The primary agriculture is unbalanced, i.e. the amount of plants is much larger than the amount of animals -- in terms of nutrients.
Since most of the production, with its content of nutrients, is exported, the same amount of nutrients (at least) needs to be imported. Most common, theese nutrients are imported in the form of inorganic fertilisers.
It is therefore very complicated to establish an 'organic' primary agriculture. Nutrients need to be imported.
From an ecological point of View, an agriculture with no nutrient circulation and an excess of plants is very immature. It can therefore be expected to leak nutrients. This leakage, 0.2 - 0.3 kg P/ha*yr is however quite small compared to what is exported, which can be 15-20 kg P/ha*yr