Current Research
Work on tropical intercropping and agroforestry is a core element of my research. Collaborative research with Professor Chin Ong at the International Centre for Research in the Semi-Arid Tropics (ICRISAT) in India and more recently at the World Agroforestry Centre (ICRAF) in Kenya has aimed to establish the principles involved in the capture and use of water, nutrients and light by the component species in mixed cropping systems. We are particularly interested in establishing whether species mixtures, particularly those which include trees, can be used to increase the quantity of natural resources captured and/or the efficiency with which these are used to produce harvestable products. The long-term goal is to improve productivity and sustainability in semi-arid farming systems. These studies have examined: (i) the impact of shading and timing of drought on growth, assimilate partitioning and yield in annual crops; and (ii) resource utilisation, microclimatic modifications and productivity in a range of intercropping and agroforestry systems in India, Kenya, Uganda and Malawi. The results have been used to test process-based models of resource capture and productivity. Work in Malawi investigated the physiological and agronomic basis for the substantial yield benefits obtained when tree prunings are incorporated into the soil before planting maize or pigeonpea crops as a form of green manure. Studies in Kenya and Uganda have examined the importance of physiological and phenological attributes in determining the severity of competition between trees and crops in systems containing indigenous and exotic tree species. We are also exploring the potential of fast-growing bamboo species for woody biomass production on contaminated land or under irrigation using wastewater, and the suitability of Jatropha curcas for biodiesel production on degraded and infertile land in East Africa.
The impact of gaseous pollutants and climate change factors is a second major strand in my research. A particular focus has been to establish the impact of ozone and sulphur dioxide on reproductive development in oilseed rape, the related species but much smaller species, Brassica napus, and populations of the temperate plantain (Plantago major) which differ in their sensitivity to ozone. These studies showed that specific reproductive processes are highly susceptible to injury, and that single or multiple exposure to realistic ozone concentrations during flowering may reduce seed yield and quality and the vigour of seedlings produced by seed from fumigated plants. Related field studies funded by the EU examined the effects of elevated atmospheric carbon dioxide, alone or in combination with elevated ozone, on the growth, physiology and productivity of spring wheat grown in open-top chambers (OTCs). This work formed part of the ESPACE-wheat programme involving 11 European research partners. A doubling of ambient carbon dioxide increased biomass and grain yield by up to 25%, while season-long exposure to elevated ozone under ambient carbon dioxide caused an equivalent reduction in productivity. Although elevated carbon dioxide provided partial protection against ozone-induced injury during vegetative growth, grain yield was significantly reduced by injury to the developing reproductive organs during or shortly after flowering.
A further EU-funded project (CHIP) examined the impact of elevated carbon dioxide and ozone on potato crops grown in OTCs. In the first field season, exposure to elevated carbon dioxide increased above-ground dry weight and tuber biomass at the time of tuber initiation and maximum leaf area, but had no detectable effect on total tuber yield at final harvest. However, tuber numbers were increased, particularly in the commercially less valuable smaller size categories. Exposure to elevated ozone did not affect tuber yield. By contrast, exposure to elevated carbon dioxide increased above-ground biomass and tuber yield at maturity by 40% in the second field season; this effect resulted from an increase in mean tuber weight rather than tuber numbers. Elevated ozone caused chlorophyll degradation and extensive visible injury but had little effect on photosynthetic characteristics or tuber yield. However, exposure to elevated carbon dioxide and ozone adversely affected important tuber quality attributes, including starch pasting properties, citric acid and glycoalkaloid content.
Expanding research interests include the fields of phytoremediation and biofortification. In phytoremediation, plants are used to extract pollutants from soils contaminated naturally or by human activities and return soil concentrations to safe levels. Our research has focussed primarily on remediation of soils contaminated with trace metals. A BBSRC LINK project examined the suitability of phytoextraction for remediating arable land contaminated by long-term application of sewage sludge. The primary objectives were to examine: (i) the relative effectiveness of hyperaccumulator species and high biomass crops, including trees, for phytoremediation; and (ii) the role of interventions such as chelate and/or herbicide-assisted phytoextraction and amendments to modify soil pH. Related studies have examined the suitability of the arsenic hyperaccumulating fern, Pteris vittata, for remediating soils contaminated with arsenic. Current studies are examining: (i) the risk to human health of consuming leafy vegetables grown in soils highly contaminated with heavy metals in peri-urban agriculture in Uganda; and (ii) the potential of bamboo to produce economically valuable commodities in Kenya using waste water that is too contaminated to be used to irrigate food crops. The former study has shown that when some tropical leafy vegetables are grown on highly contaminated sites, they may accumulate trace metals such as lead and cadmium in their shoots to concentrations which may pose a serious risk to human health if consumed in the quantities recommended by the World Health Organisation. Other current projects are examining: (i) the importance of biofortifying maize crops in Malawi with selenium to rectify the serious dietary deficiency of this essential element experienced by a large proportion of the population in many countries world-wide; and (ii) the influence of nutritional status of natural tropical wetlands on their carbon and nitrogen dynamics.
Recent and current grants
HEFCE: Centre for Advancement of Integrative Learning (CAIL), 2005-2010. I am a member of the Biosciences' CAIL Steering Group with Martin Luck (CAIL Assistant Director) and Julian Wiseman
Yara International: "Biofortification of Malawian food crops with selenium (Se)", 2008-2011. Jointly with Dr Martin Broadley and Dr Scott Young.
Members of Group
Postgraduate
David Siriri: Water and nutrient dynamics in agroforestry systems, funded by International Foundation for Science and Association of Commonwealth Universities, co-supervisor Prof Chin Ong (World Agroforestry Centre, Kenya
Adam Docherty: "Genetic control of novel ear fertility traits in wheat", funded by Homegrown Cereals Research Association, co-supervisors Dr John Foulkes and Dr Sean Mayes
Emma Wright: "Nutrient controls on carbon dynamics in tropical wetlands", funded by BBSRC PhD, co-supervisor, Dr Sofie Sjögersten
Benson Kuria: "Distribution, growth, water and nutrient use efficiency of Jatropha curcas and Tarconanthus camphorates, potentially important sources of biofuel in Kenya, funded by Association of Commonwealth Universities
Manal Al-Traboulsi: "The response of terrestrial ecosystems to CO2 leaks from sub-surface storage sites", funded by Libyan Government Scholarship, co-supervisors, Professor Jeremy Colls, Professor Mike Steven and Dr Sofie Sjögersten
Saiorse Tracy: "Profiling the changes in plant root cap gene expression in response to stresses in soil", funded by IDTC, co-supervisors, Dr Sacha Mooney and Professor Jerry Roberts
Allan Chilimba: "Biofortification of maize with selenium and zinc for improved human health in Malawi", funded by Yara International, co-supervisors Dr Martin Broadley and Dr Scott Young
Interests
Photography, narrowboating, travel, especially in mountainous regions and the tropics, hot hatches and our four cats!