Agriculture Reference
In-Depth Information
FIGURE 2:
(a) Relationship between crop yield and total fertilisation (both expressed in kgNha
−1
yr
−1
) of agricultural land of the different
French d´epartements mainly involved in the Paris food supply. The following mathematical function has been fitted to give the upper and
lower bounds of the data points: yield = Ymax · (1−exp (−Fert/Ymax)), with Ymax = 350−150 kgNha−1 yr
−1
. (b) Agricultural surplus (total
fertilisation minus crop yield) plotted against fertilisation. The corresponding theoretical sub-root water concentration, calculated assuming
a mean runoff depth of 300mmyr
−1
, is also indicated (right scale). The data available for a number of organic farms in the Seine watershed
(unpublished results) are also shown for comparison (open symbols).