mixed cropping in Burma

Growing crops as mixtures of different species in the same field was commonplace in Britain during the Improvements era but gradually fell out of favour in the 19oos as single crops became easier to manage and could command a high value on the grain market. ‘Grass seeds’ in the 1700s often meant not just one or more grass species, but a mix of a grass, a clover or several legumes and another species such as ribwort plantain. A cereal (corn) and a nitrogen fixing legume (pea) were also broadcast over the same field, as were mixtures of different cereals.

Mixed cropping is now being reconsidered in northern Europe as a possible means to producing the same with less input of fertiliser and pesticide. In our most recent outing, at the December 2016 meeting of the British Ecological Society, Pete Iannetta talked about the benefits of a barley-pea intercrop grown at the Institute (links at Latest). But for inspiration we can look to other places.

Mixed cropping is still widespread in the tropics, but the reasons for planting different species close together, sometimes in strict spatial patterns, are not always obvious. The scientific tendency is usually to look for a biophysical mechanism behind the pattern. Perhaps the two or more species take resource from different parts of the environment or use the resource more efficiently. Mixed cropping works – the two species together tend to produce 1.1 to 1.3 (110 to 130%) times the equivalent yield of the crops grown alone.

This is a useful but not a great advantage, and it may well be that the plants are grown in mixtures for other reasons also. Sometimes the arrangement might arise simply out of convenience or as a means of lowering the risk of not putting all your eggs (i.e. the few seed of one crop) into one basket (i.e. a small area of soil).

This mixed cropping, named intercropping when the plants are in rows, was frequently observed on a self-funded trip to Burma (Myanmar) during the dry season of 2014. Our interpreter, knowledgeable about local farming, was still not always able to explain what was behind the crop configurations.

Planned intercrops

The biophysical basis of the intercrop was best appreciated for perennial plants such as the pigeon pea Cajanus cajan grown at Bagan with cotton, probably one of the shrubby species, and another plant that had shrivelled to unrecognition in the dryness. The pigeon pea would have fixed and released nitrogen to the soil for the cotton to take up. In some fields, the pea had recently been cut back to stop it using water, whereas the cotton, most likely deep rooting, was in full flower and fruit and using the water and nutrients stored in the ample soil-space between cotton rows.

On the banks of the Irrawaddy, highly regimented rows of groundnut Arachis hypogaea had maize Zea mays sown within every 5th row (image below). The land would have been awash as the river rose in the wet season, when presumably the silty soil, and any nitrogen fixed previously by a legume, would have been picked up in the current and deposited somewhere else.

The crops were therefore growing on nutrient-rich alluvium and soil-stored water. The maize was starting to flower but the groundnut was still in leaf only. It was unlikely that this year’s N fixation by the groundnut would have ‘leaked out’ so early in its growth. Rather, the maize was taking advantage of additional resources, sunlight above ground and residual soil nitrogen from the bordering rows.

Elsewhere, a field of the nitrogen-fixing chickpea Cicer arietinum had been planted with widely spaced rows of sunflower Helianthus annuus.  The sunflower would have benefitted as the maize in the previous example, but it was difficult to see the advantage to the chickpea. Possibly, the farmers wanted some sunflower seed or oil and grew a few plants in what was otherwise a chickpea field.

But why plant in rows …? Rows are generally easier to establish with animal-drawn implements than are small blocks of crop. Intercrop rows also make it more difficult for a farmer to lose a large proportion of one or other species. Repeatedly, patches of a few square metres occurred in the intercropped fields where the crops were stunted or dead, probably due to poor soil or disease. Planting in rows allows both crops to experience the whole field, its good and bad parts.

Unplanned(?) intercrops

In a further set of configurations, the growers appeared not to have planned the mixture. Rather, they took advantage of a situation in which other species emerged with the sown crop.

One such was a small plot of groundnut in which plants of the Chenopodium genus (probably C. album) were growing in a random configuration. Someone nearby, who knew the practice, said that Chenopodium appeared whenever groundnut was grown. It probably emerged from the soil seedbank, stimulated by conditions peculiar to groundnut cultivation. It was encouraged – the ‘weed’ is widely used as a salad vegetable, as it was once in Britain.

Another example was a field of groundnut again, but one that appeared invaded by two or three other species. Chenopodium was there again but also maize and sunflower, and each was located irregularly, not in rows. The groundnut had been sown but the others, including the two crops, had emerged from the soil seedbank. They were ‘volunteer’ weeds, and had been left, not weeded out.

Multiple crops

In Shan agriculture, a mixed crop new to my experience was one of taro Colocasia esculenta, ginger (Zingiberaceae, species uncertain) and chillie, species of Capsicum. It was easy to walk past the field, because the chillies had been harvested and the taro tubers and ginger were mostly invisible underground.  This was an intentional mixed crop. There would have been biological interactions between the three, but perhaps the main advantage was one of getting three crops from the same bit of land in one year – the chillies first, finally the taro.

Repeatedly, crops were seen growing in intended and apparently random configurations. Fruit trees were grown in small orchards, where they usually had an understorey of legumes or mustards. Fruit trees were also dotted around the landscape, enjoying the benefit of nearby fixers and fumigants.

Palms were common, often grown in lines or groves within the general mix of annual cropping. On the high land, fruit and beverage trees were commonly grown in planned (tea and oranges) or semi-random configurations.


This brief experience, over only a few weeks, introduced the sheer diversity of crops and farming methods here, the ubiquity of legumes, the widespread use of ‘wild’ plants, and the frequent desegregation of the sown and the wild.

Perhaps the lasting impression is one of nitrogen-fixing legumes being among the commonest crops, essential to the mix, whereas in north-west Europe, they have been reduced to minor status.

In some areas, the people had a very advanced understanding of how plants complement each other and together provide human dietary needs, an understanding that has almost lapsed in mainstream farming in north west Europe.

Subsequent pages will deal in more detail with (2) perennial pigeon pea-cotton at Bagan, (3) groundnut-maize by the Irrawaddy and chickpea-sunflower near Mandalay and (4) assorted mixtures which may or may not have any biological advantage.

Sisal plants in the foreground, grown for the fibres in their leaves. The small trees just behind them have been pruned, with one ‘lung’ (a leafy branch) remaining.
Author’s note and further reading

We visited Burma, not in any official capacity, but as ‘tourists’. I had intentionally not read any of the reports from international development agencies before going there, wanting instead to get a first-hand (even if fleeting and random) feel for the soil, people, plants and agriculture. Many of the reports read since have seemed to me to be a bit impersonal, not fully accepting and promoting the great ingenuity and knowledge of the people who live and farm there.

We were more than fortunate to be guided during a crucial part of the visit by Ei Ei Lin (or Lin Latt). Her farming background and natural curiosity introduced us to many hidden wonders of (plant) life in the dry season.

For factual and largely non-judgemental information, the following report offers much on the conditions in Burma’s dry zone:

Improving water management in Myanmar’s Dry zone – for food security, livelihoods and health. 2015. International Water Management Institute (IWMI) 52 pages. doi:10.5337/2015.213. Based on 3 reports published in 2013. http://www.iwmi.cgiar.org/Publications/Other/Reports/PDF/improving-water-management-in-myanmars-dry-zone-for-food-security-livelihoods-and-health.pdf?

Books read during the visit included (and both freely available in bookshops there):

Aung San Suu Kyi. 2010. Letters from Burma. Penguin.

Emma Larkin. 2006. Finding George Orwell in Burma. Penguin Random House.

why so few estimates of nitrogen fixation?

A recent open-access paper Iannetta et al. 2016 gives a comprehensive account of the contribution of legume crops and forages to the nitrogen cycle in temperate agriculture.

Iannetta et al. 2016. A comparative  nitrogen balance and productivity analysis of legume and non-legume supported cropping systems: the potential role of biological nitrogen fixation. Frontiers in Plant Science, 21 November 2016 http://dx.doi.org/10.3389/fpls.2016.01700

Using data from existing field experiments across Europe, nitrogen fixation by legumes was estimated as a residual when other main fluxes of N were accounted for. Annual fixation ranged from 30 to 115 kg/ha of nitrogen. For comparison, the upper figure is a little higher than the fertiliser N given each year to spring cereals.

Why are these figures important? There’s a dearth of estimates or measures of biological N fixation in north temperate agriculture. But while such information is essential for designing sustainable systems, it is not in itself considered to be high-profile (and therefore fundable) science.

Hence the need to add value to existing datasets to get these first estimates. Work is in progress to measure actual fixation rate in arable fields.

Hutton Agroecology group contributions to this paper are as follows. Pete Iannetta developed the overall concept and fronted the paper. Graham Begg designed and led the statistical analysis and modelling. PI, GB and Mark Young carried out the N balance calculations. Geoff Squire and Euan James offered specialist insights.

Page 2 gives some background to the article.

Images: the red clover looked to be part of a natural patch (i.e. not sown) growing locally; the vetch root and nodules were unearthed on a field trip in Attica, Greece during the EU Legume Futures project.

the contribution of european funding

Leaving the EU will have strong and lasting implications for research, mostly negative. The present contributions of EU funding have been well presented elsewhere [1]. For a research group such as ours that has relied in recent years on EU projects for funding and development, leaving will have very serious consequences.

The benefits are not just the money that pays wages and buys lab and field gear, but the contacts, networking and the shared facilities. A group based on the fringes of the atlantic zone can share field sites and data in the Mediterranean, Continental, cold Boreal and Balkan regions; and scientists there can get access to our sites and data in return. The people you work with tend to have similar aims and ideals but work under different constraints, which sometimes make you appreciate your own.

If you gel with your contacts, they will invite you into other projects and vice versa. The bigger organisation may have the structures and attitude to manage multi-partner grants, and while they will get more money for doing the managing, it takes the burden off the smaller player. Working across Europe has been good for us.

Geneflow and seed persistence

Our first major EU project, SIGMEA [2] 2004-2007, examined the movement and persistence of genetic material in the environment. The particular emphasis was coexistence between GM and conventional crops, but the biological and physical principles are the same whatever sort of impurity is under scrutiny.

By the start of SIGMEA, we had already created a european lead in geneflow and persistence by combining whole plant biology, genetic detection, spatial-temporal modelling and statistics to examine scales from gene to landscape. Our role in SIGMEA was to coordinate work across a range of EU sites and to collate and analyse data in a systematic way though common protocols. In total, with >20 partners contributing, the project amassed >100 site-years of data. Nothing like this had been done before. The conclusions reached, by being agreed by all partners, had credibility and held sway in a contentious arena [2].

SIGMEA brings good memories: friendships made that lasted – it opened a way into Europe and eventually more EU funding.

Legume-based cropping systems

By around 2007, our sources of UK national funding had almost dried up (for various reasons) and we were in danger of being without external (i.e. non-Scotland) income. Then in a timely manner, Pete Iannetta helped form the successful Legume Futures consortium which was headed by Bob Rees of SAC (now SRUC).

Legume Futures [3] encouraged us to look at ways to design production systems that would optimise a range of functions, such as soil fertility, food web support, mineral N replacement as well as yield. We continue now improving the principles of design that began here.

Legume Futures [3] also brought together for analysis a range of field experiments from which colleagues were able to estimate the contribution of biological fixation to the nitrogen economy of cropping (see Why so few estimates of nitrogen fixation?).

Integrated Pest Management – PURE and ENDURE

Contacts from SIGMEA and other collaborations led to our involvement in EU PURE on integrated pest management [4]. PURE was the largest EU grant awarded for an agricultural project. I remember sitting in a room in Paris where the putative bid partners divvied up the responsibilities in advance of the bid going in. It was tricky negotiation.

Months later, the proposal, headed by INRA France, was favoured and the grant was secured. Agroecology@hutton had a major role (and Workpackage) in landscape scale processes, as well as other contributions. Graham Begg fronted the landscape scale developments and Nick Birch organised the Hutton input as a whole.

PURE allowed development of a new area of expertise in the group:  quantifying how individual fields contribute to defining a landscape and are in turn influenced by the landscape around them. We also worked with  INRA to improve the ‘biodiversity’ section of a decision aid named DEXiPM.

The ENDURE Network [5] existed before PURE and was was strengthened by it. The ENDURE Network was in a way self-funded in that it brought together a range of partners with interest in reducing pesticide by means of Integrated Pest Management (IPM). ENDURE continues today. Its web site and newsletters [5] offer a range of information and advice, both scientific and practical.

Environmental risk assessment

The SIGMEA and PURE projects in turn led to EU AMIGA [6], another major project that aimed to test existing guidelines on GM environmental risk assessment (ERA) and develop new tools and methodologies to aid ERA. The consortium was a late starter in the race and not the favourite. Moreover, the bid coordinators, Salvatore Arpaia from Italy and Antoine Messean from France had problems with brief cases and things being locked in buildings hours before the bid. They kept the rest of us guessing. The bid went in just 3 minutes before the 5 pm deadline. (What relief, I assure you!) After that …  we could only win (and we did).

For the first time, the Hutton was unable to host field experiments. So our contribution was mainly databasing, analysis and modelling and coordinating experiments at a distance. Examination of long term environmental effects (my responsibility) led to a system-led approach that was probably applicable to any change, not just GM cropping. Nick Birch coordinated assessments of integrated pest management across a series of experiments on maize, resistant to corn borer.

AMIGA was a successful project, well coordinated, great team work, and entertaining meetings, especially that one near an ancient church in a hill-top village in southern Italy!

The use of native seed in regeneration of vegetation

This final of the projects to date, named NASSTEC [7] is different from the others in that its main purpose is to fund doctoral students based in different parts of Europe. There is one student at the Hutton and another nearby at Scotia Seeds, but several colleagues have been involved in teaching and mentoring all the students.  This is another of Pete Iannetta’s projects.

The link between the students is that all are working on some aspect of native seeds and their possible use in regeneration of vegetation. The topic is highly relevant to two strands of Agroecology’s interests – seeds (and plant phenotypes) and legumes, the latter needed to supply the nitrogen in degraded ecosystems. The project finishes in 2017.

 The future

The group has certainly seen the benefit of EU funding. We now have more active involvement in Europe than we have with UK institutes and universities. We have >100 active contacts across >10 countries, some of whom are still working on SIGMEA data from 2004-2008.

Colleagues are still heavily involved in current EU H2020 bids. Should they be successful – and so far the signs are they are – then funding for the course of the projects (usually 3-4 years) would be guaranteed, we are told, but at this stage it is hard to see how our european collaborations in sustainable agriculture and environment can continue in the longer term.

Most partners have been sympathetic to the uncertainties caused by leaving the EU. Yet it did not take long after the referendum for the less sympathetic to start demanding that Hutton scientists (i.e. from Britain) should not lead or be part of bids. Shabby!

There may be still good times and good research ahead with European colleagues.

Here is a group photograph of the EU SIGMEA team that visited Dundee in 2004
Sources / references

[1] Royal Society of Edinburgh (Advice Paper March 2016): Inquiry into the impact of EU regulation and policy on the Uk life sciences. Royal Society: The role of the EU in funding UK research.

[2] SIGMEA www6.inra.fr/sigmea 2004-2007. Contact: geoff.squire@hutton.ac.uk

[3] Legume Futures at the European Legume Research Centre. Contact: bob.rees@scru.ac.uk,  pete.iannetta@hutton.ac.uk.

[4] PURE integrated pest management: www.pure-ipm.eu/project 2013-2016. Contact: graham.begg@hutton.ac.uk, nick.birch@hutton.ac.uk

[5] ENDURE Network – Diversifying crop protection (unfunded network, continuing): endure-network.eu

[6] AMIGA Assessing the monitoring the impact of GM plants on agro-ecosystems: amigaproject.eu 2012-2016. Contact: geoff.squire@hutton.ac.uk, nick.birch@hutton.ac.uk

[7] NASSTEC Native Seed Science, Technology and Conservation Initial Traning Network: nasstec.eu/home 2013-2017. Contact: pete.iannetta@hutton.ac.uk

[updated with SIGMEA group photograph and edits on 25 April 2017]

web thoughts

From December 2016,  the curvedflatlands web site will offer facts, opinion and discussion on the topics of food security, sustainable agriculture and the environment.

Content will draw mainly on the activities and outputs of the Agroecology group in Dundee and its wide range of collaborations and contacts around the world.

‘Posts’ on this page will generally introduce a topic for discussion, which will then be extended, perhaps after some weeks, in the main Content pages, viewable from the top menu and from the right hand sidebar.

cf_vtr_sprmn_jd_750The site will promote the personal views and achievements of those who worked on these complex systems since the late 1990s, now at the James Hutton Institute, previously the Scottish Crop Research Institute. Further information can be found under ‘This site’ in the content pages.

Other parts of the site will highlight scientific results, the people involved and the major case study area of the Atlantic croplands.

The image is an etching by Jean Duncan title ‘supermoon’. For more on Jeans’s work, see her pages on the Living Field web site.