Ecological Intensification and the sustainable use of fertilisers

Ecological Intensification (EI) is defined as the enhancement of ecosystem services to complement or substitute for the role of anthropogenic inputs in maintaining or increasing yields. EI interventions (sometimes otherwise known as ‘nature based solutions’) that potentially maintain soil fertility and improve the efficiency of nutrient cycles include the use of legumes, organic amendments (manures, living and dead mulch) and the integration of livestock. As opposed to yield response to mineral fertilisers that are manifested in the short term and are relatively consistent, the benefits of EI can be cumulative, long term and vary depending on other components of the cropping system and environment. Long Term Experiments (LTEs), for example the 180 year old Broadbalk winter wheat experiment at Rothamsted, are valuable platforms for elucidating these effects. We report on a large analysis that combined 25,565 yield records from a range of staple crops from 30 LTEs from Europe and Africa. The study found consistent effects of crop diversification (particularly the addition of legumes) and organic amendments on yield with mixed effects of changes in tillage. The effect of EI on yield was dependent on whether combinations of interventions were applied and the rate of mineral fertilisers used on the plots – EI interventions were largely substitutionary as opposed to being additive. EI, therefore, has a role in supporting the reduction of mineral fertiliser use where high rates are having negative environmental inputs and supporting yields where access to mineral fertilisers may be restricted by cost or availability. The results highlighted the need to take a systems level approach to analysing the benefits of EI. The implications of this for the design of future field experimentation are discussed in the context of a new LTE that was established at Rothamsted in 2017 to complement the historical experiments.