Mineral Nutrient Disorders of Root Crops in the Pacific Proceedings of a workshop, Nuku'alofa, Kingdom of Tonga, 17-20 April 1995 Editors: E.T. Craswell, C.J. Asher and J.N. Q'Sullivan Hosted by: Ministry of Agriculture and Forestry, Kingdom of Tonga Sponsored by: South Pacific Commission Pacific Regional Agricultural Research Programme Australian Centre for International Agricultural Research Australian Agency for International Development University of Queensland The Australian Centre for International Agricultural Researeh (ACIAR) was established in June 1982 by an Act of the Australian Parliament. Its mandate is to help identify agricultural problems in developing eountries and to commission collaborative research between Australian and developing country researchers in fields where Australia has special research competence. Where trade names are used this does not constitute endorsement of nor discrimination against any product by the Centre. ACIAR PROCEEDINGS This series of publications includes the full proceedings of research workshops or symposia organised or supported by ACIAR. Numbers in this series are distributed internationally to selected individuals and scientific institutions. © Australian Centre for International Agricultural Research, a.p.c. Box 1571, Canberra, ACT 2601 Australia Craswell, E.T., Asher, C.l and O'Sullivan, 1.N. 1996. Mineral Nutrient Disorders of Root Crops in the Pacific. Proceedings of a workshop, Nuku'alofa, Kingdom of Tonga, 17-20 April 1995. ACIAR Proceedings No. 65,142 pp. ISBN I 86320 170 X Editorial management: P. W. Lynch Typesetting and page layout: Sun Photoset Pty Ltd, Brisbane, Australia Printed by: Watson Ferguson & Co., Brisbane, Australia Contents Research, development and extension needs for overcoming nutritional limitations of root crops in the Pacific: a Workshop Summary J.N. O'Sullivan and f:P.C Blarney 5 Diagnosis of Nutrient Disorders and their Management J.F. Loneragan 10 Root Crops in the Pacific Region: their Dietary, Cultural and Economic Significance R.S. de la Peiia 19 Diagnostic Criteria for Nutrition Disorders of Sweet Potato. I: Methods and Visible Symptoms J.N. O'Sullivan, C.J. Asher and F.P.C Blamey 28 Diagnostic Criteria for Nutrition Disorders of Sweet Potato. II: Critical Nutrient Concentrations in Lcavcs J.N. O'Sullivan, F.P.C. Blamey and C.J. Asher 39 Pot Experimentation to Study Nutrient Responses of Sweet Potato in Papua New Guinea A.J. Dowling, F.P.C Blamey, J.N. O'Sullivan, CJ. Asher and M. Johnslon 44 The Use of Pot Experiments to Assess the Chemical Fertility of Selected Soils in Western Samoa J.M.A. Poiliega, L.G.G. Yapa and CJ. Asher 49 Sensitivity of Sweet Potato Lines to Ca and AI Stress in Solution Culture v.P. Ila'ava, F.P.C Blamey and CJ. Asher 53 Soil Fertility and Sweet Potato Research in Tonga - Nitrogen and Phosphorus S. Halavatau, CJ. Asher and L.C Bell 58 Mineral Depletion of a Typic Udivitrand Through Continuous Cropping with Sweet Potato W.D. Humphrey 65 The Agronomy and Mineral Nutrition of Sweet Potato (Ipomoea batatas) in the Highlands of Papua New Guinea B. Konabe and S. lvahupa 70 Effects of Nitrogen and Water Stress on Growth and Yield of Sweet Potato P. Taufatofua and S. Fukai 76 Some Aspects of Mineral Nutrition of Colocasia sp. Taro w.J. Cable 80 Diagnostic Criteria for Nutrition Disorders of Taro J.N. O'Sullivan, CJ. Asher and F.P.C Blamey 83 Correction of Nutrition Disorders of Sweet Potato and Taro: fertilizers and soil amendments F.P.C Blarney 91 The Response of Colocasia esculenta (L.) Schott and Xanthosoma sp. to Phosphorus Fertilizer on Selected Soils of Western Samoa: a progress report J.M.A. Poihega, L.G.G.Yapa and CJ. Asher 96 3 Effects of Potassium on Drought Tolerance of Taro and Tannia P. Sivan, CJ. Asher and F.P.C Blarney 100 The Relationship Between Balanced Nutrition and Disease Susceptibility in Polynesian Taro R. Tilialo, D. Greenough and E. Trujillo 105 Mineral Nutrition of Cassava R. H. Howeler 110 Mineral Nutrition of Root Crops in Fiji D. Kumar; J.L. Wainiqoio, N. Kumar; S.P. Field and A.J. Dowling 117 Review of Some Fertilizer Research on Root and Tuber Crops and Farmer Adaptive Strategies to the Short Fallow Systems in Lowland Papua New Guinea L.M. Kurika 122 Nutrient Disorders of Root Crops Growing on Raised Coral Reef Landforms Near Madang, Papua New Guinea M. Johnston 127 Mineral Nutrition of Root Crops in Cook Islands M. Purea and T. Mataora 130 The Agronomy of Cyrtosperma chamissonis, Colocasia esculenta and Ipomoea batatas in Kiribati I. Ubaitoi 133 The Incidence of Taro Leaf BI ight (PhytophtllOra colocasia) in Relation to Rainfall in Western Samoa: a progress report K. Pouono and S. Tuugasala 137 Use of Leguminous Trees to put N into Pacific Farming Systems: solution in search of a problem S. Rogers and T. losefa 140 4 Research, Development and Extension Needs for Overcoming Nutritional Limitations of Root Crops in the Pacific: a Workshop Summary J.N. O'Sullivan1 and F.P.C. Blarney1 Abstract Needs for continued work on the nutritional requirements of root crops were identified, particu­ larly the diagnosis, prognosis and correetion of nutrition disorders within the farming systems in which the crops are produced. Further work is needed also on the extension of research results, focusing on identifying and correcting local problems using means acceptable to farmers. Work­ shop participants recognised that good progress had been made in identifying visible symptoms of nutrition disorders of sweet potato (Ipomoea batatas (L.) Lam) and laro (Colocasia escuiellfa (L.) Schott), and recommended that this information be made available to agriculturalists of the region as soon as possible. Other crops on which similar research should be conducted include yam (Dioscorea spp.) and Xanthosoma sagittiJolium (L.) Schott, and perhaps Alocasia macrorrhiza (L.) Schott and Cyrtosperma chamissonis (Schott) Merr. Overall, it was concluded that the identifi­ cation and correction of nutrition disorders of root crops is an important factor contributing to sustainable farming systems in the Pacific. THIS report summarises the views and observations of workshop participants on the priorities for future research, development and extension in root crop nutrition, par­ ticularly in relation to ACIAR Project 9101. The discussion was divided into four focus areas, each of which was introduced by a discussion leader followed by general con­ tributions. (Discussion leaders were: Professor Jack Loneragan, Dr Malcolm Hazelman, Dr Steve Rogers and Mr Siva Halavatou; Dr Ramon de la Pefia chaired the session.) The importance of root crops in the region, as staple food sources, as major com­ modities for local commerce, and as export crops was reflected in the high priority given by Pacific country participants to the completion, distribution and implementation of the project findings. Knowledge of nutrient requirements and management of sweet potato (Ipomoea batatas (1..) Lam) and taro (C%casia esculenta (1..) Schott) still lags far behind that of crops such as maize (Zea mays 1..) and even cassava (Manihot esculenta Crantz), while the nutrition of yam (Dioscorea spp.) has received very little attention. This discussion was intended to highlight the priorities, preferred processes for and perceived barriers to further development of tropical root crop nutrition. Diagnosis and Prognosis of Nutrition Disorders Considerable progress has been made in the area of diagnosis of nutrition disorders in tara and sweet potato, particularly in the use of visible symptoms to characterise problems. The main refinement required here is to verify the symptoms observed on I Department of Agriculture, The University of Queensland, Brisbane, Qld. 4072 Australia 5 glasshouse-grown plants with those found in the field. Field validation is also required in the area of plant tissue analysis. Records of tissue nutrient concentrations at various times during the growth of high-yielding crops would provide useful additional data. Quick tests which can provide diagnostic answers in the field are highly desirable, especially for situations where laboratory analyses are not readily available. Leaf painting has been used successfully to demonstrate defieiencies of iron (Fe), manganese (Mn) and zinc (Zn) in sweet potato, and Fe in taro. Refinement is needed in the con­ centration of salts and wetting agents for elements other than Fe in taro. The area of sap testing has not been successfully developed in sweet potato or taro. A range of indicator test strips is available commercially for testing water for various nutrients. However, preliminary attempts to use these strips for analysis of taro and sweet potato sap were complicated by the heavy staining of the indicator strips by the sap. This has also been the experience with taro in Hawaii. Further work employing flocculants or the use of macerated plant tissue may overcome this problem. The use of fertilizer strips to confirm field diagnoses, or to differentiate between a small number of possible or co-existing deficiencies, is a simple and informative quali­ tative technique which could be used more widely. For example, phosphorus (P), sulfur (S) and nitrogen (N) deficiencies were identified as potential limitations in a com­ mercial taro nursery on Tongatapu. To evaluate the importance of these disorders, parallel strips of urea and ammonium sulphate, crossed by a perpendicular strip of triple-superphosphate, were recommended. Colour-illustrated booklets containing diagnostic information for sweet potato and taro are being prepared, and are seen as a valuable resource for research and extension personnel throughout the region. The inclusion of diagnostic keys and instructions on the collection and preservation of leaf tissue for analysis, and on the use of leaf painting techniques and quick tests, where available, would greatly increase the utility of these publications. Where possible, information assisting the reader to distinguish between symptoms of nutrition disorders and those of plant pathogens and of herbicide injury would be helpful.