The in-field rainwater harvesting tillage technique (IRWH), developed by the Agriculture
Research Council (ARC), has been scientifically tested on clay soils at Glen Agricultural
Institute by comparing with conventional tillage (mould board and disc ploughing). They
showed that the IRWH crop production technique is by far more sustainable than
conventional tillage. Great progress was made with the transfer of the information to
rural communities located in the Thaba Nchu district. More than a thousand
households applied IRWH in their homesteads during a period of three seasons of
extension. According to socio-economic surveys, IRWH contributed significantly to
reduce the risk of food insecurity at household level. Some of families who had access
to tractors and implements identified the need to apply the IRWH on their crop fields. A
tillage workshop was held at Merino village in November 2003 where several
implements were demonstrated, but no-one implement was able to create the well
known surface structure of the IRWH to the satisfactory of the community. Hence, the
first part of the study was designed to develop and test tractor drawn implements as a
primary step for out scaling the IRWH technique.
Several tractor drawn implements were designed and tested in collaboration with
Bramley Engineering Company. Only two implements were further tested, viz. the ridge
plough designed as a primary tillage tool for creating zero gradient contour rides, and
the puddler plough designed as a secondary tillage tool for preparing the micro-basins
along the ridge. These implements were demonstrated at Paradys Experimental farm of
the University of the Free State to communal farmers, which indicated that the
implements are acceptable to them. A land preparation procedure was developed for
cultivating crop field sizes up to 150 ha in association with small scale farmers.
Standard practices applied in zero tillage for weeding and pest control was adopted for
IRWH. Maize was harvested with a combine harvester equipped with precision
technology. Unfortunately maize planting commenced late due to the severe drought
and was then disrupted by long periods of continuous rain, typical of semi-arid zones.
Earlier planting areas gave yields up to 4500 kg ha-1, which provide ample proof that
economical yields can be obtained on 50 รข 150 ha crop fields. The study concludes
that it is possible to commercialize the IRWH crop production technique and hence demonstrates the bio-physical view point that it is possible for communal and small
scale farmers to practice IRWH on their crop fields.
The second part of the study focused on variation in soil properties associated with the
soil water storage on crop fields. For this study a 55 ha crop field under IRWH was
used. Soils of the field were surveyed and the area was divided into 75 plots of equal
size. These plots were used to take soil samples and soil water content. The pipette
method was used for determining the clay and silt fractions of the 300 mm soil layers,
while the neutron soil water meter was used for measuring the water content in the
same layers. A mobile EM38, linked to a global positioning system, was used to
estimate soil properties (clay plus silt content and soil water content) from the
correlation between EM readings (electrical conductivity; EC, mS m-1) and the
measured variables obtained in selected plots. The results showed reasonable good
relationships between the EC and clay plus silt content, which allowed the estimation of
a textural based management zones for the crop field. The textural relationship was
further exploited to estimate the profile available water capacity (PAWC) and hence the
delineation of PAWC management zones. A good correlation between EC and soil
water content for the profile was obtained, which laid the foundation to estimate soil
wetness spatially over the crop field. Thus, this part of the study provided conclusive
evidence that it is possible to estimate the variation in soil water storage with
electromagnetic induction methods. Hence it opens a new and exciting research field
in soil water management that will change the landscape of precision farming in the
next decade. It is envisaged that variation in soil water will be managed more
intensively over large fields, especially in semi-arid zones, to optimize inputs related
fertilization, planting rates, pests and weed control.
The last objective of the study was to improve our understanding of how rainfall
characteristics and soil physical properties influence the partitioning of rain into
infiltration and runoff in the IRWH system. A mobile rainfall simulator was used to
simulate rain storms of three different intensities, viz. low (33 mm h-1), medium (59 mm
h-1) and high (122 mm h-1). Results obtained from the experiment demonstrated the
importance of the influence of rain intensity on the infiltration parameters, such as time
to runoff, time to final infiltration rate and final infiltration rate. The correlation matrix and
multiple regression statistics make it possible to characterize the interaction between
rainfall intensity and soil physical properties to predict the various infiltration parameters. From the infiltration-runoff relations it was clear that these soils exhibit a
high potential to harvest water as required by the IRWH system.
This study left the researchers with the following research challenges, namely (i) the
socio-economic factors associated with the application of the mechanized IRWH
technique at farm scale and (ii) the application of the EM38 to estimate soil wetness
and other chemical properties in a wider range of soils and conditions.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ufs/oai:etd.uovs.ac.za:etd-08302010-104352 |
| Date | 30 August 2010 |
| Creators | Bothma, C B |
| Contributors | Dr PAL le Roux, Prof LD van Rensburg |
| 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-08302010-104352/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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