Published on 27 February 2018

On the Saclay plateau, farmers and researchers are working hand in hand to make agriculture less dependent on synthetic fertilizers without sacrificing profitability.

The Agriculture Fair, which opened on February 24, is an opportunity for urbanites to rediscover farming. But city and country can in fact work together to produce innovative agricultural practices that are less dependent on synthetic fertilizers, as a project coordinated by INRA Grignon, a member of University Paris-Saclay, amply demonstrates. The Proleg project aims to replace petroleum-based fertilizers with alternative sources without reducing farmers’ incomes. Proleg runs from 2016 to 2020 and involves farmers, researchers from INRA and the Terres Innovia technical institute, and the Île-de-France Chamber of Agriculture.

Compost, manure and pulses

To reduce synthetic fertilizers, other sources of nitrogen must be used instead. Possible sources include compost, manure, digestate (the organic matter remaining after anaerobic digestion), or the cultivation of pulses, which naturally contribute nitrogen to the soil. “We are studying both the agronomic effects of these inputs and the economic aspects, that is, their practical consequences for agriculture,” said Sabine Houot, senior research at INRA and head of the Proleg project. “We are also looking at the environmental impacts; there can be no question of introducing new contaminants into the soil through these new practices.”

This research is being carried out in the fields of the Versailles plain near Grignon (Yvelines) and on the Saclay plateau, in collaboration with the association Terre et Cité. Terre et Cité works to preserve and enhance the use of farmland on the Saclay plateau, and brings together farmers, local government, associations, companies, and research institutes such as the BASC Laboratory of Excellence.

Local waste

In Ile-de-France, there are few farms liable to contribute natural fertilizers. But there are other sources to be found in the many nearby towns. “We are studying all the organic resources that can be used for farming,” said Sabine Houot. “We look at the quantities available, the quality, and the agronomic benefits, that is, the availability of nutrients. That way we can evaluate how much synthetic fertilizer can be replaced.” One source is the green waste from surrounding towns, which is composted on a farm on the Saclay plateau, and another is the solid and liquid manure produced by the nearby Viltain farm.

This research is complementary to other studies that have been conducted for the last 20 years at a farm near Grignon, which aim to compare different methods of fertilizing. Because while the fertilizing effects of liquid manure or digestate can be evaluated after a short period, the effects of composts on the organic matter content in soil must be observed over the long term. Environmentally friendly farming using alternative sources of nitrogen to mineral fertilizers is no quick fix!

Good for the climate

Besides their advantages in making soils more fertile, these practices could have positive effects on the climate. They help to maintain carbon in the soil that would otherwise add to the greenhouse effect. As the “4 per 1000” initiative shows, increasing the amount of carbon stored in the top 30cm of soil by just 0.4% would halt the increase in the CO2 concentration in the atmosphere.

Other regions are conducting similar studies as part of the national program ProTerr funded by ADEME. The studies are located in Alsace, a densely populated area; in Brittany with its many stock farms; and in Reunion which, as an island, is disadvantaged by the cost of importing mineral fertilizers and has to manage its waste locally.

The Proleg project doesn’t just study substitutes for synthetic fertilizers scientifically; it is also going to develop a decision support tool for farmers. “It will be a computer interface enabling different scenarios to be tested,” explained Sabine Houot. “For example, if we use a given fertilizer for a given succession of crops, what will the result be for soil quality, savings in fertilizer and economic impact? This will make it possible to compare fertilizer strategies.” And more importantly, to work with farmers to test innovative practices and help them make more effective use of these alternative resources, which can contribute to the well-being of our planet.