mixedcrop – curvedflatlands

Interlacing: lessons for seed mixes today?

“… an allowance is made for interlacing.”

Stebler and Schröter’s 1889 handbook on grass and legume species and mixtures. Their method of estimating seed rate for each species in a mix. Was the recommendation of over-seeding justified? Lessons for regenerating complex forages today. An article in the series on crop-grass diversification.

Imagine … you’re making a complex seed mixture by combining seed of each of the constituent species or varieties. You work out the best combination of species for the field – three or four for one-year’s hay and maybe 15 for long-term pasture – then gauge the ideal proportion of each in the resulting hay or pasture, e.g. 20% ryegrass, 10% red clover, and so on up to 100%.

*Four of the colour plates by L Schröter in The Best Forage Plants: left to right, kidney vetch, meadow foxtail, sweet vernal and alsike.*

It was a complicated task. The composition of each species – in terms of protein, fat, fibre and so on – had to be known so that the mix would satisfy the purpose, whether hay or pasture, sheep or cattle. The amount of nutrients that each species would need from the soil had to be estimated. For example, a nutrient-demanding species might have a hard time in a nutrient poor soil or else starve other, less demanding species. Then the proportion of each species in the mix had to be calculated. And all this before science and farming were fully aware of soil-plant processes such as symbiotic nitrogen fixation.

A major contribution to knowledge at that time was the work of FG Stebler in Switzerland. His book – The Best Forage Plants [1] – was written in German, co-authored by botanist C Schröter, translated into English by McAlpine [2] and the translation published in 1889.

There was great interest in grass-legume mixtures at that time. A shift from arable to grass had begun in Britain, initiated by serial bad weather and crop failure, coupled with unbridled cheap corn imports from the USA. It was the start of a long-term slump in arable farming and a rise in pasture husbandry [3].

The book described 30 species in detail: 21 grass and 9 legumes. Most would have been familiar in mixtures used in Britain, with few exceptions such as the legume Galega officinalis which they named Officinal Goat’s-rue (‘officinal’ because of its medicinal use in parts of Europe).

Officinal Goat’s-rue, one of many colour plates by L Schröter in The Best Forage Plants, indigenous to south-east Europe but grown widely as a medicinal and forage, having a preference for warmth and deep soil, rarely sown as a forage in Britain.

How much seed of each grass and legumes species for a mixture

Stebler’s recommendations on seed rate (weight per acre) were not without controversy. He worked out from many field trials the seed mass of each species that would be needed to cover and produce good growth on an acre of field: for example, 38.6 lbs for perennial rye-grass, 18.5 lbs of cocksfoot, 22 lbs of lucerne and 15.8 lbs of red clover. (To convert to today’s units, 1 lb is 0.454 kg and 1 acre is 0.405 hectare.) So 7.72 lb of perennial ryegrass seed would be needed if its proportion was 20%.

His method went further by recommending that more seed of each component should be added than estimated by such simple proportion. The extra seed ranged from 10% to 80%, but was typically 50%. The reasoning was that the species in a mix occupy different parts of the space: roots exploring either deep or shallow soil layers, for example; or some species leafing early in the year, others later.

This is what Findlay [4] in 1925, commenting on Stebler, meant by interlacing. The quote at the top of the page, from Findlay reads “As the roots and leaves of the different ingredients do not occupy the same places …. an allowance is made for interlacing.”

Grass specialists appreciated that roots and leaves of different species interlace: they enter each other’s space, they co-occupy ground. Several species might occupy the same area of ground but in doing so they are not always competing for the same resource or if they are then it is not in the same place or time.

Is overseeding a waste?

Findley appreciated what Stebler meant, but went on to criticise the method. He wrote “at no time is there any connection between the proportion of the seeds sown and of the plants either in the hay or in the pasture”, and gave the example that a competitive grass will oust an uncompetitive one regardless of the proportions in the mix.

Findlay was right in principle: the extent and type of interlacing depend on how the species react to each other in the local conditions. Yet over-seeding is not without merit. The aim of a seed mix was to get more mass or nutrition than could be had from any species grown alone. Stebler said that to do this you had to sow more seed of each component than that based on simple proportion.

Take the very simple example of a 50:50 mix containing one grass or cereal and one legume. The legume fixes its own nitrogen (N) from the air, so will take little from the soil. Consequently, the cereal or grass has most of the soil N to itself, but if it were only sown at 50% of what it would take to cover the ground alone, then it might have a hard time extending its roots to get the N throughout the whole soil space, which includes that ‘under’ the legume. Therefore (Stebler would say) it should be sown at more than half the seed rate needed to grow it alone.

That’s not the full story because the two species would also compete for other resources – solar radiation, water, the macro- and micro-nutrients. In a 15-20 species mix for permanent pasture, very many interactions would occur between the types, and some would result in the elimination of species. The ones that went would not be the same in all soils and climates. One purpose of a mix therefore was to build in redundancy, such that the mix would still perform well even if some components disappeared.

Awnless Brome Grass, now named Bromopsis inermis Ssp. inermis, one of the many plates by L Schröter in the Best Forage Plants, capable on poor, drying soils, widely grown in Europe, also previously in Britain, but now rare here as a sown forage.

Postscript – Stebler’s influence ?

In his preface to the translation into English, McAlpine had the view that Stebler & Schröter, now accessible to English readers, would be seen as a major work of agriculture, leading to ‘a revolution in the forage culture of Great Britain’. Further on, he writes ‘I do not hesitate to affirm that if Stebler be destined as I believe he is to become a power in agriculture the effect will be to increase the production of good forage and to improve the practice of this most important branch of farming.’

Yet Findley in 1925 [3] found Stebler’s methods deficient in several respects and did not endorse them. Whatever Stebler and Schröter’s influence on British forage might have been in the 1890s, it did not last. After the mid-1900s, mineral fertiliser would come to supply most of the nutritional needs of grass and supplant forage legumes such as clovers and trefoils. As described elsewhere, the diversity of grass forages became poor and probably the knowledge of how to manage multi-species grassland faded [5].

Recent decades have seen a part-reversal of that trend, in that grass-legume mixtures are increasingly available from seed merchants. Some of the mixtures are intended for grazed swards but the emphasis seems to be on restoration for wildlife conservation.

The lesson from Stebler is that the basis of estimating seed rate in a mixed crop or pasture might need to be reconsidered. In many parts of the world, however, seed is not plentiful. The choice has to be made: eat the grain now or keep it to sow for the next crop.

To come …. More on Stebler & Schroter’s Tables on the nutritional value and needs of grass versus legumes.

Sources / references

[1] Stebler FG, Schröter C. ‘The Best Forage Plants’. Translated into English by A N McAlpine, 1889. Publisher: Nutt, London. Available to read online through Google Books. The illustrations of grasses, some reproduced here, were by L Schröter, brother of the second author. A review of the book, Wrightson J. (1889). A Review of The Best Forage Crops. Nature 39, 578-579, tells readers that the treatise omits the common fodder crops such as vetches and brassicas, and deals mainly with pasture grass mixtures.

[2] A N McAlpine, the translator of Stebler & Schröter into English, was Professor of Botany, New Veterinary College Edinburgh and Botanist to the Highland and Agricultural Society.

[3] curved flatlands article: Food security in the pandemic.

[4] Findlay, W M. 1925. Grassland in Scotland. In ‘Farm Crops’ edited by W G R Paterson. The Gresham Publishing Company, London.

[5] curvedflatlands articles: Grass mix diversity a century past – for reference to books by RH Elliott and H Stevens; and 1800s mixed crops – lessons from the Agrostographia – gives examples of the Lawson’s (Edinburgh) crop and grass mixtures.

Acknowledement Thanks to K Owen for allowing the use of her depictions of interlacing on Pictish symbol stones.

1800s mixed crops – lessons from the Agrostographia

The 1800s, especially the first three quarters of it, was a period of notable invention and experiment, building on the gains from the first phase of Improvement that began a century earlier. Mixtures of crops, of grass and of crops and grass together are repeatedly referenced in the various books and manuals published throughout the period.

Several of these mixtures are examined here, as possible pointers and templates for modern attempts to re-diversify agriculture. The main sources are those published by the Lawsons, seed merchants based in Edinburgh, notably their Agrostographia [1, 2], which appeared in various forms from 1833 to 1877. For example –

barley-sainfoin (cereal-legume) mixture, the barley sown as a ‘nurse’, sainfoin drilled at right angles to the barley (a line intercrop?)
barley-oat-weld, the first two harvested after the first season, the weld yielding the next year.
within-species field bean varietal mixtures.
legume-legume, for example, field bean and vetch/tare.
barley, oat or any corn sown with grass as a nurse to protect the more valuable grass-legume sward.

As in other articles on this web site about our cool-climate mixtures, all crops were sown as seed mixes rather than line or row intercrops (with the possible exception of barley-sainfoin).

Barley-sainfoin gridded at drilling

When considering which dicot forages to recommend, Agrostographia suggested that sainfoin Onobrychis sativa could be grown in several parts of Scotland, though it was primarily grown in more southern climates. It likes a ‘dry’ and well drained soil, and was also recommended as an addition to their perennial pasture mix on calcareous soil.

Barley and sainfoin are sown together, drilled at right angles, the barley growing quickly, ‘nursing’ the other, then harvested in late summer for grain or fodder. Sainfoin overwinters in the barley stubble, then grows into a full forage crop the next year, when it is cut for fodder. It regrows and is repeatedly cut for several years. Original drawings by K Owen.

As a sole forage, it sometimes suffered in the first year. Therefore to aid establishment, the Lawsons pointed out the practice of sowing a nurse crop, such as barley, first. Then in those situations where that crop was drilled, the sanfoin was drilled at right angles to it, in effect forming a grid, rows of sainfoin crossing rows of barley. The barley was harvested in the first year, as cereal grain or forage crop, leaving the sainfoin to over-winter as a small plant, then extend and flower the next year. It would have been cut one or more times in the summer of the second year, after which it became a perennial forage.

This practice presumably prevented the second drilling (that of the sainfoin) from interfering too much with the first. It might have created an interesting pattern if the drills were reasonably wide apart.

Unlike many mixed crops, the aim of this one was to encourage the legume to establish. Barley would have been sown at a smaller seed weight per acre than when sown for a sole crop, so as to form enough cover to protect the sainfoin without completely denying it light and nutrients. It is unclear whether any particular advantage came to the barley, since it would grow much faster than sainfoin in the first year. No information is available from that time on nodulation in the legume and whether it released any fixed nitrogen when the barley needed it. In recent experience, sainfoin grows luxuriantly at 58N, withstanding the mild maritime winters without any obvious setback [4].

Field bean variety mixtures

In their Agriculturists’ Manual (1836) and the later Synopsis (1852), the Lawsons’ list varieties of Vicia faba of which the main one grown at that time was named Common Scottish or Horse Bean. They write: “Beans enter the rotation of cropping in the early districts of Scotland, and are very successfully cultivated on all strong soils, forming an excellent preparation for wheat. The straw or haulm forms nutritious food for horses during the winter and spring months.”

This comment – on the successful cultivation of beans – contrasts with the decline in area of this crop, along with many other arable crops, during the economic depression after 1880 when agriculture made one of its shifts to grass, on this occasion because of low global grain prices.

Page from the Lawsons’ Synopsis of 1852 showing the description for Common Scottish or Horse bean, the 295th entry (after the cereals but before the forages and fruits).

The point of interest here is the comment of what appear to be crop variety mixtures, identified by the range of flower colour. The wording in the above is little different from that given in the earlier 1836 Agriculturist’s Manual, and extract of which is given below.

The authors could not be certain that the fields they referred to were intentionally sown mixtures. Many of them would have been landraces, maintained by farm-saved seed, or seed impurities or even ‘volunteers’ (which arise from seeds shed by a previous crop and emerging in the current crop). Certainly, faba bean today readily gives rise to short-lived volunteer populations on waysides and in fields of other broadleaf crops..

This note from the Lawsons’ experience shows that despite the seedsman’s quest for purity in seed stocks, diversity was hard to eradicate.

Barley-oat-weld – grain and dyestuff

The plant weld Reseda luteola was once cultivated widely for the yellow dye that can be extracted from its leaves, stems and flowers. Weld as a commercial product has been replaced by imported dyestuffs, but it remains a common wild plant, sometimes growing by roads and especially on wasteland and old industrial sites.

As a crop, it was typically sown in spring along with a corn, such as oats or barley. When they were harvested in autumn, the weld was left to overwinter, then harvested the next year. The plants “are pulled when in flower, or before the seed is fully ripe, and used either in a green or dry state” [3]. Thirsk [5], writing about weld cultivation in 1600s England, relates a similar sequence: barley or oats sown (sometimes buckwheat), weld harrowed in, the corn harvested in autumn and the weld “pulled up by the roots, dried and stored the next year”; and then an usual variation in Kent, weld undersown in barley, the field used for grazing in autumn and the weld again harvested the next summer.

The diagram shows barley and oat grown as a corn mixture, weld seedlings growing beneath them in the first year then weld plants flowering among the corn stubble the next summer [4].

Barley, oat and weld sown as a mixture in spring, the two cereals growing more quickly and harvested during the first summer for grain or fodder, weld much slower and lower. Weld over-winters as a ‘rosette’ then extends the next spring into a flowering plant, harvested green for dyestuff. Original drawings by K Owen.

Two legumes: field bean and common vetch

Agrostographia also describes an unusual mixture – the bean Vicia faba and a forage legume, common vetch Vicia sativa (also known as common tare). Common vetch, as were many other vetches and tares from the genus Vicia, was grown as a commercial fodder crop. Its cultivated forms were reported to be different from the smaller and more slender local wild form. The Synopsis [3] distinguishes the common or summer variety from the winter variety, and also the Hopetoun Tare, which appears to be a landrace selected from a field of the summer variety.

Common vetch was grown as a green fodder and also for seed. Agrostographia describes two types of crop mixture. In one, the vetch is sown with cereals. Agrostographia writes: “The practice of sowing one or other of the cereal grasses (oats or barley) among Tares is strongly recommended, not only as it ensures a greater bulk of produce from the stems of the grains rising above the Tares, but they also serve to prevent them lying on the ground, and so becoming injured in damp weather; cattle are also fonder of the fodder in a mixed than in an mixed state.” It appears from this statement that the mixed crop has at least three advantages: more grain from the cereals, support to keep the vetch off the soil and a more nutritious (balanced) fodder.

In the other mixture, vetch is grown with field bean. Two legumes – but the benefit of sowing them a mixture is unclear. Agrostographia: “When sown for their ripe seed, the Summer Tare is generally mixed with beans, or peas and beans, in the proportion of about a fourth part in bulk, or less …”. In contrast, the winter vetch, sown in autumn for seeds, was said to be generally sown alone, but the manual advises they should be sown with winter bean – “… the seeds being easily separated from the beans, when thrashed, by means of a proper sized riddle”. The beans must have given the vetch support as did the cereal crop in the other type of mixture, but what benefit came to the beans?

Corn as a nurse for grass

The main type of mixture described in Agrostographia was that of ‘grass’ comprising grasses, legumes and other dicot (broadeaf) plants. These highly diverse seed mixtures were generally more valuable and more costly to establish than crop mixes, but also more open to damage in the weeks and months after they were sown. To help grass mixtures to establish, they were sown with a corn crop, oats or barley, which was harvested or grazed after it had done its job of nursing the grass seedlings.

More on grass mixtures and corn nurses is given at Grass mix diversity a century past. Further articles on this theme are in preparation.

Sources, references, links

[1] Agrostographia; a treatise on the cultivated grasses and other herbage and forage plants. Authors: The Lawson Seed and Nursery Company. Successors to Peter Lawson and Son. Date: 1877 (6th Edition, by David Syme, Manager). Publisher: William Blackwood & Sons, Edinburgh and London. Online through sources such as the Biodiversity Heritage Library. Information in the Agrostographia was first published in 1833, though not under that name, and then as part of The Agriculturist’s Manual in 1836 [3].

[2} Agrostographia as a title is of much older origin, being that of a major compendium on grasses written in Latin, by or edited by, Johannes Scheuchzer (1684-1738), published 1719, edition of 1775 viewed. Scheuchzer is credited with being a founder of the science of Agrostology – the study of grasses.

[3] The Lawsons’ Agriculturist’s Manual (1836) and Synopsis (1852), the latter an expanded version of the Manual, are invaluable sources for 1800s crops and their varieties, both available online, e.g. through the Biodiversity Heritage Library. Details:

The Agriculturist’s Manual. Peter Lawson and Son 1836. Edinburgh, London and Dublin. Being a familiar description of the Agricultural Plants Cultivated in Europe including practical observations respecting those suited to the Climate of Great Britain; and forming A Report of Lawson’s Agricultural Museum in Edinburgh (Seedsmen and Nurserymen to the Highland and Agricultural Society of Scotland).

Synopsis of the vegetable products of Scotland. Peter Lawson and Son. 1852. Private Press of Peter Lawson and Son. Prepared for the Great Exhibition and dedicated to William Jackson Hooker, Director of the Royal Botanic Gardens of Kew.

[4] Sainfoin was grown in the Living Field garden at the James Hutton Institute, Dundee, for several years. It grew slowly in the first year but overwintered successfully and then flowered in the second and subsequent years. Weld grows easily at the Living Field, either flowering the same year as sowing or overwintering and flowering the next year. A mixture of oat, barley and weld was sown on one occasion but the weld failed!

[5] Thirsk J. 1997. Alternative agriculture: a history – from the Black Death to the Present Day. Oxford University Press.

Non-serious depiction of a barley-sainfoin mixture to show the practice of drilling barley in one direction then drilling sainfoin at right angles. Described in Agrostographia 1877. Images from plants grown in the Living Field Garden, Dundee.

form line, form square? … naargh just mix it!

Formal and informal mixed cropping. Mixed corn and mashlum (oats, beans) preferred historically in Scotland, seed mixed not sown in lines or squares. By mid-1900s, covering very small areas of cereal land. Dredge corn from SW Britain. Unintended mixed grain from volunteer weeds. Mixes grown as a safeguard. Lessons from history.

Archaeological evidence from many landscapes across the globe shows agricultural land divided into geometric shapes. Linear features may have been constructed as drove-ways to move stock from one piece of land to another; or for cultivation by teams of animals dragging a plough that was difficult to turn. Squares or or other shapes with conserved side-length, are preferred when something has to be contained, such as stock animals or valuable crops that can be surrounded by a wall or fence.

Similar features occur when more than one species of crop is grown in a field. Such intercropping or mixed cropping is widely practiced in many agricultural regions. Smallholder gardens will often consist of small blocks, sometimes even single plants, grown close to each other, sometimes under the shade of a tree-crop. Perhaps the most widely observed configuration is that of lines or rows. One species might occupy one or more adjacent lines, then another species then back to the first species, as in the example below of an intercrop of chickpea and sunflower [1].

Chickpea field in which lines of sunflower have been sown, Burma (Myanmar), image by curvedflatlands.

Not all mixed crops are grown in formal configurations. Seeds can be mixed in the bag or mechanical sower and broadcast on the land. Two or more species then emerge together to form a mixed stand.

Also, unintended mixtures can occur when seed dropped on the soil by previous crops emerges in a later one (see below). Whether unintended or planned, simple mixtures have been recorded in agriculture since records began.

A new dawn for mixed cropping in Atlantic Europe?

Three factors need to be assessed when considering the (re)introduction or expansion of mixed cropping. One is whether a biological advantage results from growing the species in a mixture: if there is, the grower gets more from the land or resources than they would if the crops were grown alone over the same area. A second is whether the mixture provides a convenience: even without a biological advantage, it might simply be easier for sowing and harvesting to grow two or more crops in a particular configuration, especially if the grower wanted a varied output (e.g. cereals, legumes, fruit, vegetables) from a small plot of land. The third is whether the mix provides a safeguard or security against unexpected events: here, a biological advantage and ease of management may combine to ensure something is produced.

The type of mixture used in previous times may also be a practical guide to what might still be feasible. In Scotland, and elsewhere in Britain, the most common sown mixtures from the 1700s to the early 1900s were intended for hay and grazing. They were rarely ‘grass only’, but comprised grasses, legumes and other broadleaf species in proportions varying with the intended use [2]. The legumes in the mix, the most abundant being white and red clover, fixed much of the nitrogen used by subsequent grain crops.

Also references are repeatedly made to assorted mixes of corn and grass, where barley or the landrace bere was sown as a ‘nurse’ for the more valuable and longer lasting hay or grazing mixture [3].

Mixed arable crops (no grass) were also mentioned in sources from the 1700s and 1800s, mainly as sown seed mixtures, very rarely if ever as line intercrops. But by the time formal agricultural census began in the later 1800s, sown crop mixtures such as mixed corn and mashlum were grown over a very small area.

Mixed corn, dredge corn and mashlum

The two most widely grown crop mixtures in the north of Britain go under the names mixed corn or mixed grain and mashlum. Mixed corn consists of two or more cereals, barley and oats for example, while mashlum consists of a cereal and a grain legume, typically oats and beans (Vicia faba). Mashlum reached its 20th century peak during WW2 (Fig. 1). The subsequent fall but continued usage of mashlum was documented on the Living Field web site [4].

Mixed corn or mixed grain appeared as a separate entry among grain crops in the Agricultural Census of 1929 [5]. Its area expanded and contracted over the next 50 years but generally remained less than 0.05% of the combined cereal area (Fig. 1). There is little information of why mixed corn was grown and also why its area was so small. Oat dominated the cereals in the earlier part of the period shown, then gave way to barley and wheat.

Fig. 1. The areas sown with mixed corn and mashlum in the Agricultural Census for Scotland [5]: mixed corn not identified from other cereals before 1929 and after 1978; mashlum grouped with other forages before 1944 and after 1960. Over the period shown, mixed corn comprised less than 0.05% of the combined cereal area.

Cereal mixtures grown elsewhere in the UK offer some explanation. A mixture of barley and oats named Dredge Corn was a feature of arable in the south west, mainly in Cornwall [6]. Its area was uncertain due the fact it was returned as ‘barley’ before 1919. As the quote at the top of the page implies, it was used as a safeguard, to ensure a reasonable yield under most conditions. It had a place in the crop rotation, sometimes replacing oats, sometimes barley, and was used in particular for a whole crop feed when the soil or the year was not capable of producing a pure crop of quality to sell as grain. The proportions varied but were typically two parts oats to one barley. Wheat was added in some cases, making a three-part mixed grain.

While it was certainly grown as a safeguard, it was also attributed biological benefits [6]. It was stated to produce more grain than barley alone and generally more than oats alone, oats being deeper rooted and thereby accessing more resource. In dry years, barley grew to fill the ‘gaps’ left by dying oat tillers. The straw was of higher feeding value than the individual crops, due to better overall structure. But perhaps most relevant to the Atlantic climate, the mix was better able than barley or oat alone to withstand the forces of wind and rain to flatten the crop. Similarly, one source reported that another variant – a mix of white and black oats – gave a greater yield (of straw) than either alone – the stronger stemmed white supporting the finer stemmed black.

Despite such reports from farmers, there is little hard information on the yield advantage given by mixtures sown on the fringes of Atlantic Europe. They might have given the 1.1. to 1.3 times advantage widely recorded for intercrops, but without the experimental data from the 1920s or earlier, there is no way of knowing.

Sown as a seed mix in April, no fertliser or pesticide: (left to right, 1 to 4) the bere barley grew quickly (1), then oat pushed through (2), bere matured first (3) and finally oat (4).

The widespread occurrence of unintended mixtures

It is the nature of small-grained cereals – oats, barley, wheat – to drop seed before or at harvest. The seed remains in the soil and, depending on conditions, emerges in a later crop. Today, such crop-weeds are commonly termed ‘volunteers’ [7]. The sown species and the volunteers in effect form a mixed crop (image below for wheat in barley). Other crops also generate volunteers. Those of oilseed rape are the most visible, but potato and field bean (Vicia faba) often produce mixed crops with cereals, though these broadleaf species may be really controlled by selective herbicides today.

Unintended mixed crops have been a feature of cereal lands probably since domestication. If the intended product was whole-crop cereals to be fed to stock, then they would have been seen as a benefit – free seed. However, they may also create a problem. They are an unwanted nuisance when they have to be separated from the crop, for example when a pure seed-harvest is needed, and they could harbour and carry over disease. Volunteer cereals are not a recent problem: records from the 1500s [8] on oats relate “that they grow amongst wheat and barley without being sowen, as an evil and unprofitable thing ..”.

Maturing barley crop, golden brown, in which volunteer wheat (upright heads, dark grey-green) has established; younger, still green plants growing in the wheel lines.

Conclusions

Mixed corn, and mixtures of corn and grain legumes, have been recorded for centuries in Scotland, and more generally in Atlantic Europe, but their benefits have not been adequately quantified. Where they were grown, it was as broadcast seed mixtures rather than line intercrops. By the early 1900s, they were minor crops. After the 1940s, agriculture was aiming for the high yields promised by intensification: mixtures almost disappeared.

Current reappraisal of crop mixtures might perhaps examine why in the early 1900s they never became major crops and why they were rarely grown as line intercrops.

Sources

[1] Photograph of chickpea-sunflower intercrop taken in Burma (Myanmar). Details on curvedflatlands at Mixed cropping in Burma.

[2] Seed mixtures for hay or grazing from the 1700s to the early 1900s are described in a related article on curvedflatlands: Grass mix diversity a century past.

[3] Crop mixtures are frequently referred to by Andrew Wight in the Present state of husbandry in Scotland (1778-84. Volumes 1 to 6), where one of the components (usually bere or barley) is most commonly a ‘nurse’ crop, protecting the others, which are usually grass mixes (grasses, legumes and other broadleaf species) to be used for hay or grazing.

[4] Mashlum, Scotland’s cereal-legume seed mix, still occasionally grown, is described on the Living Field web pages at Mashlum – a traditional mix of oats and beans and Mashlum no more! Not yet.

[5] Data in Fig. 1 are taken from the online Agricultural Statistics in Scotland one of the Historical Agriculture Publications on the Scottish Government web site. Based on the 1965 census, Coppock created an atlas in which the small area sown with mixed corn was noted with the comment that it was ‘not grown in the great majority of parishes’. Ref: Coppock, JT. 1976. An agricultural atlas of Scotland. John Donald, Edinburgh.

[6] Borlase, W. 1925. Dredge corn. In: Farm Crops, Vol 1, pages 265-269.

[7] Volunteer weeds, derived from crops, and presently common in Scotland are described at the Living Field web pages on Crop-weeds.

[8] Quote on oat from L’Agriculture et Maison Rustique by Estienne and Liebault, 1593 edition. Further details and origin on the Living Field web pages at: Ready, steady mundify (your barley) and The Library of Innerpeffray.

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.

Comment

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.

Pages: 1234