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Intercropping in China: a practice with thousands of years of history

The earliest records for melon/legumes or leeks/legumes intercropping were found in an Agricultural Book authored by Si Shengzhi (Si Shengzhi’s Book) published long time ago in the first century B.C. in China. Therefore, intercropping has been widely practiced by farmers in China for more than two thousands of years (Liu 1994). Intercropping systems of cereals/cereals, grain legume/ cereals, and cereals/vegetables were common in China in the past decades. A total of 25–28 million hectares of intercropping was distributed across all of the provinces in the country except for Tibet and Qinghai Province in the 1980s, and the area reached 33 million hectares in the 1990s (Zou and Li, 2002). In 2008, it was estimated that there was 1.5 million hectares of soybean-cultivated area, which was mainly intercropped with various other crops in southern China (Zhou et al., 2010). Wheat/maize intercropping has been an important cropping system for raising grain yields per unit of arable land in northwestern China. The area under wheat/maize intercropping was 75,000 ha in Ningxia Hui Autonomous Region in 1995, which produced 43% of total grain yields for the region, and there is 200,000 ha of wheat/maize intercropping annually in Gansu, with more than 12 tons of grain yields per hectare in 1990’s (Li et al., 2001; Li et al., 2013). 

Wheat/maize intercropping, Wuzhong，Ningxia Province @CAU

So far, in China, intercropping has been developed into a pattern of high yields (outputs) based on high inputs, which is completely different from the traditional pattern of low input systems producing lower outputs. Intercropping featured with high yields (outputs) based on moderate inputs plays some role in Chinese modern agriculture as a way of reducing environmental negative impacts and improving the efficiency of inputs. Hong et al. (2017) reported that approximately 3% of the arable land area was used for intercropping across a sample of villages across six provinces in China in 2014. The use of intercropping was stable over time, but there was large variation between villages. Hong et al. (2019) found a high prevalence (59%) of intercropping of maize with wheat and other species in Gaotai county in Gansu.

Irrigated area along Yellow River in Gansu province @CAU

Based on the Wan Fang Scholar Database (a Chinese literature database), we found that there were more than 200 hundreds kinds of intercropping (crop combinations), which were distributed throughout China (missing data from Taiwan, Hong Kong and Macao). Generally speaking, intercropping is more diverse in Eastern China than in the West, and more diverse in the South than in the North even if intercropping is widely used.

Intercropping as a theme of research in the China Agricultural University

In the Web of Science Core Collection, based on June 30, 2019, China Agricultural University (CAU) published 183 papers on intercropping or intercrop, which is ranked first, INDIAN AGR RES INST is ranked second, Chinese Academy of Science is ranked third, INRA is ranked fourth, and INT CROPS RES INST SEMI ARID TROP is ranked fifth in terms of publication number. Among the top 5 organizations, both total number of citations and average number of citations per item (4817 and 26.3) CAU are ranked first and INRA (2941 and 21.9) is ranked second. CAU research fields in intercropping included agronomy, plant science, soil science, environmental science, and agricultural multidisciplinary etc. Senior authors included Zhang F.S., Li L., Zhang L.Z. and Zuo Y.M. from College of Resources and Environmental Sciences, and Sui P. and Chen Y.Q. from College of Agronomy and Biotechnology. Research topics comprised above- and below-ground interactions between intercropped species, focusing on mechanisms underlying greater yields and efficient use of resources, such as radiation, thermal, water, nitrogen, phosphorus, iron, zinc.

Peanuts/maize intercropping, North China Plain @CAU

Before 1990s, majority of studies on intercropping had focused on crop combination and above-ground resources (i.e. light and thermal) use by row arrangement and crop species (or cultivar) selection with field experiments. Little attention was paid to belowground interactions and their effects on yield advantage and efficient resource utilization in CAU, even in whole China. Since the 1990s, CAU researchers, together with their collaborators, have worked on many areas of intercropping, especially in below-ground interactions between intercropped species. Five main topics were studied:

1. Cooperation and competitive root distribution in spatial and temporal scales between two species. For instance, faba bean and maize roots are intermingled in the soil profile, whereas wheat and maize roots show avoidance distribution in the soil profiles, provided direct evidence for interspecific facilitation and competition for resources (Li et al., 2006; 2011).
2. Nitrogen complementary utilization in cereals/legumes intercropping. There are two pathways were involved in the N complementary use. On the one hand, cereals are more competitive for soil N, which forces nodulation and symbiotic N2 fixation in intercropped legumes (Xiao et al., 2004; Fan et al., 2006; Li et al., 2009). On the other hand, maize root exudates facilitate nodulation and symbiotic N2 fixation of faba bean by signals in the system (Li et al., 2016).
3. Phosphorus acquisition in intercropping is facilitated when P-efficient species and P-inefficient species grow together, due to P mobilization of insoluble soil P (Li et al., 2003; 2004; 2007).
4. Fe/Zn nutrition of peanuts was improved when peanut was intercropped with monocots species (maize, barley, ryegrass) (Zuo et al., 2000; Zuo et al., 2008; Guo et al., 2014 ).
5. Efficient use in intercropping is derived from niche separation in water requirements between two intercropped species (Mao et al., 2012). 

In summary, CAU teams explored below-ground processes related to efficient water, nutrient use in the past three decades.

Pea/maize intercropping, Northwest China @CAU

China Agricultural University taking part of EU H2020 ReMIX project: how did it happen? What are the expectations from both sides?

There was closely collaborated on PhD students programm supported by CSC Scholarship in past two decades between CAU and Wageningen University and Research Centre (WUR). In 2009, Dr. Wopke van der Werf from WUR invited Professor Long Li and Dr. Lizhen Zhang from CAU to visit to WUR. During the three months of visiting study, colleagues from both sides discussed intercropping knowledge intensively and consequently developed a Sino-Dutch jointly proposal, and submitted to National Natural Science Foundation of China (NSFC). After two years, the proposal was granted by NSFC under the leadership of Prof. Fusuo Zhang. The collaboration on intercropping between two universities have been intensified by the project. Professor Zhang Lizhen and Professor Wopke van der Werf focus on above-ground interspecific interactions in intercropping, especially in modelling of radiation use, while Professor Long Li and Dr. Chaochun Zhang focus on below-ground interspecific interactions in intercropping. When ReMIX started to develop the research proposal, Chinese colleagues were invited to participate to the project. Although there is no funding allocation to CAU from European Commission and that no grant was acquired from the Chinese part, Professor Long Li and Dr. Chaochun Zhang are actively involved in the activities of ReMIX, and many joint activities between CAU and Wageningen University contribute to ReMIX objectives, e.g. the empirical study of species complementarities in cereal/legume intercropping, and the analysis of the contribution of plant trait complementarities to intercrop performance, based on modelling.

Different combinations of intercropping, Lishu, Jilin Province @CAU

China Agricultural University expects from ReMIX to provide more opportunity for student training, international exchange and project funding. While ReMIX expects that CAU will provide more original research ideas, since CAU engaged more in production practice.

Results after two years of project development

The cooperation between China Agricultural University and ReMIX has yielded remarkable and important results. Professor Long Li attended kick-off meeting and annual meeting in Toulouse, France, and Pamplona, Spain, and shared intercropping research progress in China. Professor Long Li and Dr. Chaochun Zhang also participated to workshops in Wageningen University, organized by Professor Wopke van der Werf in 2018 and 2019. Dr Eric Justes (scientific coordinator of the ReMIX project) visited Prof. Long Li at CAU in Beijing in July 2018, and will probably return in October 2019 for a one week modelling courses. As a result of regular contacts and a close scientific collaborations between CAU and WUR, an article was written jointly by ReMIX participants, entitled as “Designing species mixtures for high yield, yield stability and efficient use of resources: are there principles?” is provisionally accepted in Advances in Agronomy.

Part of the team from the China Agricultural University involved in intercropping research @CAU

References

Fan, F. L., F. S. Zhang, Y. N. Song, J. H. Sun, X. G. Bao, T. W. Guo and L. Li (2006). "Nitrogen fixation of faba bean (Vicia faba L.) interacting with a non-legume in two contrasting intercropping systems." Plant and Soil 283(1-2): 275-286.

Guo, X. T., H. C. Xiong, H. Y. Shen, W. Qiu, C. Q. Ji, Z. J. Zhang and Y. M. Zuo (2014). "Dynamics in the rhizosphere and iron-uptake gene expression in peanut induced by intercropping with maize: Role in improving iron nutrition in peanut." Plant Physiology and Biochemistry 76: 36-43.

Hong Y., Heerink N.B.M., Jin S.Q., Berentsen P.B.M., Zhang L., van der Werf W.(2017) Intercropping and Agroforestry in China; Current State and Trends. Agriculture, Ecosystems and Environment 244, 52–61.

Hong, Y., Heerink, N., Zhao, M.J., van der Werf, W (2019) Intercropping contributes to a higher technical efficiency in smallholder farming: Evidence from a case study in Gaotai County, China. Agricultural Systems 173: 317–324. http://dx.doi.org/10.1016/j.agsy.2019.03.007

Li L., Zhang L.Z, and Zhang F.S. (2013). “Crop Mixtures and the Mechanisms of Overyielding”. In: Levin S.A. (ed.) Encyclopedia of Biodiversity, second edition, Volume 2, pp. 382-395. Waltham, MA: Academic Press.

Li, B., Y. Y. Li, H. M. Wu, F. F. Zhang, C. J. Li, X. X. Li, H. Lambers and L. Li (2016). "Root exudates drive interspecific facilitation by enhancing nodulation and N-2 fixation." Proceedings of the National Academy of Sciences of the United States of America 113(23): 6496-6501.

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Li, Y. Y., C. B. Yu, X. Cheng, C. J. Li, J. H. Sun, F. S. Zhang, H. Lambers and L. Li (2009). "Intercropping alleviates the inhibitory effect of N fertilization on nodulation and symbiotic N-2 fixation of faba bean." Plant and Soil 323(1-2): 295-308.

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