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

Conservation agriculture: blazing a trail through research

INRA experiments with no-till farming

Experiments with no-till systems have been carried out at INRA for a number of years. The primary goal is to study its impact to the organic elements of soil fertility.

By Pascale Mollier, translated by Daniel McKinnon
Updated on 02/07/2014
Published on 11/08/2013
Direct seeding on mulch. Trials at Grignon (1998-2010). © INRA, Mathieu Carof
Direct seeding on mulch. Trials at Grignon (1998-2010) © INRA, Mathieu Carof
 

Long-term assessment of results needed

Trials for various no-till systems began at INRA in 2010, with planned long-term monitoring of their progress. At INRA’s Estrées-Mons site, the trial will use surface tilling, cutting 5–7 cm, or a single yearly tilling to grow intermediate crops, which in some instances include legume crops to reduce nitrogen fertiliser inputs, and with a variety of techniques to incorporate or remove organic matter. The trials are being carried out as a part of the OERE ACCB Project and will track physical (structure, water), biogeochemical (nitrogen, carbon), and biodiversity changes to soil composition.

At INRA’s Grignon site, two trials with different primary controlling factors have been conducted since 2008. One trial seeks to reduce annual fossil energy use by 50%, the second aims to cut greenhouse gas emissions by 50% (1). Modelling and scientific expertise were used to determine the two crop system strategies. Although emphasis was placed on the primary controlling factor in each system, due attention was still given to other environmental criteria and to maximising yields within the remaining margin of operation. “Early results indicate that these ambitious objectives are attainable with acceptable productivity levels, even though productivity was not the priority” says Thierry Doré from the Agronomy Joint Research Unit (2), who conceived the project and participates in its oversight. The first project evaluations will be carried out at the end of the inaugural crop rotation cycle, in 2014 and 2015 respectively for the two trials.

A pioneering, extreme trial at La Cage

The longest-running direct seeding under crop cover system trial at INRA was launched in 1998 in the Château de Versailles park on deep, well-drained loam soil (3). “In the field of conservation agriculture, this trial is considered ‘extreme’ because there is no tilling of the soil and there is a permanent plant cover. The trial plot resembles a kind of meadow, with a mulch of plant residues forming under the living plants” says project team member Michel Bertrand. Previous trials (4) tested a number of different cover crops and identified the many advantages of alfalfa including its resilience as a cover plant, its beneficial effect on soil porosity, and its nitrogen fixing ability. “Despite the advantages of plant cover, controlling the cover plant can be problematic. This can sometimes lead to the significant use of herbicides” says Bertrand. “The system works better with winter crops, like wheat, that have the time to become established while the alfalfa is ‘on standby’. It does not work as well with spring crops like peas, and it does not work at all with maize, which cannot tolerate competition at the start of its growth cycle.” This makes it difficult to diversify the crops in a rotation. “This year, even with a glyphosate treatment when the peas were seeded, the alfalfa still overtook the peas. In the end, we were able to harvest the alfalfa as fodder, but not the peas” says Gilles Grandeau, who conducted the trials.

Good environmental results

In line with other literature on the matter, findings from the direct seeding under crop cover trials at La Cage indicate that biodiversity benefits when there is no tillage. The presence of plant cover encourages the development of springtails, earthworms, and nematodes. The absence of tilling favours certain animals (large-size anecic worms), to the detriment of smaller ones, to the extent that overall total biomass tends to increase.

At the same time, certain elements of soil quality also improve in the upper centimetres of the soil. After five years, there is a marked increase in decomposing plant debris known as particulate organic matter. In this way carbon is rapidly stored in the topsoil and, as early as the third year, there is a pronounced and very swift improvement in the structural stability of the topsoil layer.

Sub-optimal economic performance

Wheat yields from direct seeding under crop cover plots at La Cage remain about 20% lower than intensively farmed plots and fluctuate appreciably between years. The economic performance of the no-till system is the weakest of the four systems being trialled, regardless of the cost of fuel or the selling price of wheat. “The direct seeding under crop cover system is only worthwhile if we can manage to drastically reduce competition between the intermediate crops and the cash crop without increasing the use of herbicides, which is not possible most of the time. For our soil and climate conditions, it is not the best-suited system” says Bertrand.

(1) The System Under Constraints (SIC) trial assesses four crop systems: high environmental performance, reduced energy consumption, reduced greenhouse gas emissions, and zero pesticide use with mineral fertilisation.

(2) INRA/AgroParisTech Agronomy Joint Research Unit.

(3) The La Cage trial compares four types of systems: intensive, integrated, organic, and direct seeding under crop cover. The trial has been running since 1998, making it a valuable asset, with each system developing into stable environments with unique, identifiable features.

(4) See boxed text below.

Blé cultivé en association avec du lotier. Essais conduits à Grignon (1998-2010). © INRA, Stéphane de Tourdonnet

Intercropping experiments

Trials carried out at La Cage draw on results of other experiments carried out concurrently from 1998 to 2010 at the Grignon research station. Wheat was grown in association with a variety of cover plants including red fescue, sheep fescue, white clover, trefoil, black medic, and alfalfa (1). Through the experiment, competition among plants, which confers competitive advantage to cover plants over weeds, could be studied in depth. It also demonstrated the beneficial effect of cover plants to soil structure by increasing soil porosity. Alfalfa is the most effective plant in both regards, and has the added ability to provide nitrogen to the system. However, wheat yields were shown to be sub optimal. This highlights the need for further study in this area to avoid any possible competition between the wheat and the cover crops.

(1) These crops were planted in Spring 2002 and the wheat was directly seeded on mowed, live plant cover in November 2002. The trials were compared to two control groups, one seeded directly without plant cover and one with conventional tillage.

 References:

- de Tourdonnet, S. 2008. Utilisation de cultures associées en semis direct.Techniques Culturales Simplifiées, n°46,21-23.

- Carof, M. 2006. Fonctionnement de peuplements en semis direct associant du blé tendre d’hiver (Triticum aestivum L.) à différentes plantes de couverture en climat tempéré. PhD Agronomie, INA P-G. 130 pp.

- Shili-Touzi, I. 2009. Analyse du fonctionnement d’une association de blé d’hiver (Triticum aestivum L.) et d’une plante de couverture sur une échelle annuelle par modélisation et expérimentation. PhD Agronomie, AgroParisTech. 187 pp.