Tracking ideal varieties and cropping techniques for agroecological weed management: a simulation-based study on pea

Book of abstract p.110-111International audiencePea (Pisum sativum L.) is a key diversification crop but current varieties are not verycompetitive against weeds. The objective of this study was to identify, depending on the typeof cropping system and weed flora, (1) the key pea parameters that drive crop production,weed control and weed contribution to biodiversity, (2) optimal combinations of peaparameter values and crop-management techniques to maximise these goals. For this, virtualexperiments were run, using FLORSYS, a mechanistic simulation model (Colbach et al., 2021,Field Crops Res 261:108006). This individual-based 3D model simulates daily crop-weed seedand plant dynamics over the years, from the cropping system and pedoclimate. Here, thismodel was parameterized for seven pea varieties (Cameor, China, DCG0449, Enduro, Isard,Kayanne, 886/1), from literature and experiments. The latter focused on potential plantmorphology and shading response. Differences between varieties depended on the analysedparameter, e.g., varieties were very similar in terms of leaf biomass ratio (LBR, leaf biomassdivided by above-ground plant biomass) whereas specific leaf area (SLA, ratio of total leaf areadivided by total leaf biomass) at early stages was lower for the two tested spring varieties(Cameor and Kayanne) than for the five winter varieties (except Isard). Then, ten virtualvarieties were created by randomly combining variety-parameter values according to a LatinHypercube Sampling (LHS) plan, respecting parameter ranges and correlations observed in theactual varieties. A global sensitivity analysis was run, using another LHS plan to combine peavarieties, crop rotations and management techniques in nine contrasting situations (e.g.,conventional vs organic, no-till, type of weed flora). Simulated data were analysed withclassification and regression trees (CART). We highlighted (1) Parameters that drive potential(weed-free) yield and competitivity against weeds, depending on variety type (spring vs.winter) and cropping system. These are pointers for breeding varieties to regulate weeds bybiological interactions; (2) Rules to guide farmers to choose the best pea variety, dependingon the production goal and the cropping system; (3) The trade-off between increasing yieldpotential and minimizing yield losses due to weeds when choosing pea variety andmanagement, especially in winter peas. In short, any parameter values that delayed and/orreduced crop emergence decreased potential yield and increased yield loss due to weeds.Conversely, parameter values that increased crop canopy volume (e.g., large LBR duringreproduction stages) and crop growth duration (e.g., delayed flowering onset) had theopposite effect. Shading response was crucial: the more pea varieties increased plant heightand leaf biomass per unit biomass when shaded, the better they controlled weeds. These mainrules describing pea ideotypes were the same for all performance goals, managementstrategies and analyses scales. But the key parameters depended on variety type and aims.For instance, parameters driving germination and pre-emergent growth were crucial for111reducing yield loss in winter pea but not in spring pea or for potential yield. Some varietyfeatures only fitted to particular systems, e.g., parameters delaying pea emergence were onlybeneficial in case of herbicide-spraying and disastrous in unsprayed systems.The more the grown variety differed from the weed-controlling ideotype, the moremanagement rules were needed to compensate. Conversely, if one of the two main weedcontrol levers, herbicide or tillage, was missing from the cropping system, the choice of thepea-variety and/or of other management levers became more important. We are nowapplying this methodology to identify ideal trait combinations for wheat-peaintercrops.FundingINRAE, ANR PeaMUST (ANR-11-BTBR-0002), EU Horizon 2020 (N 727217 ReMIX), FrenchMinistry of Agriculture and Food (CADAR RAID)