The risks associated with climate and its variability over the Free State Province is the major
determining factor for agricultural productivity, and has a major impact on food security across the
province. To improve productivity of agricultural lands, producers and decisions makers have to be
provided with relevant agrometeorological information that will enable them to make appropriate
decisions. This has lead to the investigation of this agroclimatological risk assessment for maize
production in the Free State. The ultimate goal was to characterize the agroclimatological risks
impacting negatively on dryland maize production and develop a climate risk tool that will assist the
stakeholders in their management of agricultural lands. First, meteorological data needed to perform
this study was prepared by looking specifically at filling the missing data gaps and using alternative
data in cases where measured data was not available to obtain good spatial distribution of weather
stations.
Frost was identified as one of the climate hazards affecting the maize plant in the Free State. Three
frost severity categories were analysed, namely 2°C, 0°C and -2°C representing light, medium and
heavy frost respectively. The onset of frost for all the thresholds was earlier over the northern, eastern
and far southeastern parts of the Free State province while places over the western and southwestern
parts of the province the first frost dates are later. The northern and eastern parts are also marked by
late cessation of frost giving a shorter frost-free period (220-240 days at medium frost severity). The
western and southwestern areas mostly have earlier cessation of frost resulting in relatively long frostfree
period with ranges from 241 to 300 days at medium frost severity level. Cessation of frost
occurring later than normal over the Free State can impact negatively on the maize crop if planted in
October and early November, especially over the highlands. Productivity of the crops can also be
hampered by earlier than normal onset of frost that affects maize at silking and grain-filling stages.
The onsets and cessation of rains together with the duration of the rainy season also play an
important role in agricultural planning. Over 300 stations across the Free State were analysed to
characterize the rainy season. The onsets of rains were found to be early over the eastern parts of the
province with median onsets on or earlier than 10 October. In most areas over the Fezile Dabi and
Motheo districts, onsets are between 11 to 30 October while over the Lejweleputswa onsets are
mostly between 21 October and 10 November. Most of the western parts of Xhariep experience later than 21 November at 50% risk level. The cessation of rains does not vary much over the Free State
with most places having their median last rains between 21 April and 30 April. Rainy season lengths
are longer over the Thabo Mofutsanyane district with over 200 days in some places. The ENSO
episodes are related to Free State seasonal rainfall variability but only have slight effect on the
cessation of rains while onsets of rains showed no differences between El Niño or La Niña phases as
compared to all the years. In El Niño years the seasonal rainfall amount is lower than normal, being
higher than normal in La Niña years which support findings from other studies. The cessation of rains
occurs earlier in El Niño years and later than normal in La Niña years.
Agricultural drought is one of the most devastating hazards affecting maize production in most
growing periods depending on the location. It is important to plant during periods which minimise
drought conditions. In this study a simple water balance model developed by FAO called WRSI was
used to quantify drought risk. When using the 120-day maize cultivar as a reference, drought index
over most parts of the Lejweleputswa, Xhariep and eastern parts of the Motheo district show high
vulnerability (WRSI<40) for October planting dates while other areas have relatively low risk of
drought. In December and January planting dates drought index over most parts of the province
showed much improvement but places that showed low risk are over the Thabo Mofutsanyane, Fezile
Dabi and pockets of northern Lejweleputswa district.
Poone AgroClimatic Suitability Index (PACSI) was introduced to integrate all the climate hazards
affecting maize production in the Free State. The index in made from the combination of frost
probability over the growing period, non-exceedence probability of onset of rains and agricultural
drought index. The index was further used to delineate the suitable areas across the Free State for
planting maize variety requiring 1420 growing degree days (heat units) to maturity. The findings
obtained from the resulting maps show areas of high maize production suitability over the Thabo
Mofutsanyane district for mid-October to early November planting dates. Places over Fezile Dabi and
northern parts of the Lejweleputswa district also showed high suitability of maize especially for
planting from mid-November to end of December. The western and southern Xhariep district area is
not suitable for planting maize while other marginal dryland maize production areas include western
Motheo, southwestern Lejweleputswa and most parts of the central and eastern Xhariep.
To conclude the study, the Free State Maize Agroclimatological Risk Tool (FS-MACRT) was
developed to provide agroclimatological risk information important to the production of rainfed maize
in the Free State Province. The tool is to be used by the farmers, extension officers, policy-makers
and agricultural risk advisors. The tool has two main parts, 1) climatological risk and 2) forecasting.
The climatological risk enables the user to obtain drought stress risk for the 100-day, 120-day and
140-day maize cultivars for planting window starting in October to January. The best planting dates
based on the risk associated with the climatology onset and cessation of both rains and frost can be
determined. Using climate forecasts obtained from the national forecasting centres, drought index can
be predicted for different planting dates giving the farmer valuable information when planning for the coming season. The tool also has the functionality of predicting onsets of rains using weather and
climate forecasts.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ufs/oai:etd.uovs.ac.za:etd-10182011-125711 |
| Date | 18 October 2011 |
| Creators | Moeletsi, Mokhele Edmond |
| Contributors | Prof WA Landman, Prof S Walker |
| 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-10182011-125711/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. |
Page generated in 0.0029 seconds