Soil soil fertility Africa Soil Health Consortium 2014

Soil & soil fertility Africa Soil Health Consortium 2014 Lecture 2: Introduction to soil and soil fertility

Objectives Gain knowlegde on the principles underpinning ISFM practises • Introduction to soil – – Soil texture Porosity Mineral fraction Organic matter • Introduction to nutrients – Understanding the function of nutrients in plant growth – Recognizing nutrient deficiencies • Soil fertility – – Understanding the concept of soil fertility Introduction to soil fertility management Conservation agriculture & organic agriculture Minimizing losses of added nutrients

Soil Organic fraction: - Soil organic matter (SOM) - Key issue in soil fertility management il s So + Mineral fraction: - Provides support to plant roots - Slowly releases nutrients into the soil solution e ac oli sp ds re Po n au f l soi d n aa a r flo Pore space: -space for roots and micro-organisms -air for micro-organisms -water storage

Pore space Porosity: volume of the soil occupied by air and the soil solution Porosity in Well-drained moist soil: sufficient moisture for plant growth and sufficient aeration for proper root function Dry soil: all pores are filled with air drought stress Flooded soil: pores are saturated with water roots cannot breathe and plants may die 0 0. 5 1. 0 1. 5 2. 0 2. 5 mm Water film Soil particle Air space Illustration adapted from Brady 1984, The nature and properties of soils, 9 th edition.

Mineral fraction Sand Silt 0 1 3 2 mm Clay 4 5 Sand: 0. 05 - 2. 0 mm Silt: 0. 002 - 0. 05 mm Clay: < 0. 002 mm Illustration adapted from: www. iconn. org

Mineral fraction Silt % Clay % Sand %

The finger test Mineral fraction

Mineral fraction & Porosity Pore Space in Sandy Soil vs. Clay Soil Sandy soil Larger pores Less total pore volume = Less porosity Clay soil Smaller pores Soil texture affects - Porosity - Water holding capacity - Nutrient retention and supply - Drainage - Nutrient leaching Infiltration Variations by Soil Texture Greater total pore volume = Greater porosity Sand Silt Clay Illustrations adapted from: http: //wegc 203116. uni-graz. at/meted/hydro/basic/Runoff/print_version/04 -soilproperties. htm

Mineral fraction & CEC Cations: positively charged ions (e. g. K+, NH 4+) Cation exchange capacity (CEC): the maximum quantity of total cations that a soil is capable of holding. Clay fraction and SOM: Small particle size Large negatively charged surface area More positions to hold cations High CEC Clay – Many positions to hold cations H+ Sand– Few positions to hold cations Ca 2+ Mg 2+ Sand NH 4+ Clay Na+ K+ H+ H+ K+ H+ Illistration adapted from: http: //www. spectrumanalytic. com/support/library/ff/CEC_Bp. H_and_percent_sat. htm

Mineral fraction & CEC depends on - Clay content - Type of clay mineral - SOM content - Soil p. H Clay minerals differ in structure • 1: 1 clay minerals – CEC varies with soil p. H – Found in most upland soils in SSA • 2: 1 clay minerals – Large inherent CEC capacity – Found in fertile lowland soils Illustration adapted from Lory ‘Structure of Clays’ www. soilsurveys. org

Organic fraction: SOM: plant and animal residues, in various stages of decompisition Picture: http: //www. guiadejardineria. com/jardineria/suelos-y-abonos/page/7/

Organic fraction: SOM - Contains essential plant nutrients - Improves the soil’s Cation Exchange Capacity - Improves the soil’s water-holding capacity - (SOM can hold up to five times its own weight in water!) Improves water infiltration Buffers soil p. H Binds with toxic elements in the soil Improves soil structure by stimulating activity of soil flora and fauna - Regulates the rates and amounts of nutrients released for plant uptake Litter layer % Organic matter 1 2 3 4 Top soil Sub soil Organic matter SOM is a key issue in soil fertility management! Illustration adapted from: http: //www. tekura. school. nz/departments/horticulture/ht 106_p 4. html 5

Soil analysis • Soil test: chemical method for estimating the nutrient-supplying power of a soil • Laboratory needs a representative composite sample of 0. 5 kg • Be aware of heterogeneity within fields when sampling!

Guidelines for soil sampling Take a representative sample!!! 1. 2. 3. 4. 5. 6. 7. 8. Check the area to be sampled for notable features (e. g. slope, soil types, vegetation, drainage). Draw a sketch map, and identify and mark the location of sampling sites. Take soil samples with a soil auger at the sampling depth (0 -20 cm or 2040 cm). Take 10 -35 sub-samples per site, the number depending on the size and heterogeneity of the field. Combine the sub-samples to one composite per site and mix thoroughly. If necessary, reduce sample weight by sub-dividing Label the sample of soil properly. Air-dry the sample and when dry, store it, properly labelled, in a plastic bag or a glass bottle for further analyses.

Nutrients Macronutrients: at least 0. 1% of plant dry matter per macronutrient Qu Sulphur (S): ite - Part of amino acids (protein formation) po or - Synthesis of chlorophyll and some vitamins mo bil - Required for N 2 -fixation by legumes i le ob i m ty ry Ver ym obil e Nitrogen (N): Very m - Amino acid/Protein oformation bile - Photosynthesis Ve Phosphorus (P): - Energy storage/transfer - Root growth Ve r - Crop maturity y mobile - Straw strength - Disease resistance - Needed in large amounts during plant growth - Required for N 2 -fixation by legumes e po ium ed M y ilit mo bil ity Qu ite Poo Calcium (Ca): - Cell growth and walls - Activates enzymes (protein formation and carbohydrate transfer) - Essential in ‘calcicole’ plants (e. g. Groundnut) for seed production. - Influences water movement, cell growth and division - Required for uptake of N and other minerals ob le bil m mo bi mo or Potassium (K): - Plant turgor pressure maintenance - Accumulation and transport of the products of Ve plant metabolism ry mo - Disease resistance bile - Required for N 2 -fixation by legumes ite ry Po Qu Ve or mo bilit y ity Magnesium (Mg): - Photosynthesis - Activates enzymes - Carbohydrate transport

Nutrients Micronutrients: less than 0. 1% of plant dry matter Iron (Fe): - Photosyntheiss - Respiration Manganese (Mn): - Photosynthesis - Enzyme function Boron (B): - Development/growth of new cells Zinc (Zn): - Nucleic acid synthesis and enzyme activation Copper (Cu): - Chlorophyll formation - Seed formation - Protein synthesis Molybdenum (Mo): - Protein synthesis and N uptake - N 2 -fixation by legumes Chlorine (Cl): - Movement of water and solutes - Nutrient uptake - Photosynthesis - Early crop maturity - Disease control Cobalt (Co): - N 2 -fixation by legumes Nickel (Ni): - Required for enzyme urease Sodium (Na): - Water movement and balance of minerals Silicon (Si) - Cell walls - Protection against piercing by sucking insects - Leaf presentation - Heat and drought tolerance

Nutrient deficiency Healthy N-deficient P-deficient K-deficient Diseased

Nutrient deficiencies

Nutrient deficiency: exercise

Nutrient deficiency: exercise P-deficient - Stunted growth - Purplish colouring K-deficient - Browning of leaf edges

Nutrient uptake Nutrient N P K S Plants take up NO 3 -, NH 4+ H 2 PO 4 - , HPO 42 K+ SO 42 - Mg Ca Fe Mn B Zn Cu Mo Cl Co Ni Na Si Mg 2+ Ca 2+ Fe 2+ and Fe 3+ Mn 2+ and Mn 3+ (BO 3)3 Zn 2+ Cu 2+ Mo 42+ Cl. Co 2+ Ni 2+ Na+ (Si. O 4)4 -

Nutrient availability Readily available - Nutrients from soluble fertilizers (e. g. KCL), readily mineralized SOM, nutrients held on the edges of soil particles, and in the soil solution Slowly available - Nutrients in organic form, such as plant residues and organic manures (particularly with a high C/N ratio), slowly soluble mineral fertilizers (e. g. Phosphate rock) and the SOM fraction resistant to mineralization Not available - Nutrients contained in rocks, or adsorbed on soil particles

Soil fertility The capacity of soil to supply sufficient quantities and proportions of essential chemical elements (nutrients) and water required for optimal growth of specified plants as governed by the soil’s chemical, physical and biological attributes. • • Chemical elements for plant nutrition Adequate soil volume for plant root development Water and air for root development and growth Anchorage for the plant structure Inherent Dynamic Soil texture Soil organic matter (SOM) Depth Nutrient- and water-holding capacity Parent material Soil structure

Soil fertility management practices • • Nutrient deficiencies prevent a good harvest Nutrient deficiencies can be expressed during plant growth Correcting nutrient deficiencies Soil acidity correction • • Use mineral (fertilizer) or organic (manure, crop residues) to supply nutrients Use special fertilizer blends containing micronutrients or manure in case of micronutrient deficiencies Healthy Ndeficient Breaking hardpans Water harvesting Erosion control Land preparation Planting date Spacing Planting practices Weeding Pdeficient Kdeficient Pest and disease management Intercropping

Soil fertility management practices • Acidity is caused by – inherent soil properties – acidity inducing management (e. g. long-term use of ammonium based fertilizer) • Acid soils have high exchangeable Al (Al toxicity) Correcting nutrient deficiencies Soil acidity correction Breaking hardpans Water harvesting Erosion control Land preparation 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 Planting date Spacing Planting practices Weeding Pest and disease management Intercropping • Apply lime to reduce exchangeable Al to +/- 15%

Soil fertility management practices • • Compaction sub-surface soil barrier to root growth Break hardpans by ploughing or chisel ploughing to 30 cm depth Correcting nutrient deficiencies Soil acidity correction Breaking hardpans Water harvesting Porous soil allows good root development Erosion control Surface crust Land preparation Planting date Spacing Planting practices Sub-surface Weeding barrier to Pest and disease roots management Intercropping Illustration adapted from: http: //locallygerminated. wordpress. com/

Soil fertility management practices • Capture more rainfall in areas that are prone to drought – Harvesting additional water (e. g. Zaï) – Promoting infiltration by coversing the soil surface with mulch • Labour intensive Correcting nutrient deficiencies Soil acidity correction Breaking hardpans Water harvesting Erosion control Land preparation Planting date Spacing Planting practices Weeding Pest and disease management Intercropping Zaï pits in Niger Pictures: fao. org Mulching of bananas, western Uganda

Soil fertility management practices • Prone to erosion: fields on steep slopes, or on gentle slopes with course-textured top soil • Measures: live barriers (e. g. grass strips), teracces, surface mulch Correcting nutrient deficiencies Soil acidity correction Breaking hardpans Water harvesting Erosion control Land preparation Planting date Spacing Planting practices Weeding Pest and disease management Intercropping Bunds on sloping land in Burundi

Soil fertility management practices • Good seedbed preparation improves germination and reduces the chance for diseases Correcting nutrient deficiencies Soil acidity correction Breaking hardpans Water harvesting • A delay in planting date often affects yield negatively • Planting time is important especially when the growing season is short Erosion control Land preparation Planting date Spacing Planting practices Weeding Pest and disease management Intercropping

Soil fertility management practices • Crops compete for nutrients, water and light • Use a correct planting density, adjusted to crop type and the environment. Consider the distance between rows, between plants within rows and the number of plants per planting hole. Crop Optimal rainfall Correcting nutrient deficiencies Soil acidity correction Breaking hardpans Water harvesting Erosion control Land preparation Poor rainfall Planting date Density Between rows Within rows ‘ 000 Plants/ha cm cm ‘ 000 Plants/ha cm Cm Beans (common) 200 50 10 133 50 15 Pest and disease management Maize 44 75 30 37 90 30 Intercropping Soybean 444 45 5 333 60 5 Spacing Planting practices Weeding

Soil fertility management practices • • • Use viable seed (at least 80% germination) Plant seeds at the correct depth and insert cuttings at correct angle Plant more seeds than required for optimal plant density. Correcting nutrient deficiencies Soil acidity correction Breaking hardpans Water harvesting • • Weeds compete with crops for nutrients, water and light. Timely removal of weeds is essential Weed before top dressing crop with fertilizer Control pests and diseases at specific growth stages Erosion control Land preparation Planting date Spacing Planting practices Weeding Pest and disease management Intercropping Delayed weeding reduces the crop response to fertilizer

Soil fertility management practices • • Intercropping arrangements: take into account specific growth features and needs of individual crops to minimize intercrop competition. Examples: delayed planting of one intercrop, adjusting spacing, strip intercropping Maize-cassava Maize-pigeonpea Correcting nutrient deficiencies Soil acidity correction Breaking hardpans Water harvesting Erosion control Land preparation Planting date Spacing Planting practices Weeding Cassava-soybean Pest and disease management Intercropping

Conservation agriculture (CA) Basic principles 1. Soil disturbance is minimized by reduced or zero-tillage 2. Use of at least 30% soil cover (mulch or cover crops) 3. Use of crop rotations/associations Advantages - Rapid planting of large areas - Reduction of soil erosion Pitfalls - Competing uses of crop residues needed for mulch - Yields may decrease on the short-term (the increase often comes on the longer-term) - Increased weed pressure caused by reduced tillage - Full CA requires a fundamental change in the farming system. This may not be practical or enomic for the farmer - Possible decrease in agronomic efficiency of fertilizer use

Organic agriculture Reliance on organic resources to provide nutrients to sustain soil fertility and produce economic crop yields However, mineral fertilizers are an essential component in sustainable agriculture in SSA • • Soil nutrients stocks in large parts of SSA have already become depleted and require replenishment Organic resources are not available in large enough quantities to replenish and sustain nutrient stocks in the soil Large and economic responses to mineral fertilizer are obtained in many parts of SSA Organic resources are bulky and their management is labour intensive ISFM: use of mineral fertilizer in combination with organic resources. The combination provides the greatest benefits!

Minimizing losses of added nutrients Losses of nutrients into the environment • Depletion of nutrients in farming systems • Eutrophication in case of excessive mineral fertilizer use (not common in SSA) Losses through • • Harvesting crops recycling Water and wind erosion Leaching Volatilization Nitrogen is the most susceptible to losses • • Very mobile, can be lost through different ways NO 3 - is susceptible to leaching.

Losses: Water and wind erosion 10 kg N/ha, 2 kg P/ha and 6 kg K/ha lost in low-input production systems in SSA Measures: grass strips, stone rows, mulch layer, soil preparation methods (e. g. Zaï), improving SOM Tied rigdes Bunds on sloping land in Burundi

Losses: Leaching • Problematic in high rainfall areas and coarse-textured sandy soils (>35% sand) • Mainly NO 3 - and exchangeable bases (K and Mg) percolate beyond the reach of crop roots Measures: • Improving soil structure to promote good root development for increased accessibility of nutrients • Growing annual crops in association with trees, which can ‘pump’ water and nutrients from deeper layers

Losses: Volatilization Denitrification of NO 3 - • NO 3 - N 2 O and N 2 (gasses) • Occurs under anaerobic conditions Measures: improved soil drainage and maintain a good soil structure to avoid anaerobic growing conditions Volatilization of NH 3 in alkaline soils (high p. H) Measures: deep placement of N-fertilizers Volatilization of NH 3 during storage and handling of manure Measures: use anaerobic storage pits

Summary Soil organic matter Soil fertility management options CEC Porosity Texture Mimimizing losses of added nutrients - Erosion - Leaching - volatilization Conservation agriculture Organic agriculture Nutrients - Functions - Availability - Mobility - Deficiencies