Influence of root and leaf traits on the uptake of nutrients in cover crops

Aims: Cover crops play an important role in soil fertility as they can accumulate large amounts of nutrients. This study aimed at understanding the nutrient uptake capacity of a wide range of cover crops and at assessing the relevance of acquisition strategies. Methods: A field experiment was conducted to characterize 20 species in terms of leaf and root traits. Plant traits were related to nutrient concentration and shoot biomass production with a redundancy analysis. Acquisition strategies were identified using a cluster analysis. Results: Root systems varied greatly among cover crop species. Five nutrient acquisition strategies were delineated. Significant amounts of nutrients (about 120 kg ha−1 of nitrogen, 30 kg ha−1 of phosphorus and 190 kg ha−1 of potassium) were accumulated by the species in a short period. Nutrient acquisition strategies related to high accumulations of nutrients consisted in either high shoot biomass and root mass and dense tissues, or high nutrient concentrations and root length densities. Species with high root length densities showed lower C/N ratios. Conclusions: The same amounts of nutrients were accumulated by groups with different acquisition strategies. However, their nutrient concentrations offer different perspectives in terms of nutrient release for the subsequent crop and nutrient cycling improvement

Response by Marta G. Rivera-Ferre

Although Dr Wager does not address directly my original article in his correspondence (Rivera-Ferre, 2008), a response to his comments is nevertheless useful to explain my position on the IAASTD report. His article, in my view, is symptomatic of the broader compartmentalization of knowledge among commentators in the agricultural sciences: researchers in the natural sciences are often not aware of the socio-economic and environmental contexts of their research. The IAASTD has produced a comprehensive report that analyses and describes many, if not all, of the economic, ecological and social functions and potentials of agriculture, which, together, form the three classical pillars of sustainability. A key conclusion from the report is that agriculture as a whole has suffered from insufficient attention given to, in particular, the environmental and social factors, including maintenance of farmers' livelihoods.Peer reviewe

Medium-Term Analysis of Agroecosystem Sustainability under Different Land Use Practices by Means of Dynamic Crop Simulation

Part 4: Modelling and Simulation SystemsInternational audienceThe role of dynamic crop models as an intellectual core of computer decision support systems in agricultural management increases significantly in recent time. However, the scope of model applications is often limited by short time scale i.e. crop simulation/forecasting is performed within a particular vegetation season. The use of dynamic models in long-term planning is still much less developed. This contribution presents the author’s efforts in development and improvement of the integrated system of crop simulation «APEX-AGROTOOL» for its use as a tool of model-oriented analysis of land use environmental sustainability. Attention is paid to the modification of the existing software in order to provide an ability to simulate agro-landscape dynamics taking into account crop rotation effects

Carbon and energy fluxes in cropland ecosystems: a model-data comparison

International audienc

A model-data intercomparison of CO2 exchange across North America: Results from the North American Carbon Program Site Synthesis

Our current understanding of terrestrial carbon processes is represented in various models used to integrate and scale measurements of CO{sub 2} exchange from remote sensing and other spatiotemporal data. Yet assessments are rarely conducted to determine how well models simulate carbon processes across vegetation types and environmental conditions. Using standardized data from the North American Carbon Program we compare observed and simulated monthly CO{sub 2} exchange from 44 eddy covariance flux towers in North America and 22 terrestrial biosphere models. The analysis period spans {approx}220 site-years, 10 biomes, and includes two large-scale drought events, providing a natural experiment to evaluate model skill as a function of drought and seasonality. We evaluate models' ability to simulate the seasonal cycle of CO{sub 2} exchange using multiple model skill metrics and analyze links between model characteristics, site history, and model skill. Overall model performance was poor; the difference between observations and simulations was {approx}10 times observational uncertainty, with forested ecosystems better predicted than nonforested. Model-data agreement was highest in summer and in temperate evergreen forests. In contrast, model performance declined in spring and fall, especially in ecosystems with large deciduous components, and in dry periods during the growing season. Models used across multiple biomes and sites, the mean model ensemble, and a model using assimilated parameter values showed high consistency with observations. Models with the highest skill across all biomes all used prescribed canopy phenology, calculated NEE as the difference between GPP and ecosystem respiration, and did not use a daily time step