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Introduction: Relay-cropping is a crop association where the implementation and harvest of the crops is delayed, leading to an asynchronous cycle of development. It enhances land productivity with two separate harvests in a year (Lamichhane et al. 2023). The main constraint of relay-cropping is the competition endured by the second crop (i.e., soybean) from the winter cereal, leading to yield losses that can range from insignificant to over -90 % (Wallace et al. 1996; Sandler et al. 2015) depending on climatic conditions. Soybean's sensitivity to water stress necessitates the development of more resistant genotypes, particularly in the context of increasing drought events and intercropping systems. To advance knowledge in this area, we conducted in situ experiments exploring soybean functional traits responses to relay-cropping and water stress under low irrigation as well as controlled conditions experiments to quantify their hydraulic resistance to water stress.
Materials and Methods: Five years of preliminary trials were conducted in southwestern France, on a farm experienced in soybean cultivation under irrigated conditions. Yields of pure and relay crops and land equivalent ratio (LER) were assessed every year. Two years of field experiments under non-irrigated conditions were performed in northern France of barley/soybean relay-cropping with four soybean contrasted genotypes . Root functional traits (mass ratio, specific length, length density, angle and nodules) were measured at barley harvest and one month after to assess the plasticity of the genotypes to relay-cropping and water stress. In controlled conditions hydraulic traits including vulnerability to embolism and residual transpiration were measured on ten contrasted soybean genotypes to quantify their resistance to drought compared to other crops and the variability among genotypes.
Results: The irrigated trials in southern France demonstrated the productivity potential of relay-cropping with a mean LER of 1.62. The cereal is not impacted by the relay-cropping, while soybean present a mean yield loss of 25 % compared to pure soybean. In northern France field trials, we demonstrated that relay-cropping can exacerbate drought stress and, consequently, competition for water between crops, leading to phenological delay and growth abortion. However, root functional traits like lateral root mean angle and specific root length were higher in relay-cropping. The experiments in controlled conditions showed that the soybean is sensitive to embolism, but the genotypes presented wide variations of resistance to embolism of 1 MPa between the most resistant genotype and the less resistant. Hydraulic segmentation was observed in soybean and petiole was highlighted as a hydraulic fuse, being more vulnerable to embolism.
Discussion: Relay-cropping increases competition for water between both species and impact the performances of the soybean. Irrigation appears as mandatory to allow soybean to sustain the competition with the cereal, specifically during the emergence and vegetative growth as they are critical stages of soybean development in relay-cropping. The soybean genotypes in relay-cropping treatments presented higher root mass ratio from 10 to 32 %. Higher specific roots length and lateral root angle indicated longer, thinner, and vertically oriented roots to favour water acquisition. The highlight of root traits plasticity brings new perspectives to identify and select appropriate genotypes for relay-cropping (Schneider and Lynch 2020). Characterisation of adapted genotypes to relay-cropping requires also to quantify the genetic variability of soybean to drought resistance notably by focusing hydraulic traits. Whereas soybean is sensitive to water stress compared to other crops, the genetic variability allows to select more resistant genotypes. Correlation between embolism resistance and the relative performances of soybean (data from Terre Inovia 2020 to 2022) genotypes shows that this trait offers prospects for improving genotypes.
References:
Lamichhane JR, Alletto L, Cong W-F, et al (2023) Relay cropping for sustainable intensification of agriculture across temperate regions: Crop management challenges and future research priorities. Field Crops Res 291:108795. https://doi.org/10.1016/j.fcr.2022.108795
Sandler L, Nelson KA, Dudenhoeffer C (2015) Winter Wheat Row Spacing and Alternative Crop Effects on Relay-Intercrop, Double-Crop, and Wheat Yields. Int J Agron 2015:e369243. https://doi.org/10.1155/2015/369243
Schneider HM, Lynch JP (2020) Should Root Plasticity Be a Crop Breeding Target? Front Plant Sci 11:. https://doi.org/10.3389/fpls.2020.00546
Wallace SU, Bacanamwo M, Palmer JH, Hull SA (1996) Yield and yield components of relay-intercropped wheat and soybean. Field Crops Res 46:161–168. https://doi.org/10.1016/0378-4290(95)00009-7
| Keywords | competition; crop association; hydraulic traits; water stress; root plasticity |
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