Effective bench terrace width for vegetable growth: a case study of Mgeta, Western Uluguru Mountains, Tanzania.
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Date
2001
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Sokoine University of Agriculture
Abstract
Terraces are the structures that need be designed to safely and economically collect and
transport water to the designed out let. Bench terraces will either hold a lot of water or a
little amount of water leading to landslides and crop stress respectively and this depends
on the terrace width. A study was conducted at Mgeta, Western Uluguru mountains in
Tanzania to determine the effective bench terrace width for vegetable growth. The
experiment was conducted in four bench terrace widths of 0.6 m, 1.0 m, 1.6 m and 2.0 m
in four blocks. It involved the assessment of catchment characteristics (physical and
hydraulic properties and stream sizes) and performance indicators in the terraces (soil
wetting pattern, the distribution uniformity, adequacy of retained soil moisture,
landslides occurrence, crop yield and specific yield). The soils of the catchment were
sandy loams with acceptable porosity (52.2% to 58.5%) which differed significantly
between the blocks (P<0.05) and acceptable bulk density (1.1 to 1.3 g/cm3) which did
not differ between blocks (P>0.05). This indicated low soil compaction. The infiltration
rates and hydraulic conductivity were very high with means of 14.6 cm/hr and 8.0 cm/hr
respectively and differed significantly between blocks (P<0.05) and this indicated high
drainage and low soil moisture retention. The soil depth was moderately deep with a
mean of 35.43 cm which indicated low soil moisture retention. The calculated stream
sizes ranged from 1.39 1/s to 2.73 1/s while the observed stream sizes ranged from 0.25
1/s to 1.5 1/s and differed significantly (P<0.05). The distribution uniformity coefficient
was highest in a 1.6 m terrace width (60%) and lowest in a 2.0 m width (21.4%). A
width of 2.0 m had the highest water equivalent depth (62.5 mm) and retained the highest level of moisture (11.5 mm). This indicated excessive loss moisture of through
deep percolation which resulted into a reduction in crop yield. The observed equivalent
water depth and soil moisture retention were lowest in a 0.6m width. Landslides did not
occur in all the terrace widths. The relative water supply (RWS) was highest in a 1,0m
width (1.02) and indicated that the moisture retained in this terrace width was adequate.
This resulted into highest specific yield (0.86 t/ha). The relative water supply was lowest
in 0.6m width and resulted into a relatively higher crop yield (0.43 t/ha). The specific
yield was highest in a 1.0 m width (0.86 kg/m3)and lowest in a 2.0 m width (0.41
kg/m3). However, the crop and specific yield in all the terrace widths were below the
recommended. It was concluded 1.6m width performed effectively and better than a rest
of the widths. Hence, 0.6m to 1.6m is a best range of terrace width in the area.
Description
Dissertation
Keywords
Bench terraces, Transport water, Mgeta, Western, Uluguru Mountains, Tanzania