A systematic representation of crop rotations

Crop rotations are allocations by growers of crop types to specific fields through time. This paper aims at presenting (i) a systematic and rigorous mathematical representation of crops rotations; and (ii) a concise mathematical framework to model crop rotations, which is useable on landscape scale modelling of agronomical practices. Rotations can be defined as temporal arrangements of crops and can be classified systematically according to their internal variability and cyclical pattern. Crop sequences in a rotation can be quantified as a transition matrix, with the Markovian property that the allocation in a given year depends on the crop allocated in the previous year. Such transition matrices can represent stochastic processes and thus facilitate modelling uncertainty in rotations, and forecasting of the long-term proportions of each crop in a rotation, such as changes in climate or economics. The matrices also permit modelling transitions between rotations due to external variables. Computer software was developed that incorporates these techniques and was used to simulate landscape scale agronomic processes over decadal periods.

New measures and tests of temporal and spatial pattern of crops in agricultural landscapes

Crops are allocated to their fields by growers according to rotational principles and such rotations may be defined and classified. Rotations evolve through the aggregate choices of crops by growers over time which create the characteristic agricultural landscapes for a given region. As agriculture becomes ever more competitive, growers increasingly should use such rotational principles to maximise efficiency. Their choices of crop allocations alter the observed temporal heterogeneity and spatial pattern of cropped landscapes. Within the European Union the forms of heterogeneity studied here are increasingly evident at the landscape scale. We present techniques to study these patterns of crops in time and space. This is essential in order to build realistic simulators of large-scale cropped landscapes within which farming practices may be studied across national boundaries. Simulation is required to provide realistic arenas to extend current models of gene flow from the field to the landscape scale, in furtherance of studies of coexistence between genetically modified and conventional and organic crops. We provide simple, empirical descriptors of cropped landscapes in terms of the degree of the non-randomness of the allocation. Non-randomness of fields is assessed in terms of (i) spatial pattern, (ii) temporal heterogeneity, and (iii) spatio-temporal heterogeneity. Four formal statistical tests of significance are presented: one of spatial pattern, two of temporal heterogeneity and one of spatio-temporal heterogeneity that may also be used to test for spatial pattern. The tests were exemplified using data taken from a study landscape of 72 arable fields farmed by 10 different growers in Burgundy, France, from 1994 to 1997. Two of the tests were based on simple χ2-statistics; two were randomisation tests. The χ2-test of spatial pattern demonstrated clustering in the distribution of set aside fields. The χ2-test of temporal heterogeneity demonstrated non-randomness for eight growers who employed 15 rotations. The randomisation test of temporal heterogeneity found significant non-randomness for one grower in three of the five crops examined. The common 3-year rotation of oilseed rape, wheat, winter barley was employed by one grower on 10 of their fields, for which significant spatio-temporal heterogeneity was shown by the proposed randomisation test. It is possible to extend the analysis of these test-statistics between – and within – units in a hierarchy, so that the methods could be used to study pattern at larger scales than landscapes, say at regional or national scales

Methodology for land use change scenario assessment for runoff impacts: A case study in a north-western European Loess belt region (Pays de Caux, France): A case study in a north-western European Loess belt region (Pays de Caux, France)

International audienceChanges of agricultural land use often induce changes in hydrological behavior of watersheds. Hence, effective information regarding runoff responses to future land use scenarios provides useful support for decision-making in land use planning and management. The objective of this study is to develop a methodology to assess land use change scenario impacts on runoff at the watershed scale. This objective implies translating qualitative information from scenarios into quantitative input parameters for biophysical models. To do so, qualitative information from scenarios should be quantified and spatialized. The approach is based on the combination of 2015 local land use change scenarios (SYSPHAMM method) based on local stakeholders expertise, a model of spatio-temporal allocation of crops to fields (LandSFACTS model) and a watershed runoff model (STREAM model). The study was conducted for regions underlain by silty loamy soils scattered across Northern Europe. It was applied on the Saussay watershed in Upper Normandy (France). The approach is illustrated through runoff assessment of one of the land use change scenarios (characterized by the ending of the set-aside obligation and the disappearance of dairy farming). This scenario appeared relevant for local stakeholders. The methodology presented suggests that assessing local land use scenarios in terms of runoff requires taking into account crop allocation diversity allowed by farmers' decision rules. This requirement accounts for runoff variability at the watershed outlet since crops spatial distribution throughout the watershed, depending on farmers' specific decision rules (i.e. cropping systems), strongly condition runoff phenomenon. Besides, choices regarding scenario implementation (quantification and spatialization) should to be made according to those cropping systems. Accordingly, taking into account crop allocation diversity due to farmers' cropping systems shows that there is a variability in terms of runoff at the watershed outlet (from 19 478 m3 to 35 004 m3 for the winter period and a low-intensity rainfall event for example). This variability can then be explored with local decision makers with the aim of finding solutions reducing runoff risks. The proposed approach provides a useful source of information for assessing the responses of surface runoff of future land use changes. Such scenarios providing impact assessment on runoff should encourage both local policy makers and local actors to actively discuss the future of land use in Upper Normandy

An Algorithm for Mixed-Mode 3D TCAD for Power Electronics Devices, and Application to Power p-i-n Diode

Cutting edge semiconductor devices for power electronic applications, such as Phase Control Thyristors (PCTs) or Bimode Insulated Gate Transistor (BIGTs), present large area and complex 3D geometry, thus requiring full scale 3D models for their simulation. Moreover, sensitivity to temperature variations and complex loading conditions call for mixed mode simulation of distributed devices coupled to external controlling circuits. In this work, we describe a strategy for coupled simulation of 3D devices and lumped circuit networks, with particular emphasis on efficient iterative solution strategies for nonlinear equations. The algorithm presented is tested on a p-i-n power diode, for which quasi-static on-state and transient switching (reverse recovery) simulations are performed

A multidisciplinary modelling approach to analyse and predict the effects of landscape dynamics on biodiversity

International audienceOver the last 40 years, agricultural extension and intensification of land use have induced profound changes in distribution and dynamics of farmland biodiversity and in the functioning of European agroecosystems. Agroecosystems are mainly private properties, whose dynamics need to be better understood in order to preserve their biodiversity. Several French research teams have recently joined their skills in a multi-disciplinary project, BiodivAgriM, whose main goal is to test, validate, and predict the consequences of different scenarii of landscape changes on the distribution, abundance and persistence of biodiversity in agroecosystems. A central goal of this project is to generate a multi-purpose modelling platform which makes it possible to couple different spatially explicit models toward the same objective, and gather rather similar models toward the same generic object (i.e., the landscape). Such a modelling approach is a real challenge. The main knowledge provided by this project was that the disciplines involved were in various maturation stages, with respect to the modelling approach, to understand the impacts of agricultural practices on biodiversity. Yet, a large panel of models is today available to address more specific questions, between human drivers and landscape, global incentives and landscape, or landscape and species. All of them are presently coupled or/and compared in order to qualify less ambitious yet relevant processes related to the landscape

Nitrogênio da biomassa microbiana em solo cultivado com soja, sob diferentes sistemas de manejo, nos Cerrados Microbial biomass nitrogen in soil cultivated with soybean, under different management systems, in the Cerrado

O objetivo deste trabalho foi quantificar o nitrogênio da biomassa microbiana do solo (NBMS), em diferentes manejos: semeadura direta (SD), uma gradagem (GR), subsolagem e duas gradagens (SG), comparado com solo sob cerrado nativo, em um Latossolo Vermelho-Amarelo argiloso, no Distrito Federal. Avaliaram-se os solos em cinco profundidades, 0-5, 5-10, 10-20, 20-30 e 30-40 cm; e em quatro épocas: antes do preparo do solo, 30 dias após a germinação (30 DAG), floração e após colheita da soja. O nitrogênio da biomassa microbiana em solo não perturbado, apresentou maiores valores em todas as épocas estudadas comparadas com os solos em diferentes manejos. Houve diferença significativa nas camadas 0-5, 5-10 e 10-20 cm, exceto aos 30 dias após a germinação. A razão porcentual no Cerrado Nmic:Ntotal foi 2,5 vezes maior que a GR, três vezes maior que a SD e cinco vezes maior que a SG. A distribuição do Ntotal foi decrescente no solo de Cerrado e nos manejos ao longo do perfil. Os teores de Ntotal reduziram-se de acordo com a profundidade em todas as épocas avaliadas. Houve correlação positiva entre os nutrientes e o nitrogênio microbiano nos diferentes manejos e solo de cerrado sob vegetação nativa.<br>The aim of this work was to quantify soil nitrogen microbial biomassa (SNMB) under different soil management systems: no-tillage (NT); one harrowing (OH); one subsoiling with two harrowings (SH). These systems were compared with native Cerrado, on a Red Yellow Latossol clay, in Federal District. Soils were studied at five depths, 0-5, 5-10, 10-20, 20-30 and 30-40 cm, over four periods: before soil preparation; 30 days after germination (DAG); flowering stage and after harvesting soybean plants. The native Cerrado showed the highest values of SNMB in all periods and management systems. Significant differences were found between 0-5, 5-10 and 10-20 cm soil layers, except at 30 DAG. The Nmic:Ntotal percentual ratio in cerrado soil was 2.5 times greater than OH system, three times greater than NT and five times greater than SH. The distribution of total N decreased in the Cerrado soil and other management systems with soil depth. Total N levels decreased with soil depth in all periods. There was a positive correlation between nutrients and microbial nitrogen in different management systems and soils under native cerrado vegetation