*2.1. Network Presentation*

Experiments were performed in a network of 137 cultivated fields located throughout Brittany (Figure 1). The soil was sampled in each field to determine its depth, layers, and textural class. In the upper layer (0–30 cm), most soils had a silty loam (n = 81) or loamy (n = 33) texture. The other soils were sandy loam (n = 15), clay loam (n = 4), silty clay loam (n = 3), and silty clay (n = 1).

**Figure 1.** Locations of experimental fields in the network in Brittany, France (red points indicate the 67 fields selected).

Before the experiments, 82 fields had annual crop rotations, 30 fields had grassland in their rotations, and the remaining 25 fields were summer fallow or cultivated with vegetables. Animal waste was regularly applied to half (n = 65) of the fields, especially on maize crops; of these fields, 26 received manure every year, with one or two applications per year. Fifty-seven fields received at least one application every four years of cattle manure (n = 36), pig slurry (n = 14), cattle slurry (n = 8), or poultry manure (n = 5).

#### *2.2. Climate*

The climate in Brittany is mild oceanic temperate, with a pronounced east-west rainfall gradient. The weather differed among the three experimental years analyzed. The year 2012 was variable, with dry periods in winter (January and February), rainy periods in April and June, and rainfall close to the mean observed from 1994–2014 in July (Figure 2). In contrast, 2013 was dry, especially in summer, with monthly rainfall that was much lower than the mean, while 2014 was rainy, especially in winter (January and February) and in summer (July and August). In addition to this inter-annual variability, the weather varied greatly among fields within a given year.

**Figure 2.** Monthly rainfall and mean air temperature from March-October for the 3 years of the experiment.
