The BHU Future Farming Centre

Information - The FFC Bulletin - 2013 V2 July

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Farming the third dimension

By Molly Shaw

Imagine our farming landscape.  All that greenery of pasture and crops is a thin layer above the soil supported by some roots thrust shallowly into the ground.  Much of our arable landscape was once crowded with tall trees, decked out with epiphytes, and carpeted with bush and moss—a complex three-dimensional, highly productive growing environment that we’ve flattened to meet our agricultural needs.  But with the simplification of the ecosystem for agriculture we have also cut down on the land’s potential for growth.  

Look upwards and imagine the spreading leaves of a tall tree.  Look downwards and imagine strong roots foraging 1-3 meters below the soil surface.  Now imagine a farming system where you can benefit from the reach of those plants—a system that is more productive and profitable than the one we’re used to.  And yes, it is feasible.  It’s called Agroforestry.  

Now if you’re at all like me, the term “Agroforestry” conjures up pictures of enthusiastic hippies puttering around small plots of trees, cultivating mushrooms and not caring a twit about profit.  But around the globe, other countries have been using trees judiciously in their farming systems for decades while still maintaining or increasing yields of pasture and arable crops and the mechanization/efficiency that we’ve come to enjoy.  Stephen Briggs, a UK farmer and researcher, won a Nuffield Scholarship and travelled to many of these sites to learn how the systems work and how feasible they would be for UK farmers to adopt [2] http://www.nuffieldinternational.org/rep_pdf/1341272658Stephen-Briggs-2011-report.pdf .  With the considerable similarities in NZ and UK farming systems, most, if not all of the lessons apply equally to NZ agriculture and horticulture.   

The Case for Agroforestry Being Feasible

  • The scene: high value trees, straight wide rows with crops beneath;
  • amenable to modern mechanization;
  • Productivity;
  • Profitability;
  • Used extensively in other parts of the world.

What does this modern highly productive agroforestry look like?

First off, the trees are actually quite sparse.  Most successful worldwide agroforestry systems have tree densities of around 100 trees per hectare, with the cropping or pasture area between trees.  The best compromise between tree growth and crop shading seems to be with row widths of 24-48 meters and tree spacings within a row of 5-15 meters.  As a general rule, when the tree height reaches the row width, the trees cast enough shade to decrease the yield of the alley crop—and this observation seems to hold true with a wide variety of tree and crop/pasture combinations.   At low tree densities, crop productivity (and therefore annual income) is maintained, while at the same time timber for future harvesting is being accumulated.

Images courtesy of Stephen Briggs

How does productivity compare to our normal agricultural fields?

  This is the amazing part.  The productivity of a well-planned agroforestry system is actually quite a bit higher than either trees or pasture/arable crops planted alone, on the order of 130-140% higher on average over the life of the trees.  This is possible because trees can occupy different niches in the environment than crops.  In a field of wheat, for instance, roots can reach a depth of 40-50 cm and the plant leaves reach less than a meter high.  In a tree plantation, tree roots occupy that top layer of soil, plus a little extra depth, while the leaves reach many meters into the air, height depending on tree species and age.  

In an agroforestry planting the crop roots still occupy the top 40-50 cm, but tree roots shift lower, occupying the soil zone 1-3 meters deep.  This is partially due to competition from the arable crop and partly due to root pruning by cultivation / tillage, but the outcome is that more of the soil profile is mined by plant roots than in either system alone.  Tree roots can use nutrients that leach out of reach of the arable crops, and can mine water from lower depths as well.  Farmland nitrogen losses can be reduced by 50% under agroforestry compared to monoculture.  Think of the potential benefit to farmers who are under increasing pressure to reduce nitrogen leaching and conserve water.  

Images courtesy of Stephen Briggs

Happy and productive stock

There are some long held beliefs in farming circles that trees and stock don’t mix, for such reasons as animals lounging under trees don’t graze as much, and stock camps concentrate nutrients.  However, most of these beliefs are founded on suspicion not research, and, as the science catches up, many of these myths are being busted.  For example cattle with access to shade actually grazed 30-40 minutes longer than cattle without, and heat stress is a major issue for lost stock productivity [1, 3].  Agroforestry systems also don’t have the same level of concentrated stock camps found under big dense shelterbelts, conversely they can be used to better manage dung deposition, keeping it away from areas prone to leaching such as water courses.  Agroforestry systems can therefore considerably increase stock performance and health, and redistribute nutrients making for even greater gains.  

Right, productivity is all well and good, but how does profitability compare to forestry and agriculture systems that we’re familiar with?  
This is also good news, believe it or not.  When trees are planted at that low density discussed above and the tree species chosen are of high value (high grade timber, for instance), the profitability of the system is greater than either crop grown alone.  This does come with a caveat though.  The farmer has to take the long-term view of profitability.  If the trees take 15 or 20 years to mature to harvest, the profit each year is expected to be slightly lower (3% is one estimate) than the arable crop planted by itself, with greater sacrifices in profitability in the years closer to tree maturity.  Then there’s a big “windfall” of profit during the tree harvest period that more than makes up for the earlier losses.  In a well planned system, trees can be progressively introduced and then harvested sequentially so once the financial benefits flow, they flow continually.  

The trees chosen for a profitable agroforestry system must be high value.  In China, the tree of choice is paulownia, a fast-growing timber tree that fixes nitrogen, grown in combination with wheat.  More recently poplar has become popular, as the market for paulownia timber became saturated.  In France, black walnut is the most popular choice because of its high timber value, although other hardwoods are used as well.

Are these numbers just coming from researchers’ hypotheses and suppositions?  How well tested are these generalizations?  
It turns out that there are many regions in the world with well established agroforestry systems popularly adopted by farmers.  Trees are grown with wheat extensively in north-central China, to the tune of 3 million hectares.  Both Canadian and the United States governments recognise the value of agroforestry and are building support into their legislation.  In central Spain and southern Portugal agroforestry occupies 3.5 million ha, nearly 3% of the land area, and has created some of the cultural landscapes such as the ‘Dehesa’ and ‘Montado’.  In France there are also has a number range of examples cited by Stephen Briggs successful agroforestry farms.  However, In many much of the rest of the EU, including the UK, farm subsidy payments limit agroforestry adoption because agroforestry doesn’t fit into the established categories of government-supported cropping systems.  However, the EU bureaucracy is increasingly recognising the value of agroforestry and altering the rules to facilitate it.  Here in New Zealand, with no direct government payments to farmers, producers are not limited by bureaucracy, only their imagination!

There are more reasons to consider an agroforestry system than simple productivity and profit numbers.  Increasing the biodiversity of our landscape is the mantra of not only environmentalists, but also specialists in pest biocontrol and carbon sequestration proponents.  As already mentioned, incorporating trees in a cropping or pasture system can reduce nitrogen leaching by 50%.  Trees in the landscape slow down wind, reducing evaporative water loss from the crops nearby.  Canterbury farmers could think of agroforestry as shelter belts that turn a profit!  

In addition the recent nor’westers that have destroyed a considerable number of center pivot irrigation systems, are, according to climate scientists, a return to normal after a decade long lull.  If correct, then shelter in Canterbury is going to become increasingly important, as pointed out by old timers who recall the massive government shelter planting programs in the 50s and 60s, the legacy of which are many of the now massive gum tree lines.  While shelter around farm boundaries will help, clearly pivots and tree rows within a farm are incompatible.  One solution to this currently being investigated is the use of buried drip tape purpose-designed for pasture.  While the benefits of drip are well understood in horticulture, where in places with hot climates, such as Israel and California, it is the dominant irrigation technique, there could be significant benefits for drip over pivots, plus, drip and agroforestry are well matched.  If pivots continue to be damaged by wind across the plains of Canterbury and potentially Hawkes Bay, then alternatives will be required: agroforestry and drip could be an answer.  

It will take creativity to think outside the monoculture box, but New Zealand farmers are not lacking in adaptability.  Gaze up above the grassy pasture, think down to the shallow water table, and imagine the potential if we were to farm that third dimension. 

Additional information

Stephen Briggs presentation 'Practical innovation in agro-ecology' from the 2013 Soil Association Conference 'Grassroots innovation for sustainable agriculture'  Accompanying audio is available from the SA website

References

1.    Betteridge, K., Costall, D., Martin, S., Reidy, B., Stead, A., and Millner, I. Impact of shade trees on angus cow behaviour and physiology in summer dry hill country: grazing activity, skin temperature and nutrient transfer issues. in Advanced Nutrient Management: Gains from the Past - Goals for the Future.  Occasional Report No. 25. . 2012. Palmerston North, New Zealand: Fertilizer and Lime Research Centre, Massey University. http://www.massey.ac.nz/~flrc/workshops/12/Manuscripts/Betteridge_1_2012.pdf

2.    Briggs, S., Agroforestry a new approach to increasing farm production: A Nuffield Farming Scholarships Trust Report. 2012. http://www.nuffieldinternational.org/rep_pdf/1341272658Stephen-Briggs-2011-report.pdf

3.    Verkerk, G., In summer, shade rules the science behind why trees help maintain dairy productivity. New Zealand Tree Grower, 2009. February. http://www.nzffa.org.nz/farm-forestry-model/resource-centre/tree-grower-articles/tree-grower-february-2009/in-summer-shade-rules-the-science-behind-why-trees-help-maintain-dairy-productivity/

 

The BHU Future Farming Centre

Information - The FFC Bulletin - 2013 V2 July

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Better than herbicides?

By Charles Merfield

 Herbicides have been the mainstay of weed control for over half a century. They turned what was often one of the most complex and time consuming activities in crop production into a relatively straight forward task.  However, fifty years on, across the globe, farmers, growers and scientists are realising that herbicides are increasingly in trouble, with growing resistance (especially in herbicide resistant crops), lack of new chemistry, mounting intolerance from consumers, and legislative prohibition. The race is therefore on to find alternatives. However, few non-chemical weeding techniques get close to the silver bullet effect of herbicides, meaning that farmers and growers need to use the ‘many little hammers’ approach [1] to get sufficient overall weed control.  However, among this complexity of tools, one stands out as being something of a sledgehammer.  

Imagine a weed control technology that could achieve all of the following:

  • broad spectrum, i.e. kills practically all weeds;
  • had a residual period as long as the crop’s production cycle;
  • could be used in any crop;
  • had a nil withholding period;
  • had no risk of releasing xenobiotic materials into the environment;
  • had exceptional reliability levels (i.e., always works); and
  • had no risk of evolved resistance.  

This may seem like an impossible list for any weed control technology, including herbicides, but it is in fact possible using a technique called intrarow soil thermal weeding (ISTW).  

The basic idea behind the technique is really simple.  Nearly all weeds in cropping systems (arable and vegetable) originate from the ‘weed seed bank’ i.e., weed seeds in the soil.  So, with the exception of perennial weeds, if there is no weed seed bank, then there will be no weeds.  The elimination of the weed seed bank is a well known side-effect of the use of steam for soil sterilisation / pasteurisation in intensive cropping systems, such as glasshouses, to control soil borne pests and diseases.  Back in the early 2000s, Danish scientists Bo Melander, Torben Heisel, and Martin Jørgensen wondered if this side-effect could be turned into the main event and be used for weed control  [2, 3] .  

However, the standard approach to soil steaming involved heating the soil for hours, often as deep as the plough layer, which was not going to be practical for weed control across a broad spectrum of cropping systems.  Bo, Torben and Martin reasoned that the most problematic weeds are those in the crop-row, especially those close to the crop plants as these have the biggest competitive effect on yield, and they are hardest to control, compared with the interrow where broad-spectrum herbicides or interrow hoeing can be used.  So focusing weed control on the crop row would significantly reduce the amount of steaming required.  Next, unlike pests and diseases that can affect crop plants from deep in the soil by attacking roots, most crop weeds can only emerge from the top five centimetres of soil.  This again meant that the amount of soil needing heating is dramatically reduced, to about 10% of that heated by standard steaming techniques.  The final part of the jigsaw was to work out just how short the heating time could be made, with the answer being as low as a minute instead of hours.  

With the puzzle complete, the researchers built a tractor mounted machine that just steamed the crop row (intrarow) to about 5-7 cm deep, and for long enough to kill the weed seeds.  The result was weed-free crop rows!  In addition, as the source of weeds had been eliminated, i.e., the weed seed bank, no further weeds could emerge from the row until new seed was introduced, either from soil mixing, or weed seed rain.  The result is a technique that is broad spectrum for all weeds originating from seeds, has a residual period as long as the crop production cycle, can be used on any crop (because the soil is steamed before planting), it uses no agri-chemicals so there are no issues with withholding periods or chemical environmental pollution, it is highly reliable, and has no risk of evolved resistance as everything has a thermal death point.  ISTW is therefore the only non-chemical weed control technique that can directly out-compete herbicides.

The only problem, was that for field scale machines, the size of steam boiler required made the technique unattractive to most producers, and, even with the significant reduction in the amount of soil heated, considerable amounts of fuel were still required.  

To address these issues the Future Farming Centre undertook a theoretical analysis and laboratory testing to see if (1) hot air could be used instead of steam, to simplify the engineering, and (2) recycle the heat to further reduce fuel consumption.  

The guts of the results are that hot air is capable of killing weed seeds in the soil so it can be used instead of steam, and that heat can be recycled / reused reducing the amount of fuel / energy required, potentially substantially.

However, there were a number of caveats discovered.  While hot air can kill weed seeds, there are important interactions between temperature and the moisture content of the heat source, soil and seeds, that needs further unpicking.  While recycling heat is possible, doing so on mobile field equipment could be a significant engineering design challenge and that it may be a better option for energy efficiency to remove soil from the field for treatment.

The results of this work have been published on the FFC website at www.bhu.org.nz/future-farming-centre/information/weed-management/istw  

This means that at present, while ISTW is a sledgehammer, or perhaps more appropriately a steam-hammer, in terms of the level of weed control it can achieve, it still requires further research and engineering to turn it into a practical technology for use across the spread of real-world farming and growing systems.  However, considering the inevitable downward trajectory of herbicides, any technique that can pull off the level of weed control that ISTW can, surely deserves some significant support, to give farmers and growers a serious weed control backstop.  

The research the FFC undertook into ISTW was funded from the Sustainable Farming Fund  (number L12-104 ) with backing from HorticultureNZ. 

References

1.    Liebman, M. and Gallandt, E.R., Many little hammers: ecological management of crop-weed interactions, in Ecology in Agriculture, Jackson, L.E., Editor. 1997, Academic Press: San Diego, CA. ISBN 978-0123782601
2.    Melander, B., Heisel, T., and Jørgensen, M.H. Aspects of steaming the soil to reduce weed seedling emergence. in 12th EWRS Symposium. 2002: European Weed Research Society. http://orgprints.org/1547/1/Abstract_NL1.pdf
3.    Melander, B., Heisel, T., and Jørgensen, M.H. Band-steaming for intra-row weed control. in 5th EWRS Workshop on Physical Weed Control. 2002. Pisa, Italy: European Weed Research Society http://www.ewrs.org/pwc/doc/2002_Pisa.pdf

The BHU Future Farming Centre

Information - The FFC Bulletin - 2013 V2 October

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United Nations Conference on Trade and Development (UNCTAD). 
Trade and Environment Review 2013:
Wake up before it is too late: Make agriculture truly sustainable now for food security in a changing climate

By Charles Merfield

The United Nations Conference on Trade and Development (UNCTAD) released a major new report in September 2013 calling for “a paradigm shift in agricultural development: from a "green revolution" to a "truly ecological intensification" approach.  This implies a rapid and significant shift from conventional, monoculture-based and high external-input-dependent industrial production towards mosaics of sustainable, regenerative production systems...”

Over 60 international experts contributed to the report which is a comprehensive analysis of the challenges and the most suitable strategic approaches for dealing holistically with the inter-related problems facing agriculture today including climate change and environmental sustainability.  

Read the summary and download the full report from the UNCTAD website

http://unctad.org/en/pages/PublicationWebflyer.aspx?publicationid=666

The BHU Future Farming Centre

Information - The FFC Bulletin - 2013 V2 July

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Drought-Proof Pastures

By Molly Shaw

With many Canterbury irrigators toppled by wind this spring, even low-land farmers will get practice coping with droughty conditions—conditions that will likely become all too familiar in the next 3-4 decades as Canterbury weather patterns change along with global weather changes.  Within our life-times, predictions are for NZ to see increased clouds from the west.  This will mean more rain on the west coast along with strong nor’west winds and warmer temperatures on the east coast, making for drier pasture and crop fields.  

Not all plants sit defenseless in the face of scorching winds.  Many plants around the world have mechanisms to cope with dry soils while continuing to grow.  White clover, our main pasture legume, just doesn’t happen to be one of these resilient individuals—though, of course, it has many other endearing features that make it the most popular pasture legume in NZ.  It pairs with ryegrass, establishes relatively quickly, and is highly productive.  It just doesn’t happen to be drought-tolerant, as dryland farmers know all too well.

 

Caption:  White clover’s growth pattern leaves it susceptible to drought.  It has a small tap root that dies out after about 18 months, and it spreads by above-ground stolons with short anchor roots.  Under ideal moisture conditions the plant does great, but when it’s dry the stolons dry out and can eventually die.  Sometimes there is enough life in the tap root to grow again after rain, but sometimes that doesn’t grow back either.  

To tolerate dry soils, legumes and other plants can use a number of mechanisms.  For example, they can grow long roots to reach deep water that is available even after the soil surface is dry, or they can adjust the chemistry of their roots and leaves to be able to suck water even from relatively dry soils.  In the end, drought tolerant plants keep up productivity under dry conditions better, and regrow faster when rain does come.  Other types of plants get even more creative when dealing with drought, from alternative photosynthetic pathways that allow them to grow at night, when it’s less droughty, to elaborate structures like plant hairs to reduce water loss from leaves.  

Researchers at Lincoln University have explored three basic strategies to improve the drought-tolerance of our pasture legumes:

Replace white clover with another similar nitrogen-fixing species

Breed white clover varieties that tolerate drought better than our main varieties

Breed white clover hybrids with other legumes to get more drought-tolerant nitrogen fixers.

Rainer Hofmann, plant physiologist and Senior Lecturer in Plant Biology at Lincoln University, has spent a significant portion of his career working on this puzzle, and explains the current status of each of the options above.  

Replace white clover with another similar nitrogen-fixing species:  Strawberry clover has been one focus of the research program.  While white clover grows a small taproot that dies out in a few months, leaving the plant to spread by above-ground stolons with shallow feeder roots, the tap root of strawberry clover is deeper and longer-lived, leading to higher productivity during dry conditions.  The trade-off is that it establishes slower, 6-9 months instead of white clover’s 3-4 months.  Since its early growth is slower it can’t be seeded with ryegrass, but is better paired with something less competitive like tall fescue. Dryland farmers may decide these trade-offs are worth it, considering the alternative is a dead pasture of white clover, but farmers with access to irrigation are unlikely to find this too attractive.  

Breed white clover varieties that tolerate drought better than our main varieties:  Kopu II, a productive white clover cultivar used extensively in NZ, has been crossed with Tienshan, a white clover variety found high up in the Chinese mountains and known for its drought-tolerance.  Sure enough, the offspring are more drought-tolerant than Kopu II.  The trade-off is that under ideal moisture conditions, the hybrids are only about 2/3 as productive as Kopu II.  Under dry conditions, Kopu II’s productivity can drop precipitously to 20-30% of its ideal, while the hybrids only drop a couple percentage points from their maximum yield.  This means that the hybrids have predictable yield which is higher than Kopu II in droughts, but lower during ideal moisture conditions.  Breeders are currently working to stabilize the traits of the new hybrids and trial them all over NZ.  It is predicted that one will be ready for commercial use in about 6 years.   

Breed white clover hybrids with other legumes to get more drought-tolerant nitrogen fixers:  In Rainer Hofmann’s view, this has been the most promising strategy so far.  White clover has been crossed with another clover species (Trifolium uniflorum).  Resulting plants still spread with stolons along the soil’s surface, but a larger tap root.  Plants have a similar growth habit to white clover but more resistance to drought.  Again, the trade-offs are slower establishment and lower yields under ideal growing conditions (about 65-75% the yield of Kopu II under ideal moisture conditions).  AgResearch has further adopted this breeding project and expects to have commercially-viable seed available in 5 years.

Drought-proofing for today:  Breeding projects and new plants for the future are all well and good, but what can farmers do this year for nitrogen fixation on dry pastures?  Two tried-and-true practices may not sound exciting but they do work.  

Lucerne is a nitrogen-fixing species with a huge tap root, hefty N-fixation, and good productivity—higher than that of white clover.  The challenge is that Lucerne is so aggressive that it doesn’t pair well with the customary ryegrass used extensively in New Zealand.  It can be planted with grasses (e.g. cocksfoot) but the grazing management will be different than a white clover/ryegrass mixture. It can be done though, and many farmers do it!  The easiest (and more widespread) use of lucerne is as a monoculture for grazing and hay production.  In these systems grazing animals get the extra fibre they need in their diet from pure grass swards or dry hay.  

Shelter belts have fallen out of fashion in Canterbury lately, but they were planted before large scale irrigation was used, at a time when water conservation was more critical.  The old shelter belts reduce water loss from pastures, but take a long time to grow.  An alternative is miscanthus grass, a bunch grass species that takes only a year to establish, grows about 3 meters tall, and dies back to the ground in the winter.  Planting just the northern and western edges of a pasture block protects about 2/3 of the block from the drying effects of scorching northwest winds during the summer months when this protection is the most critical, and center pivot irrigation can run right over the wind breaks without damaging either the equipment or the grass.  

Trade-offs:  Listing to the options for drought-proofing pastures, the “trade-off” theme emerges.  If pastures could always get more than 80 cm of rain per year, evenly spaced and more abundant in the summer months, then our beloved white clover would be the best option.  That ideal doesn’t come true for dryland farmers.  For farmers with irrigation, it comes with a cost, and irrigating at current rates may not be feasible in the future.  Taking measures to drought-proof pastures now is like paying for car insurance for a sixteen year old son driving a brand new Mustang.  Yes, there is a real cost now, but it is likely to be worth it in the future. 

For more information visit the Lincoln University Dryland pastures research website at www.lincoln.ac.nz/dryland

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Information - The FFC Bulletin - 2013 V1 July

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News

With the growing complexity of issues that agriculture and horticulture faces, from needing to produce sufficient food and fibre, through, mitigating and adapting to climate change, to maintaining soil quality, it is increasingly important for scientific institutions to collaborate.  This allows them to bring the best of their individual expertise to bear on issues while avoiding the reductionist traps that have befallen research in the past, such as solving one problem only to create a much bigger problem elsewhere in the system.  As many of the problems facing agriculture are now multidimensional, affecting multiple ecological systems, e.g. soil, air, water, and with multiple societal impacts, it is vital that research takes a multidisciplinary and whole-of-system approach.  

The FFC is therefore very pleased to announce a growing list of partner organisations both within NZ and globally, that will enable it to be even more effective in its mission of finding permanant and practical solutions for farmers and growers.  

The current partner organisations include: