2.2.12. Soil fertility
The ability of a soil to provide nutrients to plants is known as
soil fertility (Brady, 1990). In this study, an economic value is
attributed to the ability of soil to provide nitrogen (Daily et al.,
1997a).
Nitrogen is one of the main requirements of all crops. Of
the total nitrogen present in soil, the amount in available
forms in the soil is small. Under natural conditions 2% yr− 1
(Brady, 1990) of this nitrogen becomes available to plants.
The amount of nitrogen available to the crops in the next
year was estimated for each field based on soil nutrient
analysis that gives the total nitrogen percentage. This
information was used to calculate the economic value of
nitrogen availability in each field valued at the unit price of
urea (see above).