Agriculture Reference
In-Depth Information
Appendix 3 Calculating the Nitrogen Balance and Appropriate Amount of
Nitrogen Fertilizer for Wine Grapes
The amount of fertilizer required is estimated from the nitrogen (N) balance equation
= − −
(A3.1)
Table A3.1 gives some indicative results using this approach, assuming a 10 t/ha grape yield.
The first example is typical of vineyards in southeastern Australia with no
mid-row cover crop, a soil carbon (C) content of 2%, and a C-to-N ratio of 12.5. Two
rates of annual rainfall—600 and 1200 mm—are considered. The second example is
for the same two vineyards, under the same two annual rainfalls, except that a legume
cover crop is grown during the winter and cultivated in as green manure in spring. The
green manure adds 1.5 t C/ha to the soil at a C-to-N ratio of 20.
As shown in figure 3.13, N fertilizer can be applied at two growth stages requiring
about 2-3 g N per vine per week each time, depending on the vine density, as recommended
for Western Australian vineyards. The range of 18-35 kg N/ha per season is similar to
that used in the Bordeaux region, France, where an average of 30 kg N/ha per season is
applied, and also for mature vines in the Willamette Valley region, Oregon. However, the
N input can be two to three times greater for young vines (up to two years old) to get them
established and on sandy soils of low organic matter content. In all cases, the winegrower
should be prepared to adjust the fertilizer input according to plant analysis results.
N required
Inputs
Crop removal
Losses
Table A3.1
Examples of N Fertilizer Required (Measured in Kilograms Nitrogen Per Hectare)
Calculated from an N Balance for a Crop of 10 Tonnes Per Hectare
Example 1: No cover crop
Crop requirement
(shoots plus fruit) less
recycling
a
Estimated
leaching plus
gas losses
b
Amount of
N fertilizer
required
Atmospheric
N input
Net soil mineralization
5
c
10
38
5
28
7.5
d
10
38
15
35
Example 2: With a legume cover crop
Crop requirement
(shoots plus fruit) less
recycling
a
Estimated
leaching plus
gas losses
b
Amount of
N fertilizer
required
Atmospheric
input
Net soil mineralization,
including green manure
5
c
25
38
10
18
7.5
d
25
38
20
26
Note
. N = nitrogen. All figures on an annual basis.
a
Average amount of N required for growth is 76 kg N/ha (range 68-84 kg N/ha, Mullins et al., 1992), less
recycling of 50% through leaf fall and prunings.
b
Depends on soil type and rainfall (plus any irrigation).
c, d
Annual rainfall of 600 mm and 1200 mm, respectively. Atmospheric N inputs are apportioned 50%
dissolved N and 50% dry deposition, except in the higher rainfall environment where dry deposition N
decreases relative to dissolved N.
