Phosphorus Nitrogen 9 Pollution and Degradation 6 Soil Fertility 6 Soil Chemistry and Mineralogy 5 Plant Nutrition 4 Plant nutrition 4 Potassium 4 Soil fertility 4 Techniques and Methodology 4 Animal Nutrition (Physiology) 3 Animal Wastes 3 Calcium 3 Environmental impact 3 Nutrient availability 3 Nutrient deficiencies 3 Nutrient uptake 3 Plant Production 3 Socioeconomics 3 Sodium 3 Soil Physics 3 Soil organic matter 3 Sulfur 3 Techniques 3 Water 3 Water Resources 3 Zinc 3 Agriculture 2 Animal Husbandry and Production, (New March 2000) 2 Aquatic Biology and Ecology 2