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In a conservation agriculture system, crop residues are no longer mixed in a volume of ploughed soil, but maintained on the surface or partially buried. Their presence contributes to the sustainability of these systems by maintaining the agronomic and environmental balances. In this context, knowledge of the evolution of their quantity on the soil surface, from harvest to sowing of the next crop, becomes an important stake of soil management. Several authors have established a relationship between the soil cover ratio and biomass, specific to each plant species, from an identical formalism developed by Gregory (1982). The objectives of this work are to test its use in the pedoclimatic context of the Grand-Est region (France), after harvesting and during the residue degradation process, on several crops. This work has been carried out on farms practicing conservation agriculture for several years. The residues were ground during the harvest or a subsequent specific operation. Biomass data were collected using 0.5 m × 0.5 m frames, while ground cover were studied using digital photographs. The cover rates were calculated using an image analysis software. This work also compares two measurement periods: at the end of winter, several months after the harvest, and right after the summer harvest. The results show a very good correspondence between the soil cover ratio and the biomass measured on the ground, for all species and measurement periods, by adding a parameter to the Gregory (1982) formalism. The integration of spatial variability on the ground makes it possible to propose the use of a single linear adjustment that simplifies the prediction of soil cover ratio or the amount of biomass. [ABSTRACT FROM AUTHOR]

The accurate quantification of crop residue biomass left on the soil after harvesting is important, due to the agricultural and environmental issues associated with the management of soil organic matter in croplands. This quantification is difficult in farmers' fields due to a high variability of crop residue distribution on soil surface, because of harvesting operations. The objective of this study was to provide, for measuring crop residue biomass in the field, an accurate, robust and generic method for a large range of crops. This method relies on the use of sampling microplots (0.5 × 0.5 m), located along a transect and taking into account harvesting operations (harvesting direction and width) to capture this variability. This method was tested from 2009 to 2011, in farmers' plots after harvesting, on wheat, grain maize, spring barley, field pea, rapeseed, fababean and sunflower crops. The comparison of results obtained with one or two transects (one perpendicular and the other diagonally across harvesting direction) shows that the accuracy of the estimates is sufficient using a single transect, allowing for a reduction of the working time. The accuracy of this method of collection is not affected by soil management practices (shallow till versus no-till). [ABSTRACT FROM AUTHOR]