Speaker
Description
Introduction
Crop diversification in time and space, e.g. through crop rotation, intercropping and cover crops, have been shown to promote ecosystem services such as pollination, biological pest control and soil fertility, thereby reducing input dependency and mitigating agriculture’s negative environmental impacts (Kremen et al. 2012; Tamburini et al. 2020). Diversification via intercropping and cover crops is typically evaluated based on impacts directly on the studied diversified crops, but less is known about long-term legacy effects of these practices on subsequent crops in the rotation (Rodriguez et al. 2021). Little is also known about possible changes in such effects over time. We used a field experiment comprising two organically managed crop rotations to evaluate the effects of cover crops and intercropping in previous crops on grain yields, yield stability and weed abundance in three sole crops that were included in both rotations.
Materials, methods
A crop rotation field experiment was established in 2018 at the Swedish University of Agricultural Sciences (SLU), Alnarp, in southern Sweden (55°39′21″N, 13°03′30″E) on organic land managed by the Swedish Infrastructure for Ecosystem Sciences (SITES) field research station Lönnstorp. The experiment was initiated within the Horizon project DiverIMPACTS (2017-2022; www.diverimpacts.net), and consists of one reference and one diversified crop rotation. Both rotations contain the same six main crops ( add-on in the diversified rotation in parentheses): 1. winter oilseed rape (intercropped with frost-sensitive faba bean); 2. winter rye (followed by a buckwheat/lacy phacelia cover crop); 3. oat (intercropped with lupin) undersown with red clover; 4. red clover for seed harvest; 5. winter wheat (followed by a vetch/oilseed radish cover crop); and 6. spring pea (intercropped with spring barley). Each crop was present each year and replicated in four randomized blocks.
In both rotations, all crops except red clover and pea (and the pea/barley intercrop) received organically certified fertilizers, but at lower rates in the diversified rotation where the legumes in intercrops and cover crops were expected to contribute with additional N2 fixation. In total, crops in the diversified rotation received 33% less N than the reference rotation. To investigate the legacy effects of crop diversification in the crop rotation, we studied differences in grain yields and weed biomass in the three crops that were grown as sole crops in both rotations: winter rye, red clover and winter wheat. We used the coefficient of variation (CV) as an indicator of yield stability over the five years for grain yield of each crop.
Results
There were no statistically significant differences in gran yield or weed biomass between the reference and diversified rotations, for any of the studied crops. Although yields differed between years, there was no pattern of increasing or decreasing differences between the two rotations over time (Fig. 1 shows the example of rye). The CV was higher in the diversified than in the reference rotation for rye (31 vs 23 %) and clover (39 vs 29 %) , while the CV differed less in wheat (32 % in diversified vs 30 % in reference).
Discussion
The lack of differences in grain yields of the sole crops indicates that the crop diversification practices tested here did not create beneficial legacy effects via increased soil fertility or reduction of pests and weeds. At the same time, similar yields despite lower fertilization rates (including the studied crop rye, which received less fertilizer in the diversified rotation) confirms the beneficial effects of crop diversification, enabling input reduction without losing yield (Tamburini et al. 2021). Yields appeared to vary more in the diversified rotation, indicated by higher CV, which calls for further research to investigate possible causes of increased yield variations in diversified cropping systems.
We acknowledge the SITES Lönnstorp field research station for management of the experiment.
References
Kremen, C., Iles, A., Bacon, C. (2012). Diversified farming systems: an agroecological, systems-based alternative to modern industrial agriculture. Ecol. Soc. 17:44.
Rodriguez, C., Dimitrova Mårtensson, L.-M., Jensen, E.S., Carlsson, G. (2021). Combining crop diversification practices can benefit cereal production in temperate climates. Agron. Sustain. Dev. 41:48.
Tamburini, G., Bommarco, R., Wanger, T.C., Kremen, C., van der Heijden, M.G.A., Liebman, M., Hallin, S. (2020). Agricultural diversification promotes multiple ecosystem services without compromising yield. Sci. Adv. 6: eaba1715.
| Keywords | Cereals, Crop rotation, Diversification, Legumes, Yield stability |
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