Institut für Pflanzenernährung der Rheinischen Friedrich – Wilhelms – Universität Bonn Productivity and water use efficiency of important crops in the Upper Oueme Catchment: influence of nutrient limitations, nutrient balances and soil fertility. I n a u g u r a l – D i s s e r t a t i o n zur Erlangung des Grades Doktor der Agrarwissenschaft (Dr. agr.) der Hohen Landwirtschaftlichen Fakultät der Rheinischen Friedrich – Wilhelms – Universität zu Bonn vorgelegt im September 2005 von Gustave Dieudonné DAGBENONBAKIN aus Porto-Novo, Benin Referent: Prof. Dr. H. Goldbach Korreferent: Prof. Dr. M.J.J. Janssens Tag der mündlichen Prüfung: Dedication ii Dedication This work is dedicated to: Errol D. B. and Perla S. K. DAGBENONBAKIN, Yvonne DOSSOU-DAGBENONBAKIN, Raphaël S. VLAVONOU. Acknowledgments iii Acknowledgements The participation and contribution of individuals and institutions towards the completion of this thesis are greatly acknowledged and indebted. Foremost my sincere appreciation and thankfulness are extended to my promoter Prof. Dr. Heiner Goldbach for providing professional advice, whose sensitivity, patience and fatherly nature have made the completion of this work possible, he always gave freely of his time and knowledge. I would like to express my profound gratitude to Prof. Dr. Ir. Marc Janssens, for giving me the opportunity to pursue my PhD thesis in IMPETUS Project. His insights criticisms are very useful in improving this work. I am grateful to Prof. Dr. H-W. Dehne for reading this thesis and accepting to be the chairman of my defense. My sincere words of thanks are also directed to Prof. Dr. Karl Stahr of the Institute of Soil Science at the University of Hohenheim for giving me the opportunity to be enrolled as PhD student in his Institute. I am grateful to Dr. Thomas Gaiser of the Institute of Soil Science at the University of Hohenheim for helping me for administrative formalities as far as my enrolment as PhD student at the University of Hohenheim was concerned, about the first discussion on the proposal, and for his valuable contributions. I am also indebted to PD Dr. Jürgen Burkhardt, who significantly helped me in getting started with my field work and who provided valuable advice. He always organized everything concerning my stay in Germany and helped for literature, corrected many papers presented in conferences. I wish to express my warm appreciation to Mr. Valérien Agossou who gave freely of his time and shared knowledge and experience with me from the beginning to the end of this thesis. A dept of gratitude is due to Dr. Anne Marie Matthess, Dr. Bernard Agbo, Dr. Mouinou Igué, and Dr. Anastase Azontondé for their help and support My sincere thanks are also due to Dr. Romain Glele and Mr. Linssoussi Come for their help in statistical analysis. My sincere thanks are also directed to Dr. David Arodokoun, Dr. Jean Detongnon, Dr. Delphin Koudandé, Dr. Mensah Guy Appolinaire, Prof. Dr. Nestor Sokpon, Prof. Dr. Brice Sinsin, Prof. Cossi Houndagba, Prof. Dr. Euloge Acknowledgments iv Agbossou, Dr. Raphael Vlavonou, Dr. Hector Adegbidi, Dr. Pierre Akondé, Dr. Vincent Mama, Dr. Kuessi Ahiou, Mr. Toukourou, Mr Camille Bankolé Mr. Baco Nasser, Dr. Jean Adanguidi, Mrs. Conforte Mensah, Mr. and Mrs Adjikouin and Mr and Mrs Glèlè Melon for their help and support. I wish to thank the late Francine Adjikouin for helping to the assessment of potential evapotranspiration in 2002 in Dogue, for her assistance and who joined the field research group after her Master‘s Thesis. May God continue to bless and honor her soul with more appointments in the service of God and Humanity. My sincere thanks are also directed to Claude Kanninkpo, Mohamed Akadiri, Djakpa Ezeckiel, Chabi Ibrahim and Alexis Mayaba for their assistance to field research and data collection and their help. The soil and plant samples were analyzed by the highly qualified technicians especially, Angelika Glogau, Angelika Veits, Deborah Rupprecht, Waltraud Köhler and Marcus Kiefer of the Institute of Plant Nutrition of the University of Bonn and those of ex Centre National d’Agro-Pédologie in Benin. I am very grateful to the government of the people of the Federal Republic of Germany through German Ministry of Education and Science (BMBF) for financing this study and the authorities of Integratives Management Projekt für einen Effizienten und Tragfähigen Umgang mit Süßwasser (IMPETUS) especially Professor Dr. P. Speth, Dr. M. Christoph and Dr. E. van den Akker for giving me material and administrative supports during all phases of the present thesis. My thanks are also due to my colleagues of IMPETUS particularly, Dr. V. Mulindabigwi, Dr, S. Giertz, Dr. H Bormann, Dr. T. Fass, Dr. M. Schopp, K. Hadjer, B. Orthmann, T. Klein and Dr. M. Doevenspeck, for sharing experiences in Benin and creating a nice work atmosphere. Work at the Institute of Plant Nutrition was facilitated through the easy cooperation of Luc Sintondji, Mathias Nadohou, Vincent Orekan, Ali Kadanga, Deng Zhixin, Dr. I. Hartmann, Dr. Thomas Eichert, Franck Gressens, Waltraut Schäfer Dr. Jean Pierre Bognonkpe, Haben Asgedom, R. Fagbemissi, and my friend Bernd Heinz-Jürgen Kitterer. Acknowledgments v My thanks also go to uncles Siméon and Thimothée Adjigbey, my sisters Colette and Véronique, my nephews Romaric and Erick for their help and support. My deepest gratitude is due to my loving and dear wife Yvonne Dossou- Dagbenonbakin whose understanding, patience and sacrifice have greatly constituted to the successful completion of my doctoral studies. My son Errol and my daughter Perla who could not be with the father when need arose gave me the desire to go on and on. Finally, many thanks to all of them for the support, but also to those who in one way or another provided help during the realization of my thesis. Words are not enough to express my gratitude; only God knows how to reward each of you. Abstract vi Abstract Crop productivity and water use efficiency of important crops in the Upper Oueme Catchment: influence of nutrient limitations, nutrient balances and soil fertility. The Upper Oueme catchment in the West African subhumid zone is a region in Northern Benin, which actually experiences major changes in land use, water availability, and population density. In the context of the IMPETUS project, the present work aimed to i) identify nutrients which are limiting productivity on the basis of soil and plant analysis, ii) compare effects of fertilizer application nutrition to current farmer’s practice, iii) determine the water consumption per unit of biomass (maize) and per unit of area, and iv) assess (simplified) nutrient balances to predict long-term trends of nutrient availability and soil productivity. Field experiments were carried out in 2001 and 2002 using a randomized complete block design with four treatments, 2001: n = 80, 2002: n = 109) at three sites: Beterou, Dogue, and Wewe. Soils of the sites had low fertility and were PLENTOSOL and Ferric-Profondic LUVISOL in Beterou, PLENTOSOL and LIXISOL in Dogue and ACRISOL or Plenthic-LIXISOL in Wewe. Treatments were: T0: farmer’s practice or plots without mineral or organic fertilizer applied with exception of cotton, where farmers applied fertilizers as usual; T1M: 10 t ha-1crop residues; T1F: 10 t ha-1 of farmyard manure in 2001; T2: mineral fertilizer at the rates recommended; T3M: mineral fertilizer as applied in T2 + 10 t ha-1 of crop residues for mulch in 2001 and 2002, while for T3F mineral fertilizer was applied as in T2 + 10 t ha-1 of farmyard manure. Residual effects of manure application were evaluated without further OM application. Soil samples were taken before and at the end of the experiment to appreciate the nutritional status of plots. Leaves were sampled at critical stages for plant for nutrient assessment through critical Value Method CVM and Diagnosis and Recommendation Integrated System (DRIS). Yield (DM) of all the crops, their total biomass and harvest index were evaluated at harvest. A partial nutrient balance was calculated on the basis of tissue and product analysis for a high and a low – yielding sub-groups. Actual evapotranspiration was estimated by gravimetry, humidimetry and tensiometry for water use efficiency (WUE) of Abstract vii maize in Dogue in 2002. Rainfall during the crop growth was used to calculate rainfall use efficiency (RUE). Water or rainfall use efficiency was determined as the ratio between above ground biomass and rainfall for RUE or actual evapotranspiration for WUE. Crop productivities were significantly affected by farmer’s practice and the type of organic matter applied. Organic or mineral fertilizer or the combination of both increased crop productivities, RUE and WUE of maize although a relatively high variability was observed between individual plots and farmers. Nitrogen was the most limiting nutrient followed by potassium and phosphorous according to DRIS-Evaluation while the CVM method revealed most of the macronutrients as low or close to the critical level. However, only the nutritional imbalance index of maize decreased from 2001 to 2002. Standard nutrient levels and reasonable DRIS norms were established for N, P, K, Ca, Mg, S, Zn, Mn of maize, sorghum, cotton, yam and groundnut. They can be used to evaluate crop nutritional status, to correct nutritional imbalances and to improve crop productivities. They can also be used as a basis for calibrating the fertilization programs for these crops. Negative nutrient balances were observed, as inputs of nutrients were insufficient to compensate outputs. The strategies to compensate the nutrient gap are to increase the recycling of residues, to increase the application of manure, or introduce fertilizers or a combination of all three. Actual farmers' practices in maize, sorghum, groundnut and yam cropping systems lead to depletion in soil nutrient levels, as there is actually almost no return of nutrients to the fields and mineral fertilizer are only rarely applied.