Major opportunities to improve food security and household
incomes are being missed in Sub-Saharan Africa (SSA) because of inadequate
management of agricultural water, especially in rain-fed systems. Moreover,
there are challenges of coping with water scarcity and stress due to climatic
variability. Land degradation resulting from soil erosion by wind and water,
and poor management of soil fertility, also contributes to low rainwater use
efficiency. Sierra Leone receives a lot of rain, with an annual average of 2526
mm. During the wet season, typically between April and November, there is an
excess of water; more than the requirement for crop production. However, the
situation changes drastically in the dry season (December to March) when the
total rainfall is most times 6-8% of the annual rainfall. Rainwater is an
important input factor for healthy and productive ecosystems. Rainwater
harvesting (RWH) in a watershed context has a role and an impact on several
aspects of ecosystems and human well-being. In Sierra Leone, irrigation plays a
minor role as almost all farming activities are rainfed. This study takes an
integrated approach towards agricultural water management with specific
objectives designed to optimise the availability and utilization of water and
move the focus from local field level to basin or watershed scale. This
research was conducted in an Inland Valley Swamp at Njala University, located
in the Southern region of Sierra Leone. A micro-dam with a reservoir of
capacity, 26,500 m3 was evaluated to know the extent to which it can improve
cropping intensity and extend the cropping season. Losses by seepage was high,
amounting to 34% and 27% of stored water during 2014/15 and 2015/16 dry season
respectively. The reduction in seepage could be attributed to the addition of a
layer of soil with high clay content on the upstream of the dam. Despite the
seepage, there was sufficient water to support a second crop with supplementary
irrigation. Yields from the dry season crop were generally higher than those of
the rainy season. This throws more light on the potential for higher yields not
just in the lowlands as against the uplands, but also getting better yields in
the dry season as compared to the wet season. To further improve the
performance of the RWH system, a novel approach was undertaken to improve rice
yields and save water during irrigation, with the addition of Biochar. In doing
so, the effect of biochar on water productivity under various management
practices was investigated. Many studies have demonstrated that using biochar
as a soil amendment can improve the soil carbon content and water
retention. The water management
practices included: the Alternate Wetting and Drying (AWD) method, Aerobic Rice
System (ARS) and the Continuous Flooding (CF) practice. In a period of three
years (2014-2017), rice was cultivated twice a year, wet and dry season. The
highest measured wet and dry season yields, 3.2 t ha-1 and 4.7 t ha-1, occurred
during the 2015/2016 cropping season. In general, dry season yields were higher
than wet season yields, plots with biochar had higher yields than plots without
biochar, and CF plots had higher yields than ARS plots, which in turn had
higher yields than AWD plots. The water management practices had significant
effect on water productivity, with the yields under the ARS being significantly
higher during the dry season of 2015/16 (p = 0.001) and 2016/17 (p= 0.003) than
the CF and AWD. As the small reservoir (or pond) is a key component of the
watershed and is affected by various hydrologic variables, it is critical to
understand the impacts of impending climate change on its functionality.
Typically, this is done using physically-based hydrologic models coupled with
future climate data from General Circulation Models (GCMs). Simulated volume of
water in the pond from the Soil and Water Assessment Tool (SWAT) was calibrated
with observed data for the same period. (2014/15 dry season). A Nash Sutcliffe Efficiency (NSE) value of
0.82 was calculated during the validation of the model. The model also predicted a reduction in the
volume of stored water by the end of the century (2081-2100 as compared to a
baseline period (1961-2000).
Author(s) Details
Mohamed Matthew
Blango
Department of Agricultural Engineering, School of Technology, Njala
University, Sierra Leone.
Please see the book here :- https://doi.org/10.9734/bpi/mono/978-93-47485-35-0
No comments:
Post a Comment