Assessing phosphorus management among organic farming systems: a farm input, output and budget analysis in southwestern France

Organic farming is gaining interest worldwide due to its low environmental impact. However, questions still remain about its long-term sustainability, particularly in terms of nutrient management. There is debate about the ability of organic farming systems to compensate for nutrient exports due to crop and animal production. Stockless systems are considered as the most critical and they are generally associated with negative farm-gate nutrient budgets. In this study, we examined the farm-gate nutrient budgets of 23 organic farms located in southwestern France, with special focus on stockless farming systems. Phosphorus (P) was taken as a case study due to the issue of its critical management in organic farming systems. The farms were characterised on the basis of interviews with farmers and the soil nutrient status was assessed through soil sampling. Results showed that none of the farms imported rock phosphate fertiliser. On the contrary, most farms imported organic fertiliser and/or compost and manure, the latter from neighbouring farms or urban areas. As a consequence, stockless farm P budgets were not necessarily negative and options existed from achieving better nutrient cycle closure. However, soil P test was low to moderate in many cases. These results suggested that P management in organic farming systems is not simply related to the mixed versus specialised characteristics of the farms and that nutrient cycling should be addressed and assessed at a larger, e. g., district, scale.