Grasslands of the World.pdf - Disasters and Conflicts - UNEP

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Grasslands of the world
it was lip service to the “rotation” doctrine rather than consistent application
of Vil’yams’ example. Much value was attached to having a fodder crop or a
grain legume in the rotation, irrespective of the fact that these covered the soil
for no more than six months and were harvested whole, without much residue
left or returned to the soil. Maize is often harvested first for grain and in the
second pass for the stalks and foliage made into silage. If a crop-rotation effect
does appear it is perhaps just as likely to be due to “just another crop” than to
the specific effects usually attributed to semi -permanent grasses or legumes. In
actual fact, the effect may be simply one of suppression of specific weeds, pests
or diseases, and may also be brought about by other arable crops .
PHYSICAL EFFECTS OF GRASSES ON THE SOIL
Soil science used to be highly developed in Russia , not only soil classification .
The unique role that grass plays in restoring soil quality lost after cropping
was recognized in Russia earlier than in the West. In investigations carried out
by N.I. Savvinov at the Saratov Malouzenski Solonetz Station, the length of
all roots in the top 40 cm soil layer was, six months after sowing, almost three
times greater in Agropyron pectiniforme than in alfalfa of the same age (Larin,
1956). Intensity, rather than depth, of rooting was considered important.
Soil organic matter and methods of increasing it are commonly associated
with high soil quality, because a soil rich in organic matter is often productive
and can sustain arable cropping for long periods. Such a soil will also trap rainwater
rather than let it cause erosion (Klimentyev and Tikhonov, 1995).
Cultivation, in contrast, is accompanied by a decline in organic matter and
by subsequent mineralization. Under continuous cropping without inputs,
little organic matter is added or returned whereas losses are much greater. In
capitalized farming systems in temperate climates, with high input of fertilizers
and mechanical or chemical weed control , organic matter is commonly
regarded as less critical and organic matter may be left to find its own level and
may be maintained by crop residues . High, albeit not the highest, yields have
been obtained under continuous cropping without special attention to adding
organic matter.
Evidence has been presented to indicate that a grass break in crop rotations
preserves soil structure and punctuates the nutrient drain in crop removal.
Improved structure may reveal itself in less erosion or in better plant establishment
and, finally, in better yields . However, the immediate effects on topsoil
structure are the most obvious. Erosion control also applies to conditions of
grazing . Overgrazed land is not only more liable to erosion, it suffers more
from drought , due to loss of snow cover and of rainwater.
MIXED FARMING BASED ON CROP-GRASS ROTATIONS
In Russia , alternatives to deal effectively with maintaining soil quality and
combating soil erosion are not within easy reach of the small-scale farmer