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What is Semiarid agriculture?


Semiarid agriculture in this context is defined as agricultural production in semiarid areas constrained by low rainfall, poor or low nutrient soils, high temperatures, high solar radiation, and low precipitation.

High transpiration and evaporation rates in vegetated areas are also dominant hydrological features of a semiarid agricultural environment. Therefore, natural fragility of dry land ecosystems renders them extremely vulnerable to inappropriate land use and exploitation. Farmers often over-cultivate the few available areas of fertile land in an attempt to increase production. This implies that these dry land communities are likely to become vulnerable to climatic variations.

Characteristics: land use and degradation

Land use in semiarid agriculture is characterized by subsistence agriculture and nomadic pastoralism. Because livestock is considered an important component in the livelihoods of semiarid communities, degradation has always been attributed to this sub-sector (Sidahmed and Yazman, 1994).

The United Nations Environment Program (UNEP) singled out human impact and, specifically, livestock grazing as the causes of the irreversible degradation that has prevailed during the past two decades (Pearce, 1992).

According to the Word Resources Institute (WRI, 1992), over grazing is the pervasive cause of soil degradation. It has been estimated that overgrazing causes land degradation of 49 and 80% in semiarid regions of Africa and Australia, respectively.

Rangeland Degradation Since 1945

Rangeland Degradation Since 1945
Percentages indicate the contribution of overgrazing to total degraded area. Source: WRI (1994)

Challenges in semiarid agriculture
According to world population statistics, approximately one billion people live in semiarid regions worldwide and yet the number of people living and deriving their livelihoods from the productivity of these marginal lands is growing by the day.

This ever-increasing population is creating a strain on the existing food sources and thus putting food security of these areas in jeopardy. Moreover, these less favored lands are characterized by erratic weather conditions, limited rainfall, and low soil fertility.

Semiarid areas have at least one entirely rainless month/year and the amount of rainfall ranges from 500 to1000 mm per annum in most areas. This means that conditions of water deficit, water stress, or drought are common.

In cases of extreme drought stress, crops yield poorly or not at all if drought stress during reproductive growth is severe and persistent.

Changes in severity of drought contribute to dry land degradation and desertification. This process has been evident In the Sahel region (West Africa) where rainfall levels have declined by 20 to 40% in recent decades accompanied by severe land degradation.

The amount of rainfall that can be effectively utilized for crop growth in these lands is also low. However, this effective rainfall can be increased through water harvesting.

On the other hand, high temperatures also pose serious limitations in crop productivity especially when water supply is inadequate. This can be manifested through poor development of crop yield structures (poor floral initiation) and ultimately poor yields. Cultivation in semiarid areas is also associated with long periods of high winds, which can remove fertile topsoils causing soil erosion.

Challenges related to soils are either due to low nutrients, presence of alkaline, saline, or acidic soils. The majority of semiarid soils are prone to salinity and this poses a major constraint to crop production.

In acidic soils, aluminium toxicity has been implicated in reducing crop growth. All these constraints present a huge challenge to increasing agricultural productivity in semiarid areas.

Agricultural researchers, policy makers and other key stakeholders that are actively involved in promoting or increasing agricultural productivity in semiarid areas all seem to agree that the solution to this challenge lies in sustainable agricultural production.

This concept of sustainable agricultural production entails improved management of the available and limited resources and use of improved crop production technologies that can enhance sustainable production in semiarid areas.

Improved use of the limited resources can be achieved by managing the natural resources sustainably; for example, use soil and water conservation measures to prevent land degradation (mainly through soil erosion and run off), and conserve soil fertility and improved use of the water resources through rainfall harvesting.

Rainfall harvesting, defined as capture, diversion, and storage of rainwater for plant growth, can increase water availability, soil fertility and crop production. It can also provide even broader environmental benefits especially in arid and semiarid regions.

However, greater involvement of the farmers from planning through sensitization/education and implementation stages is needed to expand the contributions of water harvesting in sustainable agricultural production and development in semiarid areas.

Development of appropriate genotypes suitable for the semiarid environment through appropriate genetic enhancement or biotechnology programs will go a long way towards increasing agricultural productivity while ensuring sustainable agricultural production.

For example use of genetically enhanced early maturing genotypes or genotypes tolerant to salinity are likely to be more productive in semiarid areas where water deficits and salinity, respectively, are more severe.
Read more on related pages:

Semi-arid agriculture - Syngenta Foundation for Sustainable Agriculture