Reactive nitrogen (N) flows (all forms of N except N-2) are greatly increasing worldwide. This is mainly due to the ever larger use of inorganic N fertilizers used to sustain the growing food production. N flows have major impacts on water, air and soil quality as well as on biodiversity and human health. Reconciling the objectives of feeding the world and preserving the environment is a great challenge for agriculture. One of the main ways to increase food production while reducing its detrimental effects is to increase the efficiency of N use. N use efficiency (NUE) is a commonly used indicator to estimate efficiency of N use at the farm scale, It is defined as the ratio of farm N outputs to N inputs. However, it has some inconsistencies and biases, which raises questions about its reliability for assessing N efficiency of farming systems, As a consequence, we propose a new indicator, called system nitrogen efficiency (SyNE), which is based on NUE and improves upon it in several ways. First, life cycle inventory references are used to estimate N emissions linked to the production of inputs outside the farm. Second, net N flows are calculated by subtracting inputs and outputs of the same product in the farming system. Third, manure is not considered an end product, unlike crop and animal products. Finally, the annual change in N in soil organic matter is estimated. SyNE therefore expresses the efficiency of a farming system in transforming N inputs into desired agricultural products. It takes into account all sources of N, including the annual change in soil N stock as well as N losses occurring during the production and transport of inputs. To test the relevance of this new indicator, 38 mixed farms were surveyed in Brittany, France, and their NUE and SyNE were calculated and compared. Sensitivity analysis was performed to estimate the contribution of each variable to both indicators. We demonstrate SyNE is a useful indicator for comparing the N efficiency of different farming systems. We discuss its use in combination with system N balance (SyNB), a N loss indicator at the system scale. The combination of both indicators gives a more reliable estimate of the productive efficiency and potential environmental impacts of N in various farming systems

Improving nitrogen (N) efficiency is a priority for increasing food production while reducing its environmental impacts. N efficiency indicators are needed to achieve this goal, but current indicators have some limitations. In particular, current N efficiency indicators are not appropriate tools to compare farming systems with different types of production because animal N efficiency is, by nature, lower than crop N efficiency. A novel N efficiency indicator called “relative N efficiency” was developed to address this issue. It was calculated as the ratio of the actual N efficiency of the farming system to the weighted mean of the potential efficiency of each type of product output provided in literature reviews. Relative N efficiency was calculated for 557 farms of various types from France and Italy. The relative N efficiency indicator was validated by comparison with a statistical approach based on multiple linear regression. Statistical analysis showed that relative N efficiency was independent of production type and could therefore be used for unbiased comparison of different farming systems. Relative N efficiency was particularly interesting when comparing mixed farming systems with different proportions of animal and crop production.

Agroecology represents a pertinent option to improve the sustainability of agriculture. To promote its application, agroecological concepts should be taught to students and professionals in the agricultural sector. However, most agricultural courses are not adapted to teach these concepts due to little interactivity or interdisciplinarity, and a lack of a systems approach to farm management. Serious games help to fill these gaps by simulating complex models in which players can learn by doing. We thus developed a serious computer game, called SEGAE (SErious Game for AgroEcology learning), which represents a mixed crop-livestock farm and assesses impacts of farming practices on indicators related to environmental, economic, and social sustainability. Its pedagogical interest was evaluated through two types of surveys given to university students who played the game during a one-week workshop: A knowledge survey on agroecology, and a feedback survey based on flow theory. Results showed that students increased their knowledge of agroecology significantly, particularly those who had had little knowledge of crop production. More than 86% of the students enjoyed the game, appreciating its interaction and feedback. Thus, SEGAE is an interesting tool to help students acquire knowledge of agroecology in a fun way by facilitating interdisciplinary and collaborative learning.