Introduction to Soil Fertility and Quality

Introduction to Soil Fertility

• Soil fertility refers to the quality of soil that allows it to provide the necessary compounds in the right amounts and proportions for plant growth. It differs from soil productivity.
• Soil productivity is the soil's ability to produce a specified plant under a specific management system. Fertile soil isn't always productive.

Importance of Soil Fertility and Quality

• Global population growth is converting agricultural lands into residential and commercial areas, reducing arable land.
• Balanced soil is crucial for producers to meet food and fiber demands.
• Soil fertility is a key factor for successful crop production, measuring the capacity of soil to supply plant nutrients.
• Intensive fertilizer use and cropping with high-yielding varieties have increased food production but caused soil and environmental problems, leading to nutrient over-exploitation and mining.
• "Soil quality" is now often used instead of "soil fertility", defined as the sum of all socially valued functions of the soil, predominantly determined by soil functions.

Soil Functions

• Production function: Soil serves as a medium for plant growth, ensuring the supply of food, feeds, fiber, and fuel.
• Transformation function: Nutrients in the soil are taken up by plants, transformed into available forms, distributed into the plant system, and efficiently converted into yield.
• Habitat function: Soil provides a living space for various flora and fauna, with a diverse quantity of organisms inhabiting it.
• Degradation function: Microorganisms degrade/transform plant and animal residues into nutrients, closing the nutrient cycle.
• Self-regulation function: The soil maintains ecosystem functions, acting as a filter, buffer, and storage, playing a vital role in nutrient cycling, retaining and breaking down harmful substances, and storing carbon dioxide.

Factors Affecting Soil Productivity

• Factors affecting soil productivity include all elements affecting plants' physical, chemical, and biological conditions, including those affecting fertility, water and air relationships, and biological agents' activity such as insects, pests, diseases, and microorganisms.
• Internal factors include genetic or hereditary factors that are not manipulated like soil type and texture.
• External factors can be regulated to a certain extent and encompass climatic, edaphic, biotic, animal, and physiographic factors, as well as anthropogenic factors like cultivation skill.
• Climatic factors: Precipitation (rainfall), solar radiation, atmospheric gases (CO2, NO2, N2O, O2), and wind velocity.
• Edaphic or Soil factors: Soil moisture, soil air, soil temperature, soil mineral matter, inorganic and organic components, and soil reaction.
• Biotic factors: Plants have competitive and complementary nature, competition between weeds and crop plants, and plants grow as parasites, bacteria of symbionts.
• Animals: Earthworms, small and large animals affect soil productivity.
• Physiographic factors: Geological strata (parent materials) and topography.

Historical Development of Plant Nutrition and Soil Fertility

• The development of the human race began the cultivation of plants, marking the dawn of agriculture.
• Previously, man hunted almost exclusively for food, living a nomadic lifestyle. Over time, settlements developed, leading to the skill of agriculture.
• Mesopotamia (now Iraq), located between the Tigris and Euphrates rivers, displays evidence of very early civilization, cannal construction
• Canals were constructed in ancient Athens to transport sewage from cities to farmland.
• Ancient Egyptian murals depict agricultural practices such as tillage, planting, irrigation, and harvesting, but not fertilization.
• During Greece's golden age (800-200 BC), it was recognized that manures increased productivity and prolonged land use, and beneficial effects of saltpeter on plants were also observed. Saline soils could be detected in a taste test.
• Roman art revealed details about agriculture, including the Roman god of manure, Stercutius, worshipped by old women and children. Additionally featured Saturn and Ceres (Roman God and Goddess of agriculture).
• Agricultural practices were believed to have been invented 8,000-10,000 years ago in the area between the Nile Valley in Egypt and Indus in India.

Important People in the Development of Soil Fertility

• Theophrastus (327-287 B.C.): Suggested that plants with high nutrient requirements also had high water requirements, emphasized the value of green-manure crops and legumes.
• Pietro de Crescenzi: Published a book on agricultural practices during 1233–1320.
• Francis Bacon (1561 – 1624): Thought that principal nourishment of plants derived from water and believed the purpose of soil was to protect plants from heat and cold.
• Jan Baptiste van Helmont (1577 – 1644): Chemist and physician, his willow tree experiment "proved" that water was the sole nutrient of plants.
• Robert Boyle (1627-1691): Reported van Helmont's work, confirmed van Helmont's findings and stated that plants contained salts, spirits, earth, and oil formed from water.
• J.R. Glauber (1604 – 1668): Suggested saltpeter (KNO3), not water, was the "principle of vegetation".
• Jethro Tull (1674–1741): Thought plants ingest small particles, cultivating the soil enabled easier uptake, wrote "Horse Hoeing Husbandry", and developed the horseshoe and seed drill.
• John Woodward (1700's): Believed plant growth is influenced by something beyond water.
• Albrecht Thaer (1752-1829): Believed in the Humus Theory, stating that plants live on humus-derived extracts from which they rebuild plant tissue facilitated by plants' "internal vital force".
• Philip Carl Sprengel (1787-1859): Concluded salts in humus extracts were real plant nutrients, came up with a list of compounds required for plant growth, and discussed the idea of fertilizers.
• Theodore de Saussure (1800s): Believed that the soil provides only small amounts of nutrients required by plants and plants obtain C from the air.
• Justus von Liebig (1802 – 1873): German chemist, stated the Law of the minimum in 1862 for predicting crop response to fertilization.
• J.B. Bousingault (1802-1882): French chemist who experimented and maintained a balance sheet. He was the first scientist to conduct a field experiment.
• J.B. Lawes and J.H. Gilbert (1843): Established an agricultural experiment station at Rothamsted, England, 12 years later, concluded that crops require both phosphorus and potash.
• John B. Lawes: Patented a process of phosphate rock acidulation in 1842, leading to the commercial production of superphosphate in England in 1845.

Soil Fertility Research During the Twentieth Century

• Ammonia synthesis by the Haber-Bosch process was an early 20th-century discovery that led to a Nobel Prize for Haber.
• Soil science became a recognized faculty of agricultural science in the early to mid-20th century.
• Soil fertility scientists assess nutrient levels in soil and judge crop yield levels through simple extraction media, termed crop response curves, which could be mathematically modeled or depicted.
• Extraction solutions such as Trougs, Brays, Mehlichs, and Olsen were consistently employed to assess available nutrients in the soil.
• One of the most used techniques in plant and soil analysis was devised by Kjeldahl (1879).
• Plant essential nutrients are estimated using automated spectrocolorimetry, atomic absorption spectroscopy, emission spectroscopy, X-ray fluorescence spectroscopy, mass spectroscopy, and radioisotope techniques.

Soil-Plant Relationships - Chapter Aims

• Determine the role of essential elements in plant growth
• Know the functions of each nutrient in the plant
• Understand how plant roots absorb nutrients
• Know the mobility of nutrients in the soil
• Understand the deficiency symptoms of elements
• Understand the transformation of nitrogen, phosphorus, potassium, and sulfur in soils and related processes
• Identify the causes of soil fertility decline

Definition of Terms

• Nutrient: A substance required by an organism for normal growth and reproduction.
• Plant Nutrient: A "food" composed of chemical elements essential for plant growth and development.
• Nutrition: The process of supplying and absorbing chemical compounds necessary for the growth and metabolism of an organism.
• Deficient: An essential element at a low concentration in a plant that severely limits growth and produces distinct deficiency symptoms, causing low crop yield and inferior product quality.
• Insufficient: The level of an essential nutrient is below its actual content in a plant or available in an inadequate amount, affecting plant growth and development.
• Toxic: A high concentration of an element in plants that severely affects growth and produces toxicity symptoms.
• Excessive: A concentration of an essential nutrient that is sufficiently high but not toxic, results in a corresponding shortage of other nutrients.

Essential Elements in Soils and Their Forms

• Essentiality of Elements: Only 17 elements are considered essential out of the periodic table's 100+ elements. An element is deemed essential if its deficiency prevents a plant from completing its life cycle, is specific and irreplaceable, and is directly involved in plant nutrition.
• Beneficial Elements: Required by specific plants. Cobalt (Co) is required by bacteria for nitrogen (N) fixation in legumes.
• Silica (Si) is not essential but is highly beneficial, helping plants cope with multiple stresses. Other beneficial elements include sodium (Na) and vanadium (V).
• Essential Elements and Their Available Forms: Plants require 17 elements, found in nature, to grow and develop properly.
• Macronutrients: Elements used in large quantities such as carbon (C), hydrogen (H), oxygen (O), nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sulfur (S).
• Micronutrients: Elements used in small quantities, including iron (Fe), boron (B), copper (Cu), chlorine (Cl), manganese (Mn), molybdenum (Mo), zinc (Zn), and nickel (Ni).

Available Forms of Essential Elements

• Non-mineral Macronutrients:
• Carbon (C): taken up as CO2, H2CO3
• Hydrogen (H): taken up as H⁺, OH⁻, H2O
• Oxygen (O): taken up as O2
• Primary Macronutrients:
• Nitrogen (N) taken up as NO3⁻ (nitrate), NH4⁺ (ammonium)
• Phosphorus (P): taken up as H2PO4⁻, HPO42⁻ (phosphate)
• Potassium (K): taken up as K⁺
• Secondary Macronutrients:
• Calcium (Ca): taken up as Ca2+
• Magnesium (Mg): taken up as Mg2+
• Sulfur (S): taken up as SO42⁻ (sulfate)
• Micro-nutrients: are taken up as:
• Boron (B): taken up as H3BO3 (boric acid), H2BO3⁻ (borate)
• Copper (Cu): taken up as Cu2+
• Iron (Fe): taken up as Fe2+ (ferrous), Fe3+ (ferric)
• Manganese (Mn): taken up as Mn2+
• Zinc (Zn): taken up as Zn2+
• Molybdenum (Mo): taken up as MoO42⁻ (molybdate)
• Chlorine (Cl): taken up as Cl⁻ (chloride)
• Nickel (Ni): taken up as Ni2+

Profile Distribution of Elements

• Soil nutrients vary not only by location and soil type, but also by horizon within the profile.
• Soil undergoes vertical exchange of materials between atmosphere, biosphere, and lithosphere, causing vertical chemical and physical gradients.
• Changes in the distribution of nutrients can have a significant impact on land productivity, nutrient quantity and timing availability, and ecology.
• The type, thickness, and position of soil horizons provide information about soil-forming factors like climate, topography, and vegetation type.
• Mechanisms that shape the vertical distribution of soil nutrients: weathering, atmospheric deposition, leaching, and biological cycling.

Role of Essential Elements in Plant Nutrients

• Elements utilized within plant structure consist of carbon (C), hydrogen (H), and oxygen (O), obtained from air (CO2) and water (H2O).
• Macronutrients are divided into primary (nitrogen, phosphorus, and potassium) and secondary (calcium, magnesium, and sulfur) nutrients.
• Micronutrients, needed in minute amounts, facilitate plant survival and act as enzyme activators, including Fe, B, Cu, Cl, Mn, Mo, Zn, Co, and Ni.

Roles and Deficiency of Nutrients

• Nitrogen, phosphorus, and sulfur are macronutrients that most likely limit plant growth due to nutrient deficiencies.
• Nutrient deficiencies can be caused by inadequate levels in the soil, unavailability due to pH levels or soil temperature, or improper water levels or soil compaction.
• Deficiencies are indicated by morphological changes in plants, each element deficiency presenting different symptoms.
• Mobility determines where the effect of a deficiency is shown on plants. For example, nitrogen, potassium, and magnesium deficiencies first appear in older leaves.
• Deficiency of one element can cause multiple symptoms/ the same symptoms can be from multiple elements
• List of deficiencies:
• Carbon (C): Source-Air, Mobility- NA, Symptoms- Mostly not deficient because sources are everywhere
• Hydrogen (H): Source-Water, Mobility- NA, Symptoms- Mostly not deficient because sources are everywhere
• Oxygen (O): Source-Air/Water, Mobility- NA, Symptoms- Mostly not deficient because sources are everywhere
• Nitrogen (N): Source-Air/Soil, Mobility-Mobile, Symptoms- Light green color of leaves, older leaves show symptoms first
• Phosphorus (P): Source-Soil, Moblity-Mobile, Symptoms- Leaves show purplish to red coloration
• Potassium (K): Source-Soil, Mobility- Mobile, Symptoms- Scrotching and burning of leaf margins
• Calcium (Ca): Source-Soil, Mobility-Immobile, Symptoms-Failure in the development of terminal buds, dead spots in the mid-rib of leaves
• Magnesium (Mg): Source-Soil, Mobility-Mobile, Symptoms-Light green venation in leaves, cupping of leaves
• Sulfur (S): Source-Soil, Mobility-Mobile, Symptoms- Similar to N deficiency but seen on top leaves as a contrast to N deficiency symptoms
• Boron (B): Source-Soil, Mobility-Immobile, Symptoms- Terminal buds die, rosette formation, flower; and fruit setting adversely affected
• Copper (Cu): Source-Soil, Mobility-Immobile, Symptoms- Leaf tops become white, leaves narrow and twisted, stunted growth
• Iron (Fe): Source-Soil, Mobility-Immobile, Symptoms- Yellowing and or whitening of leaves; in rice nurseries and sorghum plants may turn pale or white
• Manganese (Mn): Source-Soil, Mobility-Immobile, Symptoms- Green veins against a pale lamina, abscission of leaves, a grey speck of oats, marsh spots of beans
• Zinc (Zn): Source-Soil, Mobility-Immobile, Symptoms- Stunted growth pale to the white coloration of young leaves
• Molybdenum (Mo): Source-Soil, Mobility-Mobile, Symptoms- N deficiency; whiptail disease of cauliflower
• Chlorine (Cl): Source-Soil, Mobility - Mobile, Symptoms-Chlorotic leaves; leaf necrosis.
• Nickel (Ni): Source-Soil, Mobility-Immobile, Symptoms- Whole leaf chlorosis along with necrotic leaf tips

Biochemical Classification of Elements & Nutrient Availability & Uptake

• Classification of Nutrients: Classified according to amounts nutrients taken up by plants:
• Macronutrients are taken up in large amounts.
• Micronutrients are taken up in small amounts.
• Macronutrients are divided into:
• Primary nutrients like nitrogen,phosphorus, potassium, and secondary nutrients:calcium, magnesium, and potassium Elements are classified based off biochemical and physiological functions:
• Group I: basic structural elements: C, H, O, Ca
• Provide energy for growth
• Group II: Accessory structural elements N, P, & S. Accessroy structural elements of vital living tissues involve in energy storage
• Group III: regulator & carriers K, Ca, Mg Involved in synthesis & translocation. maintain balance
• Group IV: catalysts and activators Fe, Mn, Zn, Cu, B, Mo, Cl Involve in oxidation-reduction

Factors affecting nutrient availability

• Nutrient availability is affected by:
• Phosphorous is best at 6.0-7.5
• Phosphorous binds iron while alkaline: unavailable for for plant uptake
• Iron is soluble in acids, calcium is soluable above 7.0; available micronutrients, manganese zinc, and iron are available Generally; availability of nitrogen, potassium, calcium, and magnesium decreases at pH below 6.0 and above pH 8.0.
• Maintaining pH for efficiency is important for soil testing.
• Mechanisims of Nutrient Uptake is done by:
  • Root interception
  • Mass flow
  • Diffusion
  • Passive uptake
  • Active uptake

Soil Nutrient Supply and Plant Growth & Linear Response Plateau Model (LRP)

• Plant growth depends on nutriends:
• If positive interaction happens: higher crop yield
• If negative interaction happens: lead to decline in crop yield
• Plants need a mininum level for growth
• Excess nutrient uptake cause poor of toxicity results to too much growth
• Crop yields depends on these different factors properties, climate, genetic, and fertility which is why there different testing for economic optimum. fertilizer rate

Law of the Minimum (Liebig)

• States the growth of plants is limited by the plant nutrient:
• supply of nutrients can limit ctop yield w/c can affect heat & water which affect addition to the plant
• Plant growth will never be greater

Mitscherlichs Equation & Nutrients Effects

• Law of Diminishing Returns is an expression to the fertilization on crop yields.:
• Mitsherlichs' Law states that the plan cannot grow indefinitely & there is max. amount of production
• mit hypothesis law of decreasing yield.

Nitrogen, Phosphorus, Potassium and sulfur Economy in Soils & Plant

Nitrogen: Roles in Plant include amnio acid/nucleic:hereditary countrol Deficiency: of N can result in plant leaves turning yellow Toxicity: Excessive vegetatative Forms of nitrogen taken: organic/inorganic forms Phosphorus: Plant that is phosphorus: genetic. seed yield and production and cell membrade

• deficiency: plant is stunted with thin stem
• toxicity access soil easily flows into water Potassium:
• roles in plant: metabolism, and drought tolerance
• deficiency: recognized most plants and can't translocation is inadequate
• toxicity: Excess uptake causes magnesium, manganese and zinc Sulfur roles:amino acids need proteins
• deficicny: -yellow leaves and more from Sandy soil low organic. more with high rainfall
• toxicity: uptake of elements and is yellowing from at edges

Micronutrients & Soil Depletion

• Soil is a micronutrient & there are 8 including Zn,Fe, Mn, Cu, B, Mo, cl & Ni, the main components which are essential for crop growth :

• Zinc and Iron need plant

• Copper for soil, Manganese , and chlorine

• Soil erodes with : Leaching & runoff, floods from water with Wind erosion with tillage, the top soil. & with mono croppping also, there are also micro organisms that affects acidity when is too low

• Lastly, you can also have over excess amount the soil where most soil are affected as the result of human such overgazing and farming, or even with slashing and burning to farming etc.