Monitoring and metrics to boost circularity in horticulture

Tracking production processes is strategic to monitor productive factor streams and improve crop sustainability by maximization of resource circularity in horticultural systems. The latter concept implies that production waste and waste streams are efficiently minimized or totally removed from the system thus maximizing material value through its reuse and recycle. The definition (what), the characterization (quality) and the quantification (amount and timing) of both inputs and outputs are the basal information to reach high degree of circularity and consequently economic and environmental sustainability in intensive horticultural cropping systems such as greenhouse horticulture. On the contrary, lack of proper monitoring of the cultivation process can lead to excess costs, waste, low input use efficiency, and poor produce quality with lower incomings and higher environmental burdens. In this context, we must precisely define what is important and useful to be accounted and monitored taking into consideration a set of performance indicators directly related to: i) crop management (e.g., water quality, salt or agrochemical accumulation in the system, substrate status), ii) input factor use (e.g., water, agrochemicals, energy quantity per product unit), iii) output factors (e.g., wastewater) and boundary conditions (e.g., indicators for material flow analysis, life cycle assessment). A potential approach consists in grouping same subjects into clusters, i.e., similar farm types in the same area with similar agro-ecological conditions and needs, to have a standardized reuse of waste (e.g., drainage water, substrates, plastics, etc.). Metrics and indicators should be also based on crop type and geographic area (i.e., Southern vs Northern Europe, dry and wet climatic conditions), from which mostly depend the different product and factor use on the medium-long period. This allows to annually assess progresses or inefficiencies in the input-output use against more global targets/standards of efficiency (e.g., water and carbon footprint). This paper provides an overview of possible metrics, indicators and available technologies to support measurements in order to increase circularity in intensive greenhouse horticulture. Major critical gaps and opportunities, which can contribute for a wider implementation of recycling and reuse activities and processes, are also discussed taking into account a heterogeneous scenario (i.e., high tech vs low tech, crops, growers' needs and know-how) of the European greenhouse horticulture.