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Steward, P.

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Steward
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Steward, P.
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0000-0003-3985-4911

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    Agile agronomy for climate action
    (IITA, 2023) Rosenstock, T.; Schmitter, P.; Steward, P.; Ramirez-Villegas, J.; Snapp, S.S.; Mcdonald, A.; Bonilla Cedrez, C.; Corbeels, M.; Mabhaudhi, T.; Dossou-Yovo, E.; Vanlauwe, B.
    Publication
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    Conservation agriculture improves adaptive capacity of cropping systems to climate stress in Malawi
    (Elsevier, 2021) Komarek, A.; Thierfelder, C.; Steward, P.
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    Conservation agriculture enhances resistance of maize to climate stress in a Malawian medium-term trial
    (Elsevier, 2019) Steward, P.; Thierfelder, C.; Dougill, A.J.; Ivy Sichinga Ligowe
    Smallholder farming in southern African needs climate-smart agricultural approaches to adapt to current climate stress and climate variability, and increasing risk of these under future global climate change. There are a range of climate-smart systems that have been proposed and conservation agriculture (CA) based on minimum soil disturbance, crop residue retention and crop rotation is one of them. A CA trial established in 2007 in Malawi was used during cropping -seasons 2015–2016 (El Niño) and 2016–2017 (La Niña) to assess the performance and resistance of different CA maize systems under climate-related stress at anthesis, a climate sensitive growth stage. Large in-situ rainout shelters were used to simulate increased daytime temperatures and in-season droughts of 18–19 days and 27 days. CA systems better resisted climate stress around anthesis than conventional tillage practices as CA systems showed greater resistance to drought than conventional practice. This was expressed by higher CA maize grain yields, biomass yields or harvest index under conditions of natural (El Niño) or 19 day simulated drought. However, under 27 day drought simulation the resistance benefit of CA was no-longer significant. Crop diversification improved the resistance of CA systems to climate stress, more so when diversification was over time (rotation) than in space (intercropping). In all years CA systems substantially outyielded conventional practice, this highlights the benefits of medium-term (eight years) CA management before the rainout shelter experiment started. Our results from natural and simulated drought conditions confirm that CA systems can increase adaptive capacity to an increased risk of climate stress associated with projected global climate change. We show that large-scale rainout shelters are a useful means of accelerating our understanding of how long-term agricultural management practices can enhance resistance to climate stresses.
    Publication
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    The adaptive capacity of maize-based conservation agriculture systems to climate stress in tropical and subtropical environments: a meta-regression of yields
    (Elsevier Masson, 2018) Steward, P.; Dougill, A.J.; Thierfelder, C.; Pittelkow, C.M.; Stringer, L.C.; Kudzala, M.; Shackelford, G.E.
    Conservation agriculture is widely promoted across sub-Saharan Africa as a sustainable farming practice that enhances adaptive capacity to climate change. The interactions between climate stress, management, and soil are critical to understanding the adaptive capacity of conservation agriculture. Yet conservation agriculture syntheses to date have largely neglected climate, especially the effects of extreme heat. For the sub-tropics and tropics, we use meta-regression, in combination with global soil and climate datasets, to test four hypotheses: (1) that relative yield performance of conservation agriculture improves with increasing drought and temperature stress; (2) that the effects of moisture and temperature stress exposure interact; (3) that the effects of moisture and temperature stress are modified by soil texture; and (4) that crop diversification, fertilizer application rate, or the time since no-till implementation will enhance conservation agriculture performance under climate stress. Our results support the hypothesis that the relative maize yield performance of conservation agriculture improves with increasing drought severity or exposure to high temperatures. Further, there is an interaction of moisture and heat stress on conservation agriculture performance and their combined effect is both non-additive and modified by soil clay content, supporting our second and third hypotheses. Finally, we found only limited support for our fourth hypothesis as (1) increasing nitrogen application rates did not improve the relative performance of conservation agriculture under high heat stress; (2) crop diversification did not notably improve conservation agriculture performance, but did increase its stability with heat stress; and (3) a statistically robust effect of the time since no-till implementation was not evident. Our meta-regression supports the narrative that conservation agriculture enhances the adaptive capacity of maize production in sub-Saharan Africa under drought and/or heat stress. However, in very wet seasons and on clay-rich soils, conservation agriculture yields less compared to conventional practices
    Publication