Large areas of cultivated land in Ethiopia frequently suffer from drought, causing low
crop yields and food insecurity. It was hypothesized that it may be possible to alleviate
this problem by employing infield rain water harvesting (IRWH). Three representative
semi-arid ecotopes in the Rift Valley were selected to test this hypothesis. They were the
Melkassa Hypo Calcic Regosol, The Dera Calcic Fluvic Regosol and the Mieso Hypo
Calcic Vertisol. The climate, topography and soils of the ecotopes were characterized in
detail.
Rainfall runoff studies were carried out over two rain seasons on replicated plots on these
ecotopes comparing two soil surface treatments. They were conventional tillage (CT),
simulating the initially fairly rough surface which results after normal tillage; and no
tillage (NT), simulating the flat crusted surface expected on the runoff strip of the IRWH
system. Rainfall amounts, rainfall intensity at one minute intervals, and runoff, were
measured for each storm during the two rain seasons on each ecotope. The results were
used to calibrate and validate the Morin & Cluff runoff model in order to enhance the
extrapolation capability of the study results to other similar ecotopes.
The study yielded the following useful results.
· The rainfall pattern on all the ecotopes was characterized by occasional storms with
fairly high amounts and high intensities (Pi) which greatly exceeded the final
infiltration rates of the soil, causing a high proportion of the rain (P) to runoff (R), i.e.
producing a high R/P ratio. For the NT treatment final overall R/P values for the two
seasons on the Melkassa, Dera and Mieso ecotopes were 0.45, 0.52 and 0.32,
respectively. These high values indicate that IRWH should produce a significant
increase in yield due to its ability to reduce R to zero while concentrating the runoff
in the basin area and increasing the water available for transpiration and therefore
increasing yield.
· Because of the textural and mineralogical properties of the topsoils, particularly the
two Regosols soils; they disperse and form crusts easily when impacted by high intensity rain. The result was that after cultivation at the start of the rain season the
surface of the CT treatment soon became very similar to that of the NT treatment.
Accordingly no significant difference was found between the runoff from the NT and
CT plots on the Melkassa Regosol and Dera Regosol. There was, however, a
significant difference in this respect on the Mieso Vertisol with a more stable surface.
· Runoff prediction in all the ecotopes were well done by the M & C model.
· Two separate strategies were developed to estimate the maize yield increase that
could be expected on the Melkassa Regosol by employing IRWH. From the nearby
Melkassa Research Station it was possible to obtain maize yields for 15 seasons
(1989-2003). These were used together with climate data, the CROPWAT model, and
the runoff measurements, to estimate the benefit of IRWH. The two strategies
produced yield increase estimates of 33% and 40% compared to CT.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ufs/oai:etd.uovs.ac.za:etd-06132007-152255 |
| Date | 13 June 2007 |
| Creators | Welderufael, Worku Atlabatchew |
| Contributors | Dr M Hensley, Dr PAL le Roux |
| Publisher | University of the Free State |
| Source Sets | South African National ETD Portal |
| Language | en-uk |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.uovs.ac.za//theses/available/etd-06132007-152255/restricted/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University Free State or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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