Syndromes of production in intercropping impact yield gains

By Chunjie Li and Wopke van der Werf.

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Intercropping is the mixed cultivation of crop species on the same field. Intercropping is widely used by smallholder farmers in developing countries and is gaining increasing interest in developed countries. Intercropping may contribute to the sustainable intensification of agriculture because it offers weed suppression, pest and disease control, efficient use of light and conservation of soil resources, and yield increase. Land sparing is the most obvious advantage of intercropping, which is usually quantified by the land equivalent ratio (LER). LER does not represent the size of the yield increase in intercropping but the relative gains in the use efficiency of land. We therefore focused on another metric for intercropping yield advantage, the net effect. The net effect characterizes the yield increase achieved in intercrops compared to the expected yields when taking into account the sole crop yields of the intercropped species and their share in the mixture.

Many field studies on intercropping for grain production have been done in China over the past thirty years. This has resulted in ample data on intercropping from China. We first did a meta-analysis based on the intercropping studies from China (Li et al., 2020). We then merged this dataset with another, global, dataset on yield in intercropping (Yu et al., 2015) and found that the yield gain of intercrops in China was four times as high as outside China. Then we analyzed why there was such a large difference in the yield gain between the two data sets.

We found that no single factor could account for the difference in yield gain between the two datasets. Instead, we could distinguish two syndromes of production in intercropping, where each syndrome is characterized by the selection of species (with or without maize), the temporal complementarity between species (simultaneous growing period or temporal niche differentiation), the use of strip intercropping or of fully mixed or row intercropping, and the fertilizer input. Thus, a syndrome of production was characterized by a set of management practices. 

Intercropping of wheat/maize in China (photo credit: Fusuo Zhang) and intercropping of durum wheat/winter pea in France (photo credit: Laurent Bedoussac)

These two syndromes of production address different production objectives. On the one hand, systems with maize, commonly used in China, represent a strategy of intercropping based on high inputs, high outputs, and a comparatively large intercropping advantage in terms of absolute yields per hectare. These systems are based on strip intercropping with narrow strips (usually in the order of 1-2 m wide), and a relay sequence in the sowing and harvesting of the intercropped species. On the other hand, systems without maize were often cultivated with low inputs, and had substantially lower intercropping benefits in terms of absolute yield per hectare. These intercropping systems were usually grown as simultaneous intercrops, with simultaneous sowing and harvesting of the two species, and with the species grown most often in alternate rows or completely mixed, but not often in strips. This type of system addresses the aim of developing an agricultural system that exploits species complementarities to drastically lower inputs, but these systems had lower outputs than the systems of the first syndrome.

Intercropping systems under both low and high input conditions can save resources, which contrasts with the classical view that intercropping with legumes provides major intercropping advantages especially at low levels of input. The advantages of the two syndromes of production in intercropping uncovered by this meta-analysis confirm that intercropping increases outputs and saves fertilizers in both low and high input systems. We think these results are encouraging, as intercropping can ensure food security while reducing the environmental impact of agriculture in different socio-economic settings.  

Link of the paper: https://www.nature.com/article...

References

Li C, Hoffland E, Kuyper TW, Yu Y, Li H, Zhang C, Zhang F, van der Werf W (2020) Yield gain, complementarity and competitive dominance in intercropping in China: A meta-analysis of drivers of yield gain using additive partitioning. European Journal of Agronomy 113:125987. https://doi.org/10.1016/j.eja....

Yu Y, Stomph T-J, Makowski D, Van der Werf W (2015) Temporal niche differentiation increases the land equivalent ratio of annual intercrops: A meta-analysis. Field Crops Research 184, 133-144. https://doi.org/10.1016/j.fcr....     

Chunjie Li

PhD, China Agricultural University

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