Introducing ground cover management in pesticide emission modeling

Abstract

Ground cover management (GCM) is an important agricultural practice used to reduce weed growth, erosion and runoff, and improve soil fertility. In the present study, an approach to account for GCM is proposed in the modeling of pesticide emissions to evaluate the environmental sustainability of agricultural practices. As a starting point, we include a cover crop compartment in the mass balance of calculating initial (within minutes after application) and secondary (including additional processes) pesticide emission fractions. The following parameters were considered: (i) cover crop occupation between the rows of main field crops, (ii) cover crop canopy density, and (iii) cover crop family. Two modalities of cover crop occupation and cover crop canopy density were tested for two crop growth stages, using scenarios without cover crops as control. From that, emission fractions and related ecotoxicity impacts were estimated for pesticides applied to tomato production in Martinique (French West Indies) and to grapevine cultivation in the Loire Valley (France). Our results demonstrate that, on average, the presence of a cover crop reduced the pesticide emission fraction reaching field soil by a factor of 3 compared with bare soil, independently of field crop and its growth stage, and cover crop occupation and density. When considering cover exported from the field, ecotoxicity impacts were reduced by approximately 65% and 90%, compared with bare soil for grapevine and tomato, respectively, regardless of the emission distribution used. Because additional processes may influence emission distributions under GCM, such as runoff, leaching, or preferential flow, further research is required to incorporate these processes consistently in our proposed GCM approach. Considering GCM in pesticide emission modeling highlights the potential of soil cover to reduce pesticide emissions to field soil and related freshwater ecotoxicity. Furthermore, the consideration of GCM as common farming practice allows the modeling of pesticide emissions in intercropping systems. Integr Environ Assess Manag 2022;18:274-288. © 2021 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Keywords: Active ingredient; Cover crop; Environmental modeling; Farming practices; Life cycle assessment.

Figure 1

Illustration of initial pesticide distribution fractions to air ($f_{\text{air}}$), off‐field surfaces ($f_{\text{dep}}$), field crop leaves ($f_{\text{field→crop}}$), cover crop leaves ($f_{\text{field→cover}}$), and field soil surface ($f_{\text{field→soil}}$)

Figure 2

Cover crop planted on grapevine cultivation in Anjou, in the Loire Valley (A) and spontaneous cover on tomato production in Martinique, French West Indies (B)

Figure 3

Initial (A) and secondary (B) emission distribution fractions for two crop growth stages, $f_{\text{intercept,crop}}=0.3$ and $f_{\text{intercept,crop}}=0.8$, respectively, corresponding to the installation (a, c) and flowering stage (b, d), for grapevine (a, b) and tomato (c, d) for a range of effective area fractions of crop‐free field that is covered by cover crop ($f_{\text{eff,cover}})$. Vertical lines represent the cover crop setup of the case study with $f_{\text{eff,cover}}=0.35$ and $f_{\text{eff,cover}}=0.7$

Figure 4

Contribution to total impact score expressed in PAF m³ d/kg pesticide applied, from each environmental compartment, for the tomato and grapevine scenarios, considering the presence of cover, using either the initial or secondary distribution, and indicating whether the fraction emitted to cover is assigned to agricultural soil or not (results are mean results obtained with the two pesticides)