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

Summary

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.