IntroductionSustainable Agriculture: Definitions and GoalsFactors Determining SustainabilitySoil Fertility Essential Plant NutrientsCriteria for EssentialityBasis for Classification of Nutrients as Primary, Secondary, and MicronutrientsPrimary Nutrients, Secondary Nutrients, and MicronutrientsFunctions of Essential Nutrients in PlantsSoil the SustainerSoil Organic MatterSoil WaterSoil AirSoil Mineral MatterSoil ColloidsSoil Living OrganismsSoil ColloidsClay MineralsOxide MineralsOrganic MatterHumus, Its Structure and PropertiesC:N RatioFactors Affecting the Organic-Matter Content of SoilsSoil AcidityAcidsThe pH ConceptDetermination of Soil pHActive and Potential AcidityBuffering CapacityNature of Soil AcidityFactors Affecting Soil AciditySoil pH and Crop ProductionLime RequirementLiming MaterialsFineness of LimestoneSoil Salinity and SodicityCoverage and Special FeaturesCriteria for Determining Salinity/Sodicity ClassificationReclamation and Management of Saline SoilsCrop Production on Saline SoilsReclamation and Management of Sodic SoilsCrop Production on Sodic SoilsNitrogenSoil Organic N Mineralization of Soil Organic NitrogenFactors Affecting NitrificationNitrogen ImmobilizationAmmonium Fixation (Nonexchangable Ammonium)NH4 vs. NO3- Nutrition of PlantsBiological Nitrogen FixationNitrogen Fertilizers or Industrial Nitrogen FixationEfficient Nitrogen ManagementIncreasing N Use EfficiencyNitrogen Availability IndicesNitrogen-Deficiency SymptomsPhosphorusSoil PhosphorusPhosphate Retention or Fixation in SoilFactors Affecting the Retention of Phosphorus by SoilPhosphate Fertilizer Reaction Products in SoilIntensity (I) and Quantity (Q) Factors in Phosphorus AvailabilitySoil Testing for PhosphorusPhosphorus-Deficiency Sym