The empirical results support the opening assumption that jointness can be sensitive to the intensification level. The estimation of jointness only for an average case in a given production system including farms with a wide range of intensity can fail to account for the variability of jointness across farmers. The switch from complementarity to substitution can even be observed within a given production system. Policy recommendations should take the intensification level into account. Recent-developments in farm policies in the industrial world are consistent with these empirical results. From a wider perspective, we show that the objectives of efficient public policy and of trade neutrality should be distinguished. Whenever good information and low administrative costs allow for this, the optimal policy is always an agri-environmental payment proportional to the NCO. This optimal policy will have effects with opposite signs for extensive and intensive situations. For the most extensive farming systems where the commodity and the non commodity outputs are complementary, such a targeted payment increases the private output and therefore increases trade in the exporting country case and decreases trade in the importing country case.
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