Agriculture Reference
In-Depth Information
Box 5.4
Estimating the Appropriate Amount of N Fertilizer for Wine Grapes
The amount of fertilizer required for one season is estimated using an
N
balance
approach:
Amount of N required
Losses (B5.4.1)
Some results using equation B5.4.1, assuming a 10 t/ha grape yield, are given
in table B5.4.1.The first example is typical of a vineyard in southeastern Australia,
for which atmospheric N input is low. The second example is more typical of a
northern European vineyard where atmospheric inputs are higher, and the soils,
through past fertilizer and manure inputs, are more fertile (Schaller 1991). Inputs
from the net mineralization of soil N, and a leguminous green manure crop, can
be included by following the procedure outlined in table 5.5. Volatilization of
NH
3
, even when urea is used, can be minimized through fertigation, but water
application must be managed to avoid leaching losses.
In both cases, the amount of fertilizer N required is not large (12-32 kg
N/ha/yr). This is consistent with the practice in the Bordeaux region, where ca. 30
kg N/ha/yr are applied, and also for mature vines in the Willamette Valley of
Oregon, United States. However, the rate of N input may be two to three times
greater on young vines (up to 2 years old), and on sandy soils of low organic
matter content. In all cases, the grower should be prepared to adjust the fertilizer
input on the basis of tissue testing for N (section 5.2.1).
Inputs
Crop removal
Table B5.4.1
Examples of N Fertilizer Required for a Crop of 10 t/ha, Calculated from an N Balance
Example 1
Crop Requirement
(Shoots Plus Fruit)
Less Recycling
a
(kg N/ha)
Estimated Amount of
Leaching Plus N Required as
Gas Losses
b
Atmospheric
Inputs
Net Soil
Mineralization
Green
Manure Crop
Fertilizer
c
10
10
10
Example 2
10
10
10
2
0
0
20
c
37.5
37.5
37.5
10
27.5
c
2
15
32.5
25
22.5
Crop Requirement
(Shoots Plus Fruit)
Less Recycling
a
(kg N/ha)
Estimated Amount of
Leaching Plus N Required as
Gas Losses
b
Atmospheric
Inputs
Net Soil
Mineralization
Green
Manure Crop
Fertilizer
25
d
25
d
25
d
c
20
20
20
2
0
0
20
c
37.5
37.5
37.5
20
12.5
c
2
30
22.5
50
22.5
a
Average amount of N required for growth
75 kg N/ha (range 68-84) (Mullins et al. (1992)
less recycling of 50% through leaf fall and prunings
b
Depending on soil type and surplus rainfall (plus any irrigation); see table 7.6.
c
See table 5.5.
d
Source:
Data from Schaller (1991) for German viticultural areas
