots in barley (Pang et al. 2007). Increased rates of top-dressed urea were reported to reduce flooding effects in wheat sown on sodic soils in India (Swarup & Sharma 1993). However, despite the importance of N fertiliser application in ameliorating the adverse effects of waterlogging, little or no research has been conducted to explore the potential of CRFs in mitigating the
effects of waterlogging. Most studies have focused on conventional N sources (Swarup & Sharma 1993), with no deliberate attempt to explore the potential CRFs. In this study, two experiments were conducted to understand the role of N fertiliser application in improving plant growth and development during and after waterlogging. The first experiment focused on assessing selected wheat and barley varieties for tolerance to prolonged waterlogging, on the hypothesis that waterlogging will significantly decrease the growth and
development of all selected wheat and barley varieties. Following the identification of waterlogging intolerant wheat and barley varieties, a second experiment was conducted to assess their response to N fertiliser application with the hypothesis thatCRF will
significantly increase the growth and physiological responses of selected wheat and barley varieties than conventional split-applied urea.