DYSPALLOC, a model to simulate farmers’ cropping plan decisions in
their spatial and temporal dimensions
Schaller N1, Aubry C1, Boussard H2, Joannon A2, Martin P1
1
AgroParisTech INRA UMR 1048 SAD-APT, BP 01, 78850 Thiverval-Grignon, France;
[email protected]
2
INRA UR 980 SAD Paysage, 65 rue de Saint-Brieuc, 35042 Rennes Cedex, France
Keywords: model for action, farm scale, decision rules, crop succession, landscape
organization
Introduction
Farmers’ cropping plan decisions have an impact on the spatial and temporal crop
organization at farm and landscape levels, which in turn strongly impact many environmental
issues (soil erosion, biodiversity, coexistence between GM and non GM crops, crop pest
management etc.). It is generally accepted that managing landscape organization, considering
both landscape composition and configuration, is a way to reconcile agricultural production
and preservation of ecosystem services at the landscape scale (Foley et al., 2005). We thus
consider it necessary to understand farmers’ cropping plan decisions in their spatial and
temporal dimensions, to anticipate their potential consequences on landscape organization.
These decisions include choosing crops, allocation of crops to plots, and splitting agricultural
plots (Schaller et al., 2010). The spatial dimension of cropping plan decisions is particularly
important for understanding the spatial arrangement of crops in agricultural plots. Likewise,
the temporal dimension of cropping plan decisions particularly matters for understanding
when decisions are made during a year and when it could be opportune to coordinate farmers’
decisions to favorably orientate the landscape organization (Dury et al., 2011).
In this paper, we present DYSPALLOC, a conceptual model of decisions for DYnamic-andSPatially-explicit-ALLOcation-of-Crops-to-land, built on the basis of a French case study.
The aim of this study is (i) to represent and simulate farmers’ cropping plan decisions in their
spatial and temporal dimensions at the farm scale, and (ii) to evaluate the model.
Materials and Methods
Farmers’ decisions were represented through a generic framework derived from the “model
for action” (Sebillotte and Soler, 1990) and including decisional variables, determinants, and
decision rules (Schaller et al., 2010). The necessary data for using such a framework requires
specific on-farm surveys. We carried out the surveys in the Niort plain region (France). We
chose a reduced sample of 9 farms, in order to carry out 3 successive and detailed surveys
about farmers’ cropping plan decisions over time. We selected the farms so as to account for
the regional diversity in farming systems and farm territory spatial structure. We indeed
hypothesized that these two criteria highly influence farmers’ decisions. All surveys (in May,
November 2009 and May 2010) were semi-structured and aimed at encouraging the farmer to
explain how he spatially allocated crops to land and split his farming territory into plots and
to specify the reasons of his choices over different time scales. The surveys thus gave the
possibility to identify farmers’ plans regarding the choice of the cropping plan for 2010 and
to check possible adjustments over time.
After having made an inventory of the elements constituting cropping plan decisions in space
and time (based on the 9 farms), we focused on 4 farms (saturating the diversity in farming
systems and farm territory spatial structure) in order to build the conceptual model
DYSPALLOC, before carrying out an evaluation procedure on the 5 other farms.
Results and Discussion
Figure 1 represents the global structure of the DYSPALLOC model. It simulates a planned
cropping plan in year n for year n+1 at the farm scale. The model represents farmers’
decisions when the farm is in a “coherence phase” of its life cycle (Chantre et al., 2010),
which is a time period during which the strategic decisions remain stable (labor, equipment,
crop combination, etc.). We chose to represent the cropping plan decision process through the
same model for all farmers, but the diversity in each farmer’s decision rules can be accounted
for through the input data. DYSPALLOC requires input data regarding the farm territory (e.g.
area, soil types), the possible crops in the farming system, and crop succession decision rules.
The model proceeds in 3 time steps:
(i) The first time step represents the strategic decisions which are made once for the entire
“coherence phase”. The strategic decisions include the crop functional hierarchy, which
determines if a crop or a crop category will have priority access to land; the definition of
permanent plot boundaries and of strategic suitable crop areas, which determines in which
plots crops will be possibly allocated; and the definition of crop blocks, which defines groups
of plots having the same possible crop succession over time.
(ii) The second time step represents annual decisions made by farmers during year n for
planning the cropping plan for year n+1. These annual decisions consist first in identifying
the possible crop allocations to existing plots considering constraints due to past allocations.
Then the model proceeds in planning the compulsory crop allocations to plots (when only one
choice is possible) and in planning preferential crop allocations to plots, according to
preferential criteria (when several choices are possible). The main preferential criteria are:
water access, spatial regrouping of crops, and minimization of the distance between the
farmstead and forage crops. At this stage, the model provides a planned cropping plan for
year n+1, with a crop or crop category allocated to each plot.
(iii) The third time step represents infra annual decisions made by farmers during the year
n+1. These decisions make it possible to adjust the previous plan to new events occurring
along the year and giving farmers new information. These events can be related to climate,
market prices or commercial opportunities, technical operations, water access etc. These infra
annual decisions give the possibility to explain the differences between the planned cropping
plan and the final one.
In addition to these 3 time steps, another original feature of DYSPALLOC relies on the fact
that it accounts for agricultural plot splitting: it describes 3 types of plot splitting. The first
type represents the splitting of administrative CAP islets1 depending on their individual
characteristics; they are split into homogeneous pieces of land regarding soil type and water
access (the split plots are called “elementary islets”). The second type of plot splitting is
related to the global farm structure and to crop successions. The “elementary islets” are
indeed split into “permanent plots” when their area is too large to ensure both crop succession
and the stability of crop areas over time. The third type of plot splitting is the definition of
“temporary plots” inside the “permanent plots” in order to temporarily adjust annual crop
areas.
1
CAP islet = spatially continuous land area used by agricultural authorities to calculate the European CAP
subsidies
The evaluation procedure consisted of a comparison of the simulated planned cropping plans
(before the third time step) via DYSPALLOC with the real planned cropping plans, identified
through the surveys. We applied this procedure to the 5 surveyed farms that were not used for
building the model. The difference between simulated and real planned crop areas on farms
was less than 6% in all cases, and less than 3% in 4 of the 5 farms. DYSPALLOC spatially
allocated the correct crops in the correct plots in 69 to 100% of the cases (84% on average),
which represented 71 to 100% of the total farm area (86% on average) (Figure 2).
Inputs
Inputs for
infra annual
decisions
Strategic
decisions
Crops
Elementary islets
definition
Crop blocks definition
Annual Identification of temporary
plots and of possible crop
decisions
allocations to plots
Farm
territory
Crop successions
rules
Strategic suitable
crop area definition
Functional crop
hierarchy
Permanent plots
definition
Compulsory crop
allocation to plots
Plan of crop allocation
to the other
temporary plots
Output = planned and spatialized
cropping plan for year n+1 at farm scale
Infra annual
decisions
Possible successive adjustments of the planned crop allocation to plots
Explanation of the final spatialized cropping plan in year n+1
Figure 1. Global structure of the DYSPALLOC model: cropping plan decisions are made
over 3 time steps (strategic, annual and infra annual)
% of well allocated plots (number of plots)
% of well allocated farm area
100%
80%
60%
40%
20%
0%
Farm 1
Farm 2
Farm 3
Farm 4
Farm 5
Figure 2. Validation of the DYSPALLOC model (proportion of correctly allocated plots and
farm area)
Conclusions
DYSPALLOC is a useful model to simulate farmers’ cropping plan decisions at the farm
scale. It represents (i) its spatial dimension by accounting for agricultural plot splitting and
crop spatial organization in those plots and (ii) its temporal dimension by accounting for the
three type steps at which farmers’ decisions are made (strategic, annual, infra annual). This
conceptual model combining decision rules and calculations could be implemented in
computer tools in order to simulate the impacts of farmer decisions on spatial and temporal
landscape organization. It could also be used to examine farmer leeway and flexibility in
cropping plan choices for improving landscape organization.
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