To what extent does organic farming rely on nutrient inflows from conventional farming?

Organic farming is increasingly recognized as a prototype for sustainable agriculture. Its guidelines ban the use of artificial fertilizers. However, organic farms may import nutrients from conventional farming through material exchanges. In this study, we aimed at estimating the magnitude of these flows through the quantification of nitrogen, phosphorus and potassium inflows from conventional farming to organic farming. Material inflows and outflows were collected for two cropping years on 63 farms. The farms were located in three French agricultural districts distributed over a gradient of farming activity defined by both the stocking rate and the ratio of the farm area under arable crops. Our results showed that on average, inflows from conventional farming were 23%, 73% and 53% for nitrogen, phosphorus and potassium, respectively. These inflows were strongly determined by the farm production systems. However, for farms similar in terms of production systems, the inflows also depended on the local context, such as the proximity of organic livestock farms: the reliance of organic farming on conventional farming was lower in mixed than in specialized districts. These results highlight the necessity to quantify the contribution of nutrient inflows from conventional farming when assessing organic farming and development scenarios.