Agriculture Reference
In-Depth Information
especially for salinity and sodicity, an appropriate compromise is to take samples
from the surface soil (0-15 cm) and subsoil (45-55 cm). Chapter 6 deals with the
topic of benchmarking soil health in vineyards on the basis of soil chemical, physi-
cal, and biological properties.
Soil Testing for Salinity
Soil salinity is routinely measured using a conductivity meter that responds to the
total concentration of dissolved salts in the soil (see “Water Quality,” chapter 2).
A sieved sample of soil is made into a glistening paste with distilled water; the EC
of the resultant solution—the saturation extract—is called the EC e . In Australia,
EC iscommonlymeasuredina1:5soil-to-waterextractsowhensoil EC values are
reported, the method of measurement must be specified. Appendix 2 gives a table
for converting from EC (1:5)to EC e .
Chapter2discussessoilsurveysandmakingEMmeasurements,whichcan
be calibrated to indicate salinity levels in salt-affected soils by means of a set of soil
samples and a conductivity meter. Chapter 5 discusses the tolerance of V. vinifera
and rootstocks to salinity. The effect of Na + ions in creating soil sodicity is dis-
cussed in box 2.4, chapter 2.
Correcting Nutrient Deficiencies and Toxicities
Among vines, soil, and the atmosphere, there is a natural cycling of nutrients in
which the winegrower can intervene at various points. This intervention can be
through foliar sprays (appropriate for correcting micronutrient deficiencies), fer-
tilizers(mainlyforthemacronutrientsN,P,K,Ca,andMg),manures,andcom-
post.Eachofthesemethodsisdiscussedinsubsequentsections.heeicacyof
nutrient management by these means depends on the point in the cycle at which
intervention occurs and its timing in relation to the growing season.
Nutrient cycling is best illustrated with reference to N, which is a key nutrient
afectingcanopygrowth,fruityield,mustfermentation,andultimatelywinequality.
Nitrogen Cycling
Figure 3.12 shows the N cycle in a vineyard. Atmospheric N 2 gas enters the cycle
through legume N 2 fixation (see box 5.2, chapter 5). There are also “free-living”
bacteria and Cyanobacteria in soil that can fix N 2 , but their contribution in vine-
yards is small compared with that of legumes in cover crops.
The N-containing gases nitrous oxide (N 2 O) and nitric oxide (NO) enter
the atmosphere from natural or anthropogenic sources. Nitric oxide is oxidized
in sunlight to nitrogen peroxide (NO 2 ), which dissolves in water droplets to
Search WWH ::




Custom Search