Bean crop using direct seeding under cover. Experiment in Ponta Grossa (Brazil). © INRA, INRA, Stéphane de Tourdonnet

Conservation agriculture: blazing a trail through research

The trinity of conservation agriculture

Although nearly a century old, conservation agriculture was only officially defined in 2001. Despite this effort of standardisation, the term still covers a wide range of agricultural systems, all of which have in common the absence of tillage.

By Pascale Mollier, translated by Inge Laino
Updated on 02/04/2014
Published on 11/06/2013

Maize crop using direct seeding beneath Cajanus cover. Experiments carried out by a farmer near Unai (Brazil, Cerrados).. © Cirad, Eric Scopel
Maize crop using direct seeding beneath Cajanus cover. Experiments carried out by a farmer near Unai (Brazil, Cerrados). © Cirad, Eric Scopel

The term “Conservation agriculture” was coined by the FAO in 2001 during the First World Congress on Conservation Agriculture in Madrid.

What exactly is being conserved? Principally, the fertility of farmland, by protecting it against harmful processes, especially erosion.

The FAO’s definition consists of three core principles that must be applied simultaneously:

- Maximum soil coverage from previous crop residue (ie mulch), cover crops used in intercropping, or live permanent cover crops

- Absence of soil disturbance by tillage and the radical reduction - or indeed elimination - of ploughing

- Prolonged and diversified crop rotations, by alternating crop families (legumes, grains, cruciferous), intermediate cropping and different crop combinations.

In the interest of standardisation and because these techniques can be applied in varying degrees, the FAO has set the minimum threshold of soil coverage by previous crops at 30% after seeding - the minimum needed to curb the effects of erosion, according to the USDA (1).

Different countries, different driving forces

Historically speaking, soil coverage was the first component of conservation agriculture to develop, to protect land from erosion. In the United States, the natural disasters caused by wind erosion (cf Dust Bowl, section 3), prompted farmers to use direct seeding techniques, in which seeds are planted into ground strewn with the residue of previous crops. This practice caught on in the 1960s thanks to government incentives, and in particular to the widespread use in the 1990s of non-selective herbicides (eg glyphosate) which kill weeds before planting and eliminate the need for tillage.

In Brazil, conservation agriculture was developed to keep water erosion in check; in Australia and Kazakhstan to remedy the effects of drought.

In Africa, conservation agriculture is slowly gaining ground in some 15 countries, in relatively small areas and only with partial implementation of the three core principles. Since 1920, permanent soil coverage with mucuna, a legume, has been practiced in Nigeria, and more recently in Benin with success. No-till systems are developing in Ghana, but without the use of permanent soil coverage and with recourse to herbicides, as with cotton crops in northern Cameroun.

In Europe, economic factors – savings on time and fuel - often trump the fight against erosion, and direct seeding is rare. Conservation agriculture involves simplified farming techniques without tillage but with topsoil disturbance, or occasional tillage, mostly on large farms that specialise in annual crops (straw cereals and rapeseed).

One term, many interpretations

To protect land against erosion, maximal soil coverage is paramount. A radical reduction of tillage is secondary, because any kind of soil disturbance tends to destroy and bury cover plants.  

However, when erosion is not a critical factor, the tables turn: eliminating soil disturbance becomes all-important, not only to save on time and fuel, but also to preserve soil.

Both cases raise the issue of weed control, since tillage is no longer used. Different systems propose different solutions: surface tilling techniques and false seed beds  (2); stepped-up use of herbicides; modifying crop rotations (eg alternating autumn and spring planting); and using weed-smothering plant covers. The latter is the most problematic, because plant cover must keep weeds in check without hindering the growth of primary crops.

It is worth noting that only those systems that use direct seeding with soil coverage and diversified crop rotations correspond to conservation agriculture as defined by the FAO.

The values behind the idea

Farmers who adhere to conservation agriculture cite respect for the natural functioning of soil and for nature as a whole, as well as an antidote to the artificialisation of farming. Originally inspired by the need to protect soil against erosion, conservation agriculture is increasingly associated with the absence of tillage, in the same vein of organic farming which prohibits the use of synthetic fertilisers and pesticides. Researchers at ISARA (3), within the framework of the PEPITES project (4), have observed some cross-over between these two schools of thought: adherents of conservation agriculture are looking to organic farming for ways to reduce inputs (especially herbicides), while organic farmers want to cut back on soil disturbance and promote seeding under crop cover to protect the quality of their land.

(1) USDA: United States Department of Agriculture, a US federal government department in charge of agriculture and food policy.
(2) The false seedbed technique consists of lightly turning soil to loosen and eliminate weeds.
(3) Philippe Fleury et al. Agriculture biologique et agriculture de conservation : ruptures et transversalités entre deux communautés de pratiques. Colloquium with SFER/RMT DevAB/Laboratoire Cultures et sociétés en Europe. Strasbourg, 23-24 June 2011.
(4) PEPITES project: French National Research Agency (ANR) project (2009-2013) dedicated to conservation agriculture. Partners: INRA, Cirad, IRD, Supagro Montpellier, Isara Lyon, AgroParisTech, BASE, Nourricia, Embrapa, Fofifa. Cf section 4 of this report.

At a glance

Land consecrated to conservation agriculture (broadly defined) in 2011: 117 million ha worldwide, ie approximately 8% of global cultivated land.

Percentage of arable land: USA: 50% for SCTs, 25% for direct seeding; Mercosur countries (Argentina, Brazil, Paraguay): 70%; Canada: 50%; Australia: 90%; France: 17%.
Source (in French)