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International audience; In experimental trials the spatial distribution of soil properties is a key factor to evaluate and determine the credibility of the research outcomes. To evaluate the spatial distribution of soil properties at different depths in the present study, the electrical resistivity method was selected because of its non-destructive nature and high spatial resolution. The investigation was conducted on BT1 (Burning versus mulching) the world's oldest sugarcane trial (established 25 October 1939) located on the premises of the South African Sugarcane Research Institute (SASRI). The experimental area, covering 7200 m(2), is divided in 32 plots with three crop residue retention treatments. These treatments are either fertilized and not fertilized. The RM15 resistance-meter equipped with a multiplexer was used to collect geophysical data. The latter was used to generate apparent electrical resistivity maps corresponding to three approximate depth ranges: (0-0.5 m, 0-1.0 m and 0-2.0 m). The spatial resolution of the shallowest map (0-0.5 m), was 0.5 m x 1.0 m. Bulk density and soil water content, for the 0-0.1 m depths, were also determined from samples collected on a grid of 4 m x 5 m. All data collected were georeferenced using a spatial resolution of 4 m x 1 m with the Digital Elevation Model (DEM). The results of this survey showed the effectiveness of geophysical mapping to reveal detailed information regarding soil spatial variability and to understand and establish the relationships between soil fertility and soil physical properties. Detailed analysis of these results led to the identification of two different soil types on the trial site: a Mollic Cambisol in the upper slope of the trial with a depth of < 1.0 m and a deeper Mollic Nitisol in the lower slope. Additionally, close to the southern edge of the site, higher values of electrical resistivity revealed a layer of colluvial deposits, that has not been considered in the past. The relationships between electrical resistivity and investigated soil properties (soil water content, bulk density, aggregate stability and fertilizer) initially seemed paradoxical. Although there is still a need for further investigations, the current study decently establishes the rather unexpected relationships. The most striking finding was the high resistivity in fertilized plots associated with the application of potassium chloride fertilizer which led to a decreased soil aggregate stability.

Sugarcane is a multipurpose crop whose components may be used, in addition to sugar production, for various energy carriers or end-products (electricity, liquid biofuels and heat) which enhance its economic potential. For many years, plant breeders and agronomists have focused on increasing sucrose yields per hectare and millers on increasing recoverable sucrose per ton of sugarcane in sugar mills. Attempting to exploit the energy potential of sugarcane more fully, calls for a more holistic approach focusing on both sucrose and lignocellulosic components of sugarcane biomass, and gaining some insight into the management practices required to optimize sugarcane cropping systems in these respects. Such options include genotype selection, harvest date with respect to the crop's growing cycle, crop type (plant crop vs. ratoon crops) and harvesting systems (mechanical vs. manual). The effects of these factors are strongly modulated by climate and soil properties, and these interactions are overall poorly known. Here, we set out to examine sugarcane infield management × environmental interactions with respect to (i) sugarcane yield and partitioning of the aboveground biomass; and (ii) sugarcane milling products (recoverable sucrose yield and amounts of coproducts) and their derived energy carriers. Three Saccharum cv. cultivars (R570, R579 and R585) were planted in three locations on La Reunion Island with contrasting management practices and climatological conditions. Quality characteristics of the samples were assessed by conventional and near infrared spectroscopy methods. Product, coproducts and potential energy production were measured and computed using transfer equations and a mill-operating model. Yields and quality characteristics from cultivars and harvesting systems were affected differently by environmental factors - low temperature and radiation, and water stress. The current study also provides valuable information on how combinations between environments, genotypes and practices affect yield and partitioning of the aboveground biomass, and food and energy production. (Resume d'auteur)