A ‘textbook’ plant typically comprises about 85% water and 13.5% carbohy-
drates. The remaining fraction contains at least 14 mineral elements, without
which plants would be unable to complete their life cycles. These essential
mineral elements include six macronutrients – N, K, P, S, Mg and Ca – which
are present in relatively large amounts in plant tissues (mg g−1
of dry tissue),
and several micronutrients, including Fe and Zn, which are present in smaller
amounts (µg g−1
of dry tissue).
In most agricultural settings, commercial fertilizer
provides only one source of N used for crop production.
Animal manure, biological N ﬁxation, mineralization from
soil organic N, and deposition of N from the atmosphere
can also contribute to soil fertility and surface water
contamination. Because there are multiple sources and
sinks of N in the soil, the relationship between N fertilizer
application rate and nitrogen loss in drainage water is not
always consistent across locations and across studies.
If the soil becomes saturated, oxygen may become
scarce and in anoxic conditions, denitrifying bacteria may
convert the nitrate to nitrogen gases (NO, N2O, and N2).
Nitrogen converted to these gases becomes unavailable for
plant uptake or for surface water contamination.
Additionally, saturated soil during the growing season is
harmful to many crops like maize that cannot tolerate low
oxygen concentrations in the root zone for more than a few