Agriculture Reference
In-Depth Information
In summary, N applied at or soon after bud burst has a major effect on
vine growth and crop load during the current season. Nitrogen supplied after
fruit set has a major effect on berry N concentration and on N storage in the
trunk for the following season. Normally, the fertilizer split between these times
wouldbe1:1,butwinegrowerscanadjustthisaccordingtotheirexperience.
Table3.10summarizesrecommendationstoprovideadequateNtovineswith
minimal N losses.
Balancing the Nitrogen Supply
heamountofNfertilizerrequiredduringoneseasondependsonthenetefect
of N inputs (from soil mineralization, legume cover crops, compost, and rain), N
removed in harvested fruit, whether prunings are mulched and returned to the
soil, and any losses. Appendix 3 gives examples of how the N balance and N fertil-
izerrequiredarecalculated.
AdequateNisimportantnotonlyforyieldbutalsoformaintaininganopti-
mum berry N concentration for fermentation. Yeast strains vary in the efficiency
with which they use organic and mineral N for growth. The critical measure of
berry N for satisfactory fermentation is the yeast assimilable nitrogen (YAN),
comprising NH
4
-N and amino acid N (excluding proline). Juice YAN should be
in the range of 200 to 480 mg N/L, depending on the yeast strain, with the opti-
mum around 250 mg N/L for red varieties and 250 to 350 mg N/L for whites.
Table 3.10
Recommendations to Minimize Nitrogen Losses in Vineyards
Recommendation
Expected outcome
Do not apply soluble N fertilizers after harvest
Prevents NO
3
−
being leached by autumn
and winter rains
Do not fertigate before flowering
Prevents leaching when soil is still wet
from winter
Incorporate urea into the surface soil or wash in
with irrigation water (do not apply too much
water before the urea has been converted to
NH
4
+
ions, which are not readily leached)
MinimizesNH
3
loss by volatilization,
especially in warm to hot regions;
avoids soil acidification at depth
Use a legume crop as green manure in the
mid-rows
Provides a slow release of mineral N to
the vines as it decomposes; useful on
sandy soil
Use a controlled release fertilizer (CRF) or slow
release fertilizer (SRF) in-row
Provides a slow release of mineral N;
useful on sandy soil; some slow-release
fertilizers are acceptable for organic
viticulture
Apply sufficient N to balance losses and removals
in product (see “Balancing the Nitrogen
Supply” in this chapter)
ProvidesadequateNforgrowthbut
prevents excess mineral N building up
in the soil
