Identifying indicators of the spatial variation of agricultural practices by a tree partitioning method: The case of weed control practices in a vine growing catchment

Abstract

Environmental impact assessments of agricultural practices on a regional scale may be computed by running spatially distributed biophysical models using mapped input data on agricultural practices. In cases of hydrological impact assessments, such as herbicide pollution through runoff , methods for generating these data over the entire water resource catchment and at the plot resolution are needed. In this study, we aimed to identify indicators for simulating the spatial distribution of weed control practices (WCP) in a French vine growing catchment. On the basis of interviews of 63 winegrowers, a spatially explicit database was developed that included 1007 vine plots and information regarding practices and potential explanatory variables. Four practices were differentiated according to the methods used (chemical weed control, shallow tillage, grass cover or a combination) that determine the intensity of herbicide use and potential surface runoff. Three groups of explanatory variables corresponding to three assumed levels of spatial organisation of WCP (the plot, the farm and the local government area (LGA)) were tested and compared. In the first step, selection of explanatory variables within each group was performed using a tree-partitioning method that combined the advantages of the CART algorithm (building an interpretable and controlled model) and the Random Forest algorithm (limiting overfitting) algorithm. In the second step, the performance of the selected variables for reproducing the observed repartition of practices was evaluated by a stochastic use of the tree, leading to a set of equiprobable spatial distributions of practices at the plot resolution. The results indicate that plot characteristics related to alley width play an important role in the weed control choices; however, to take into account the total diversity of the WCP, it appears to be necessary to focus on the farm holding variables and, in particular, on the variable LGA. However, the interpretation of these results is still difficult. Specifically, the great relevance of the variable LGA to discriminate the practices may be related to various factors, one of which is the distribution of soil properties within the Peyne catchment that still requires more precise characterization. The results also indicate that the combination of the three groups of variables leads to the highest-performing simulations of the spatial distribution of WCP. Nevertheless, the farm holding variables provided little additional spatial information, which supports the idea that they may be omitted without significantly impacting the final results.

Spatial and temporal diversity of service plant management strategies across vineyards in the south of France. Analysis through the Coverage Index

“…Our questionnaire addressed a large number of issues, including vineyard structure; soil conditions; compost practices; service plant spatial design, service plant management practices and indicators guiding decision-making. However, several other issues could have been addressed by the questionnaire, such as the plantation framework for improving CI calculation, as alley width can play an important role in the weed control choices (Biarnès et al, 2009). A better characterization of the service plant strategy by group of similar plots instead of the whole vineyard will help to understand the trade-off between services and disservices for more precise water and soil conditions.…”

Use and fate of 17 pesticides applied on a vineyard catchment

“…The run-off coefficient (%) provides essential information about the hydrological behaviour during a rainfall event. Knowledge on the run-off to infiltration ratio is required to assess the potential vulnerability of surface water and groundwater [25,31,12]. The runoff coefficient RC is calculated for each event by normalising the total run-off generated during a rainfall event (V run , m 3 ) by the total rainfall amount over a rainfall event (V rain , m 3 ) (Equation (1)).…”

“…At larger scales, often the assumption is used that actual application rates are equal to the recommended application rates [10,11]. The use of farmer surveys, only possible with a limited number of farmers, may obtain more accurate data in terms of spatial input variability and application dates [12]. Some studies have underscored that pesticide applications in vineyard areas often result in contamination of surface or groundwater [13,14,15,16].…”

Innovations developed within supply chains hinder territorial ecological transition: the case of a watershed in Martinique

“…Lastly, our network analysis revealed two key characteristics of the sociotechnical regime. The first was that the research and advice available differed depending on the supply chain, which led to an imbalance in the farmers' resources available for innovation as already shown by Biarnès et al (2009). The second characteristic was that the structure of the network segmented by the supply chain (comparable with silo structure) fixed the scope of innovation to the domain of each supply chain.…”