In drought-prone arid and semi-arid areas, limited plant available water exerts a tremendous
negative effect on crop production, leading to undesirable low crop productivity, untold food
insecurity, and never-ending poverty. In-field rainwater harvesting (IRWH or In-field RWH)
is specifically designed to trap rainfall within the field and optimise its use to benefit crop
yield and quality, and improve water use efficiency (WUE) in these regions. Two RWH-crop
field experiments were established in the semi-arid area of the Hatfield Experimental Farm,
University of Pretoria, South Africa. The first RWH-potato experiment was conducted during
the 2009/2010 growing season while the second RWH-Swiss chard experiment was carried
out during the 2010/2011 growing season. Three cropping systems were involved: (1)
conventional tillage (CT), (2) tied-ridges (TR), and (3) IRWH with three different design
ratios of runoff area to cropping area (1:1, 2:1 & 3:1). The runoff area of each design ratio
was either bare (B) or plastic-covered (P) and this resulted in six IRWH treatments.
Therefore, there were a total of eight treatments: CT, TR, 1:1B, 1:1P, 2:1B, 2:1P, 3:1B and
3:1P. For both growing seasons, the total plot area yields and WUEs of TR and CT were in
general higher than those of the IRWH treatments. This is because TR and CT had more
plants per plot than the IRWH treatments and the rainfall recorded for the specific seasons
were sufficient, so there was little advantage in collecting/harvesting additional water. In
terms of yields and WUEs expressed on the net cropped area, the IRWH treatments had
higher yields and WUE than CT and TR because they captured more runoff than the latter
treatments. Field trials are expensive, laborious and time consuming, therefore models were
developed to predict potential runoff and crop growth and yield of different RWH techniques
or design ratios. During the current investigation, runoff models such as the linear regression,
curve number (CN) and Morin and Cluff (1980) models were used to describe and simulate
runoff generation from this ecotope. The empirical rainfall-runoff linear regression model
indicated that runoff efficiency declined as runoff length increased. The statistics revealed
that the CN and Morin and Cluff (1980) models simulated runoff very well. Moreover, the
use of a generic crop growth Soil Water Balance model (SWB) showed potential to simulate
crop growth and yield for different RWH techniques and design ratios. During the present
study, the SWB model was modified by incorporating linear runoff simulation models in
order to predict the soil water balance and crop yield under different RWH design scenarios.
Field data collected on the study ecotope contributed to the parameterization and calibration of the SWB model for the crops involved. The SWB model was in general, successfully
calibrated for the potato crop, while the calibration for the Swiss chard crop was generally not
as successful, most probably because of the continuous growing and harvesting system
followed (approach for pastures). The scenario simulation results for potato suggested that for
the study ecotope, if land is limiting, CT, TR and smaller design ratios (1:1) are the best
options in terms of yield per total plot area. However, if land is not limiting, larger design
ratios (2:1 and 3:1) are better options, according to the yields per net cropped area outcomes.
The SWB model shows promise as a useful tool to assist in the selection of the best RWH
strategy and the ideal planting date under specific conditions with minimal input
requirements. However, there is a need to upgrade it to a 2D SWB model for better accuracy
under a range of conditions. / Dissertation (MScAgric)--University of Pretoria, 2014. / lk2014 / Plant Production and Soil Science / MScAgric / Unrestricted
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:up/oai:repository.up.ac.za:2263/43198 |
| Date | January 2014 |
| Creators | Ndayakunze, Ambroise |
| Contributors | Steyn, J.M. (Joachim Marthinus), 1963-, ndambroise@yahoo.com, Annandale, J.G. (John George), 1959- |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Dissertation |
| Rights | © 2014 University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. |
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