Soil Fertility Management Practices Africa Soil Health Consortium 2014 Lecture 3: Soil Fertility Management Practices in detail.

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Slide 1 Soil Fertility Management Practices Africa Soil Health Consortium 2014 Lecture 3: Soil Fertility Management Practices in detail Slide 2 Objectives Understanding how organic inputs function as a source of nutrients Understanding how mineral fertilizers function as a source of nutrients Efficiency The 4 rights for effective fertilizer use Understanding the role of improved germplasm in ISFM Understanding the role of Biological Nitrogen Fixation by legumes in ISFM Slide 3 Organic inputs Slide 4 Organics as a source of nutrients: a few definitions and principles Decomposition: biochemical breakdown of dead organic tissue into its inorganic constituent forms Mineralization: process of converting essential nutrient elements from their organic forms into their inorganic forms (or: nutrient release) Soil organic matter (SOM): organic materials in various stages of decomposition Slide 5 Soil Organic Matter -Contains essential plant nutrients -Improves the soils cation exchange capacity -Improves the soils water-holding capacity (SOM can hold five times its weight in water!) -Improves water infiltration capacity -Buffers soil pH -Binds with toxic elements in the soil -Improves soil structure by stimulating activity by soil flora and fauna -Regulates the rates and amounts of nutrients released for plant uptake Slide 6 SOM as a source of N Organic N from SOM NH 4 + (ammonium) NO 3 - (nitrate) Plants Mineralization Fungi & Bacteria Nitrification Nitrifying bacteria Immobilization Slide 7 Organic matter decomposition Organic matter decomposition depends on -Quality of organic material -C:N ratio -Lignin and polyphenol contents -Soil environmental conditions -Micro- and macrofauna in the soil Synchrony Match between nutrient release and uptake Slide 8 Organics as a source of nutrients C:N ratio N content >2.5% or C:N ratio Slide 9 Organics as a source of nutrients C:N ratio N content >2.5% or C:N ratio Organics as a source of nutrients Characteristics of organic resource N >2.5% Yes No Lignin

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