Who said organic farming was less productive?

By Stephan Kamrad

A while ago Joanna reported on a chemical free, organic pest control method that has a lot of advantages to conventionally used pesticides. Studies have shown that organic and comparable agriculture is more sustainable, as measured by indicators like species richness, soil fertility and nitrogen uptake. But even by most experts it is usually dismissed as a fantastical ideal that conflicts fundamentally with our need to feed the growing human population. This month, a new meta-study, published in the Proceedings of the Royal Society B, by scientists from the University of California reveals that the productivity gap between organic and conventional farming might be much smaller than widely believed.

Not so great after all? Credit www.CGPGrey.com

Not so great after all? Credit www.CGPGrey.com

The researchers analysed 115 studies covering over 30 countries and 50 crop species. Organic farming, defined by having no synthetic inputs, was found to be on average 19% (±4%) less productive than conventional farming. But interestingly, this obviously quite a drastic gap shrinks down to 9% (±4%) when the organic farmers use a polycrop system compared to a conventional monoculture. In polycrops, multiple species are grown together, e.g. in alternating rows, resulting in a greater biodiversity than conventional monocultures. This makes them less susceptible to disease and pests and certain combination of crops can act as biological pest repellants and natural fertilisers. In Joanna’s example in Kenya, maize was planted together with Desmodium (which repels the vicious Stemborer moth and also fixes atmospheric nitrogen). Another popular example found in British gardens is intercropping of tomatoes, onions and marigold.

The yield gap was also much smaller (8±5%) when organic farmers used crop rotations, i.e. planted a different crop in each growing season, a system which was once (in the Middle Ages) quite popular in Europe.

But where is the catch? If these techniques are so effective, why are they not used everywhere? More diverse systems are much more difficult to manage. Massive machinery cannot easily be used with companion crops and it is often advantageous for farmers to sell only one or a few crops in bulk. For small farmers in developing countries these techniques are easier to adapt but farmers often are not aware of the possibilities.

All this of course might be slightly too optimistic. After all, non-organic agriculture can also make use of intercropping (rare) or crop rotations (more common). In studies where conventional farming (i.e. the use of pesticides, weed-killers and synthetic fertilisers) was combined with polycropping or crop rotation, the yield gap returned to its original value or was even higher.

Interestingly, the yield gap also depends on what type of crop is under consideration. The yield ratio of organic to conventional farming is lowest for cereal crops, where a lot of effort has gone into the development of high intensity, large scale monocultures but often comes close to 1 for fruits and nuts, were less effort has been made in developing high output systems.

In our world, it is very hard to convince a farmer that he should tolerate a 9% or even 20% yield decrease for the prospect of a healthier agro-ecosystem, that is diverse, unpolluted and resilient to stress and disease. Diversification (be it over time as in crop rotations or over space as in polycrops) can raise organic farming yields and make it more competitive to conventional farming. With more investment it may be possible for the yield gap to be reduced even further.

Reference:

Ponisio LC, M’Gonigle LK, Mace KC, Palomino J, de Valpine P, Kremen C. (2015) Diversification practices reduce organic to conventional yield gap. Proc. R. Soc. B, 282:20141396. DIO: dx.doi.org/10.1098/rspb.2014.1396

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Plant factories: making organic pesticides?

By Tom Evans

In many peoples opinion, pesticides were one of the great tragedies of 20th century agriculture. They symbolized man’s dominance over nature: of the synthetic taming the organic – a cruelly ironic leitmotif of the modern world. In our post-Green Revolution era, most agricultural scientists see pesticides as anathema. Not only do they destroy the land and its biodiversity, but they also apply selection pressure onto insects to evolve resistant strains. The focal challenge of contemporary agriculture, then, is to devise new ways we can tame nature without inadvertently breeding resistance, or further damaging our precious ecosystems.

The bombyx mori silk moth

The bombyx mori silk moth

A recent paper in Nature Communications is part of a global effort to do just that. And, unsurprisingly, the answer comes through working with – not against – nature. A team of researchers from Kansas State University has genetically engineered a species of tobacco to produce chemicals known as pheromones. Plants do not usually make pheromones; in fact, they’re chemicals that insects produce, and they are usually involved in the communication systems of insects. For example, female silkmoths attract mates by producing a pheromone called bombykol. Male silkmoths can smell thispheromone from up to 10km away and follow the scent trail until they locate the female producing it.

So why has this group of scientists created a plant that makes pheromones?

The idea is we can harvest pheromones from plants and then use these natural chemicals in fields to control insects. At the moment industrially producing pesticides is bad for the environment, as well as the health of those working in pesticide factories. It’s also quite costly. By genetically engineering plants to synthesize pheromones, a so-called “plant factory” for pheromones could theoretically be established in the future, providing an environmentally friendly and cheap form of pest control. And moreover, the message is clear: nature is not our enemy, but our closest ally.