Agriculture Reference
In-Depth Information
Vine row
+ −
NH
4
and NO
3
from
atmosphere, fertilizers
Leaf fall,
prunings
N
2
fixation
Volatilization
NH
3
Cover crop (with clover)
+
Organic N
Ammonification
NH
4
fertilizers
Immobilization
NH
4
+
N
2
Nitrification
−
N
2
O
NO
3
Uptake
Denitrification
Leaching
Figure 3.12
The nitrogen (N) cycle in a vineyard. (White, 2003)
form nitric acid and contributes to “acid rain.” Ammonia gas released to the air
from NH
4
-N fertilizers, animal dung, and urine (see box 3.2) also dissolves in
water droplets or is adsorbed as NH
4
+
ions on dust particles, to be returned to
the land in rain or as “dry deposition.” These N inputs are most significant in
industrialized areas where they can be as much as 60 kg N/ha/year, but inputs
are as low as 5 kg N/ha/year in rural areas that do not have large animal feedlots
or dairies.
Nitrogen Fertilizers
Table 3.9 gives the more important water-soluble N fertilizers used in viti-
culture. Fertilizers such as Nitram (NH
4
NO
3
) and urea ((NH)
2
CO) supply
only N (“single” fertilizers), whereas others such as KNO
3
and (NH
4
)
2
SO
4
supplymorethanonenutrientandarecalledmultinutrientfertilizers.Mixed
or blended fertilizers are made by mixing single or multinutrient fertilizers
and are usually identified by their N-to-P-to-K ratio. For example, the mixed
