Soil Fertility Management Practices Africa Soil Health Consortium

  • Slides: 52
Download presentation
Soil Fertility Management Practices Africa Soil Health Consortium 2014 Lecture 3: Soil Fertility Management

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

Objectives • Understanding how organic inputs function as a source of nutrients • Understanding

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

Organic inputs

Organic inputs

Organics as a source of nutrients: a few definitions and principles • Decomposition: biochemical

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

Soil Organic Matter - Contains essential plant nutrients - Improves the soil’s cation exchange

Soil Organic Matter - Contains essential plant nutrients - Improves the soil’s cation exchange capacity - Improves the soil’s water-holding capacity (SOM can hold five times its weight in water!) - Improves water infiltration capacity - Buffers soil p. H - 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

SOM as a source of N Nitrification Nitrifying bacteria Immobilization Organic N from SOM

SOM as a source of N Nitrification Nitrifying bacteria Immobilization Organic N from SOM NH 4+ (ammonium) NO 3 - (nitrate) Mineralization Fungi & Bacteria Plants

Organic matter decomposition Synchrony depends on Match between nutrient release and uptake - Quality

Organic matter decomposition Synchrony depends on Match between nutrient release and uptake - Quality of organic material - C: N ratio - Lignin and polyphenol contents - Soil environmental conditions - Micro- and macrofauna in the soil

Organics as a source of nutrients Supply of nutrients from SOM depends on -

Organics as a source of nutrients Supply of nutrients from SOM depends on - Quantity and frequency of application of organic inputs - Quality of organic inputs - Soil type and environmental conditions, providing the environment for mineralization C: N ratio • N content >2. 5% or C: N ratio<16 nutrients are released in the short term (e. g. Biomass of legumes, composted crop residues) • N content <2. 5% or C: N ratio> 16 nutrients are immobilized for prolonged periods (e. g. Straw) Graph from: http: //passel. unl. edu/pages/informationmodule. php? idinformationmodule=1130447040&topicorder=5&maxto=8

Organics as a source of nutrients Supply of nutrients from SOM depends on -

Organics as a source of nutrients Supply of nutrients from SOM depends on - Quantity and frequency of application of organic inputs - Quality of organic inputs - Soil type and environmental conditions, providing the environment for mineralization C: N ratio • N content >2. 5% or C: N ratio<16 nutrients are released in the short term (e. g. Biomass of legumes, composted crop residues) • N content <2. 5% or C: N ratio> 16 nutrients are immobilized for prolonged periods (e. g. Straw) Polyphenols & Lignin • Some groups of polyphenols bind nitrogen • Ligning: main component of wood, difficult to break down • High polyphenol & ligning mineralization is very slow

Organics as a source of nutrients Characteristics of organic resource N >2. 5% Yes

Organics as a source of nutrients Characteristics of organic resource N >2. 5% Yes No Lignin <15% Polyphenols <4% Lignin <15% Yes No Incorporate directly with annual crops Mix with fertilizer or high quality organic matter Mix with fertilizer or add to compost Surface apply for erosion and water control

Organics as a source of nutrients Leaf colour Green Yellow Leaves fibrous (do not

Organics as a source of nutrients Leaf colour Green Yellow Leaves fibrous (do not crush) High astringent taste (makes your tongue dry) Leaves crush to powder when dry No Yes Incorporate directly with annual crops Mix with fertilizer or high quality organic matter Mix with fertilizer or add to compost Surface apply for erosion and water control

Crop residues Using crop residues - Return to the field to provide mulch and

Crop residues Using crop residues - Return to the field to provide mulch and nutrients - Animal feed (and return manure to the field) - Composting (and return to the field) - Fuel source - Construction material (e. g. for wall or roof) Nitrogen Millet Sorghum 4 -10 Phosphorus 1 Potassium 15 -27 Soybean Groundnut 4 -9 Maize Rice Dryweight (g/kg) 5 -8 4 -9 8 -13 12 -20 0 -1 7 -15 0 -1 7 -17 1 -2 9 -18 1 -3 8 -12 1 -2 13 -27 Exercise: How many kg soybean residues do you need to fertilize a 1 ha field with a rate of 40 kg P/ha? Assume that the soybean residues contain 1. 5 g P/kg of residue.

Crop residue management Millet Sorghum Nitrogen 4 -10 4 -9 Maize Rice Dryweight (g/kg)

Crop residue management Millet Sorghum Nitrogen 4 -10 4 -9 Maize Rice Dryweight (g/kg) 5 -8 4 -9 Phosphorus Potassium 1 15 -27 0 -1 7 -15 0 -1 7 -17 1 -2 13 -27 Soybean Groundnut 8 -13 12 -20 1 -2 9 -18 1 -3 8 -12 Exercise: How many kg soybean residues do you need to fertilize a 1 ha field with a rate of 40 kg P/ha? Assume that the soybean residues contain 1. 5 g P/kg of residue. Answer: Soybean contains 1. 5 g P/kg of residue. This means that soybean residues contains 0. 15 % P. 40 kg/0. 15% = 40 kg/(0. 15/100) = 26, 667 kg soybean residues are needed to supply 40 kg P. 26, 667 kg residues is 27 full oxcarts!

Organic inputs: pros and cons Advantages • Builds up SOM (SOM has many benefits)

Organic inputs: pros and cons Advantages • Builds up SOM (SOM has many benefits) • Provide essential nutrients • Nutrients are released slowly and provide a continuous supply over the cropping system and nutrient losses are small Disadvantages • Low nutrient content requires application in large amounts • Large quantities of organic matter not always available – Land required for production of organic inputs – Trade offs in using crop residues – Handling of organic inputs requires labour • Organic inputs can increase disease pressure

Mineral fertilizers • Mineral fertilizers can supply most of the essential macro- and micro-nutrients

Mineral fertilizers • Mineral fertilizers can supply most of the essential macro- and micro-nutrients • Completely soluble: e. g. Urea, KCl, DAP • Partly soluble: e. g. Rock phosphate, dolomite • Basal (‘starter’) fertilizer: – Contains nutrients (e. g. N, P, K, Mg) required for early stages of plant growth, or nutrients which are not easily lost from the soil – Is applied at planting • Topdressing – Often N based fertilizer – Second application, later in the season Top dressing young maize plants with N fertilizer

N fertilizers • Atmospheric N 2 NH 3 – Legumes – Industrial: Haber-Bosch process

N fertilizers • Atmospheric N 2 NH 3 – Legumes – Industrial: Haber-Bosch process • Nitrate (NO 3 -) and ammonium (NH 4 -) – Directly available for plants • Nitrification: NH 3 NO 3 - + H+ – NO 3 - is easily leached – Nitrification causes acidification through release of H+ • Types of N-fertilizer – Urea, compound NPKs, anhydrous ammonia, calcium ammonium nitrate (CAN), ammonium nitrate, ammonium sulfate

P fertilizers Phosphate Rock Process Needs to be ground into fine powder P 2

P fertilizers Phosphate Rock Process Needs to be ground into fine powder P 2 O 5 content +/-32% Solubility Sparingly soluble Manufactured P fertilizers PR is reacted with sulfuric or phosphoric acid - Triple superphosphate (TSP): 46% - Single superphosphate (SSP): 20% Fully soluble Mined Phosphate or Phosphate Rock (PR) from sedimentary or igneous origin P availability - Slow release Directly available - Soil p. H needs to be <5. 5 to start a reaction with PR Suitability - Tree crops Annual crops - Remineralization of degraded fields Picture from: http: //www. rsmm. com/miningphos. htm

K fertilizers • Manufactured from large deposits of water-soluble K minerals • The salts

K fertilizers • Manufactured from large deposits of water-soluble K minerals • The salts commonly also contain Mg and S • K-fertilizers – Potassium chloride (KCl): 60% K 2 O – Potassium sulfate (K 2 SO 4): 50% K 2 O Finite resources - Reserves of raw materials for P and K fertilizers are finite - Potash reserves: sufficient for 250 years - Phosphate reserves: sufficient for 300 -400 years Picture: Potash evaporation ponds, Utah. http: //en. wikipedia. org/wiki/Potash

Multinutrient fertilizers More expensive • Complex multinutrient fertilizers – Used in horticulture • Compound

Multinutrient fertilizers More expensive • Complex multinutrient fertilizers – Used in horticulture • Compound fertilizers – Mixing single nutrient fertilizers slurry granulated product • Bulk blend fertilizers – Mixing different ‘dry’ fertilizers to achieve a specific nutrient composition Cheaper

Fertilizer: excercise A farmer wants to compare the cost of applying nutrients in the

Fertilizer: excercise A farmer wants to compare the cost of applying nutrients in the form of a compound (17 -17 -17) with straight fertilizers (urea, TSP and KCl). Calculate the difference in cost between 1 bag of compound NPK fertilizer and applying the same amounts of nutrients from Urea, TSP and KCL. Nutrient content (%) N Compound 17 -17 -17 Urea (46% N) TSP (46% P 2 O 5) KCl (60% K 2 O) 17 46 – – P 2 O 5 17 – 46 – Price ($/50 kg bag) K 2 O 17 – – 60 32 17 22 30

Fertilizer: excercise worked out Step 1 • 50 kg bag of NPK (17 -17

Fertilizer: excercise worked out Step 1 • 50 kg bag of NPK (17 -17 -17) contains – 17% of 50 kg = 8. 5 kg N – 17% of 50 kg = 8. 5 kg P 2 O 5 – 17% of 50 kg = 8. 5 kg K 2 O Step 2 • For 8. 5 kg N you need 8. 5/0. 46 = 18. 5 kg urea • For 8. 5 kg P 2 O 5 you need 8. 5/0. 46 = 18. 5 kg TSP • For 8. 5 kg K 2 O you need 8. 5/0. 6 = 14. 2 kg KCl Step 3 • 18. 5 kg urea costs (18. 5/50) * $17 = $6. 3 • 18. 5 kg TSP costs (18. 5/50) * $22 = $8. 1 • 14. 2 kg KCl costs (14. 2/50) * $30 = $8. 5 Step 4 • Total costs of straight fertilizers = $6. 3 + $8. 1 + $8. 5 = $22. 9 • One bag of compound 17 -17 -17 costs $32 • Farmer saves $32 - $22. 9 = $9. 1 by using a combination of straight fertilizers

Mixing straight Fertilizers

Mixing straight Fertilizers

Fertilizer use efficiency • Nutrients applied to the soil are M – Taken up

Fertilizer use efficiency • Nutrients applied to the soil are M – Taken up by crops aximiz e – Retained in the soil as nutrient stocks Min – Lost from the soil through leaching or volatilization imize • Agronomic efficiency (AE): The amount of additional yield obtained per kg nutrient applied • AE depends on – Recovery fraction (how much of the applied nutrients is taken up by the crop? ) – Internal use efficiency (how much additional yield per kg of nutrient taken up by the crop? )

Recovery fraction(RF) Additional uptake • RF (X): recovery fraction of applied nutrient X –

Recovery fraction(RF) Additional uptake • RF (X): recovery fraction of applied nutrient X – units: kg X uptake/kg X applied • X_uptake_F: plant X uptake at harvest when nutrient X is applied – Units: kg X uptake/ha • X_uptake_C: plant X uptake at harvest without nutrient X applied – Units: kg X uptake/ha • X_applied: Rate of X applied – Units: kg X/ha

Internal use efficiency IE (X): internal efficiency of nutrient X – Units: kg crop

Internal use efficiency IE (X): internal efficiency of nutrient X – Units: kg crop product/kg X uptake Y_F: Yield with nutrient X – Units: kg/ha Y_C: Yield without nutrient X – Units: kg/ha Additional yield Additional uptake

Agronomic efficiency (AE) Economic benefits of improving agronomic efficiency of fertilizer: - Larger yield

Agronomic efficiency (AE) Economic benefits of improving agronomic efficiency of fertilizer: - Larger yield increases with a given quantity of fertilizer - Less fertilizer is required to achieve a particular yield target

Agronomic efficiency: exercise Two farmers apply 50 kg N/ha fertilizer. Their fields vary in

Agronomic efficiency: exercise Two farmers apply 50 kg N/ha fertilizer. Their fields vary in soil fertility, affecting crop yields and fertilizer use efficieny. Calculate the agronomic N efficiency for each farmer. Farmer 1 Farmer 2 Field history: Degraded field, cultivated for many years without application of fertilizer or manure. Field history: Fertile, but N-deficient field that received moderates of manure in the past. Yield without N application: 400 kg/ha Yield with 50 kg N/ha: 900 kg/ha Yield without N application: 2000 kg/ha Yield with 50 kg N/ha: 4500 kg/ha

Agronomic efficiency: exercise worked out Farmer 1 Farmer 2 Field history: Degraded field, cultivated

Agronomic efficiency: exercise worked out Farmer 1 Farmer 2 Field history: Degraded field, cultivated for many years without application of fertilizer or manure. Field history: Fertile, but N-deficient field that received moderates of manure in the past. Yield without N application: 400 kg/ha Yield with 50 kg N/ha: 900 kg/ha Yield without N application: 2000 kg/ha Yield with 50 kg N/ha: 4500 kg/ha Agronomic N use efficiency = (900 -400) / 50 = 10 kg grain/kg N Agronomic N use efficiency = (45002000) / 50 = 50 kg grain/kg N

The ‘ 4 Rs’ for effective fertilizer use 1. 2. 3. 4. Apply the

The ‘ 4 Rs’ for effective fertilizer use 1. 2. 3. 4. Apply the right source of nutrient At the right rate At the right time At the right place . . . To meet crop demand

R 1: Right fertilizer product Matching the fertilizer source and products to the crop’s

R 1: Right fertilizer product Matching the fertilizer source and products to the crop’s needs and soil’s properties • Straight fertilizers vs. compound fertilizers • Balanced fertilization (interactions between nutrients) • Choice of fertilizer depends on crop, current and past use of manure, soil properties and climate conditions • Methods to indentify which nutrients should be applied: soil analysis, nutrient omission trials, nutrient deficiencies on crops • Avoid depleting nutrient stocks on the longer term • Use good quality fertilizer

R 2: Right fertilizer rate Matching the amount of fertilizer to the crop’s needs

R 2: Right fertilizer rate Matching the amount of fertilizer to the crop’s needs Take into account: • Nutrient requirements of the crop • The soil’s capacity to supply nutrients • The amount of nutrients applied in organic inputs • The amount of nutrients applied to previous crops • Target yield – attainable yield under local climatic conditions – Farmers’ goals • Costs of fertilizers and value of crop products • Fertilizer responses

R 2: Right fertilizer rate – fertilizer responses Fertilizer responses • Large/poor/very poor responses,

R 2: Right fertilizer rate – fertilizer responses Fertilizer responses • Large/poor/very poor responses, related to initial soil fertility Approaches to address these • Cash constrained farmers can priotize fertilizer use in most responsive fields only • Additional application of organic resources or other soil amendments or management practice might be required on otherwise nonresponsive soils • Applying small doses of fertilizer on fertile fields can sustain fertility in the longer term

R 3: Right time for fertilizer application Create synchrony: Make nutrients available when crops

R 3: Right time for fertilizer application Create synchrony: Make nutrients available when crops need them • Basal fertilizer application: N, P, K, and other nutrients required for early crop growth are applied at or just after planting • Top dressing: Fertilizer N is highly mobile apply N in several split applications at key stages during crop development • Leaf colour charts or chlorophyll meters to determine the crop’s N demand • If the crop develops poorly due to e. g. low rainfall, top dressing can be cancelled • Slow-release N fertilizers and deep placement of fertilizer N improve synchrony

R 4: Right placement of (basal) fertilizer Apply fertilizer there where the crop can

R 4: Right placement of (basal) fertilizer Apply fertilizer there where the crop can access the nutrients • Broadcasting – Low labour requirements, often used for top dressing • Banding – Fertilizer is placed at 5 -8 cm depth and covered with soil. Seeds are planted on top. Use for basal application. • Spot application – Small amounts of fertilizer are placed in or close to planting hills. Preferred where plants are widely spaced and where soil and climatic conditions increase the chance for nutrient losses through leaching) • Deep placement – Slow-release N fertilizers are placed in the soil in flooded fields

R 4: Right placement of (basal) fertilizer Fertilizer Seeds Fertilizer

R 4: Right placement of (basal) fertilizer Fertilizer Seeds Fertilizer

A 5 th right of fertilizer use in SSA Make sure that scarce fertilizer

A 5 th right of fertilizer use in SSA Make sure that scarce fertilizer resources are delivered to the part of the cropping system that delivers the maximum economic benefit to the farmer • Identify the part of the cropping system where fertilizer inputs will deliver the greatest return • Consider the whole cropping when planning fertilizer use – Maize/legume rotation: legumes may benefit from residual P applied to maize. – Maize/legume intercropping: apply N only to maize because legumes can meet their N requirements by biological N 2 fixation.

Soil amendments Lime • Increases p. H • Prevents Al and Mn toxicity in

Soil amendments Lime • Increases p. H • Prevents Al and Mn toxicity in acidic soils (p. H <5. 5) • Supplies Ca • Increases P and Mo availability • Can increase microbiological activity/processes Liming requirements • Depend on soil acidity level and Al 3+ tolerance of crops • Strongly acidic clay soils need more lime than weakly buffered sandy soils Liming materials • Limestone or calcium carbonate (Ca. CO 3) • Other materials are expressed in calcium carbonate equivalent (CCE) • Limestone: dolomitic/calcitic Gypsum • Ca. SO 4. 2 H 2 O • Rehabilitates sodic soils • Supplies Ca • Occurs as a natural deposit in (semi-) arid regions • Sparingly soluble in water

Improved germplasm Seeds, seedlings and other planting materials that have been bred to meet

Improved germplasm Seeds, seedlings and other planting materials that have been bred to meet particular requirements of the environment in which they are to be grown Local susceptible variety Improved variety Nsansi Yield = G (genotype) x E (environment) x M (management)

Improved germplasm Yield from unfertilized BH 540 was slightly higher than fertilized local varieties

Improved germplasm Yield from unfertilized BH 540 was slightly higher than fertilized local varieties Yields more than doubled when both fertilizer and improved germplasm was used

Improved germplasm Seeds, seedlings and other planting materials that have been bred to meet

Improved germplasm Seeds, seedlings and other planting materials that have been bred to meet particular requirements of the environment in which they are to be grown Genetic yield potential - When grown in the targeted environment - Greater harvest index (HI) - Additional traits (e. g. rice with high vitamin A content or high-quality protein maize) - Adapted/tolerant to environmental stresses such Al toxicity or drought Pest and disease resistance - Higher yields - Healthy plants give higher returns on used nutrient inputs - Disease free planting materials - GMO planting material Nutrient use efficiency - Higher HI higher agronomic efficiency - More extensive or deeper root system to capture more nutrients Yield = G (genotype) x E (environment) x M (management)

Availability of improved germplasm • Knowledge & information – Available varieties for a particular

Availability of improved germplasm • Knowledge & information – Available varieties for a particular region – Places where they can be purchased – Prices • Ability to obtain – Agrodealers or other input supply networks – Local, community-based seed mutiplication – Continuity of supply • Quality of material – – Purity Free of diseases and pests Uniform in size High viability Picture: Taskcape, UK

Biological nitrogen fixation by legumes Atmosphere: 79% nitrogen (N 2, gas) Rhizobia interact with

Biological nitrogen fixation by legumes Atmosphere: 79% nitrogen (N 2, gas) Rhizobia interact with the legume roots and form nodules. Rhizobia transform N 2 gas into mineral NH 3+. Picture: N 2 Africa

Legumes • • Food Fodder Fuelwood and poles Soil fertility • Multi-purpose legumes

Legumes • • Food Fodder Fuelwood and poles Soil fertility • Multi-purpose legumes

Dual purpose grain legumes

Dual purpose grain legumes

Components of successful BNF Ove (GL x GR) x E x M • •

Components of successful BNF Ove (GL x GR) x E x M • • rrid ing! GL: legume genotype GR: rhizobium genotype (strain) E: environment (climate and soils) M: agronomic management Opportunities - Legumes benefit from residual basal fertilizer (especially P) applied to cereals when grown in rotation or as intercrop - Use of direct application of fertilizers on legumes when there are good market opportunities

GL x GR Promiscuous Cowpea Specific Groundnut Common bean (GL x GR) x E

GL x GR Promiscuous Cowpea Specific Groundnut Common bean (GL x GR) x E x M Soybean Chickpea

GL x GR

GL x GR

Inoculation = applying rhizobia to the seed Legumes need inoculation when • The soil

Inoculation = applying rhizobia to the seed Legumes need inoculation when • The soil does not contain compatible rhizobia • The population of compatible rhizobia is small • Indigenous rhizobia are less effective in fixing N 2 compared with selected inoculant strains Inoculants are very cost effective compared to mineral fertilizer!

Inoculation Be aware! Inoculants contain living rhizobia which die when: - Exposed to sunlight

Inoculation Be aware! Inoculants contain living rhizobia which die when: - Exposed to sunlight - Exposed to high temperatures - Stored in an open package

Legume contributions to soil fertility Contribution to soil fertility: Amount of N 2 fixed

Legume contributions to soil fertility Contribution to soil fertility: Amount of N 2 fixed in relation to amount of N taken away with harvest. Green manures and tree legumes The greater the biomass, the larger the inputs from N 2 fixation. • Low uptake, despite extensive research and development • Tree legumes: max 600 kg • >2 t/ha dry matter green manure N/ha/year gives 1 t/ha additional grain yield • Grain legumes/green manures: in following cereal crop max 300 kg N/ha/season • High labour and land requirements! • N inputs from grain legumes depends on residue management • A niche opportunity

Arbuscular Mycorrhizal Fungi (AMF) • Many plants naturally form symbioses with AMF • AMF

Arbuscular Mycorrhizal Fungi (AMF) • Many plants naturally form symbioses with AMF • AMF can also be prepared as commercial products and used as inoculant • Benefits of symbiosis with AMF – Enhance nutrient and water uptake – Reduce pest and disease damage – Improve soil structure

Summary Organic inputs - Decomposition - Crop residues - Pros and cons Improved germplasm

Summary Organic inputs - Decomposition - Crop residues - Pros and cons Improved germplasm - Benefits - Availability - Quality Soil amendments - Lime - Gypsum AMF - Symbiosis between plants and mycorrhizal fungi Mineral fertilizers - Single nutrient - Mutiple nutrient - Solubility - Fertilizer use efficiency (AE) - The 4 rights BNF by legumes - Legume-rhizobia symbiosis - Promiscuous and specific legumes - Inoculation