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Description
Introducing service crops into rotations may help to reduce dependency to inputs. Service provision largely depends on biomass production (Vrignon-Brenas et al., 2016b). Relay intercropping into winter cereal may favor conditions for service crop emergence, without impairing cereal yield (Gardarin et al., 2022). Nonetheless, this technique is complex and service crop establishment could fail, preventing its large adoption by farmers. Soil and climate conditions can explain variability of success (Vrignon-Brenas et al., 2016a). It is also the result of competition for resources in a complex system formed by winter cereal, service crop and weeds. This study takes profit from 15 years of experiment on such technique to determine what are the key factors to succeed in establishing the service crop for the provision of expected services.
The database used gathers data from 46 on-farm trials settled in south eastern part of France between years 2008 and 2023. Most of them were organic (39), or in transition to organic (6) or conventional (1). In these experiments red or white clovers were sown as service crops (SC) into a winter cereal (WCC) at the end of winter. A total of 1097 quadrat of 0.25m² sampled at cereal crop harvest were compiled. Cereal, service crop and weeds (W) dry biomass were measured at cereal harvest. A Hierarchical Clustering on Principal Components permitted to determine typical groups of situations. Other data were collected such as crop and weeds density at cereal flowering, characterization of soil, climate and agricultural (crop sequence and management) conditions. A multivariate regression tree (MRT) was built as a first exploration on how these data explained SC biomass variability.
4 groups (G1 to G4) of situations are statistically defined. Mean dry biomass measured at cereal harvest for all groups are 9 T DM/ha, 0.5 T DM/ha and 0.3 T DM/ha for cereal, weeds and clover respectively. G1 represents situations where WCC biomass is high (12.8 T DM/ha) and largely dominant, preventing W and SC to grow (respectively 0.3 and 0.1 T DM/ha in average). In the other groups, WCC biomass is much lower (mean dry biomass of the group of 7.1, 7.7 and 6.2 T DM/ha in G2, G3 and G4 respectively). G2 gathers situations where growth conditions appear to be constraining and total (WCC+SC+Weeds) biomass production is low. G3 situations presented high SC biomass (1.9T DM/ha) and reduced W biomass (0.2T DM/ha). G4 situations are the exact reverse with high biomass of W (3.6T DM/ha) and almost no SC (0.1T DM/ha). The latter gathers few situations (n=54), mainly corresponding to one field trial. MRT suggests that, except in some rare instances where climate conditions are especially favourable, SC biomass is largely penalized first by WCC higher biomass. Clover density at wheat flowering lower than 250pl/m² is also penalizing SC biomass production (n=667). Rainfall accumulation and/or fine soil texture appear to be favourable for this SC density, provided that W infestation is controlled.
Vrignon-Brenas et al (2016a) mentioned a minimum SC biomass of 0.5T DM/ha to ensure weed regulation after WCC harvest. Such SC biomass is rarely observed here while situations with almost no SC biomass at cereal harvest are much more frequent. Competition with WCC appeared to be the first cause of SC failure. The threshold of penalizing WCC biomass determined here corresponds to highly productive organic conditions but reduced conventional ones. It suggests that this technique is poorly adapted in such conditions, at least without changing WCC sowing (e.g. interrow width). Situations of group 4 highlights how important it is that weed infestation is moderate to permit clover establishment. Finally, the analysis we process here suggest that some soil and climate conditions are more favourable for SC establishment and survival. Further analyses are needed to better define these conditions.
Gardarin, A., Celette, F., et al. 2022. Intercropping with service crops provides multiple services in temperate arable systems: a review. Agron. Sustain. Dev. 42, 39. https://doi.org/10.1007/s13593-022-00771-x
Vrignon-Brenas, S., Celette, F., et al. 2016a. Biotic and abiotic factors impacting establishment and growth of relay intercropped forage legumes. Eur. J. Agron. 81, 169–177. https://doi.org/10.1016/j.eja.2016.09.018
Vrignon-Brenas, S., Celette, F., et al. 2016b. Early assessment of ecological services provided by forage legumes in relay intercropping. Eur. J. Agron. 75, 89–98. https://doi.org/10.1016/j.eja.2016.01.011
| Keywords | service crop; on-farm experiment; conditions of success; agroecology |
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