247-1 A Tactical Decision Support System to Optimise Nitrogen Management.
Process-based crop growth models are dedicated tools to assess the impacts of different cropping systems inputs, i.e. agro-environmental conditions, management and weather, on the crop harvestable organs. However, N management optimization remains very complex as the expected impacts are delayed in time from the moment of N application. Quantifying the risk associated to hypothetical climatic time-series representative of the local conditions is a suitable approach.
The STICS model was used to simulate the growth of a winter wheat crop. 300 synthetic weather time-series representative of the local weather were derived from 30-years historical records using the LARS-Weather Generator. Decision rules, integrating agronomic, economic and environmental objectives, were derived to optimize farmers’ revenues while minimizing detrimental environmental impacts, when optimizing N management practice.
To improve the decision-making process, an advanced tool was designed, embedding all these components and including a retro-active loop accounting for phenological development. The tool determines first the timing of N application for Zadoks stages 23, 30 and 39. Two fix doses of 60kgN.ha-1are always applied at stages 23 and 30. At stage 39, the tool enters in a tactical N optimization process, evaluating the best N rate using 300 climatic projections.
Results suggest that the third N application should most of the time be reduced in comparison to the current farmers' practice. Following economic constraints (selling price and N cost) and environmental pressure, 3 years out of 4, 10 to 30kgN.ha-1 could be systematically saved, increasing the N use efficiency by 5 to 20%.