WATER PRODUCTIVITY IN RAINFED AGRICULTURE Redrawing the rainbow of water to achieve food security in rainfed smallholder systems WATER PRODUCTIVITY IN RAINFED AGRICULTURE Redrawing the rainbow of water to achieve food security in rainfed smallholder systems DISSERTATION submitted in fulfilment of the requirements of the Board for Doctorates of Delft University of Technology and of the Academic Board of the UNESCO-IHE Institute for Water Education for the Degree of DOCTOR to be defended in public on Wednesday, 23 June 2010 at 12.30 hours in Delft, The Netherlands by Hodson MAKURIRA born in Bindura, Zimbabwe Master of Science in Water and Environmental Resources Management UNESCO-IHE, Delft, The Netherlands This dissertation has been approved by the supervisors: Prof. dr. ir. H.H.G. Savenije Prof. dr. S. Uhlenbrook Committee members: Chairman Rector Magnificus TU Delft Prof. dr. A. Szöllösi-Nagy Vice-chairman, Rector UNESCO-IHE Prof. dr. ir. H.H.G. Savenije TU Delft/ UNESCO-IHE, The Netherlands Prof. dr. S. Uhlenbrook UNESCO-IHE/ TU Delft, The Netherlands Prof. dr. D. Mazvimavi University of the Western Cape, South Africa Prof. dr. ir. P.van der Zaag UNESCO-IHE, The Netherlands Prof. dr. W. Bastiaanssen TU Delft, The Netherlands Prof. Bob Su University of Twente, The Netherlands Reserve member Prof. dr. ir. T.N. Olsthoorn TU Delft, The Netherlands CRC Press/Balkema is an imprint of the Taylor & Francis Group, an informa business © 2010, Hodson Makurira All rights reserved. No part of this publication or the information contained herein may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, by photocopying, recording or otherwise, without written prior permission from the publishers. Although all care is taken to ensure integrity and the quality of this publication and the information herein, no responsibility is assumed by the publishers nor the author for any damage to the property or persons as a result of operation or use of this publication and/or the information contained herein. Published by: CRC Press/ Balkema PO Box 447, 2300 AK Leiden, The Netherlands e-mail: [email protected] www.crcpress.com – www.taylorandfrancis.co.uk – www.balkema.nl ISBN 978-0-415-60120-7 (Taylor & Francis Group) ABSTRACT The challenge of food insecurity is severe in sub-Saharan Africa (SSA) where, generally, low and highly variable rainfall coupled with high evaporation rates and rapidly degrading soils combine to produce declining grain yields. Soil moisture and nutrient balances are essential ingredients for good crop yields. Water scarcity is perceived to be the most limiting factor to crop productivity (CP) in SSA. With a projected population of 1.1 billion in 2010 which is growing at a rate of 2.2 % a-1, SSA will continue to face the challenges of hunger and poverty for the foreseeable future unless if interventions are made to control the situation. In SSA the seasonal grain yields are low with average maize grain yields, for instance, hardly exceeding 1 t ha-1 which is very low when compared with potential levels of 6 t ha-1. The solution to water shortages for agriculture has traditionally been advanced as irrigation. However, irrigation has only benefited a few owing to the high investment costs required to set up irrigation schemes thus leaving the majority (80- 90%) of the population in SSA relying solely on rainfed agriculture for their livelihoods. Rainfall is generally unreliable in SSA with seasonal rainfall ranging between 300- 1200 mm a-1. Within seasons, rainfall variability is very high. So is potential evaporation which easily exceeds 1000 mm a-1 in many places. This implies that every little available raindrop should be converted to productive use to improve CP. The challenge of water scarcity as a result of insufficient seasonal rainfall and dry spell occurrences during seasons is compounded by inefficient agricultural practices by smallholder farmers where insignificant soil conservation efforts are applied. When these dry spells occur at critical growth stages, significant yield reductions occur even where the total seasonal rainfall may be considered good. vi The farmers also lack resources to purchase the most appropriate farming inputs which also help the crops to cope with water and nutrient deficits. Interestingly, a lot of research has gone into coping mechanisms against dry spells, soil and water conservation and farm management. However, on the ground the situation has not improved and, if anything, yields continue to decline. There appears to be a problem with research, so far, in offering sustainable solutions to the persistent low crop water productivity in smallholder rainfed farming systems. This research tackles this problem. The hypothesis of this research is that many of the past research efforts have taken a fragmented approach to deal with the challenges highlighted here. Fragmented approaches are difficult to implement. A holistic approach to assist traditional farming systems should include hydrological aspects, agronomy, soil science, catchment conservation and socio-economic aspects for better success. In this research the Makanya catchment in northern Tanzania has been taken as a pilot study site. The area receives gross rainfall of below 400mm/season which is clearly insufficient to meet water requirements of the preferred crops such as maize. System innovations (SIs) have been introduced and tested as alternative farming practices. These include a combination of conservation agriculture, diverting runoff onto field plots and enhancement of in-field soil moisture through trenching and soil bunding (fanya juus) within cultivated fields plots. These techniques have been selected for study because they do not require large capital investments and, hence, are affordable to many farmers yet they have the potential to significantly improve yields. Comprehensive on-site observations of rainfall, soil evaporation, runoff contribution, seasonal grain yields of the maize crop and general crop performance have been conducted using a participatory approach with local smallholder farmers. Indirect methods have been applied to confirm these observations and also, to model the performance of the studied system. Electrical resistivity tomography (ERT) has been applied as a geophysical technique to confirm the observations from the Time Domain Reflectory (TDR) methods of monitoring soil moisture. The HYDRUS2D Water productivity in rainfed agriculture vii model has also been applied to simulate two-dimensional sub-surface lateral moisture flows in relation to applied water on the field site with conservation agriculture. A spreadsheet based water balance model has been applied to better understand the water partitioning processes under different scenarios and to quantify crop productivity. Results from the research show that rainfall is generally low and ranged between 150 - 300 mm/season during the research period. Rainfall variability is high between seasons and between the studied sites. The maize grain yields obtained are also low and range from an averaged minimum of 0.23 t ha-1 under the current agricultural practices to a maximum of 2.82 t ha-1 when SIs were applied at all sites. Average yield values show that, in addition to the rainfall received, a combination of diversion of runoff onto field plots, ripping along planting lines, promotion of soil moisture storage by use of fanya juus and the application of manure produced the best yield results of up to 4.8 t ha-1 in a good season at one site. Water partitioning analysis has confirmed that the SIs applied resulted in an increase in transpiration values of about 49%. An explanation on the reasons for this increased efficiency has been obtained by reference to both direct and indirect analytical techniques. The research has successfully applied different analytical techniques to better understand soil and water interactions at field scale. It has been successfully demonstrated that there is indeed scope to increase crop water productivity provided the local farmers adopt more efficient cultivation techniques. Significant yield increases occur as a result of diverting more water and these further improve when other SIs such as ripping, application of manure and cover cropping, are introduced. This confirms that no single solution exists to solve the problem of low yields which are obtained in smallholder farming systems. The SIs that have been tested offer improved food security through increased grain yields and also facilitate alternative cropping within the field as a result of heterogeneous conditions which are created within the field as a result of alteration of the field water balance. However, even with these promising results, the research has shown that there is room to further improve the efficiency of crop water use through improvement in research approaches and exploration of better techniques. viii Water productivity in rainfed agriculture ix ACKNOWLEDGEMENTS When a former academic supervisor steps forward to offer to supervise you “again” at a higher level, it gives one a sense of confidence and pride that one didn’t do such a bad job after all during the first contact. I would like to express my since appreciation to Professor Huub Savenije for giving me that sense of confidence after guiding me through my MSc research so many years ago. I will always admire your total commitment to see the best out of your students. To Johan Rockström for setting the tone for this research and all the support during those early stages. I hope you will be proud of this final product. To Stefan Uhlenbrook, you came at the right time when the morale was low and the ship seemed to be losing direction. I will always treasure your valuable efforts to keep the product scientifically sound. To Aiden Senzanje, last but not least, of the supervisory crew. You gave me constant support and those encouraging remarks, often off-air, kept me going. This work is a product of part of a complex multi-disciplinary research. My sincere thanks to all those who formed part of the SSI research team at one point or another. These include Marloes Mul, Victor Kongo, Elin Enfors, Job Rotich, Kenneth Masuki, Claudious Chikozho, Jenniffer Kinoti, Jeltsje Kemerink, Charles Hans Komakech, Jayashree Pachpute, Siza Tumbo and Line Gordon. I also benefitted a lot from interactions with staff and fellow PhD'ers at UNESCO-IHE and TU Delft. I had contact with many MSc researchers from University of Zimbabwe, Sokoine University, TU-Delft, UNESCO-IHE, Stockholm University, Stuttgart University and x University of Freiburg. Thier direct and indirect contribution to my work is highly valued. To Eliza, Walter, Iddi, Wilson (may his soul rest in peace) for providing me with the research sites and participating in the research. You all had your unique contributions which helped to shape this research. Equally important was the contribution from Maliki, Msangi and Kapombe who served as the research assistants. The initial days of my work were challenging and I wish to acknowledge the tremendous support received from Professor Pieter van der Zaag and Professor Simbi. I will never forget those big fights with the administration of which, in my view, there was no outright winner. To Joseph Mwalley who came in with the idea of the fanya juus and helped to set them up. I hope the Lexus is still on the road. My profound appreciation to the Soil Moisture Group of the Sokoine University of Agriculture for hosting this research. Equally, I wish to express my gratitude to the University of KwaZulu Natal for affording me the opportunity to acquire more depth. Special mention goes to Simon Lorentz (instrumentation) and Vincent Chaploit (data analysis). To colleagues who have walked the path before me and gave me tremendous support. These include Marieke de Groen, Innocent Nhapi, Themba Gumbo, and Lawrence Nyagwambo I also owe this product to the entire Civil Engineering staff compliment who covered up for me during the times when I was away on “academic duty”. Zvikomborero Hoko, your support is highly acknowledged. My research collaborated with the Challenge Programme in the Mzingwane Catchment. I would like to encourage my colleagues who are still walking the walk (David, Alex and Collin) to keep on keeping on.