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Cover crops (CCs) are known to improve soil fertility and cash crop performances. Introducing CCs mixtures is a promising approach to increase multifunctionality of the ecosystem services provided by CCs. However, the effect of CC mixtures on subsequent crop yield remain contrasted. Indeed, the extent to which yields are increased by CCs depends on the type and management of CCs, the type of cash crop, the application of fertiliser to the cash crop, the soil and climatic conditions. In the context of climate change, drought is a major environmental factor that limits crop growth, photosynthesis and yield. Sunflower, which is adapted to environments with low N and water requirements, has different drought-tolerance strategies, depending on the variety. However, little is known about the variability in the response of drought-tolerant sunflower varieties to CCs in low-input systems.
The study’s aims were to characterise CC ecosystem services mainly related to C, N and water and how ecosystems services of CC influence responses of sunflower varieties that differed in drought sensitivity. CC and sunflower varieties were organized in a randomized non-complete block design with a split-plot arrangement in 2021-2022 and 2022-2023. CC treatments consisted of a pure grass CC (rye), a mixture of legume CC (purple vetch/fodder pea), 3 mixtures of legume and non-legume CC (faba bean/white mustard/phacelia; fodder pea/rye/ purple vetch and faba bean/indian mustard/phacelia) and a relay CC treatment (forage sorghum then faba bean). The control of CC treatments is a bare soil kept free of weeds mechanically by two passes of a cultivator during intercrop. Sunflower varieties had different drought tolerance strategies for leaf expansion (LE) and transpiration (TR): a conservative strategy for LE and TR (MAS 86OL), a conservative strategy for LE and productive strategy for TR (MAS 89M), a productive strategy for LE and a conservative strategy for TR (MAS 98K) and a productive strategy for LE and TR (CARRERA CLP). Implantation, development, growth, N statue and productivity were evaluated on sunflower varieties preceded by CCs by low- and high-throughput phenotyping measurements. Various variables of growth and development were based on image processing tools using UAV RGB images.
The results indicate that CCs affected late N release absorption by sunflower, increasing the seed filling period. Indeed, maturity stage was delayed by an average of 194 °C.d for Faba bean/Mustard/Phacelia in 2021-2022 and 344 °C.d after Pea/Rye/Vetch in 2022-2023, compared to Faba bean/Forage sorghum and bare soil, which can lengthen grain filling period by average of 342 °C.d in 2022-2023 (equivalent to 17 days in average).
Optimized choice of CC allows equivalent yields to intensively tilled bare soil, while increasing carbon restitution and weed control in low-input agricultural systems. Mixtures with C:N ratio lower than 19 were composed of more than 60 % of legume species biomass led to early and high N uptake from the vegetative stage while other CCs with higher C:N ratio composed of legume and non-legumes led to late and high N uptake after flowering. The composition of CCs led to higher yields compared to other CC treatments but similar yields to intensively tilled bare soil. However, in a multifunctional approach to the ecosystem services provided by CCs, carbon restitution and weed control were higher after CCs than after intensively tilled bare soil. Moreover, these results are similar to those of the study of Ait-Kaci et al. (2022) which showed no clear trend of sunflower yield increase after CC mixture with legume in a four-year field experiment.
Sunflower growth can be improved by optimizing the choice of CC and sunflower varieties. During the drought year, higher biomass was observed for productive sunflower for leaf expansion in presence of early and late N release by CCs. Our results can guide sunflower variety selection and CC type and management in low-input systems to better match N release from CC residues with subsequent cash crop response during vegetative and post-flowering phases. Further research is needed to understand the responses of varietal traits to the agroecological system.
Ait Kaci Ahmed, N., Galaup, B., Desplanques, J., Dechamp-Guillaume, G., Seassau, C., 2022. Ecosystem Services Provided by Cover Crops and Biofumigation in Sunflower Cultivation. Agronomy 12, 120. https://doi.org/10.3390/agronomy12010120
| Keywords | Agroecological transition ; Climate change adaptation ; Climate change attenuation ; Drought ; Ecosystem services |
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