Z S inc in oilS c n and rop utrition Brian J. Alloway International Zinc Association The designation employed and the presentation of material in this information product do not imply the expression of any opinion whatsoever on the part of the International Zinc Association and the International Fertilizer Industry Association. This includes matters relating to the legal status of any country, territory, city or area or its authorities, or concerning the delimitation of its frontiers or boundaries. Mention of any proprietary products in this report does not necessarily imply that their use is endorsed by either the author or the publishers. Zinc in SoilS and crop nutrition B. J. Alloway Second edition, published by IZA and IFA Brussels, Belgium and Paris, France, 2008 International Zinc Association International Fertilizer Industry Association. 168, Avenue de Tervueren, Box 4 28 rue Marbeuf B-1150 Brussels, Belgium 75008 Paris, France Tel: + 32 2 776 00 70 Tel: + 33 1 53 93 05 00 Fax + 32 2 776 00 89 Fax: + 33 1 53 93 05 45/ 47 (www.zincworld.org) (www.fertilizer.org) Layout and graphics: Hilaire Pletinckx 1 FOREWORD Zinc (Zn) is an essential micronutrient and has particular physiological functions in all living systems, such as the maintenance of structural and functional integrity of biological membranes and facilitation of protein synthesis and gene expression. Among all metals, Zn is needed by the largest number of proteins. Zinc-binding proteins make up nearly 10 % of the proteomes in eukaryotic cells, and 36% of the eukaryotic Zn-proteins are involved in gene expression (Andreini et al., 2006, J. Proteome Res. 5: 3173-3178). Tolerance to environmental stress conditions has a high requirement for Zn to regulate and maintain the expression of genes needed to protect cells from the detrimental effects of stress (Cakmak, 2000, New Phytol. 146:185-205). Zinc deficiency appears to be the most widespread and frequent micronutrient deficiency problem in crop and pasture plants worldwide, resulting in severe losses in yield and nutritional quality. This is particularly the case in areas of cereal production. It is estimated that nearly half the soils on which cereals are grown have levels of available Zn low enough to cause Zn deficiency. Since cereal grains have inherently low Zn concentrations, growing them on these potentially Zn-deficient soils further decreases grain Zn concentration. It is, therefore, not surprising that the well-documented Zn deficien- cy problem in humans occurs predominantly in the countries/regions such as India, China, Pakistan and Turkey where soils are low in available Zn, and cereals are the major source of calorie intake. Zinc deficiency in humans is a critical nutritional and health problem in the world. It affects, on average, one-third of the world’s population, ranging from 4 to 73 % in different countries (Hotz and Brown, 2004, Food Nutr Bull 25: 94-204). The recent analyses made under the Copenhagen Consensus in 2008 (www.copenhagenconsensus.com) identified Zn deficiency, together with vitamin A deficiency, as the top priority global issue, and concluded that elimination of the Zn deficiency problem will result in immediate high impacts and high returns for humanity in the developing world. It is, therefore, highly important to develop cost-effective and quick solutions to the Zn deficiency problem. Low Zn in plant tissues is a reflection of both genetic- and soil-related factors. A basic knowledge of the dynamics of Zn in soils, understanding of the uptake and transport of Zn in plant systems and characterizing the response of plants to Zn deficiency are essential steps in achieving sustainable solutions to the problem of Zn deficiency in plants and humans. This book “Zinc in Soils and Crop Nutrition” by Brian Alloway contributes significantly to our better understanding of the complexities of Zn dynamics in soil and plant systems. It contains very valuable basic and practical information for a wide audience, including students, agronomists and scientists who are involved in research, extension or education in soil science, plant mineral nutrition, plant physiology and also human nutrition. Detailed information on the prevalence and diagnosis of Zn deficiency problems for a number of countries and crop plants is an excellent feature of this book. This book has been available electronically since 2004. It has now been decided to publish this updated version in a print format. This is a great idea that will further contribute to a wide distribution of the useful information contained in the book. I would like to congratulate Prof Brian Alloway on this excellent achievement, and thank the International Zinc Association (IZA) and the International Fertilizer Industry Association (IFA) for their support which has made the publication of such a valuable book possible. Ismail Cakmak Sabanci University July 2008, Istanbul 1 ABBREVIATIONS AND GlOSSARy AAS atomic absorption spectrophotometry (analytical method for trace elements) AB-DTPA ammonium bicarbonate with DTPA, soil test reagent Acrisols red-yellow coloured soils typical of humid tropical, sub-tropical and warm temperate areas, often found associated with Ferralsols (FAO-UNESCO Soil Classification). Adsorption retention of ions on the surface of the soil solid phase Aerobic rice rice grown without continuous flooding under aerobic soil conditions (also called upland rice) Aerosols particles < 30 µm in diameter suspended in air Alfisols moist mineral soils with medium to high base status which contain a horizon of clay accumulation. Occur in cool-hot humid areas and also semi-arid areas AM arbuscular mycorrhizae (fungi which colonise the root and assist in the absorption of soil ions from the soil solution) - also called vesicular arbuscular mycorrhizae (VAM) Anion negatively charged ion (e.g. hydroxyl ion OH- ) Arenosols sandy textured soils (sand particles 0.05-2 mm in diameter) whose properties are dominated by the high sand content (e.g. low clay contents and low available water capacities) ASNS alternate submerged, non-submerged rice growing system (an alternative to continuously flooded paddy rice (see also GCRPS) Auxin compound regulating plant growth (e.g. IAA-indole acetic acid) Biofortification process of increasing the content (‘density’) of micronutrients, such as zinc, in food crops, especially cereals. There are two types: agronomic biofortification involves using fertilisers to increase the density of zinc in cereal grains; genetic biofortification uses specially-bred crops which have been selected on the basis of their ability to concentrate zinc and other micronutrients in their edible parts, such as grains. Biosolids another name for sewage sludge – the insoluble residue from waste water treatment Bread wheat used for baking bread (in contrast to durum wheat) C plants plants with a basic photosynthesis mechanism which fixes carbon dioxide in only one stage 3 C plants plants which fix carbon dioxide in two stages and can raise its concentration in their leaves 4 above ambient levels Ca calcium CaCO calcium carbonate 3 Calcisols soils in which there is a substantial accumulation of calcium carbonate (calcareous soils), characterized by a ‘calcic’ horizon (>15% CaCO equivalent) 3 Calcite calcium carbonate (CaCO) 3 Cation positively charged ion (e.g. zinc occurs as divalent cation Zn2+) Cation Exchange the sum of exchangeable cations that can be adsorbed by a soil, soil constituent or other material at a Capacity (CEC) particular pH Cd cadmium CGIAR Consultative Group on International Agricultural Research (co-sponsored by FAO, International Bank for Reconstruction and Development (World Bank), the UN Development Programme and the UN Environment Programme) 2 Chlorophyll green pigment in plants involved in photosynthesis Chlorosis lack of chlorophyll formation resulting in yellow stripes and patches on leaves (major symptom of zinc deficiency) CIMMYT International Maize and Wheat Improvement Centre Clay minerals aluminium silicate minerals with a large surface area, clay particles < 2 µm in diameter. Clay minerals give soils part of their adsorptive capacity, cohesiveness and water retention Co cobalt Co-precipitation occlusion of metal ions in precipitates of iron, manganese and aluminium oxides CSIRO Commonwealth Scientific and Industrial Research Organisation (Australia) Cultivar (cv) cultivated variety of a plant species with distinctive characters (often vary considerably in zinc efficiency/tolerance to deficiency) Cu copper Cut soils soils in which the topsoil has been removed during levelling of fields for irrigation DAP diammonium phosphate (high analysis phosphatic fertiliser, 21% N 23% P) usually with very low contents of metal impurities dS m-1 deciSiemens per metre (measure of electrical conductivity [EC] in the soil solution – used in the assessment of salinity in soils) Diagenesis the process by which sediments derived from the weathering of rocks are converted into sedimentary rocks and may eventually undergo weathering and form the parent material of sandy soils (Arenosols etc) DTPA diethyl triamine penta-acetic acid, soil test reagent Durum wheat used for making pastas and semolina, not good for baking (unlike bread wheat) EDTA ethylene diamine tetra-acetic acid, a chelating agent used for soil tests and for soluble micronutrient fertilisers Enzyme an organic compound (often containing a metal, such as zinc) which catalyses a specific reaction within a cell FAO Food and Agriculture Organisation of the United Nations FAO-UNESCO sponsors of the soil map of the world (and soil classification) 1974 Fe iron Ferralsols deep red-yellow soils of the humid tropics which have undergone severe weathering, are strongly acid and normally have low total contents of most micronutrients (called Oxisols in the USDA Soil Taxonomy classification). Ferromagnesian rock-forming minerals containing relatively high concentrations of iron and magnesium minerals (e.g. augite, olivine) Fertigation supplying fertiliser nutrients in irrigation water Galvanised steel coated with a corrosion-resistant layer of zinc GCRPS ground cover rice production system (alternative to continuously flooded paddy rice) genotypes plants with different genetic makeup (e.g. species and cultivars) Gleysols soils which are either permanently or intermittently wet with reducing conditions at shallow depth GM genetically modified (i.e., crop cultivar) Gypsiferous soils soils in semi-arid/arid regions with a high content of gypsum often forming a gypsic horizon Gypsum calcium sulphate (CaSO ) which has a neutral reaction, unlike calcium carbonate which is alkaline. 4 ha hectare: unit of land area (10,000 m2, 2.47 acres) HarvestPlus a Global Challenge Program of the Consultative Group on International Agricultural Research (CGIAR) dedicated to reducing micronutrient malnutrition through the biofortification of staple food crops. 3 HC hazardous concentration for 50% of species 50 Hydrozincite zinc hydroxycarbonate (Zn (OH) (CO ) (solid) 5 6 32 ICP-AES inductively-coupled plasma atomic emission spectrometry (analytical technique for trace element ions in solution) Igneous rocks rocks which have crystallized from molten magma (e.g. basalts, granites) ILZRO International Lead Zinc Research Organisation Interveinal between the leaf veins (e.g. interveinal chlorosis symptoms) IPNI International Plant Nutrition Institute IRRI International Rice Research Institute K potassium kg ha-1 kilogrammes per hectare (application rates for zinc fertilisers) Latent deficiency deficiency of an essential nutrient (e.g. zinc) in plants without the appearance of obvious symptoms (also called sub-clinical or hidden deficiency) Ligand organic group which, combined with a metal ion, forms a complex molecule LOEC lowest observed effect concentration (toxicology) Loess wind-blown (aeolian) silt particles (can form soil parent material) MAP monoammounium phosphate (high analysis phosphatic fertiliser, 11% N, 21% P) usually with very low contents of metal impurities Metalloproteins proteins containing metal ions in their structure (includes metallo-enzymes) Mg magnesium mg kg-1 milligrammes per kilogramme (equivalent to ppm or µg g-1) Micronutrient element required in small but critical concentrations for normal healthy growth of plants and/or animals (e.g. zinc) also called ‘essential trace element’ Mn manganese N nitrogen Necrosis abnormal death of part of leaf or other plant tissue (necrotic spots) NH Ac ammonium acetate, soil test reagent 4 Nitisols deep, red, clay-rich soils, formed on base-rich parent materials; not so severely weathered and leached as Ferralsols and are some of the most fertile tropical soils (FAO-UNESCO Soil Classification). NKP fertilisers nitrogen, phosphorus and potassium (macronutrients) fertilisers O oxygen Okra vegetable OsZIP Oryza sativa zinc-iron regulated-protein-a transporter protein involved in the Translocation of zinc from the root to the developing grain Oxisols deep red soils of humid tropical regions (USDA Soil Classification-see Ferralsols FAO-UNESCO) P phosphorus Paddy the flooded field in which lowland rice is grown (c.f. upland rice) Pb lead PEC predicted environmental concentration-background concentration pH measure of acidity or alkalinity of a solution (scale 0-14, 0-7 is acid, 7 is neutral, and 7-14 is alkaline) Phytate phosphorus-containing compound (inositol hexaphosphate) found in cereals which can bind zinc and reduce its availability to monogastric animals, such as humans Phytosiderophore substance secreted from the roots of certain plant species which mobilizes iron and other cations from soil in the vicinity of the root 4 PNEC predicted no effect concentration (toxicology) Poacae the graminae family (grasses and cereals – the most important plant family with regard to human nutrition) Proteoid roots clusters of dense root branchlets (5-10 mm long) supporting a high density of root hairs which significantly increases the root absorbing area PZC pH at which a variable charge soil constituent (e.g. iron oxide) is neutral (neither positively nor negatively charged) Rhizosphere thin layer (approx 2 mm thick) around plant roots which is a zone of intense microbial activity due to root secretions etc S sulphur Sedimentary rocks rocks which have formed from sediments which are the products of weathering of pre-existing rocks (e.g. sandstones, mudstones, limestones, clays) SOD superoxide dismutase (enzyme) Soil Taxonomy USDA soil classification system Solonchak soils with high concentrations of salts at some time of the year in the topsoil (salts are mainly sodium chloride and sodium sulphate) Solonetz salt-affected soils developed under the influence of salts such as sodium bicarbonate, sodium carbonate, sodium silicate and magnesium carbonate Sub-clinical deficiency of an essential nutrient (e.g. zinc) in plant or animal without the appearance of deficiency obvious symptoms Superphosphate phosphatic fertiliser (7-9% P) usually with significant concentrations of metal impurities (e.g. zinc) (ordinary) Tarai soils shallow water table soils found in the foothills of mountain ranges (term used in India and adjacent countries) t ha-1 tonnes per hectare (equivalent to 1.1 tons per acre) Trace element elements which occur in relatively low concentrations in plant and animal tissues (<100 mg kg-1) and in rocks all trace elements together comprise <1% of total elemental composition Triple - phosphatic fertiliser (18-22% P) with lower contents of metal impurities than ordinary superphosphate superphosphate USDA United States Department of Agriculture UNESCO United Nations Educational, Social and Cultural Organisation VAM vesicular arbuscular mycorrhizae (fungi which colonise the root and assist in the absorption of soil ions from the soil solution) Vertisols deep clayey soils (>30% clay) dominated by clay minerals that expand on wetting and shrink on drying, forming cracks to at least 50 cm when dry. Topsoil falls down these cracks and, in time, the soil profile becomes inverted YEB youngest emerged leaf blade, for plant tissue analysis YFEL youngest fully emerged leaf (used in plant analysis) YOB youngest open blade, for plant tissue analysis yr-1 per year Zinc efficiency the extent to which a plant cultivar is able to grow and develop in soils with low available supply capacities for zinc Zn zinc ZnO zinc oxide ZnSO zinc sulphate 4 5 Acknowledgments The author is pleased to acknowledge the International Zinc Association (IZA) and the International Fertilizer Industry Association (IFA) for agreeing to publish this book. The first edition was commissioned by the IZA in 2003 and was made available as either a CD or as a downloadable document from the world wide web (www.zinc-crops.org). Following the international ‘Zinc Crops 2007’ conference in Istanbul in May 2007, jointly sponsored by the IZA, the IFA, HarvestPlus and Sabanci University, the original report was extensively revised and updated for publication as the second edition. The author thanks Professor Ismail Cakmak of Sabanci University, Istanbul for writing the Foreword. The following individuals and organizations are also gratefully acknowledged for permission to use photographs: Yara, Dr V. Shorrocks, Dr R. Holloway, the International Plant Nutrition Institute (IPNI) and the International Rice Research Institute (IRRI). Thanks are also extended to Drs Bridges, Batjes and Nachtergaele and the publisher, Acco (Leuven and Amersfoort) for permission to use maps from the Atlas of the World Reference Base of Soil Resources; Dr M.V. Singh of the Indian Institute of Soil Science, for permission to use his map of zinc deficiency in India and Dr Chunqin Zou of the China Agricultural University, Beijing, for permission to use the map of zinc in soils in China. The author also extends his thanks to the reviewers for their helpful comments on drafts of the first and second editions of this book. These were: Dr P.K. Aggarwal of the Indian Agricultural Research Institute, Dr C. Witt, formerly of IRRI, now at IPNI, Dr Sarah E. Johnson-Beebout of IRRI, Patrick Heffer of IFA, Dr Robert Holloway of the South Australia Research and Development Institute and the University of Adelaide, Professor Michael McLauchlin of the University of Adelaide and the Commonwealth Scientific and Industrial Research Organisation (CSIRO), Dr Kevin Moran of Yara and Dr David Rowell of the Department of Soil Science, University of Reading, although responsibility for its accuracy remains with the author. Finally, but most importantly, the author gratefully acknowledges the work by Michael Martin of Martin Associates, Brussels and Hilaire Pletinckx in converting the basic document for the first edition into a professionally laid out and illustrated publication. About the Author Brian J. Alloway, BSc (Agriculture), PhD, FIPSS, is an Emeritus Professor of Soil Science of the University of Reading, having formerly been Professor and Head of the Department of Soil Science. Prior to moving to Reading in 1993, he held lecturing posts in Earth Sciences and in Environmental Sciences in the University of London. He has more than 40 year’s experience of research on trace elements in soils and plants, both with regard to micronutrient deficiencies in agriculture and also to contamination of soils with trace elements. Since leaving the University of Reading in 2001, he has held visiting professorships at the University of Plymouth and the Free University of Brussels and has worked as a consultant on commissions from various organizations, including the International Zinc Association, the International Copper Association and Borax Europe Ltd. In addition to a large number of scientific papers, he has edited two books: “Micronutrient Deficiencies in Global Crop Production” (2008; Springer) and “Heavy Metals in Soils” (1990, 1995; Blackie Academic and Professional). He was also a member of the editorial board of “Essentials of Medical Geology” (Editor-in-Chief O. Selinus; 2005; Elsevier) and is co-author, with D.C. Ayres, of the textbook “Chemical Principles of Environmental Pollution” (1993, 1997; Blackie Academic and Professional). 6 CONTENTS FOREWORD 1 2.3.1.3.2 Protein Metabolism 33 ABBREVIATIONS AND GlOSSARy 2 2.3.1.3.3 Membrane Integrity 33 ACKNOWlEDGMENTS 6 2.3.1.3.4 Auxin Metabolism 34 2.3.1.3.5 Reproduction 34 ABOUT THE AUTHOR 6 2.3.2 Mechanisms of Zinc Uptake by Plants 34 CONTENTS 7 2.3.3 Relative Sensitivity of Crops to Zinc Deficiency 35 ExECUTIVE SUMMARy 9 2.3.3.1 Zinc Deficiency Tolerance Mechanisms in Wheat 37 1. INTRODUCTION 12 2.3.3.2 Zinc Deficiency Tolerance Mechanisms in Rice 37 2. FUNDAMENTAl ASPECTS 2.3.3.3 Interactions Between Zinc and Other Plant Nutrients 38 2.1 Origin and Behaviour of Zinc in Soils 14 2.3.3.3.1 Zinc Phosphorus Interactions 38 2.1.1 Introduction 14 2.3.3.3.2 Inactivation of Plant Zinc 2.1.2 Total Zinc Concentrations in Soils 14 by High Phosphorus 40 2.1.3 Factors Controlling the Total Zinc Content of Soils 16 2.3.3.3.3 Zinc-Nitrogen Interactions 41 2.1.3.1 Composition of the Soil Parent Material 16 2.3.3.3.4 Interactions of Zinc with Other 2.1.3.2 Inputs from Atmospheric Deposition 17 Macronutrients 41 2.1.3.3 Agricultural Inputs 17 2.3.3.3.5 Interactions of Zinc with Other 2.1.3.3.1 Livestock Manures 17 Micronutrients 41 2.1.3.3.2 Fertilisers 18 2.3.3.4 The Role of the Rhizosphere in the Supply 2.1.3.3.3 Sewage Sludge 18 of Zinc to Plants 42 2.1.3.3.4 Industrial Waste Products 18 2.3.3.4.1 Proteoid Roots 43 2.1.3.3.5 Agrochemicals 19 2.3.3.4.2 Responses of the Rhizosphere to Iron 2.1.4 Forms of Zinc in Soils 19 and Zinc Deficiencies 43 2.1.4.1 Zinc in the Soil Solution 20 2.3.3.4.3 Effect of the Zinc Status of Plants 2.1.4.2 Adsorption of Zinc by Soil Constituents 21 on their Susceptibility to Disease 44 2.1.4.3 Secondary Minerals 22 2.4 Causes of Zinc Deficiency in Crops 44 2.1.5 Factors Affecting the Availability of Zinc in Soils to Plants 22 2.5 Zinc Toxicity 46 2.2 Soil Types Associated with Widespread Zinc 2.6 Zinc in Crop Products and Human Nutrition 49 Deficiency in Crops 24 2.6.1 Biofortification of Cereal Grains and Pulses with Zinc 51 2.2.1 Calcareous Soils (Calcisols) 24 2.6.1.1 Genetic Biofortification 51 2.2.1.1 Soils with a Calcic Horizon 24 2.6.1.2 Agronomic Biofortification 52 2.2.1.2 Soils with a Petrocalcic Horizon 24 2.2.1.3 Soils with a Gypsic Horizon 24 2.7 References 54 2.2.1.4 Shallow Soils over Limestone or Marl 25 2.2.1.5 Calcareous Soils Formed in Alluvium or Loess 3. SyMPTOMS OF ZINC DEFICIENCy IN without a Calcic Horizon 25 AGRICUlTURAl AND HORTICUlTURAl CROPS 2.2.1.6 Slightly or Moderately Calcareous Soils 25 2.2.1.7 Calcareous Very Clayey Soils 25 3.1 Introduction 59 2.2.1.8 Calcareous Soils in Australia 26 2.2.1.9 Response of Crops on Calcareous Soils to 3.2 Types of Deficiency Symptoms 59 Fertilisation 26 3.3 Biochemical and Histological Changes in Zinc 2.2.2 Sandy Soils (Arenosols) 26 Deficient Plants 59 2.2.3 Ferralsols: Strongly Weathered Deep Tropical Soils 27 2.2.4 Vertisols 28 3.4 Factors to be Considered in Using Visible 2.2.5 Saline and Sodic (Salt-Affected) Soils 29 Symptoms for Diagnosis 60 2.2.6 Gleysols 30 3.5 Zinc Deficiency Symptoms in Selected Crops 61 2.2.7 Global Distribuion of Main Soil Types Associated 3.5.1 Cereal Crops (Food Staples) 61 with Zinc Deficiency 30 3.5.1.1 Rice 61 2.3 Zinc in Plant Nutrition 30 3.5.1.2 Wheat 62 2.3.1 Physiological Aspects of Zinc in Plants 30 3.5.1.3 Maize (Corn) 63 2.3.1.1 Low Molecular Weight Complexes of Zinc 31 3.5.1.4 Barley 63 2.3.1.2 Zinc in Proteins 31 3.5.1.5 Sorghum 63 2.3.1.3 Physiological Functions of Zinc 32 3.5.1.6 Oats 64 2.3.1.3.1 Carbohydrate Metabolism 32 3.5.2 Pasture Grasses, Legumes and Forage Crops 64 3.5.2.1 Alfalfa 64 7 3.5.2.2 Pasture Grasses and Clovers (Various Species) 64 6.2 Individual Countries or Regions with Zinc 3.5.3 Other Field Crops 65 Deficiency Problems 95 3.5.3.1 Cassava 65 6.2.1 Sub-Saharan Africa 95 3.5.3.2 Chickpea 65 6.2.2 South Asia 96 3.5.3.3 Beans 65 6.2.2.1 Bangladesh 96 3.5.3.4 Oil Seed Rape 65 6.2.2.2 India 97 3.5.3.5 Flax and Linseed 66 6.2.3.3 Nepal 99 3.5.3.6 Cotton 66 6.2.2.4 Pakistan 99 3.5.3.7 Groundnuts 66 6.2.2.5 Sri Lanka 100 3.5.3.8 Soya Bean 67 6.2.3 East Asia 100 3.5.3.9 Sugar Cane 67 6.2.3.1 China 100 3.5.3.10 Lentils 68 6.2.3.2 Indonesia 101 3.5.3.11 Tobacco 68 6.2.3.3 Japan 101 3.5.4 Fruit Crops (Tree, Bush and other Fruits) 68 6.2.3.4 Philippines 101 3.5.4.1 Avocado 68 6.2.3.5 Taiwan Province of China 101 3.5.4.2 Citrus Trees 69 6.2.3.6 Thailand 101 3.5.4.3 Pome Fruits (Apple and Pear) 69 6.2.4 West Asia 101 3.5.4.4 Apricot, Peach and Cherry 70 6.2.4.1 Afghanistan 101 3.5.4.5 Grapes 70 6.2.4.2 Cyprus 101 3.5.4.6 Bananas 70 6.2.4.3 Iran 102 6.2.4.4 Iraq 102 3.5.4.7 Pineapple 71 6.2.4.5 Israel 102 3.5.4.8 Guava 71 6.2.4.6 Jordan 102 3.5.4.9 Strawberry 71 6.2.4.7 Lebanon 103 3.5.4.10 Berry Crops (general) 71 6.2.4.8 Saudi Arabia 103 3.5.5 Nut, Seed and Leaf Tree/Bush Crops 71 6.2.4.9 Syria 103 3.5.5.1 Cocoa 71 6.2.4.10 Turkey 103 3.5.5.2 Coffee 72 6.2.5 Western and Central Europe 104 3.5.5.3 Tea 72 6.2.6 Eastern Europe and Central Asia 104 3.5.5.4 Pecan 72 6.2.7 Oceania 104 3.5.6 Vegetable Crops 72 6.2.7.1 Australia 104 3.5.6.1 Carrot 72 6.2.7.2 New Zealand 106 3.5.6.2 Onion 72 6.2.8 North America 106 3.5.6.3 Potato 73 6.2.8.1 Canada 106 3.5.6.4 Tomato 73 6.2.8.2 United States of America 106 3.5.6.5 Lettuce 73 6.2.9 Latin America and the Caribbean 108 3.5.7 Other Economically Important Crops 74 6.3 General Statement 108 3.5.7.1 Rubber 74 6.4 References 110 3.5.7.2 Oil Palm 74 3.5.7.3 Tung-Oil Tree 74 7. ZINC IN THE NUTRITION OF THE MAJOR 3.6 References 75 CEREAl CROPS 7.1 Introduction 113 4. DIAGNOSIS OF ZINC DEFICIENCy IN SOIlS 7.2 Yields of Cereals and Removal of Zinc from Soil 114 AND CROPS 7.3 Rice 116 7.3.1 Zinc Deficiency in Rice 117 4.1 Introduction 76 7.3.2 Prevention of Zinc Deficiency in Rice 120 4.2 Soil Sampling and Analysis 76 7.3.3 Correction of Zinc Deficiency in Rice Crops 121 4.3 Plant Analysis 79 7.4 Wheat 121 4.4 Biochemical Tests of the Zinc Status of Plants 82 7.4.1 Bread Wheat 122 4.5 References 83 7.4.2 Durum Wheat 123 7.4.3 Zinc Deficiency in Wheats 124 5. ZINC FERTIlISERS 7.4.4 Correction of Zinc Deficiency in Wheat 124 7.5 Rice-Wheat Cropping Systems 125 5.1 Types of Zinc Fertilisers 84 7.6 Maize 125 5.2 Zinc Fertiliser Applications 85 7.6.1 Zinc Deficiency in Maize 126 7.6.2 Treatment of zinc Deficiency in Maize 127 5.3 References 91 7.7 Concluding Comments on Zinc Deficiency in Cereals 127 6. AREAS OF THE WORlD WITH ZINC 7.8 References 129 DEFICIENCy PROBlEMS IN CROPS 8. DISCUSSION AND CONClUSIONS 132 6.1 FAO Global Study of the Micronutrient Status of Soils 93 9. RECOMMENDATIONS FOR FUTURE RESEARCH PRIORITIES 135 8