DIVERSE - DIVerse crop residues Engender Resilience of Soil functions and Ecosystem services

This project will test the idea that cover crop green manure mixtures are a tractable means to increase the diversity of carbon compounds entering soils and that this increased biochemical diversity leads to a greater diversity of enzymes produced by the soil microbial community, and, in turn, the potential to make more nutrients available to crops during and after disturbances such as floods and droughts. There is a recognised need to sustainably intensify our food production systems this century to meet global demand. The increases in crop yield potential achieved by genetic improvements have not translated into on-farm yield increases of the same magnitude due to sub-optimal growing conditions. Sub-optimal quality and health of the soils on which crops are grown is a major constraint to the realisation of the genetic yield potential. Crops have failed to achieve their yield as a result of unsustainable soil management that has reduced the ability of the soil microbial community to deliver underpinning functions and services (e.g. nutrient mineralisation). Sustainable soils are those that can consistently achieve crop yield potential by delivering ecological functions despite disturbances (e.g. floods and drought) which are expected to become more frequent and severe as our climate changes. The energy required for the soil microbial community to deliver these functions in agricultural soils is provided by organic compounds entering the soil in the form of root exudates, crop residues or organic manures. When a single carbon substrate is added to a soil (e.g. by incorporating the residues of the previous crop in an arable rotation), a microbial community that is most adapted to exploiting that substrate is activated. When applying several biochemically contrasting substrates, the number of ecological niches increases and the groups of organisms capable of exploiting each of these niches are stimulated. The functional diversity of the soil microbial community is thus increased and the capability to deliver ecosystem functions (e.g. nitrogen mineralisation) is more secure since the suppression of one group of organisms due to a disturbance (e.g. a flood or a drought) can be compensated by other groups, thereby enhancing resistance and resilience of the soil microbial community to disturbance. Cover crop green manures offer a tractable means to introduce biochemically contrasting crop resides into arable crop rotations because their inclusion does not significantly change the agronomic management of the cash crop. Crop residue diversity can be increased further by incorporating cover crop mixtures comprised of species from a diverse range of plant families since each plant family produces unique plant secondary metabolites. Thus, the incorporation of diverse cover crop mixtures provides biochemically diverse organic compounds that may alter the structure of the soil microbial community and increase the range of organisms capable of metabolising nitrogen-containing organic compounds. This greater diversity and functional redundancy of the soil microbial community may enable the mineralisation of nitrogen associated with the soil organic matter to be maintained after a flood or drought event, when plant demand is restored. This project will track the fate of carbon applied to soils as unary, binary, tertiary and quaternary mixtures of contrasting cover crop residues using by labelling them and determining which members of the soil microbial community incorporate them into their biomass. Pot and field experiments will investigate whether increasing the diversity of cover crop residues incorporated into soils alters the structure of the soil microbial community, increases the potential for the soils to mineralise nitrogen, before, during and after flooding and drought, and increase the delivery of beneficial ecosystem services (crop yield and nutrient use efficiency).