Soil Fertility, Conservation, and Management

Soil Fertility, Conservation and Management

• Soil fertility and plant nutrition are important components of crop production

Conventional farming

• Conventional farming systems typically utilize synthetic fertilizers

Organic farming

• Organic crop production depends on organic material sources and microbial inoculants/organisms
• Organic methods are sued for sustaining soil health and supplying nutrients to the plants

Soil Fertility for Crop Protection

• Techniques to attain and sustain acceptable soil fertility levels for crop production differ between conventional and organic farming
• Soil fertility management is important for adequate plant nutrition leading to better yields, cost-efficiency, and ecological balance

Requisites of Soil Fertility

• To be fertile, soil must have favorable conditions for plant root development and function

Favorable Physical Properties

• Good aeration and drainage
• Proper moisture holding capacity

Favorable Chemical properties

• Optimal reaction (pH)
• High buffer capacity
• High nutrient holding capacity (CEC)
• Absence of toxic materials (salinity, toxic organic and inorganic compounds)

Favorable Microbiological Properties

• Active functioning of beneficial organisms
• Suppressed activity of harmful organisms

Abundant and Well-Balanced Nutrient Supply

• Macro-nutrients: N, P, K, Ca, Mg, S
• Micro-nutrients: Zn, Cu, Mo, Mn, Fe, Cl, B, Ni

Criteria of Essentiality

• A deficiency of the element makes it impossible for the plant to complete its life cycle
• Deficiency symptoms of the element can be prevented or corrected only by supplying the element
• The element is directly involved in the plant nutrition

Essential Nutrient Elements

• Plants need a balanced nutrition for optimum growth, requiring 18 essential nutrient elements
• Elements are grouped by source and scarcity related to plant needs
• Elements derived from the atmosphere and water are Carbon (C), Hydrogen (H), Oxygen (O)

Soil Elements

• Primary macronutrients: N, P, K
• Secondary macronutrients: Ca, Mg, S
• Micronutrients: Fe, Mn, Zn, Cu, Cl, Mo, Ni, B, Co

Unavailable Form of Element in Soil

• Element is part of a compound and inaccessible to plants until "decomposed"

Decomposition

• Decomposition is the breakdown of organic substances by physical and biological mechanisms
• Decomposition recycles plant nutrients, producing humus

Exchangeable Form of Element in Soil

• Elements exist as cations or anions adsorbed on organic compounds or clay minerals
• The exchangeable ions are partly available to plants
• The ion exchange involves the movement of cations (positively charged) and anions (negatively charged) through the soils.

Solution Form of Element for Soil

• This is considered the most available
• Plant nutrients dissolve in the soil solution
• Plants absorb essential elements from the soil solution for growth and development

Forms of Nutrients in Soil

• Nutrients in organic sources are unavailable until decomposed or mineralized
• Nutrient elements usually exist in combined forms

Ions and Nutrient Uptake

• Plants take up nutrients as ions
• Ions are electrically charged forms of each nutrient
• Cations are positively charged
• Anions are negatively charged
• This explains how nutrients are held and released for plant use

Cations

• Positively charged ions attracted to negatively charged soil colloids like H+, Ca2+, Mg2+, K+, Na+, and NH4+
• Soil colloids are inorganic and organic particles with a high surface area per unit weight

Anions

• Negatively charged ions not retained by the exchange process
• Anions are easily lost in drainage water through leaching
• Important anions in agricultural soils: H2PO4-, HPO42-, SO42-, HCO3-, NO3-, Cl-, MoO42-, and OH-

Ion Exchange

• Involves cation and anion movement, with negatively charged soil particles attracting cations and repelling anions like nitrates, sulphates, and chlorides

Cation Exchange in Soils

• Cation exchange is an ion exchange process involving cations on clay minerals, amorphous inorganic phases, and organic matter
• More cations are attached to soil particles than exist in the soil water solution

Cation Exchange Capacity (CEC)

• The ability of soil to adsorb and exchange cations called CEC is the total positive charge soils can absorb
• Low CEC soils are less fertile with low clay content
• High CEC soils mean more nutrients, high clay content, organic matter, and soil fertility

Mobility of Nutrients

• Nutrient mobility describes how easily nutrients move in the soil and plants.
• See below a breakdown of the mobility in plants and soils:
• Carbon (C) in the form of CO2, H2CO3 has not mobility listed in plants or in soil
• Hydrogen (H) in the form of H+, OH-, H₂O has not mobility listed in plants or in soil
• Oxygen (0) in the form of 02 has not mobility listed in plants or in soil
• Nitrogen (N) comes in 2 forms NO3-, NH4+. It is mobile in plants, and mobile as NO3- or immobile as NH4+ in the soil
• Phosphorous (P) comes in 2 forms NO3-, NH4+. It is semi mobile in plants, and immobile in the soil
• Potassium (K) comes in the form K+. It is very mobile in plants, and someone mobile in the soil
• Calcium (Ca) comes in the form Ca2+. It is immobile in plants, and somewhat mobile in the soil
• Magnesium (Mg) comes in the form Mg2+. It is somewhat mobile in plants, and immobile in the soil
• Sulfur (S) comes in the form SO4-. It is mobile in plants and soil
• Boron (B) comes in the form H3BO3, BO3-. It is immobile in plants and very mobile in the soil
• Copper (Cu) comes in the form Cu2+. It is immobile in plants and in the soil
• Iron (Fe) comes in the form Fe2+, Fe3+. It is immobile in plants and in the soil
• Manganese (Mn) comes in the form Mn2+. It is immobile in plants and mobile in the soil
• Zinc (Zn) comes in the form Zn2+. It is immobile in plants and in the soil
• Molybdenum (Mo) comes in the form Mo04. It is immobile in plants and somewhat mobile in the soil
• Chlorine (Cl) comes in the form CL-. It is mobile in plants and in the soil
• Nickel (Ni) comes in the form Ni2+. It is immobile in plants and somewhat mobile in the soil
• Copper (Cu) comes in the form Cu2+. It is immobile in plants and in the soil
• Cobalt (Co) comes in the form Co2+. It is immobile in plants and somewhat mobile in the soil

Nutrient Mobility

• The term "Nutrient mobility" refers to the ability of macro and micronutrients to move within the soil and plant
• Mobile nutrients move from one location to another within the plant, going to where they are of greater demand
• Immobile nutrients remain permanently positioned, and stay that way once those specific parts of the plant are formed

Deficiency Symptoms Related to Mobility

• Nutrients have variable mobility degrees in the plant, influencing deficiency symptom locations
• Immobile elements do not easily move, causing deficiency symptoms in new growth
• Mobile elements scavenge from older growth when limiting, causing deficiency symptoms in older growth
• Mobile nutrient deficiency means older leaves senesce while younger leaves stay green
• Deficiency of an immobile nutrient affects newer leaves more

Plant Nutrient Uptake

• Plant nutrient uptake is the entry of nutrients into cellular material, following the same pathway as water
• Plants primarily absorb nutrients through their roots, but sometimes through their leaves
• There are three mechanisms of plant nutrient uptake: mass flow, diffusion, and root interception

Mass Flow in Nutrient Uptake

• Mass flow is the movement of dissolved nutrients via water uptake through transpiration
• This process accounts for mobile nutrient uptake, such as N, K, and Ca

Diffusion in Nutrient Uptake

• Diffusion occurs when nutrients move from high to low concentrations due to an imbalance or gradient

Root Interception

• Root interception, or contact exchange, happens through root and soil colloid contact
• Good soil structure is crucial for root growth and contact exchange
• Root interception nutrient uptake is boosted by a growing root system and mycorrhizal infections

Mycorrhizae

• Mycorrhizae are symbiotic fungi associations with plant roots
• Roots give fungi anchor points and produce threads (hyphae); fungi grow and integrate into roots
• Hyphae access smaller soil pores, helping absorb nutrients and water beyond plant reach

Essential Elements in Soils and their Functions

• Nutrient elements in the soil must be present in available forms, proper amounts, and balanced concentrations for good crop growth

Macronutrient Elements

• Needed in relatively large quantities to maintain growth and development
• Provide energy to plants and are present in detectable quantities in plant tissues
• Involved in organic molecule synthesis and osmotic potential development

Carbon (C). Hydrogen (H). Oxygen (O)

• C, H, and O make up about 95% of plant dry weight, obtained from CO2 and H2O converted into simple carbohydrates through photosynthesis; elaborated into complex amino acids, proteins and protoplasm
• Mainly used to synthesize carbohydrates, proteins, fats, and related compounds; major constituents in plant compounds
• Play a dominant role in photosynthesis and respiration
• Involved in forming both simple and complex organic compounds like carbohydrates, starch, and proteins
• Maintain plant cell structure
• Provide energy for growth and development through oxidative breakdown of carbohydrates, proteins, and fats during cellular respiration

Nitrogen (N)

• Nitrogen (N) is essential, limiting, required in great amounts, and needed for chlorophyll production
• Chlorophyll enables food production for growth and aids nutrient uptake
• A component of amino acids (protein building blocks)
• It is the main component of nucleic acids and proteins, also a constituent of chlorophyll and protoplasm
• Increases in the growth and development of all living tissues, including the quality of leafy vegetables fodders, and increases in protein content of food grains
• Nitrogen supplied by synthetic fertilizers is prone to leaching (washed out) or volatilization
• Nitrogen is highly reactive and may transform from solid, liquid, and gaseous forms.
• The nature of Nitrogen makes it vulnerable to losses of up to 62% of applied nitrogen in lowland rice cultivation
• Biological nitrogen fixers are used to supply nitrogen
• Rhizobium is popular for legumes
• Anabaena, (azolla) is important in supplying lowland rice with nitrogen as green manure and compost in upland cultivation
• Sesbania and Indigofera are used in the lowlands to supply part of the nitrogen requirements of rice.

Phosphorous

• P plays a major role in energy storage/transfer in plant respiration and photosynthesis as ADP/ATP and DPN/TPN
• Energy stored in P compounds supports growth, cell metabolism, and forms cell membranes
• Seeds have higher P concentration, needed in large quantities in young cells (shoots and root tips)
• Aids root branching, flowering, seed and fruit development
• Found in root cells, fruits, and seeds
• Present in larger amounts in seeds compared to other parts of plant
• A constituent of every living cell (like nitrogen), specifically phospholipids, nucleoproteins, and phytin (storage form in seeds)

Potassium (K)

• Assists ATP production and is essential for protein synthesis.
• Promotes the translocation of photosynthates (sugars) during sugar and starch formation,
• Storage in fruits or roots, photosynthesis,
• Balances electrical charges at ATP production sites, maintaining anion-cation balance in cells
• Needed for the activation of certain enzymes and adequate potassium nutrition
• Helps increase resistance to cold, drought, and disease
• Unlike N and P, K does not form organic compounds in the plant
• Is still vital for plant growth because it is known to be an enzyme activator promoting metabolism

Calcium (Ca)

• Helps build strong cell walls, which is vital to plant tissue
• Has a role in the formation of cell wall membranes and maintain cell plasticity, which effects cell division (keeps cell integrity/membrane permeability)
• Acts as an enzyme activator in protein synthesis and
• A carbohydrate transfer agent
• Combines with anions; acts as detoxifying agent
• Improves crop yields by reducing soil acidity

Maanesium (Ma)

• The predominant role of Mg is that it is a major constituent of the chlorophyll molecule
• It activates enzymatic reactions involved in the following: photosynthesis; phosphorylation processes (aids in phosphorus translocation); the movement of sugars
• Mg is required to stabilize both the ribsome structure and the structure of nucleic acids

Sulfur (S)

• A structural component of plant related molecules like amino acids, enzymes, chlorophyll and plant proteins
• Actively involved in the metabolism of certain B vitamins (biotin, thiamine, co-enzyme A) and ferredoxin.

Micronutrient Elements

• These are essential plant nutrients needed in small amounts; deficiencies greatly affect plant growth and yield

Iron (Fe)

• Fe is essential in the heme-enzyme system in plant metabolism
• Involved enzymes: catalase, peroxidase, cytochrome oxidase, and other cytochromes
• Strongly associated with protein metabolism, including protein ferredoxin, nitrate and sulfate reductions

Zinc (Zn)

• Component of enzymes or a functional cofactor of many enzymes including auxins (plant-growth hormones)
• Essential to carbohydrate metabolism and intermodal elongation
• Required in the systhesis of tryptophan and of idoole acetic acid (IAA) in plants

Copper (Cu)

• Concentrated in plant roots, copper plays a part in nitrogen metabolism
• copper is a component of constituent of enzymes, most importantly cytochrome oxidase, ascorbic acid oxidase and phenolase lactase
• it is an important co-enzyme that promotes the formation of vitamin A in plants

Manaanese (Mn)

• Mn is a catalyst in several enzymatic and physiological reactions in plants
• A constituent of pyruvate carboxylase, it is involved in the plant's respiratory process
• activates indole acetic acid oxidase, which then oxidizes indole acetic acid. Controls the oxidation reduction in plant cells during the phases of light and darkness Mn is necessary in Photosystem II, where participants in photolysis

Molybdenum (Mo)

• Necessary for nitrate reductase and for nitrogenase
• Structural component of the enzyme that reduces nitrates to amonia
• Proteins stop/growth ceases with out it

Nickel (Ni)

• Required for the enzyme urease to break down urea and liberate nitrogen for plant-use
• Needed for seeds to germinate and for Fe absorption
• Plants grown without additional Ni will gradually reach a defficient level at about the time they mature and begin reproductive growth
• If Ni is deficient plants may fail to produce viable seeds.

Chlorine (Cl)

• Cl assists in the process of osmosis,
• Promotes the balance of ionic action

Boron (B)

• B associated with lignin synthesis
• Important for cell health and calcium level

Silicon (Si)

• Effective to crop health and resistance