Adapting to extreme weather events under current and future climate conditions will be necessary to maintain industry profitability and sustainability. To develop strategies to adapt and assist recovery from these extreme climate events, a robust adaptation knowledge framework must be developed within the context of climate change scenarios. The objectives of this project was to examine the impact of extreme events (flooding and drought) under current and future climate (elevated CO2 and temperature) on soil fertility and function; and how these changes in soil processes affect cotton productivity through better understanding of soil-plant interaction and environmental sustainability.

Climate change impacts

• TE was the dominant factor in cotton productivity, accelerating the rate of plant development and vegetative growth while elevated CO2 (CE) had a strong impact on leaf physiology.

• Vegetative growth was dominated by the interactive effects of elevated temperature (TE) and CE on phenology, physiology and soil nutrients, and crop responses were similar in the two soils.

• However, during reproductive growth, the effects of TE and CE were limited by soil N availability, inducing changes in resource allocation between vegetative and reproductive growth.

• Such positive responses observed in the first season disappeared in the second season, as cotton productivity was influenced by legacies of CE and TE on soil and microbial properties.

• In particular, the legacy of CE effect through crop residue on soil and microbial properties strongly reduced soil N availability, altering resource allocation more towards belowground and less towards seed cotton yield.

• CE and TE also altered the abundance and composition of soil bacterial community, which showed strong correlations with soil chemical properties and soil processes, suggesting that shifts in soil microbial community could impact crop productivity through changes in nutrient cycling and availability.

Implications for Growers

• More N fertiliser will be required to prevent N limitation at CE for crop production under future climate.

• The responses of soil nutrients and microbial community should be an integral part of climate adaptation strategies.

• The response of non-harvestable biomass to these environmental changes should also be considered and implemented as a part of residue management strategies.

Extreme weather impacts

• The magnitude of flooding and drought impact on cotton productivity was greater at future CO2 and temperature regimes, suggesting that inter-annual variability in yield is likely to increase under more extreme climates.

• We also found that flooding and drought had contrasting consequences for soil N availability, with drought-induced loss of biological activity resulting in a large amount of residual N in the soil.

• Flooding and drought events occurred in the previous season can affect the soil and microbial properties and that those changes can indirectly influence cotton productivity of the subsequent season.

• In particular, changes in the abundance of nitrifier communities were strongly linked to soil processes that provide plant available N.

Implications for Growers

• Differential fertiliser management strategies are needed to minimise the legacy impact of extreme weather events. Our results suggest that more N fertiliser will be needed to ensure the productivity of subsequent crop following a flooding event, while the opposite is needed following a prolonged drought event.

• Soil microbial communities play an important role in minimising impact of climate change and extreme weather events on cotton productivity. Thus, the management practice which promotes soil health and microbes should be adopted for improved and sustainable cotton production.