Recherche d’un indicateur susceptible de rendre compte de la qualité de l’état structural de la couche arable dans les études relatives à l’incidence des pratiques culturales sur le maintien de la fertilité physique des sols

Research of an indicator to estimate the quality of the structural state of the arable layer in studies related to the impact of farming practices on soil fertility

Context

In the domain of soil management practices, the maintenance of the fertility and the safeguarding of the environment seem today elements impossible to circumvent in the processes of decision-making. In the context of sustainable agriculture, the quality of the structural state of the tilled layer constitutes an important element in development and assessment of new farming systems more respectful of the capital soil. In the same way, to assess and compare the environmental sustainability of different agro-systems within a network made up of reference farms, the definition of indicators likely to account for the quality of soil structural state of a tilled soil at a given time becomes a need.

Objectives

By the details which it makes it possible to reveal, only the morphological characterisation of a pit dug perpendicular to the direction of tillage and traffic is able to really assess the quality of the structural state of the tilled layer. Its primarily descriptive character results in a certain subjectivity, which makes its use not very compatible with the concept of a network of reference. On the other hand, a former study (Roisin C., 2003; Roisin C., 2007) showed that quantifying structural heterogeneity of soils by means of penetrometric measurements allows to obtain perfectly objective parameters linked to but not sufficient to account to the structural quality of cultivated fields. The objective of this project is to connect these heterogeneity parameters with other more traditional ones such as bulk density, porosity, cohesion, etc and to work out, thanks to the installation and to the follow-up of reference cropping systems, an indicator giving an overall picture of the soil structure and its changes over time.

Expected results

Initially, this indicator should make it possible to quantify the impact on the structural state of modifications of management practices concerning - the crop rotation (in particular the proportion of cereals in the rotation) - the soil tillage system (ploughing, loosening or simplified drilling) - the policy of organic matter restitution - the contribution of products acting on the microbial activity of the soil. In the second time, when the importance of each one of these particular factors and their interactions can be specified, this indicator should allow the best taken into account of the aspect “maintenance of the capital soil” in models intended to direct the agricultural policies towards a greater sustainability.