CS 351 SOIL MANAGEMENT FERTILITY SOIL FERTILITY COMPONENT

CS 351 SOIL MANAGEMENT & FERTILITY (SOIL FERTILITY COMPONENT) Dr. Andrews Opoku

Course outline 1. Introduction-Growth & Yield factors v Definition of terms - soil fertility, soil productivity, soil quality v Units used in soil fertility work 2. The Nutrient elements v Nutrient cycling v Chemical forms, levels & factors affecting availability 3. Maintenance of Soil Fertility v Fertilizers/Manure & their use

Growth and yield factors Maximum growth or yield is obtained when none of the growth factors is present in less than the amounts required.

Growth and yield factors Genetic factors. The genetic constitution of a given plant species/ variety limits the extent to which that plant may grow and produce, and no matter how favourable the environmental conditions, these limits cannot be extended.

Growth and yield factors Environmental factors The physical environment is commonly grouped into 4 classes: 1. Climatic factors – temperature, rainfall or moisture supply, light, humidity, wind etc. 2. Physiographic factors – determined by the general geological strata, by topographical features – including relief & drainage ground water, attitude, slope and erosion. 3. Edaphic factors – including soil structure, composition of soil air, aeration, soil reaction (acidity & alkalinity) supply of mineral nutrient elements 4. Biotic factors – brought about by living organisms – like man, animals and plants.

The Concept of Soil Fertility • Is the quality that enables a soil to provide the proper nutrients, in the proper amounts and in the proper balance, for the growth of specified plants • when other growth factors – such as light, tempt, moisture and the physical condition of the soil are favourable.

The Concept of Soil Fertility A soil can only be fertile if it is a favourable environment for root growth. And a soil can only be a suitable environment for plant roots if: – it is adequately drained and aerated. – if its salt content and content of exchangeable sodium ions are low – if its p. H falls in a suitable range.

Soil Productivity The capability of a soil to produce a specified plant under a specified system of management. Soil productivity is basically an economic concept and not a soil property. It involves : – Inputs ( a specified management system) – Outputs (yields of particular crops) – Soil type.

Soil Quality Concept

Soil Quality Concept Soil quality is the capacity of a specific kind of soil to function, within natural or managed ecosystem boundaries, to sustain plant and animal productivity, maintain or enhance water and air quality, and support human health and habitation Soil quality is the capacity of a soil to: 1. Protect environmental quality 2. Sustain plant and animal productivity 3. Promote human health.

Units Types 1) Laboratory units: %, ppm, μg/g, μg/ml, mg/kg, mg/l, m. e. /100 g, cmol(+)/kg 2) Field units: lb/acre, kg/ha Laboratory units ppm – is a unit of conc. analogous to the % (percent) unit (i. e. parts per 100) - it is commonly applied to soil or solution concentration of nutrient elements. E. g. 5 ppm. K means 5 parts K per million parts soil

Units Eg. A soil contains 0. 112%N Convert this to i). ppm, ii). μg/g , iii). mg/kg, iv). lb/acre, & v). kg/ha i) ppm 0. 112 % N = 0. 112 parts N/100 parts soil = 0. 112 x 104 parts/100 x 104 parts soil = 1120 parts N/106 parts soil = 1120 ppm N

Units Eg. A soil contains 0. 112%N Convert this to i). ppm, ii). μg/g , iii). mg/kg, iv). lb/acre, & v). kg/ha ii. μg/g 0. 112% N = 0. 112 g N/100 g soil = 0. 00112 g N/g soil = 1. 12 mg N/g soil = 1120 μg N/g soil

Units Eg. A soil contains 0. 112%N Convert this to i). ppm, ii). μg/g , iii). mg/kg, iv). lb/acre, & v). kg/ha iii. mg N/kg 0. 112 % N = 0. 112 kg N/100 kg soil = 0. 00112 kg N/kg soil = 1. 12 g N/kg soil = 1120 mg N/kg soil

Units Eg. A soil contains 0. 112%N Convert this to i). ppm, ii). μg/g , iii). mg/kg, iv). lb/acre, & v). kg/ha iii. mg N/kg 0. 112 % N = 0. 112 kg N/100 kg soil = 0. 00112 kg N/kg soil = 1. 12 g N/kg soil = 1120 mg N/kg soil

Units Eg. A soil contains 0. 112%N Convert this to i). ppm, ii). μg/g , iii). mg/kg, iv). lb/acre F. S, v). kg/ha iv. lb/ac F. S Area = 1 acre Depth = 6 in Mass = 2 x 106 ib

Units Eg. A soil contains 0. 112%N Convert this to i). ppm, ii). μg/g , iii). mg/kg, iv). lb/acre F. S, v). kg/ha iv. lb/ac F. S 0. 112 % N = 1120 ppm N = 1120 parts N /106 parts soil = 1120 lbs N/106 ib soil = 1120 x 2 lb N/2 x 106 lb soil = 2240 lb N/ac. FS. (furrow slice)

Units Eg. A soil contains 0. 112%N Convert this to i). ppm, ii). μg/g , iii). mg/kg, iv). lb/acre F. S, v). kg/ha v. kg/ha 2240 lb N/ac = 2240 lb/ac x 2. 471 ac/1 ha x 0. 454 kg/1 lb = 2512. 9 kg N/ha

Nutrient elements

Plant nutrients A plant nutrient is said to be essential if: 1. A deficiency of the nutrient makes it impossible for the plant to complete its life cycle. 2. Such deficiency can be prevented or corrected only by supplying this element. 3. The element is involved directly in the nutrition of the plant.

MACRO NUTRIENTS • Carbon • Hydrogen • Oxygen • • • Nitrogen Phosphorus Potassium Calcium Magnesium Sulphur

Plant nutrients Micronutrients • • Iron Manganese Boron Molybdenum Copper Zinc Chlorine These are obtained by plants from the soil

Nitrogen

Nitrogen N is extremely important for Agriculture N should be managed carefully – Plants need it in large amounts – It is fairly expensive to supply – It is easily lost from the soil

NITROGEN Atmospheric N 2 N fert Immobilization Nitrogen cycle

Nitrogen Transformations • Mineralization • Immobilization • Nitrification • Fixation • Denitrification • Volatilization

NITROGEN N – Mineralization • The microbial conversion of organic N to mineral-N immobilization Amino acid NH 4+ Bacteria/ fungi NO 3 Nitrosomonas / nitrobacter mineralization N – Immobilization • This is the conversion of inorganic N to organic form in microbial tissue.

Mineralization of N-compounds The process takes place in essentially 3 steps: - aminization, ammonification and nitrification. Aminization Conversion of proteins and allied compounds to amines and amino acids by heterotrophic bacteria and fungi. Proteins R–NH 2 + CO 2 + Energy Heterotrophic Fungi/bacteria

Ammonification It is conversion of amines and amino acids to NH 4+ by heterotrophic bacteria and fungi Heterotrophic R – NH 2 + H 2 O R-NH 2 NH 3 + R –OH + Energy Fungi/bacteria NH 3 + H+ NH 4+

Ammonification Fates of NH 4+ 1) fixed by clay minerals, 2) may be converted to NO 2 - or NO 3 - by nitrification 3) used by plants (NH 4+), 4) volatilization High p. H Soils > 7. 5

Soil conditions affecting Ammonification 1) C: N ratio Material FYM (composted) FYM (Fresh) Saw dust C: N ratio 20 100 400 2) Aeration: well – drained aerated soil 3) p. H : Generally fungi act best in p. H < 5. 5; Bacteria in p. H >5. 5

Nitrification is the biological oxidation of ammonia to nitrate. 2 NH 4+ + 302 → 2 NO 2 - + 2 H 2 O + 4 H+ + Energy 2 NO 2 - + O 2 → 2 NO 3 - + Energy

Nitrification 2 - step process 1. 2 NH 4+ + 3 O 2 ---> 2 NO 2 - + 4 H+ + 2 H 20 + E Nitrosomonas/Nitrosococcus 2. 2 NO 2 - + O 2 --> 2 NO 3 - + E Nitrobacter Process is acid causing due to release of 4 H+

Nitrification 1. Reactions require molecular oxygen 2. Reaction releases H+ ions resulting in the acidification of the soil. 3. Reactions involve microbial activity and therefore soil conditions (moisture supply, temperature & p. H) should be optimum for microbial activity.

Gaseous Losses of Soil N Gaseous losses of N occur mainly as N 2 O, NO and NH 3. Mechanisms for the losses are: a) Denitrification b) Chemical reactions involving nitrites under aerobic conditions c) Volatilisation of ammonia

Gaseous Losses of Soil N a) Denitrification: is the biochemical reduction of nitrates under anaerobic conditions to gaseous N-compounds. NO 3 - NO 2 O NO N 2 O O Factors Affecting Denitrification i) Soil moisture and oxygen supply ii) Availability of organic substrate iii) Soil p. H and temperature O N 2 O

Gaseous Losses of Soil N Reaction of nitrites under aerobic conditions Nitrites in a slightly acid solution will evolve gaseous N when brought in contact with certain ammonium salts, with simple amines such as urea, and even with Non-nitrogenous sulphur compounds and carbohydrates. Possible reaction: 2 HNO 2 + CO(NH 2)2 → CO 2 + 3 H 2 O + 2 N 2 ↑

Biological nitrogen fixation Conversion of N 2 in the soil atmosphere into NH 4+ by specialized groups of micro-organisms. 1. Non-Symbiotic (free living microbes): - Clostridium – anaerobic - Azotobacter – aerobic, - blue-green algae

2. Symbiotic N Fixation Rhizobium 1. Bacteria invades host plant root 2. Response of host plant root is to grow a nodule for the bacteria to live in. 3. Cowpea Bacteria takes N 2 from the air and converts it into R-NH 2 in bacteria and some is in the form of NH 4+ Nodulation Fate of N Fixed by Rhizobium: 1. 1) used by host plant, 2. 2) leaks out of root to become available to surrounding plants, Host plantbacteria complex

Non-Biological Fixation 1) Atmospheric electrical discharge (lightning) Oxidation of N N 2 + 3 O 2 2 NO-3 10 -20% of NO 3 - via atmospheric deposition 2) Industrial process

N - balance Non Symbiotic fixation Commercial fertilizers immobilization val o em Symbio tic fixation Crop residues and manure Soil organic matter pr o r C Available soil N Rainfall Gaseous losses Erosion losses Fixation by clay minerals Atmosphere Lea chi ng los se s

Distribution of N in soils 1) Drainage : Under poor drainage, decay of O. M. is very slow Organic N is high, Mineral N is low 2) Topography: On slopes, N content is lost faster than that on summit or valley bottom.

Distribution of N in soils 3) Texture: N, content decreases as texture becomes coarser. 4) Seasonal effect: – Nitrate level slowly increases during the dry season due to low leaching. – Nitrate levels increase rapidly at the beginning of the rainy season due to increased bacteria activity and mineralization in the presence of low leaching. – During the rainy season level of N falls and remains fairly constant until the next dry season due to leaching of N compounds from the soil.

N in Plant Nutrition – is an essential constituent of all living matter. – important in the formation of protein. – forms an integral part of chlorophyll molecule. – an adequate supply of N is associated with vigorous vegetative growth and deep green colour.

N deficiency Symptoms • A stunted yellowish appearance • Yellowing or chlorosis, usually 1 st appearing on the lower leaves, the upper leaves remaining green • In severe shortages – leaves will turn brown and die.

Phosphorus • Discovered by Hening Brand in 1669 • Name Origin: phôs (light) and phoros (bearer) “phosphorus = light-bearer” • Atomic number 15 • Atomic weight 30. 974 • One isotope 32 P

Soil Phosphorus • Lithosphere is the main source and reservoir of P • Lithosphere – 0. 12% = 1200 ppm • Soil solution – 0. 2 to 0. 3 ppm • Total P content of soil depends – O. m content – Parent material – Degree of weathering

Forms of soil P Soil P Organic P Inositol P Nucleic acid Inorganic P Phospholipids Ca- P HPO 4 -2 H 2 PO 4 - Fe, Al - P

Inorganic P 1) Insoluble or nearly insoluble P compounds • Acid soils - Free Fe and Free Al combine with phosphate Al 3+ + H 2 PO 4 - + 2 H 2 O H+ + Al(OH)2 H 2 PO 4 (soluble) • (insoluble) Alkaline soils – Free Ca and Mg combine with Phosphate 2 PO 43 - + 3 Ca 2+ Ca 3(PO 4)2 (soluble) (Insoluble )

Inorganic P 2) Insoluble phosphate-clay complexes Al 3+ + Al (OH)2 Precipitated form Dissolved form Fixation by Al and Fe 4 Fixation by Ca Reaction with clays 5 + 2 H+ 6 Soil p. H 7 8

Soluble phosphate forms H 3 PO 4 = phosphoric acid, H 2 PO 4 - = 1º orthophosphate, HPO 4 -2 = 2º orthophophate, PO 4 -3 = phosphate

Calcium Phosphate Compound 6 â Ca(H 2 PO 4)2 â monocalcium phosphate â Ca. HPO 4 â p. H 8 â dicalcium phosphate Ca 3(PO 4)2 â tricalcium phosphate â Ca 5(PO 4)3 OH 2 â hydroxyapatite â Ca 5(PO 4)3 F â Fluorapatite

P Fixation

P Fixation P “Fixation” – refers to the processes whereby available phosphorus forms combinations with other soil constituents and thus becomes unavailable to plants.

Mechanisms for P fixation 1) Precipitation reaction between P and other ions in soil solution to form hydroxy-phosphates Al(OH)2+ + H 2 PO 4(soluble) Ca 2+ + HPO 42(soluble) Al(OH)2 H 2 PO 4 (insoluble) + 2 H+ Ca. HPO 4 (Insoluble ) 2) Adsorption reaction between soluble P and insoluble soil components Al 2 O 3. 3 H 2 O + 2 H 2 PO 4(soluble) 2 Al(OH)2 H 2 PO 4 + 2 OH(insoluble)

Most Available P between p. H 5. 5 - 7

Factors affecting P fixation 1) Type of clay minerals and amount of clay in soil 2) Presence of OH- of Fe, Al and Mn 3) Soil reaction 4) Presence of organic matter

The presence of Organic matter in the soil Om reduces P fixation; 1. 2. 3. the formation of phospho-humic complexes which are more easily assimilated by plants anion replacement of the phosphate by the humate ion. the coating of sesquioxide particles by humus to form a protective cover.

Potassium Sources of K in Soils K-containing minerals. Eg: – Potash feldspars (KAl. Si 3 O 8) – Muscovite – Biotite KAl 3 Si 3 O 10(OH)2 KAl (Mg, Fe)3 Si 3 O 10 (OH)2 Micas

Fate of K+ in soil K+ ion liberated by weathering may 1. be lost through leaching 2. taken up by plants or other living organisms in the soil 3. be held on the cation exchange positions of the soil colloids; or 4. be converted to less available forms.

Factors affecting K Equilibrium in Soils Conversion of soil and added potassium to less available forms is influenced by: 1. Types of Colloid • Humus and clay are the two major soil colloids • Humus – has high capacity to retain cations in the exchangeable form – has very low capacity for the fixation of K.

Factors affecting K Equilibrium in Soils • Clay mineral – Clays of the 2: 1 type such as montmorillonite and illite fix K very readily and in large amounts. – Clays of the 1: 1 type such as kaolinite fix little K 2. Wetting and Drying – The 2: 1 type minerals fix K only upon drying (contraction). – Some release of the ions occurs upon rewetting of the soils (expansion) 3. p. H – K fixation increases with application of lime or higher p. H.

Luxury Consumption • Absorption of nutrient elements in excess of the amount required for optimum growth. Luxury K K content of plant K required for optimum growth Required K Available K in soil

Leaching Losses of K • More K is lost by leaching in contrast to N & P (particularly P). • Leaching is common in heavily fertilized sandy soils.

Problem of K in soils 1. A very large proportion of K at a given time is relatively unavailable to plants. 2. K is subject to wasteful leaching losses since its available form is very soluble. 3. The removal of this element by crops is high, especially when high levels are available in the soil.

Secondary Macronutrients • Ca Mg and S are secondary macronutrients • They are required by plants in lesser amounts than NPK but in larger quantities than the micronutrients. • They are essential for correcting the reaction of soil. • Ca, Mg for reclaiming acid soils • S for reclaiming alkaline soils • They are prone to leaching

Magnesium Mg is the only mineral element in the chlorophyll molecule

Magnesium • It is absorbed by plants as the ion Mg 2+. Sources of soil Mg Weathering of rocks such as: – Dolomite , Ca Mg (CO 3)2 or – Olivine , Mg. Fe. Si. O 4 – Biotite , K (Mg Fe)3 Al Si 3 O 10 (OH)2

Calcium Ca is absorbed by plants as Ca 2+ Source of Soil Ca • Weathering of rocks such as: – Dolomite Ca. Mg (CO 3)2 – Calcite Ca. CO 3 – Apatite Ca 5(PO 4)3·(Cl, F, OH) – Calcium feldspars

Sulphur • S is an essential element particularly associated with protein synthesis. • Plant available form of S = SO 42 -. • Sulphur fertilization is becoming important because of changes in the use of some fertilizers • SSP (18% P 2 O 5; 8 -10% S) to TSP (45% P 2 O 5; <3% S) • AS (NH 4)2 SO 4 (21%N; 24%S) to CO(NH 2)2 (urea) (46%N)

Micronutrients Nutrient elements required by plants in relatively small amounts. • • Iron Manganese Boron Molybdenum Copper Zinc Chlorine These are obtained by plants from the soil

Micronutrients Source of micro nutrients 1) soil parent material 2) organic matter - In uncultivated lands there is a greater concentration of micronutrients in the surface soil where O. M. levels are high.

Micronutrients Plant available forms of micro nutrients Nutrient Iron Manganese Boron Copper Plant available form Fe 2+ or Fe 3+ Mn 2+ BO 33 Cu 2+ Molybdenum Zinc Mo. O 42 Zn 2+ Chlorine Cl-

Nutrient mobility and deficiency symptoms • For nutrients which are mobile in plants deficiency symptoms 1 st appears on the lower and older leaves. • Eg: N, P, K, Mg, and Zn. N deficiency

Nutrient mobility and deficiency symptoms • Nutrients with limited mobility in plants produce symptoms on new leaves or growing points. Eg: calcium, sulphur, boron, iron, copper, and Mn. S deficiency

Thank you Good LUCK

Soil aeration

Salinization