Agriculture Reference
In-Depth Information
rotation system with food crops to benefit soil fertility and soil organic matter and
thus contribute to sustainability of the agricultural system.
transient grazing systems
In parts of Africa, and in some other parts of the world, transient grazing systems
have long been and in some cases continue to be important. Such systems involve the
systematic movement of animals during each year depending on plant growth and
thus feed availability. A classical example is the grazing of livestock in the interior
delta of the Niger River in West Africa during the dry season and their movement
to desert areas during the rainy season when the interior delta floods. This system
persisted for centuries but has been compromised by conversion of much of the dry
season grazing land in the delta to crop production in response to human population
growth. Also, some land has been lost to oil production and to reduced security due
to wars and insurgence stemming from conflicts over oil.
Pastoral grazing systems on land that is too arid, cold, infertile, or steep for crop
production occur on large areas of land and provide valuable animal products, often
critical for a reliable food supply for pastoral peoples.
grazing systems Integrated with cereal Production
In dry climates, including notably North Africa and much of the Middle East, live-
stock grazing (largely sheep and goats) is closely integrated with cereal production
by yearly alternating cereals with grazing. Grasses and forbs that grow during the
rainy season of the fallow (noncereal) year are an important source of feed during
that season. Following grain harvest, animals graze the stubble, including the straw,
spilled grain, and weeds. Straw may be used to supplement diets late in the stubble-
grazing season and at the start of the rainy season. In drought years when rain is
inadequate to produce a grain crop, the cereal foliage may be grazed. Plant nutrients
in crop residues and in plants other than cereals are largely returned to the land,
contributing to sustainability of the system.
Adverse effects of some grazing systems
Problems associated with grazing systems include soil erosion due to loss of plant
cover and overgrazing and impacts on wildlife habitat and biodiversity. Overgrazing
can be avoided by adjusting stocking rate. Several factors make it difficult to achieve
an optimum level of plant use for long-term sustainability. The wide seasonal and
yearly variation in rainfall means that the optimum number of animals on average
for a given area may result in underutilization of forage in a high-rainfall year and
damage to the plant biota in a drought year. More detailed descriptions of man-
agement of grazing lands are available (Bradford et al., 1999; Bradford, 2001). For
pastoral peoples, wealth is often based on numbers of animals owned rather than
on productivity of the herd or flock. The animals owned may be the primary buffer
against crop failure or drought. Higher stocking rates than desirable ecologically
have contributed to the tarnished reputation of livestock grazing as a cause of envi-
ronmental degradation.
