A SOILSCAPE SURVEY TO EVALUATE LAND FOR IN-FIELD RAINWATER HARVESTING IN THE FREE STATE PROVINCE, SOUTH AFRICA by Semere Alazar Tekle A dissertation submitted in accordance with the requirements for the Magister Scientiae Agriculturae degree in the Faculty of Natural and Agricultural Sciences, Department of Soil, Crop and Climate Sciences at the University of the Free State, Bloemfontein, South Africa. September 2004 Supervisor: Dr. P.A.L. le Roux Co-supervisor: Dr. M. Hensley DECLARATION I declare that the thesis hereby submitted by me for the Masters of Science in Soil Science degree at the University of the Free State is my own independent work and has not previously been submitted by me to another University / Faculty. I further cede copyright of the thesis in favour of the University of the Free State. Semere Alazar Signature …………………………….. Date: September, 2004 Place: Bloemfontein, South Africa ii ACKNOWLEDGEMENT I am grateful to my promoter Dr. P.A.L. le Roux for his consistent guidance, timely responses, valuable suggestions, invaluable support and unfailing encouragement throughout the research period. My sincere gratitude to my co-promoter Dr. M. Hensley for his unreserved sharing of his long time research knowledge and experience and fatherly advices. My gratitude also to all the staff members of the Department of Soil, Crop and Climate Sciences, particularly to: Prof. C.C. du Preez, the Department Head, for his consistent care and guidance throughout my stay in the University; Mrss. Elmarie Kotze, and Rida van Heerden administrative and logistical things, throughout my study period in the University; and Yvonne Dessels for helping me in many ways regarding laboratory materials and analysis. Mr. Edwin Moyeti, and Mr. Frans Joseph. for their valuable support in my field and laboratory works. My gratitude to Dr. C.H., Barker and Slabbert, E. from the Department of Geography for providing the digital data for the study area and their support in GIS part of the study. I am greatly indebted to my parents, brothers and sisters for their patience and dedication in bringing me up to this level as well as for their consistent and invaluable encouragement. Special thanks my sponsors, the World Bank, project coordinator, the Eritrean Human Resource Development (EHRD) and the University of the Free State. I would also like to thank all my friends, who offered me with their moral and expert advice throughout the research period. My special thanks go to: Teklemariam Bairay, Solomon Afeworki, Mehari Tesfazghi, Kindie Tesfaye, Girma Mamo and many others who helped me morally and otherwise. iii ABSTRACT A SOILSCAPES SURVEY TO EVALUATE LAND FOR IN-FIELD RAINWATER HARVESTING IN THE FREE STATE PROVINCE, SOUTH AFRICA Land evaluation is currently important in South Africa. Soilscape surveys can make a contribution in this connection by bridging the gap between land type surveys and detail surveys. Land Type Dc17 (area = 237 651 ha) east of Bloemfontein include the densely populated areas near Botshabelo and Thaba Nchu. The objective of this study was to subdivide Land Type Dc17 into smaller more homogeneous land units, to estimate the area of each unit suitable for maize and sunflower production using the In-field Rainwater Harvesting technique (IRWH), and to estimate attainable yields of these crops on the available areas. The soilscape survey technique was developed to serve this goal. Soilscape is defined for this specific study as a mapping unit consisting of a portion of land mappable at a scale of 1:50 000 in such a way that it facilitates the identification of potentially arable land. Earlier Northcote (1978) described soil landscapes as areas of land that have recognizable and specifiable topographies and soils, that are capable of presentation on maps, and can be described by concise statements The delineation of 66 soilscapes was done on 1:50 000 maps. Detailed pedological investigations were made on selected pedosequences of some soilscapes using 1:10 000 maps, soil pits, auger holes and depth probe observations. Nine soilscapes with a total area of 82 222 ha were found non-arable. For the remaining 57 soilscapes, covering an area of 155 429 ha, the improved knowledge gained during the detail studies was extrapolated to estimate the area of each one suitable for IRWH. The result was 56 875 ha, or 24 % of the total area of Dc17. The results of previous field experiments on relevant ecotopes predict the following maize yields in tons/ha/yr: conventional tillage = 82 000; simplest type of IRWH = 127 000. It is therefore estimated that this land type can provide the staple maize diet for about 600 000 people using IRWH. iv The soilscape survey technique proved successful within this land type, but should be refined for application to other land types and other feasibility studies. v OPSOMMING ‘n SOILSCAPE-OPNAME OM DIE LANDGESKIKTHEID VIR AFLOOPOPGARING IN DIE VRYSTAAT PROVINSIE, SUID-AFRIKA, TE BEPAAL Landevaluering is huidiglik belangrik in Suid-Afrika. Soilscape opnames kan ‘n bydrae maak in hierdie verband. Dit kan die gaping tussen landtipe- en detailopnames oorbrugLandtipe Dc17 (oppervlakte = 237 651 ha) oos van Bloemfontein sluit die digbewoonde gebiede van Botshabelo en Thaba Nchu in. Die doel van hierdie ondersoek was om Dc17 in meer homogene eenhede te onderverdeel, die oppervlakte geskik vir die produksie van mielie en sonneblom met die Afloopopgaringtegniek (AO) vir elke eenheid te raam, beraming van die moontlike obrengste van hierdie gewasse op die geskikte grond. Die soilscape opname tegniek is hiervoor ontwikkel. Die afbakening van die 66 soilscapes is uitgevoer op 1:50 000 kaarte. Detail pedologiese ondersoeke is gemaak op geselekteerde toporeekse van sekere soilscapes. Daarvoor is 1:10 000 kaarte, toetsgate, boorgate en diepte metings as waarnemings gebruik. Nege soilscapes, met ‘n totale oppervlak van 82 222 ha, ongeskik vir bewerking, is geïdentifiseer. Op die oorblywende 57 soilscapes, met ‘n oppervlak van 155 429 ha is die verbeterde kennis, wat opgedoen is gedurende die detail studies, is ge-ekstrapoleer om die geskikte oppervlakte van die oorblywende soilscapes, vir AO te raam. Die resultaat was 56 875 ha, of 24 % van die totale oppervlakte van Dc17. Die resultate van vorige veldproewe op soortgelyke ekotope voorspel die volgende mielie-opbrengste (ton/ha/j): konvensionele bewerking = 82 000; eenvoudigste soort AO = 127 000 Daar word geraam dat hierdie landtipe stapelvoedsel aan 600 000 kan voorsien indien AO toegepas word. Die soilscape-opnametegniek is suksesvol toegepas in hierdie landtipe, maar dit moet verfyn word vir toepassing in ander landtipes en ander uitvoerbaarheidstudies. vi TABLE OF CONTENTS DECLARATION ..........................................................................................................................................................ii ACKNOWLEDGEMENT ........................................................................................................................................ iii ABSTRACT .................................................................................................................................................................. iv OPSOMMING ............................................................................................................................................................... v LIST OF TABLES .................................................................................................................................................... viii LIST OF FIGURES .....................................................................................................................................................ix LIST OF ABBREVIATIONS .................................................................................................................................... x LIST OF APPENDICES ............................................................................................................................................xii INTRODUCTION.........................................................................................................................................................1 1.1 INTRODUCTION ....................................................................................................... 1 1.2 MOTIVATION .......................................................................................................... 2 1.2.1 Background................................................................................................. 2 1.2.2 Socio-economic conditions in the study area.............................................. 3 1.2.3 The feasibility of IRWH for the subsistence farmers in the study area....... 5 1.2.3.1 Climatic requirement of sunflower and maize.................................................................................... 5 1.2.3.2 Soil factors .......................................................................................................................................... 8 1.2.3.3 The IRWH technique ........................................................................................................................ 12 1.2.3.4 Results of relevant field experiments................................................................................................ 13 1.2.4 Summary.................................................................................................... 16 1.3 HYPOTHESIS ........................................................................................................