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

Conservation agriculture: blazing a trail through research

No-till agriculture: easier said than done

Eliminating tillage allows organic material to accumulate at the surface, but can have a negative effect on soil structure.

By Pascale Mollier, translated by Inge Laino
Updated on 02/04/2014
Published on 11/08/2013
Seeding drill designed for direct seeding.. © INRA, Stéphane de Tourdonnet
Seeding drill designed for direct seeding. © INRA, Stéphane de Tourdonnet

Eliminating tillage means that other methods must be used to reproduce its many beneficial effects, including:

- burial and incorporation of organic material from previous crop residue

- burial and incorporation of fertilisers and soil-enriching agents

- aeration and restructuration of soil, fostering the formation of an efficient seed bed where plants take root easily and water and air circulate freely

- weed management (burial of seeds and plants) and prevention of fungal disease.

For more on weed management, see section 5.

Tillage also has an effect on the dynamics of organic matter. Studies carried out over the past 30 years (2) in Boigneville by the French Technical Institute for farmers and agriculture (ITCF) (1) and INRA have shown that no-tillage systems (superficial soil disturbance and direct seeding) promote a greater accumulation of organic matter in topsoil (+14% and +13% of initial stock respectively) than systems with tillage (+7%). Within the framework of these studies, methods that include the use of Carbon 13 have also shown that decomposition of organic material is about twice as slow with direct seeding than with tillage. Moreover, soil can be enriched with organic matter thanks to intermediate crops, as shown in the 2013 study on nitrate-trap crops (cf section 11).

Dealing with soil compaction

Depending on climate and soil type, eliminating tillage may lead to the physical deterioration of soil. While this is less of an issue south of the Paris Basin - where crops are harvested in summer and seeding takes place in autumn for winter crops - it is cause for concern in the north where crops are harvested later (maize, beet), and rain makes soil more susceptible to compaction. Soil compaction is also an issue in western France, where forage maize is used in livestock systems. A study implemented in the early 1990s at the experimental site of Estrées-Mons (3) has shed light on the importance of harvesting periods.

The factors of soil compaction

Research has also taken an interest in the regenerative capacity of soil. Since the 1990s, research at INRA has focused on the role of climate in this process (4): when soil dries out, its clay content tends to shrink and swell, creating cracks and therefore porosity, which is beneficial to soil structure. It is not advisable to eliminate tillage altogether in soils with a clay content below 15%, which is the case for most cultivated soil in France. Other studies have focused on the role of cover crop roots in the decompaction of soil (5).

More recent INRA studies have analysed the role of soil macrofauna, particularly earthworms, in decompaction (6). The studies, which are innovative both in terms of methodology used (X-ray tomography, which reveals the network of tunnels created by the worms) and results obtained, showed that it takes two years for worms to restore the original levels of porosity to compacted soil.

(1) ITCF is now known as Arvalis-Institut du végétal.

(2) Balesdent, J. 1997. Organic material in soil. Chamber of Agriculture, supplement  n°856, 17-22.

(3) Boizard, H., Soil & Tillage Research 2013: Using a morphological approach to evaluate the effect of traffic and weather conditions on the structure of a loamy soil in reduced tillage.

(4) C.R.Acad. Agric. Fr., 2012, 98, n°1. 8 February 8 2012.

(5) Carof, M. et al. 2007. Hydraulic conductivity and porosity under conventional and no-tillage and the effect of three species of cover crop in northern France. Soil Use and Management 23, 230-237.

(6) Capowiez, Y. et al. 2012. Role of earthworms in regenerating soil structure after compaction in reduced tillage systems. Soil Biology & Biochemistry 55, 93-103.

SCTs in France: an overview

- 1970s: First experiences of simplified cultivation techniques (SCTs) (oil crisis and time-saving strategies with very short intermediate crops such as maize followed by wheat)

- 1980s: interest dips (costly chemical weed control, inadequate equipment, and favourable economic context making cost reduction less of a priority)

- 1990s: renewed interest (availability of affordable glyphosate, improved seeding equipment, a “greener” CAP, regulations to simplify tilling in winter and promote the use of intermediate nitrate-trap crops

- 2000s: implementation of exchange networks - BASE (in French), FNACS (in French), revue TCS (in French), stepped-up research on no-till agriculture

In 1994, SCTs were used on 10% of cultivated surface area for primary crops, 21% in 2001 and 34% in 2006.

In 2011, direct seeding represented a mere 4% of land used for growing common and durum wheat, 1% for barley and sunflower, and 0.5% for rapeseed. (Source: Agreste).