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It is generally known that managed, drained peatlands act as carbon (C) sources. In this study we examined how mitigation through the reduction of the intensity of land management and through rewetting may affect the greenhouse gas (GHG) emission and the C balance of intensively managed, drained, agricultural peatlands. Carbon and GHG balances were determined for three peatlands in the western part of the Netherlands from 2005 to 2008 by considering spatial and temporal variability of emissions (CO2, CH4 and N2O). One area (Oukoop) is an intensively managed grass-on-peatland area, including a dairy farm, with the ground water level at an average annual depth of 0.55 (±0.37) m below the soil surface. The second area (Stein) is an extensively managed grass-on-peatland area, formerly intensively managed, with a dynamic ground water level at an average annual depth of 0.45 (±0.35) m below the soil surface. The third area is a (since 1998) rewetted former agricultural peatland (Horstermeer), close to Oukoop and Stein, with the average annual ground water level at a depth of 0.2 (±0.20) m below the soil surface. During the measurement campaigns we found that both agriculturally managed sites acted as C and GHG sources and the rewetted former agricultural peatland acted as a C and GHG sink. The ecosystem (fields and ditches) total GHG balance, including CO2, CH4 and N2O, amounted to 3.9 (±0.4), 1.3 (±0.5) and −1.7 (±1.8) g CO2-eq m−2 d−1 for Oukoop, Stein and Horstermeer, respectively. Adding the farm-based emissions to Oukoop and Stein resulted in a total GHG emission of 8.3 (±1.0) and 6.6 (±1.3) g CO2-eq m−2 d−1, respectively. For Horstermeer the GHG balance remained the same since no farm-based emissions exist. Considering the C balance (uncertainty range 40–60%), the total C release in Oukoop and Stein is 5270 and 6258 kg C ha−1 yr−1, respectively (including ecosystem and management fluxes), and the total C uptake in Horstermeer is 3538 kg C ha−1 yr−1. Water bodies contributed significantly to the terrestrial GHG balance because of a high release of CH4. Overall, this study suggests that managed peatlands are large sources of GHGs and C, but, if appropriate measures are taken, they can be turned back into GHG and C sinks within 15 years of abandonment and rewetting. The shift from an intensively managed grass-on-peat area (Oukoop) to an extensively managed one (Stein) reduced the GHG emissions mainly because N2O emission and farm-based CH4 emissions decreased.

This paper presents the results of field studies conducted in Togo (Djakakope and Sevekpota) to assess the effect of potassium (K) on cassava yield, water use efficiency (WUE) and transpiration as affected by nitrogen (N) and phosphorus (P) availability under rainfed conditions. It was shown that an adequate K fertilizer supply was requisite for increasing cassava productivity and enhancing resilience to water stress.

The dynamics of soil phosphorus (P) fractions were investigated, in the rhizosphere of fababean (Vicia faba L.) and maize (Zea mays L.) grown in calcareous and acid soils. Plants were grown in a mini-rhizotron with a thin (3 mm) soil layer, which was in contact with the root-mat, and considered as rhizosphere soil. Hedley sequential fractionation was used to evaluate the relationship between soil pH and P dynamics in the rhizosphere of fababean and maize. Soil pH influenced the dynamics of P fractions in both calcareous and acid soils. Fababean and maize roots decreased rhizosphere pH by 0.4 and 0.2 pH units in calcareous soil, and increased rhizosphere pH by 1.2 and 0.8 pH units in acid soil, respectively, compared with the no-plant control. The acid-soluble inorganic P fraction in the rhizosphere of calcareous soil was significantly depleted by fababean, which was probably due to strong rhizosphere acidification. In contrast, maize had little effect on this fraction. Both fababean and maize significantly depleted the alkali-soluble organic P fractions in calcareous soil, but not in acid soil. Fababean and maize utilised different P fractions in soil, which was partly due to their differing abilities to modify the rhizosphere. This study has decoupled successfully the effects of chemically induced pH change from plant growth effects (such as mineralisation and P uptake) on P dynamics. The effect of soil pH on plant exudation response in P-limited soils has been demonstrated in the present study.

Crop growth models help to formalize expert knowledge to assess and design cropping systems with multiple criteria (i.e. production and externalities). The process of modelling to develop an operational tool requires different skills from conceptualization of the biophysical system to the coding of the equations. The focus of this paper is on the procedure to develop a new crop model from an existing one, using a crop modelling framework. First, the conceptual model is co-developed by scientists of different backgrounds, having theoretical and/or practical knowledge of the crop. Then, to translate the conceptual model into an operational tool, there is a need for communication between these experts and software engineers coding the model. We illustrate the approach with a case study of changing a wheat crop model into a pea model.

Biological N2 fixation can fulfil the N demand of legumes but may cost as much as 14% of current photosynthate. This photosynthate (C) sink strength would result in loss of productivity if rates of photosynthesis did not increase to compensate for the costs. We measured rates of leaf photosynthesis, concentrations of N, ureides and protein in leaves of two soybean cultivars (Glycine max [L.] Merrill) differing in potential shoot biomass production, either associated with Bradyrhizobium japonicum strains, or amended with nitrate. Our results show that the C costs of biological N2 fixation can be compensated by increased photosynthesis. Nodulated plants shifted N metabolism towards ureide accumulation at the start of the reproductive stage, at which time leaf N concentration of nodulated plants was greater than that of N-fertilized plants. The C sink strength of N2 fixation increased photosynthetic N use efficiency at the beginning of plant development. At later stages, although average protein concentrations were similar between the groups of plants, maximum leaf protein of nodulated plants occurred a few days later than in N-fertilized plants. The chlorophyll content of nodulated plants remained high until the pod-filling stage, whereas the chlorophyll content of N-fertilized plants started to decrease as early as the flowering stage. These results suggest that, due to higher C sink strength and efficient N2 fixation, nodulated plants achieve higher rates of photosynthesis and have delayed leaf senescence

The Agricultural Production and Externalities Simulator is a modular simulation system targeted at estimating the biophysical behaviour of agricultural production systems in response to the interaction of soil-weather and different options of agro-technical management. APES is currently meant to be used at field scale, simulating 1-D fluxes (future version will also use 2-D fluxes to account for multiple cropping). All modules of this release are first prototypes linked to test the hypothesis on the component based structure and to evaluate consequent modelling and technical issues; outputs should not be analyzed to evaluate model performance at this stage.

International audience; Crop models are widely used for a range of applications. Individual models, however, are typically developed for a specific objective and are not easily reusable. Adapting a model to different objectives, such as different crop and/or soil management practices, often requires modification of the original model structure. To overcome this limitation, we aim at combining model concepts and information about their interactions with communication technology to provide a modern and flexible system that will allow model users (at first modelers) to apply the tool effectively.This paper describes a methodology to create such a system by usingg an object-oriented design approch. This approach allows creating a framework that comprises different conceptual approaches (e.g. light use efficiency, photosynthesis…), and organizes and synthesizes knowledge and information through “if-then”-type of rules. The novelty of our research does not reside in the modularization of a crop model, but rather in the incorporation of expert knowledge In the framework, to facilitate generic and process-oriented modeling that goes beyond traditional approaches based on monolithic models.A preliminary result of this approach is presended in this paper. It has been implemented within the Agroculturation Production and Externalities Simulator (APES) of the EU-IP SEAMLESS project to simulate the growth and productivity of crops with different phenological patterns. It illustrates how expert knowledge is applied in the selection of existing conceptual approaches in a flexible way to meet different simulation objectives. Future developments are discussed