Agriculture Reference
In-Depth Information
100
Macroaggregation
(temporary)
Microaggregation
(persistent)
0
1
2
3
4
Soil organic C (%)
Figure 7.7
The relationship between soil aggregation and the soil's organic C content (redrawn from
White 1997).
The role of organic matter, roots, and organisms in stabilizing micro- and
macroaggregates in the soil is discussed in section 3.2.2. Key indicators of aggre-
gation are the organic C content and the nature of the organic C components, as
shown in figure 7.7. In vineyards, growing cover crops and mulching are two im-
portant ways to increase soil organic matter and improve biological activity.
7.3.1
Cover Crops
Cover crops are grown in the inter-rows and may comprise annual or perennial
species, grasses, legumes, and other broadleaf plants.
Winter annuals
. These are grown mainly to protect the soil from erosion dur-
ing winter and to improve the soil's ability to resist compaction when wet. Sown
in autumn to allow germination and growth before the coldest part of the win-
ter, the crop should be mowed in early spring to minimize the risk of frost dam-
age to the vines. The crop is usually incorporated into the soil in early summer
to minimize competition for water and nutrients, and to act as a green manure
(section 5.3.2). Many species of winter annuals are used, depending on the cli-
mate, such as the following:
• Cereals: barley (
Hordeum vulgare
), wheat (
Triticum aestivum
), triticale (a
hybrid of wheat and rye), and oats (
Avena sativa
), with and without
legumes such as vetch (
Vicia sativa
), field pea (
Pisum sativum
), faba bean
(
V. faba
), and subterranean clover (
Trifolium subterraneum
)
• Grasses: fescue (
Vulpia myuros
), annual bluegrass (
Poa annua
), and annual
ryegrass (
Lolium rigidum
), with and without legumes
Legume crops fix N
2
and may add a net 50-100 kg N/ha/yr when cultivated
into the soil. This extra N may contribute to excess vigor in vines on more fer-
tile soils. Grasses with their fibrous root systems are better for improving soil struc-
